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by O. Chanute

January 1893.

Ocular demonstration being always more satisfactory than description, those readers who have been sufficiently interested in the subject to try the experiments which have been described with paper planes (falling by gravity) may also like to see for themselves how an aeroplane behaves when motive power is applied. They can probably obtain in a shop one of the toys which have already been alluded to, under the head of "Screws to Lift and Propel," as one of the series produced in 1879 by M. Dandrieux, and which is shown in fig. 59.

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FIG. 59. -- DANDRIEUX -- 1879.

This is a true aeroplane, the wings being fixed, and the propulsion being produced by the screw at the front, which represents the antennae of the butterfly. This screw is driven by the unwinding of the rubber threads, and has practically no pitch except that produced by the yielding of the posterior edge of the gold-beater's skin, of which the vanes are composed. Its peculiar shape, giving a maximum of surface near the outer end, with a rigid an. terior edge and an elastic posterior edge, is the result of a good deal of experiment, and may furnish a useful hint for those desiring to experiment upon a larger scale. The wings are also of gold-beater's skin, and instead of being stretched tightly upon the frame. the anterior margin only is made rigid, the rest of the surface being left quite loose, so that it may undulate when under forward motion, as in the case of M. Brearey's device, which will presently be described. This feature in construction, which differs greatly from that which obtains in the case of birds and insects, whose wings are elastic, but do not undulate, is said to be intended to compensate for defects in workmanship and equilibrium. Upon being tested in still air within doors, the toy will be found quite erratic in flight. It will generally go up to the ceiling, and then flutter in various directions until the power is exhausted, and seldom twice pursue the same course. Out-of-doors it will rise some 20 or 30 ft., dart about, or drift with the wind, until the rubber threads are unwound, and then glide down to the ground sustained by its aeroplane alone.

As a matter of course the sustaining surfaces have to be made very large in proportion to the weight, in order to prevent injury in alighting. One of these little toys, computed by the writer, weighs 86 grains or 0.0123 lbs., and measures 50 sq. in. in aeroplane surface, or 0.3472 sq. ft.

this being in the proportion of 28 sq. ft. to the pound, or about 0.7 of that of the real butterfly, which, being much smaller, measures some 40 sq. ft. to the pound, and which in consequence is capable of but slow flight, although it is not infrequently found by aeronauts floating about in the upper air a mile or so above the earth, a fact to which further reference will be made when we come to consider the prevalence of upward trends in aerial currents.

The propulsion of a loose undulating surface was at about the same time, somewhat differently and quite independently, proposed by M. F. W. Brearey, the Honorary Secretary of the Aeronautical Society of Great Britain. He patented, in 1879 the apparatus shown in fig. 60, in which a flexible fabric is attached to a central spine and to vibrating wing arms at the front, which latter beat up and down like the wings of a bird. The effect of this action is to throw the fabric into a state of wavelike motions, both lengthwise and in a smaller degree also laterally, which are said to cause the apparatus to be both supported and propelled in the air, while an adjustable tail regulates the angle of incidence. The wing arms are flexible and stayed to a bowsprit by cords, and the power for an actual machine is to be placed in a car or body affixed along the central spine.

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FIG. 60. -- BREAREY -- 1879.

M. Brearey records that he took the idea from watching the movements of a "skate" fish in an aquarium, which in swimming undulated its whole body, and that he found that when applied to propulsion in air the loose fabric greatly added to the stability, so that the device might be considered as a sort of dirigible parachute, which would come down safely if the motive power became exhausted from any cause. In the various models which he made to illustrate the experimental lectures, with which he was accustomed to popularize "the problem of flight ' in Great Britain, he used the torsion of indict-rubber to produce the revolution of the crank which vibrated the arms, thus getting a dozen strokes or so, and he claimed that the smaller model (5 ft. X 8 ft.) flew from his hand, on one occasion at least, perfectly horizontally to the extent of 60 ft., no angle of incidence of the apparatus being perceptible. The larger model was 6 ft. wide by 10 ft. long, with about 16 sq. ft. of surface, and a weight of 3.1 lbs. (of which 0.44 lbs was added ballast, which it easily carried), being thus in the proportion of some 5.15 sq. ft. per pound of weight, with which the falling velocity would be about 9 ft. per second, or equal to a descent from a height of 1.27 ft., but which was nevertheless found to be too heavy to be safely used in public experiments over the heads of an audience. From his experiments M. Brearey drew the following conclusions as to the possibilities of his apparatus:

We are thus at liberty to contemplate the construction of an aerial vehicle whose dimensions would suffice to maintain, in wave-action, 600 or 700 sq. ft. of canvas, actuated by steampower, and capable of supporting the additional weight of a man, whose weight, together with the machine, would certainly not exceed 500 lbs.; and we can contemplate the man as being able to move a few feet backward or forward without much affecting the stability of the machine. His descent under the parachute action can thus be graduated at will. This can also be effected by a cord attached to the tail, which by that means can be elevated or depressed at pleasure. Placed upon wheels it has, of course, yet to be ascertained what distance of pre. liminary run would be required, assisted by the action of the fabric, before it would rise from the ground.

Subsequently (his second American patent is dated in 1885 M. Brearey further proposed the superposition of two or more sets of such "wave-action" aeroplanes, and the important addition of what he calls the "pectoral cord," which consists in an elastic cord (or suitable spring) attached to some point underneath each of the lower set of wing-arms and passing underneath the carriage, car or central spine, so that it may be thrown into tension on the up stroke, and restore the power thus stored upon the down stroke of the wing-arms This device is designed to imitate in its action the functions of the pectoral muscle of a bird. The tension of this cord or spring is regulated in accordance with the weight to be sustained, and is said to be perfect when, upon the whole apparatus being committed free to the air, the wing-arms are retained at a suitable diedral angle against the upward pressure. It follows from this action that the up stroke, being assisted by the air pressure which sustains the weight of the apparatus, expends less power than the down stroke, and that nearly all the power can be used in depressing the wing-arms to compress a wave of air, which undulating backward and outward along the loose fabric may assist the air pressure already due to the forward speed in sustaining the aeroplane, and serve at the same time to propel it.

M. Brearey, however, seems to have applied this "pectoral cord" chiefly to those of his models which showed the wing-action proper, and in the practical demonstration which he gave to the Aeronautical Society of Great Britain, at its meeting in 1882 he said:

Working in the field of experiment, I am enabled to state that the power requisite to propel and-sustain a body in the air has been greatly overestimated, even by those who took the more favorable estimate in view of the ultimate attainment of flight. I am not aware, however, that the true reason for the minimum display of actual power exerted in the flight of birds has ever been propounded. Certainly it has never before been demonstrated by actual experiment.

The action of the pectoral muscles of the bird alone accounts for this. Consequently the advantage would be altogether lost in anything but a reciprocal action. The bird commits himself to the air, and the pressure of the air underneath the wings forces them upward. The weight of the bird is indicative of the pressure; and as a consequence of this automatic raising of the wing by the pressure of the air underneath, we should imagine that the elevator muscle need not be strong. As a matter of fact, we find it is weak. I doubt whether any muscular effort is made to elevate the wing at all in flight, but when not in flight, the bird of course requires the power to elevate its wing in preparation for it.

Committed, then, to the air, the elastic ligaments connected with the winks are stretched to that degree which allows of the wings being sufficiently raised for effective support without flapping, and without, as I conceive, any muscular exertion upon the part of the bird. The limited power of the elevator muscle may here come into use occasionally in aid of the under air-pressure, and with the further effect of stretching the ligaments. Now it will be argued that' in the downward stroke there must be as much muscular force employed as will raise or, at least, prevent from falling, the weight of the bird; but this is not so, because the reaction of these ligaments, which have been stretched entirely by the weight of the bird, assists materially the action of the depressor muscle.

M. Brearey here produced a model having wings measuring 4 ft. from tip to tip. He showed the elastic cord underneath the wings but for the purpose of the first experiment he detached it. He then wound up the indict-rubber strands 32 times, and showed that this, although sufficient to flap the wings with energy while held in the hand, was insufficient to cause the model to fly. This was demonstrated by letting the model free. He explained its inability to fly from its want of power to bring the wings down with sufficient force.

He now unwound the action and proceeded to wind it up again 32 times, and attached the pectoral cord. Holding the model in his hand, he called attention to the fact that it was powerless to flap the wings because the two forces were in equilibrium. It required the addition of another force to effect flight, and he asked what that other force could be except weight? If now It flew, he proved beyond the possibility of doubt that weight was a necessity for flight. The model was then set free, and flight was accomplished.

He also showed that the model would only fly without the attached pectoral cord when wound up 40 times. With the cord it would fly when wound up only 13 times, thus showing the great saving in power which accrued through the action of the pectoral cord.

M. Brearey then produced a model of his "wave aerial machine," having 4 sq. ft. of loose surface weighted to 1/2 lb., and he demonstrated by its flight that the principle was equally applicable to that.

It may be questioned whether this "wave action" is likely to prove economical of power in either sustaining or propelling an aeroplane, for it seems difficult to conceive that a wave of air compressed at the front by the wing arms should travel back to the rear, unconfined as it is either at the bottom or sides. Still, the loose surface may add to the stability, as claimed for the Dandrieux toy, and it would certainly diminish by its yielding the strains that would otherwise occur at the points of attachment of a rigid surface in an aeroplane; but M. Brearey's wave action seems to be chiefly applicable as a dirigible parachute, and a small model upon this principle, but without motive power, was once liberated as an experiment by Captain Templer, from a balloon which had risen 200 ft. or 300 ft. from Woolwich Arsenal, and it traveled back again to the arsenal, half a mile, against the wind.

It seems somewhat singular that so few efforts have been made to devise dirigible parachutes, a system which M. de Ia Landelle constantly extolled, as constituting the first requisite step toward eventual flight by working out the problem of absolute stability and safety. The only one of these devices which the writer has been able to find recorded is that of M. Couturier, patented in France in 1875 and this is so briefly described in the Aéronaute for November, 1878 that its mode of operation cannot be made out.

The "pectoral cord" attachment is probably a valuable device for flapping wings, as furnishing that inequality of effort between the up and the down stroke which undoubtedly obtains in bird flight. This effect was produced in a "wave-action" model exhibited by M. Brearey at the aeronautical exhibition of the Aeronautical Society of Great Britain of 1885 by a "trunk engine" designed and built by M. Hollands, which, however, was not shown under steam, as the boiler was only just completed in time for the exhibition; but M Hollands said that the model flew well, and supported weights, when the engine was supplied with compressed air through an indict-rubber tube. He does not seem to have stated what power was exerted.

While almost all inventors and experimenters of aeroplanes have proposed some sort of motive power, and have found their designs paralyzed very soon by the want of a sufficiently light motor, there have been at various times, as already intimated, keen observers of the flight of soaring birds, who have held that once under way in a sufficient breeze, the performance involves no muscular movement whatever, save in balancing, and that the wind alone furnishes sufficient motive power (if blowing from lo to 30 miles per hour) to enable man to soar and to translate himself at will in any direction even (paradoxical as it may seem) against the wind itself.

Chief among these observers in recent days stands M. Mouillard, of Cairo, Egypt, who has spent over 30 years in watching birds soar in tropical latitudes, and who published, in 1881 a very remarkable book (in French), "L'Empire de l' air," which should be read by all those seriously interested in the solution of the problem of flight. This book, the result, as the author explains, of a passionate, vocation which began at the age of 15 is almost wholly a record of personal observations and deductions. Its sub-title designates it as an "essay upon ornithology as relating to flight," but it is far more than that, for it not only describes the flight and manoeuvres of birds, and gives good reasons for the author's belief that they can be imitated by man, but it describes four attempts which he has made to do 50 with various forms of apparatus.

M. Mouillard underrates, perhaps, the value of mathematical investigation, and he sometimes errs in his explanation of physical phenomena; but his observations are unrivaled, and they are presented with a particularity of circumstance, a vivacity and a charm which photograph them at once on the mind of the reader. He begins by explaining the difference between useful and unfruitful observations of creatures so willful, so swift, and so shy as the birds; then he describes the various modes of flight (both rowing and sailing), and the movements of the various organs, such as the wings and the tail; the influence of their shape in determining the mode of progression and the speed of the various species, and he shows conclusively that if these organs are properly shaped therefor, the heavier the bird the more perfectly he soars, and can, once initial speed is gained, sail indefinitely upon the wind without further flapping his wings This is the keynote of the book; observation after observation is described, anecdote after anecdote is related, to impress upon the reader that there need be no flapping whatever, if only the wind be strong enough; and that when there is no wind, the soaring bird must come down to the ground or resort to flapping, like the rowing birds.

Then the effect of the speed of the wind is discussed. It is shown that certain species of soaring birds with broad wings, such as the kites, the eagles, and the vultures can sail upon a wind blowing at 10 to 25 miles per hour, but must seek shelter when it increases to a gale, while the sea-birds, with long and narrow wings, such as the gulls, the frigate bird, the albatross, sport indefinitely in the tempest blowing at 50 or more miles per hour. He arrives at the conclusion that when man succeeds in imitating the manoeuvres of the soaring birds, he will utilize the moderate winds, and attain to speeds of about 25 to 37 miles per hour.

M. Mouillard also passes in review the individual mode of flight and characteristics of the various species of birds, both the rowers and the sailers; comprising some 13 different types, and giving tables from his own measurements of weights, surfaces, dimensions, etc., which have been compiled by M. Drzcwiecki, and have already been quoted by the writer under the head of "Wings and Parachutes;" while he finally expresses a strong opinion that the easiest type for man to imitate is the great tawny vulture of Africa (Gyps fulvus), which weighs some 16.50 lbs., and spreads some 11 sq. ft. of surface to the breeze.

M. Mouillard explains how, in his opinion, the manoeuvres of this bird can be imitated, so as to obtain both a sustaining and a propelling effect from the wind, and he describes (much too briefly) the four several attempts which he had then made to demonstrate the correctness of his theory of the possible soaring flight of an aeroplane for man.

The third of these aeroplanes, as described in 1881, is shown in fig. 61. It consisted of two thin boards, properly stiffened, to which were attached ribs of "agave" wood (an African aloe, exceedingly light and strong), which ribs carried the fabric constituting the two wings. The two boards were hinged vertically together (somewhat imperfectly) at the center, and the operator stood upright in the central space at c, suspended by four straps attached to the boards near the hinge; two of these straps passing over the shoulders and two between the legs. Moreover, light wooden rods extended from the feet to the outer ends of the boards, so that the angle of the wings with each other could be varied at pleasure.

Standing upright, with this apparatus strapped on, the hinge was about at the height of the pit of the stomach, the arms being extended out flat upon the boards, and slipping under straps; M. Mouillard trusting to such shifting of his body within the space c as he could effect by resting his weight on his arms, to produce the necessary changes in the center of gravity of the apparatus, which were required by the changes in the angles of incidence.

The whole apparatus weighed 33 lbs., but was found unduly light, as the parts yielded and the wood cracked when tested with vigorous thrusts of the legs. It had been hastily constructed, with such materials as the country afforded, and the builder was not satisfied with it.

M. Mouillard gives but a scanty description of his experiments with this aeroplane in "L'Empire de l'Air," so little, indeed, as to suggest further inquiry; but he has since written another book, which he entitles "Le vol sans battements" (flight without flapping), which is now nearly ready for the press, and wherein he records further observations, explains more fully his ideas and the results of his meditations, giving freely, as he expresses it, "all that he knows" and in which there is a fuller account of the experiment in question.

From this forthcoming book M. Mouillard has kindly furnished the following extract concerning the experiment with the apparatus shown in fig. 61.

It was in my callow days, and on my farm in the plain of Mitidja, in Algeria, that I experimented with my apparatus, No. 3, the light, imperfect one, the one which I carried about like a feather.

I did not want to expose myself to possible ridicule, and I had succeeded by a series of profound combinations and pretexts in sending everybody away, so that I was left all alone on the farm. I had already tested approximately the working of my aeroplane by jumping down from the height of a few feet. I knew that it would carry my weight, but I was afraid to experiment in the wind before the home folks, and time dragged wearily with me until I knew just what the machine would do; so I finally sent everybody away-to promenade themselves in various directions-and as soon as their backs were turned, I strolled into the prairie with my apparatus upon my shoulders. I ran against the air and studied its sustaining power, for it was almost a dead calm; the wind had not yet risen, and I was waiting for it.

Near by there was a wagon road. raised some 5 ft. above the plain. It had thus been raised with the soil from ditches about 10 ft. wide, dug on either side.

Then came a little puff of wind, and it also came into my head to jump over that ditch.

I used to leap across easily without my apparatus, but I thought that I might try it armed with my aeroplane; so I took a good run across the road, and jumped at the ditch as usual.

But, oh horrors! once across the ditch my feet did not come down to earth; I was gliding on the air and making vain efforts to land, for my aeroplane had set out on a cruise. I dangled only one foot from the soil, but, do what I would, I could not reach it, and I was skimming along without the power to stop.

At last my feet touched the earth. I fell forward on my hands, broke one of the wings, and all was over; but goodness ! how frightened I had been ! I was saying to myself that if even a light wind gust occurred, it would toss me up 30 to 40 ft. into the air, and then surely upset me backward, so that I would fall on my back. This I knew perfectly, for I understood the defects of my machine. I was poor, and I had not been able to treat myself to a more complete aeroplane. All's well that ends well. I then measured the distance between my toe marks, and found it to be 138 ft.

Here is the rationale of the thing. In making my jump I acquired a speed of 11 to 14 miles per hour, and just as I crossed the ditch I must have met a puff of the rising wind. It probably was traveling some 8 to II miles per hour, and the two speeds added together produced enough pressure to carry my weight.

I cannot say that on this occasion I appreciated the delights of traveling in the air. I was too much alarmed, and yet never will I forget the strange sensations produced by this gliding.

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Fig. 61. -- MOUILLARD -- 1865

 Then M. Mouillard repaired the injured aeroplane, and he tried it again a few days later. Of this later experiment he says in "L'Empire de l'Air":

I had no confidence, as I have already stated, in the strength of my aeroplane. A violent wind gust came; it picked me up; I became alarmed, did not resist, and allowed myself to be upset. I had one shoulder sprained by the pressure of the two wings, which folded up against each other like those of a butterfly when at rest.

M. Mouillard then determined to make no more experiments with this incomplete machine, but to build a better one, with which he could control all the maneuvers necessary for soaring, but shortly afterward his circumstances led him to leave the farm and to remove from Algeria to Cairo, Egypt. Here, in a great city, he no longer had the facilities for experimenting that he possessed on the farm, for he had to go out some distance to secure space and privacy for each experiment. Then came illness; the former gymnast became a cripple, so that he could no longer perform for himself the acrobatic maneuvers necessary to experiment with a soaring apparatus, but still he persevered, and he describes in "L'Empire de L'Air" the design for the fourth apparatus, of which he began the construction in 1878, but which was interrupted by ill-health.

Since the publication of his book in 1881 M. Mouillard is understood to have been continuously engaged in perfecting and simplifying his proposed soaring apparatus, and in trying experiments (by proxy) with models on a small scale. He says that he will soon be prepared to have the matter tested on a large scale, and that he has never wavered from absolute conviction in the truth of the principles which he laid down in "L'Empire de l'Air," in which he expresses himself as follows:

I hold that in the flight of the soaring birds (the vultures, the eagles, and other birds which fly without flapping) ascension is produced by the skillful use of the force of the wind, and the steering, in any direction, is the result of skillful maneuvers so that by a moderate wind a man can, with an aeroplane unprovoked with any motor whatever rise up into the air and directed himself al will, even against the wind itself.

Man therefore can, with a rigid surface and a properly designed apparatus repeat the exercises performed by the soaring birds in ascension and steering and will need to expend no tone whatever save to perform the maneuvers required for steering.²⁸

"The exact shape of these aeroplanes need not be discussed in this chapter, for it will be seen further on that there are scores of shapes and devices which can be employed, but all forms of apparatus, however dissimilar, must be based upon this idea, which I repeat."

Ascension is the result of the skillful use of the power of the wind, and no other force is required.

M. Mouillard then continues:

It will doubtless be very difficult for many persons to admit that a bird can with a moderate wind, remain a whole day in the air with no expenditure of power. They will endeavor to suppose some undetermined pressures or some unseen flapping. In point of fact, the human understanding does not readily admit the above truth; it is astonished, and seeks for all the evasions it can find. All those who have not seen say, when ascension without expenditure of force is mentioned to them, "Oh, well, there were some motions which escaped your observation. "

It even occurs sometimes that a chance or superficial observer, who has had the luck to see this maneuver well performed by a bird, when he turns it over in his mind afterward feels a doubt invading his understanding; the performance seems so astonishing, so much against ordinary experience, that the man asks himself whether his eyes did not deceive him For this observation, in order to carry absolute conviction, must hear upon the performance of the largest vultures, and they alone; and this is the reason: it is because all the other birds which ascend into the air by this process do not perform the necessary decomposition of forces required in all its naked simplicity."²⁹

To be convinced, a man must see; for to see the performance even once is better than a whole volume of explanations. Therefore, O reader, if you are interested in this subject, go and see for yourself, and be edified. Go to the regions where dwell the birds which perform these demonstrations; and when you have beheld them for a few instants, being already initiated as to what to observe, comprehension will at once come into your understanding.

Whoever has seen a boy's kite ascend into the air, and considered that the string may be replaced by a weight, if only the equilibrium be secured and maintained, will have no difficulty in granting the correctness of M. Mouillard's assertion that the power of the wind is quite sufficient to secure ascension, but it will not so readily be understood how it is also sufficient to secure progression even against the wind. It will, indeed, be conceived that an aeroplane possessed of initial velocity can soar in a circle in the wind like a bird, and by changing its angle of incidence, descend somewhat when going with the wind. and rise again in consequence of the greater "lift" when facing the wind, thus gaining in height at every lap, and eventually utilizing the elevation thus gained in gliding in any desired direction, always provided that the equilibrium be maintained but this involves very delicate manoeuvres, which will be further considered when we come to sum up the results of all the experiments with soaring devices, and indeed the subject warrants a paper by itself which may be placed in an appendix.

It may, however, be said here that the French aviators., after having long doubted the reality of the performance of sailing flight by the birds, whose evolutions they were unable to watch in their climate, have had so many corroborations furnished to them by trustworthy witnesses, that they now generally admit that a soaring bird can sustain himself indefinitely on a wind, without flapping, and that man may learn to imitate him if only a proper apparatus be designed, and the operator possesses the necessary knowledge and skill to work it, so as to perform the right manoeuvres and at the right time.

²⁸ The italics are M. Mouillard's own.
²⁹ The present writer has seen the feat performed by gulls many times.

 

 

Aeroplanes  Part IX

by O. Chanute

February 1893.

But these wonderful performances of the "sailing birds" are chiefly witnessed in tropical or semi-tropical regions -- those in which the steady trade winds or the regularly incoming sea breezes afford daily to the birds the power of performing their evolutions in search of food. In the more temperate regions the wind does not blow every day with just the right intensity, the casual soaring bird is frequently compelled to resort to flapping, and the would-be inventor has his thoughts directed to some form of a power machine; generally some combination of aeroplanes with propelling screws, which differs a good deal from the simple. compact, and severe outlines indicated by nature.

The form of the soaring bird is reducible to three elements. First, a comparatively large body, shapely, but unsymmetrical fore and aft, presumably the solid of least resistance to the air; second, a symmetrical pair of wings, convex on top, and more or less concave beneath, with a sinuous and stiff front edge; and, third, a tail, which varies greatly in its proportion among the various species. For these features, most of the inventors have substituted a small, boat-like body, a combination of flat planes and flat rudders, both horizontal and vertical, which last is not found to exist in the bird.

A good case in point is found in the instance of Mr. Krueger, who patented in the United States, in 1882 a flying machine consisting in three flat horizontal planes set one behind the other, the front one being triangular in plan, while the rear one might be shaped like the tail of the swallow. These were to be adjustable, so as to guide the machine up or down. Beneath them was to hang a ship or vessel, and above them were to be set still other planes, sloping like the two sides of a roof, in order to act as a parachute. Four propelling screws were to be arranged between the three sustaining planes, while four adjustable keel cloths, vertically affixed both above and below the sustaining planes, were to steady the course and to furnish the steering power.

No particular motive power was proposed, and no method indicated {or maintaining the stability, so that it is quite safe to say that no experiments were ever tried with this apparatus upon any practical scale. lt has been here mentioned to illustrate how misguided ingenuity sometimes runs to complications, while leaving untouched the really essential requirements.

The next inventor to be noticed, M. Goupil a distinguished French engineer, began otherwise: by taking thought of the motive power and of the equilibrium. After having tried a few preliminary experiments, he designed in detail a light steam-engine and boiler, the weight of which he estimated at 638 lbs. for a machine of 15 horse power gross, or 42.5 lbs. per horse power. He also designed a condenser of like capacity, estimated to weigh some 220 lbs. (15 lbs. per horse power), so that the water could be used over and over again; and he then figured that the rest of the flying apparatus, without cargo, might weigh 242 lbs., thus making a total of 1100 lbs., so that if the steam-engine worked up to two-thirds of its theoretical efficiency and developed 10 effective horse power, the total apparatus would have been in the proportion of 110 lbs. per horse power but might be reduced to about 44 lbs. per horse power through the use of aluminium instead of other metals.

These estimates of weights of motor and condenser have been since then more than confirmed by the achievements of M. Maxim and other inventors, but before seeking to realize them M. Goupil determined to investigate the all important question of equilibrium.

Both observation and mathematical considerations had satisfied him that much of the longitudinal stability of the bird in the air was due to the raking shape, fore and aft, of the under part of its body, which, presenting to the air an increasing and more effective angle of resistance when pitching oscillations occur, tended to restore the balance and to prevent the animal from taking either a "header" or a "cropper." This he determined to test experimentally, and he accordingly built, in 1883 an apparatus similar to that represented by fig. 62 omitting, however, the screw, the lower framework, and the stays to the wings.

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FIG. 62. -- GOUPIL -- 1883.

The alar spread was 19.68 ft. from tip to tip of wings, the length was 26.24 ft. from the head tip to the end of the tail, and the mid-section was 26 go sq. ft. in area, while the sustaining surface was no less than 290 sq. ft., the weight being 110 lbs.

It will be noticed that this was a marked departure from the ordinary aeroplane types, there being an ample body to contain machinery, and the wings being decidedly concavo-convex, while other inventors have generally endeavored to diminish the body as much as possible and to gain support from various combinations of plane surfaces.

M. Goupil's object was to make a series of preliminary experiments with this apparatus, in order to ascertain its stability, the effect of the wind upon such a system, and the resistance to be expected, as well as the sustaining power. He accordingly applied neither motor nor screw, but exposed it to the natural wind when blowing from 18 to 20 ft. per second, say, about 13 miles per hour, at which velocity the resulting air pressure is generally assumed to be 0.85 lbs. per square foot. These experiments took place in December, 1883, at which season the winds were quite variable, and the apparatus was anchored by various ropes so as to prevent it from rising more than 2 it. from the ground.

Exposed head on to a wind of 18 to 20 ft. per second, the body being inclined at an angle of 1 in 10 and the wings at 1 in 6 (about 10°), this apparatus lifted up clear of the ground the weight of two men besides its own, making a total of 440 lbs.! The thrust or end resistance did not exceed 17.6 lbs. M. Goupil tested this several times, and expresses himself as surprised at the low resistance to penetration against the wind evidenced by this apparatus, which was mounted upon two small wheels.

When the wind increased to more than 20 ft. per second he could no longer control the machine. There being no stays or guys to the wings, such as are shown in fig. 62 the apparatus was twisted out of shape, and the wind took greater effect upon the deformed side. Then a wind gust occurred; the efforts of five men were required to control the apparatus, and one of the wings (constructed with white pine) was broken.

The inclement season and other considerations of a personal nature prevented M. Goupil from pursuing these experiments further at that time. He had gathered valuable preliminary data, and had caught a glimpse of a very. important fact concerning the effect of concavo-convex surfaces, but his own affairs had a more immediate claim upon his personal attention.

He therefore desisted for a while and allowed the subject to remain in abeyance until he could take it up again, but he published, in 1884 a very remarkable book, "La Locomotion Aerienne," in which he advanced a number of important and new theoretical considerations concerning the solution of the problem of aerial navigation, gave data concerning the steam-engine, the condenser, and the various sizes of bird-like aeroplanes which he had designed, and generally evinced such a grasp and comprehension of the question that it seems a marvel that the book is not more frequently referred to by the French writers on aviation.

This experiment of M. Goupil opens up quite a new field of inquiry concerning the effects of concave, bird-like surfaces, when exposed to an air current. Calculated by the data which have been gathered by experiments upon plane surfaces, the "drift" and total resistance does not seem to vary greatly from what might be expected, but there is an enormous, an almost incredible increase of the lifting power.

Thus there was said to be a total end thrust of 17.6 lbs. in the apparatus when exposed to a wind of about 13 miles per hour, at which the air pressure would be presumably some 0.85 lbs. per square foot. The angle of incidence of the wings was practically 10°, and we may, without serious error, assume the resistance of the body to have been one-tenth of that due to its mid-section while that of the edges of the wings (presumably 0.20 ft in average thickness) would be about one-third of their plane cross-section. As the sustaining surface was 290 sq. ft., we then hare, using the table of ""lift"" and "drift" heretofore given, the following estimate:

RESISTANCE OF THE GOUPIL AEROPLANE.
Drift 10 290 X 0.85 X 0.0585 = 14.42 lbs.
Body 26.9 X 0.85 ÷ 10 = 2.28 lbs.
Edge of wings 19.7 X 0.2 X 0.85 ÷ 3 = 1.11 lbs.
Total 17.81 lbs.

which agrees closely with the amount said to have been ascertained by experiment; but when we come to calculate the lifting force we have:

Lift 10°--290 X 0.85 X 0 332 = 82 lbs.,

while the apparatus is said to have actually lifted 440 lbs., or more than five times as much!

Of course various allowances must be made in considering the results of an experiment carried on in a variable wind, and where so little motion of the apparatus 2 ft.) could be allowed. The thrust may have been measured while the breeze was steady, and the uplift to have occurred during a wind gust, deflected possibly by surrounding objects so as to produce a greater angle than 10° with the wings; still, in any case, the result of this experiment and also of other experiments by M Phillips , which are to be-described hereafter, leads to the inference that much greater supporting power is to be obtained from concavo-convex surfaces than from the flat planes which hitherto have been chiefly proposed for aeroplanes.

This increase in supporting power might indeed have been expected from the theoretical consideration: that the concave lower surface would produce a higher co-efficient of pressure, while the convex upper surface would deflect the current of air impinging at an acute angle thereon, and thus produce a partial rarefaction; and also from the much stronger practical consideration that this is the way the wings of birds are shaped; and yet very few experiments and proposals seem to have been made with bird-like aeroplanes.

This neglect may possibly be due to the fact that the proportions, the shape, the concavity and the convexity of natural wings differ from each other among the various species, so that the moment that we discard the flat plane, a multitude of combinations present themselves, which may require long and careful experimenting before the best shape for an artificial machine is ascertained.

It is understood, however, that M. Goupil has planned a whole systematic series of such experiments to elucidate this important matter, and that he hopes soon to be in position to carry them on.

In March, 1884 the Aéronaute published a paper by M. De Sanderval, giving an account of some very interesting experiments, which he had tried with a pair of artificial wings no less than 39 ft. across and 13 ft. wide in the middle. These wings formed an aeroplane, or rigid plane of canvas, stretched upon wooden arms, which latter, however, possessed a certain flexibility.

In a first set of experiments, this aeroplane, loaded with ballast to the amount of 176 lbs., was allowed to glide in calm air along a cable 1.300 ft. long, which both supported and guided it, and which was inclined at a slight angle. It was also allowed to drop in still air from a height of 131 ft.., and then still further experiments were tried with men riding on the machine when the wind was blowing.

For this purpose the aeroplane and its operator were suspended by a long rope from the middle of a cable, stretched in some cases between two hills and over a ravine, and in other cases between two high masts erected near the sea-shore.

M. De Sanderval states that he was attached some 5 ft. above the aeroplane and a little in front of its center of figure, so that by pulling upon four oblique cords he was enabled to shift his weight either forward or back, and to the right or left at pleasure.

When the wind blew and the apparatus was restrained by a head-rope, the effect was much the same as when gliding free in calm air, with, however, the unfavorable difference that when near the ground it was less steady by reason of whirling currents.

In a light wind the apparatus would rise until the suspending rope became horizontal, thus relieving it of its weight-carrying function, and the aeroplane would then oscillate at the pleasure of the operator.

When the wind increased to 18 miles per hour the apparatus would sustain the operator and two assistants.

Subsequently, M. De Sanderval gave an account of his experiments to the French Academy of Sciences, and this was reprinted in the Aéronaute for November, 1886 with the somewhat uncalled-for comment that "it is a pity that the author should not have stated the time, the place, nor the witnesses, as such extraordinary facts need verifying."

The following are the facts as stated:

My first apparatus consisted in two wings, each 1968 ft. long, thus giving an aggregate spread of 39.36 ft. by a maximum width of 13 ft. These wings were of canvas stretched upon bamboos and upon wooden arms. The canvas was divided into a series of parallel sheets or flaps, each 4 3/4 in. wide, and perpendicular to the dorsal l net They were suitably fastened, and a net was stretched above them, so that they might flap and open upon the upstroke, like the feathers of birds, which oscillate upon the quill which divides them into two unequal portions.

Standing upright upon a light board, and connected by straps to a central spine, I was enabled by thrusts of the legs to develop their maximum effort; but with this apparatus, which worked quite well, I was enabled to settle but one fact, and that is, that man cannot develop sufficient energy to sustain himself in calm air. I therefore gave up the thought of beating wings.

I then rebuilt the apparatus, transforming the wings into a rigid plane, and replacing the flapping strips by an unbroken canvas.

This apparatus, weighing 99 lbs., and loaded with 176 lbs. of ballast, was caused to glide under a cable 1,300 ft. long, stretched between two bluffs. There was no deflection in the cable when the aeroplane glided across at speed, but the deflection was about 26 ft. when the apparatus was stopped in the middle.

If then released (by tripping a hook) it would at first drop almost vertically: then after the first second it would glide forward at increasing speed, while the rate of vertical fall diminished; but upon the slightest disturbance in the equilibrium, consequent upon any divergence between the center of gravity and the center of pressure, the inert ballast would aggravate the oscillation, and the apparatus would plunge down to smash. It seemed evident to me that if intelligence were applied to regulate the position of the center of gravity, steady progression would result.

I then suspended the apparatus by a long rope attached in the middle of the cable, and substituted my own person for the ballast. I found that with an intelligent live control the apparatus would oscillate in the wind according to my pleasure. as I have already indicated in a previous communication. The supporting surface of 301 sq. ft. sufficed to sustain a man at a comparatively slow rate of fall, and by a wind of 22 miles per hour it lifted me up wish two assistants, and sustained us in the air during the entire period that we kept the holding-back line taut, by maintaining a proper angle of incidence.

The last and more interesting experiment which I attempted was based upon these previous results, and also upon the fact that soaring birds can rise into the air on a helical path, or else maintain themselves a long while at the same altitude without beating their wings, provided always that they possess sufficient horizontal speed as regards the air. I therefore experimented with an apparatus somewhat similar to the preceding, but round in shape, suspended by a vertical rope 650 ft. long³⁰, and caused it to swing around in a circle, so that the suspending rope described in its path the outer periphery of a cone. In this experiment I could feel a notable reaction against my weight, but it required a much longer suspending rope to allow so large an apparatus to swing in a circle of sufficient diameter to permit its gaining the necessary speed, and to manoeuvre freely. I believe, however, from the feeling produced upon my mind by the experiment, that I had really taken possession of space within the limits of my somewhat irregular speed, and also, from my observations of soaring birds advancing against the wind on rigid wings, that man can succeed in reproducing sailing flight.

If one had an unlimited height to fall in, affording plenty of time to think and to act, he would probably succeed in guiding himself at will. In calm air man does not possess sufficient energy to sustain himself, but either in a sufficient wind, or with a proper horizontal speed of his own, he finds himself under different circumstances, and derives from the air quite enough supporting power. It is through the operation of this dynamic equilibrium that he will eventually succeed in compassing practical flight.

I caused to be constructed, from manuscript notes furnished by M. Biot, a very ingenious apparatus intended to comply with the above conditions, and I experimented with it. This apparatus consisted in two great wings supported on a light carriage, which gained its initial speed by rolling down a long incline covered with an asphalt floor. It rose into the air pretty well, but always with the disadvantage that the experiment could not be sufficiently prolonged to furnish decisive results; each time upon coming down the apparatus was injured.

It appears to me that a long, vertical rope, such as that previously described, swinging around so as to describe a cone of extended base, must afford greater chances for careful experiment and for eventual success.

The writer has been unable to find any further records of experiments by M. De Sanderval. He seems to have been bathed by the lack of means to maintain equilibrium, but even had he possessed the appliances and the skill to bring the center of gravity to coincide with the center of pressure, as often and as fast as the angle of incidence changed, it may be questioned whether he could have acquired, without a very long apprenticeship, that instinctive use of them which constitutes the science of the birds.

It is inferred from the description that M. De Sanderval experimented with plane surfaces, although it is possible that under the action of the wind they may have assumed those concavo-convex shapes which we have seen to obtain with the birds and to be more effective than flat planes. In any case, he is to be commended for having made an earnest: if unsuccessful effort to learn how to soar in a wind like a bird, the possibility of which performance for man will be further discussed hereafter.

In 1848 M. Armour the author of several papers which will be found in the reports of the Aeronautical Society of Great Britain, patented a flying machine, in which he proposed the use of aeroplanes or wings, oscillating upon springs transversely to the line of motion, these wings being set behind each other as well as superposed. It is not known whether any experiments were tried with this curious device, which seems to be a combination of fixed wings (or aeroplanes) with oscillating wings, but it seems doubtful that it can prove efficient.

There was a second aeronautical exhibition in 1885 under the patronage of the Aeronautical Society of Great Britain, but the total number of exhibits was only 16 as against 78 in 1868.

Among these exhibits the model which attracted most attention was that of M. C. Ring, of Denmark, which consisted of an aeroplane with a pair of arched wings, somewhat similar in the front-edge view to the arched wings of the gull and of the albatross. In plan, however, these wings were rectangular instead of the approximately triangular shape which obtains with the birds. These aeroplanes were to act as sustaining surfaces, the angle at which they met the wind being determined by the position of a large flat tail, and the propulsion being furnished by four wing-propellers oscillating beneath the aeroplane, and driven in the model by twisted rubber.

The apparatus was supported by a string fastened vertically above its center of gravity to the crosspiece of a light framework. It propelled itself slowly, but was incapable of free flight, probably in consequence of defective equilibrium.

M. Ring also exhibited a model of a gun-cotton engine in which small charges were to be exploded between two pistons, moving in opposite directions in a long cylinder; but the model was not a working one, and no attempt was made to construct a full-sized engine.

Reference has already been made to a "trunk steam-engine," shown by M. S. Hollands at this exhibition. He gave a description of this and of two other types of light steam-engines with which he had experimented, at subsequent meetings of the Aeronautical Society of Great Britain.

The first was a "direct-acting" engine, rotating at high speed twin vertical screw fans (right and left) in opposite directions, and a model of this machine, developing 1/16 horse power was said to have weighed 6 oz. for the engine and boiler, or at the rate of only 6 lbs. per horse power. It was first intended to generate the steam by burning liquid fuel, but M. Hollands subsequently concluded that hydrogen gas, carried highly compressed in a suitable reservoir, and burned with an admixture of twice its volume of air, would prove preferable for lightness and heating efficiency. He estimated that the weight of this type of motor, including not only the engine and boiler, but also the water therein, the fuel-gas reservoir and the driver's stand, would be 11.5 lbs.per indicated horse power.

The other engine was "geared" so as to rotate two right and left fans on concentric vertical shafts, one inside of the other, through the intervention of toothed -mitre gear. The function of these two vertically superposed fans was to lift only; a smaller horizontal fan being carried on a prolongation of the crank-shaft, and its thrust aided by the reaction of the exhaust steam ejected through a suitable nozzle. The weight of this engine per horse power is not stated.

Both these arrangements, it will be observed, involved discharging the exhaust steam into the air, and thus wasting some 20 to 22 lbs. of water per horse power per hour, M. Hollands not seeing his way to adding an aerial condenser (to recover the steam) in any form, within any admissible limits of weight. He stated that the power necessary was one indicated horse power for every 30 lbs. of the whole weight, so that without a condenser the flight of such an apparatus as he proposed would have been limited by the very small quantity of water which it could lift.

M. Hollands however, made some experiments on the best form of lifting screw-blades, and stated that he had found it advantageous to make the fan blade concave on the driving or lifting side, and that the angle of maximum efficiency was 15° with the plane of motion at the tip and 30° at the root. The form which he found most efficient was two-bladed; with the blades narrowest at the tips, slightly concave on the lifting side, the tip slightly drooping, each blade being approximately the shape of an elongated shallow spoon or scoop, and with a pitch equal to about two-thirds of the fan's diameter, giving a mean angle of blade of 22° 30' with the plane of motion. These blades were of thin sheet steel, and their forms will be noted as confirming what has already been stated as to the advantages of the bird-like form of wing. M. Hollands said further:

I find another advantage accrues also from the use of these very thin, sharp edged hollow blades--viz., that there is no appreciable resistance to rotation that does not contribute to lifting effect. A marked contrast to this desirable quality is presented in the results given by flexible bladed fans, constructed to vary their pitch automatically, being normally of coarse pitch (when still), but decreasing their pitch when rotated, and further decreasing it with increase of speed. Some experiments I made with fans of this description showed an unmistakable loss of power, as compared with the other type above described, due apparently to the energy absorbed in deflecting the elastic blades; which deflection, with a given speed, causes a constant strain and resistance, with no compensating useful effect.

In 1888 W. Beeson patented, in the United States, the singular soaring device shown in fig. 63. He had already patented, in 1881 a soaring apparatus consisting of two or more sets of adjustable superposed sails stretched on inverted A frames, which he expected to raise into the air like a kite, and then sail upon the wind, but he apparently abandoned this device in favor of the simpler form shown in fig. 63.

Click on Picture to enlarge

FIG. 63. -- BEESON -- 1888.

This consisted in a mainsail A and a tail or back-sail B, both of which were supported on a plate or board C, ranging fore and aft. This plate was convexed at its upper edge so that the sail A might extend over, forward and downward to a cross-bar forming the front edge, and thus enclose a head pocket to catch the wind. A forked pendulum-bar, I, was pivoted to the plate C, and it supported at its lower end a trapeze arrangement to carry the operator, who by means of three light cords extending to his hand might alter the angle of incidence of the mainsail A of the tail B, or of the rudder R. The mainsail and tail being, moreover, connected by an adjustable bar, which caused the mainsail to act upon the tail automatically, so as to maintain the equilibrium at all angles of incidence through the compound lever thus formed.

M. Beeson states in his patent that "this machine is self supporting in a light wind, say, of lo miles or more per hour, and that when once raised by a kite or otherwise, and cut loose, it will of itself perform the evolutions of a soaring bird and rise to any altitude."

The writer confesses that he has tried the experiment with a small model and has failed; and so, in the hope that some of his readers may be more fortunate, he has given this account of what seems to be a remarkably simple device--if it will work.

³⁰ Stated at 200 meters; may be a misprint.

 

 

Aeroplanes  Part X

by O. Chanute

March 1893.

At the Paris Exposition of 1889, Commandant Renard, of the French Aeronautical Department, exhibited, in connection with the dirigible war balloon "La France," an apparatus which he had designed some years before (1873) as embodying his conception of a flying machine, and which he termed a "dirigible parachute."

This is shown in fig. 64, and consists in an oviform body, to which is pivoted a couple of standards carrying a series of narrow and long superposed flat blades, intended to sustain the machine when gliding downward through the air.

Click on Picture to enlarge

FIG. 64 -- RENARD -- 1889.

The dotted lines in the side view indicate the maximum angle of inclination which it was proposed to give to this similitude of a Venetian blind, and it is evident that by setting it at the proper angle, and dropping the apparatus from a balloon, it can be made to travel back against the wind a considerable distance, and also that it ma' be steered laterally by the addition of a rudder. Beneath the body a sort of skate will be noticed, probably intended to glide over the ground in alighting, or in obtaining initial velocity to rise should a motor be applied; but the French War Department is reticent concerning its experiments in aerial navigation, and the writer has been unable to gather any information concerning the working of this apparatus.

It will be noted that Commandant Renard proposed to equip this machine with flat blades, thus conforming to the predilection in favor of plane surfaces exhibited by most of the experimenters with aeroplanes already noticed except Captain Le Bris and M. Goupil who took a different view as to the best shapes to employ. In point of fact, as already intimated, those who have succeeded in the air, the true experts in gliding, the soaring birds, do not perform their evolutions with plane surfaces. Their wings are more or less convex on top and concave beneath, and are warped surfaces of complicated outlines. It is true that in many cases they do not differ greatly from planes, and the mind of man so strongly tends to the simplification of complicated shapes, that most inventors have assumed that the effect on the air will be practically the same.

Flight is possible with flat planes, as witness the butterfly, the dragon fly, and insects generally, but such creatures are endowed with greater relative power, as already explained; and, moreover, the elasticity of their wings produces change of shape under action. In the case of the birds, although the outer ends of the feathers are elastic, yet the wing is stiffer as a whole, and the curved surfaces may prove more efficient than planes in obtaining support from the air.

this view seems to have prevailed with Mr. H. F. Phillips, for he patented, in 1884 a whole series of curved shapes, intended to be used in conjunction with suitable propelling apparatus for raising and supporting an aerial machine in the air. These shapes were to be utilized in a set of narrow blades arranged at suitable distances apart; the idea being to defect upward the current of air coming into contact with their forward edges when under motion, so as to cause a partial vacuum over a portion of the upper surface of the blade, and thus to increase the supporting effect of the air pressure below the blade.

These shapes were the result of a series of experiments tried by Mr. Phillips in artificial currents of air, produced by induction from a steam jet in a wooden trunk or conduit, and described in London Engineering in its issue of August 14, 1885.

A cross-section of the shapes patented will be found on fig. 65 Nos. 1-8. The following table gives the results observed, the last column having been added by myself:

 

PHILLIPS'S EXPERIMENTS ON SHAPES.

Description of Form.	Speed of Air Current. Feet per second.	Dimensions of Forms -- Inches.	Lift, Ounces.	Thrust, Ounces.	Foot Pounds Per Pound
Plane	39	16 x 5	9	2.	86.7
Shape 1	60	16 x 1.25	9	0.87	5.80
Shape 2	48	16 x 3	9	0.87	4.64
Shape 3	44	16 x 3	9	0.87	4.25
Shape 4	44	16 x 5	9	0.87	4.25
Shape 5	39	16 x 5	9	0.87	3.77
Shape 6	27	16 x 5	9	2.25	6.75
Rook's Wing	39	0.5 sq. ft.	8	1.00	4.87

The intent of these experiments seems to have been to ascertain the speed of current required to sustain various forms and areas of surfaces, carrying the same weight in a soaring attitude. For this purpose they were exposed to the varying current with their long edges transversely thereto, and they were loaded with a weight applied one third of the width back from the forward edge, which point was thought to be the center of pressure. These shapes were swung by two wires attached to their front edges, and when they assumed a soaring attitude in the velocity of current required to sustain the weight, the "thrust" or drift was then measured.

Click on Picture to enlarge

FIG. 65. -- PHILLIPS -- 1884-1891.

The most efficient shape is, of course, that which requires the least expenditure of power, or the smallest number of foot-pounds per pound of weight to keep it afloat and this is seen to be shape No 5, which soared with 3.77 foot-pounds per pound, or at the rate of 146 lbs. sustained per horse power, while the flat plane absorbed more than twice as much power.

The comparison would have been more satisfactory if the soaring angles of incidence had been stated. This is given for the plane only as having been 15° by measurement. This agrees fairly well with calculation; for if the "thrust" is to the "lift" as the tangent of the angle of incidence, then we have 2/9 = 0.222 = tang. 12° 32'. But all the results obtained were probably somewhat vitiated by assuming that the center of pressure was uniformly one-third of the distance back from the front edge, and therefore applying the load at that point.

We have already seen that this center of pressure varies with the angle of incidence in accordance with JoOEssel's law, and the load should have been attached accordingly. If, for instance, the possible soaring angle were 4°, we should have for the position of the center of pressure, back from the front edge, a distance of 0.2 + 0.3 sin 4° = 0.22 per cent, So that it seems probable that if its load had been applied at 22 per cent. instead of 33 per cent. back from the front edge the flat plane would have soared at a flatter angle than 15° and would have shown less "thrust," because the effect of placing the weight so far back was to tilt the plane unduly, and thus to increase both the angle of incidence and the thrust. It is not known whether JoOEssel's formula applies to curved surfaces; but be this as it may, it is reasonable to believe that it would be but little modified, so that perhaps the error in locating the center of pressure operated to the disadvantage of the curved forms nearly as much as to that of the plane. We may, therefore, accept the general statement that greater weights per horse power can be sustained in the air with concavo-convex surfaces than with flat planes; but it seems very desirable that further experiments should be made, for it is quite possible that, in consequence of the loading of the blades at a point differing from the center of pressure, the shapes patented by Mr. Phillips are not absolutely the most efficient forms.

It will be interesting, in this connection, to note how these various shapes behaved. It was found that in order to get the maximum efficiency from any given surface, the greatest depth of hollow should be one-third of the total width from the forward leading edge, and that the amount of concavity of the lower surface and the convexity of the upper surface should bear a relation to the speed of the air current. Thus in shapes 1 and 2 the under surface was nearly flat, and the upper curvature not great, while speeds of current of 60 ft. and 48 ft. per second were required respectively to produce a soaring attitude. In shape 3 the curvature was more marked, and the required speed fell to 44 ft. per second. Shapes 4 and 5 were made broader, with a moderate degree of curvature both above and below, and the speeds of current to produce soaring were 44 ft. and 39 ft. per second respectively. Shape 6 was an extreme case, in which the distinguishing features of the experiments were purposely carried to excess; for when impinged upon by a current of air of 27 ft. per second in the direction of the arrow a₀, it was seen (by a fine attached ribbon) that there was an induced current flowing outward in the direction a₁,

Shapes 7 and 8 were used to demonstrate that the impinging air is deflected upward by the forward part of the upper surface, and that a partial vacuum results in the after part; they were not loaded with weights, and when exposed to a current of air of sufficient velocity, coming in the direction of the arrow, they rose into the position shown in the figure,

In 1890 Mr. Phillips patented an aerial vehicle in which these curved surfaces were applied to an apparatus similar to the "dirigible parachute" of Commandant Renard, except that there were to be two (or more) series of curved blades behind each other at suitable distances apart, They were to be attached to an elongated body, which he indicated might be of fish shape, and, say, 30 ft. long, The cross-blades, which he termed "sustainers," might be 15 ft. long, 6 in. wide, and 2 in, apart, so many being superposed as to furnish the required supporting air surface. Each set of "sustainers" was to be held in place by a number of vertical bars of angular form! so as to offer the least resistance to the air.

The propelling power was not indicated specifically, save the general statement that it should be "suitable," but a rudder was located at the top of the front series of curved blades, being affixed to a spindle bar terminating below (at the body) with a lever arm. A shifting weight was also provided, capable of being moved across the body, transversely to its line of motion, in order, when moved to either side, not only to depress it, but, by the resistance of the air acting on the surface of that weight, to check forward motion on that side, and thus cause the machine to describe the curve required.

The patent drawings show the vertical standards carrying the blades as being rigidly attached to the body instead of being pivoted thereto, as in the case of Commandant Renard's device, and hence the angle of incidence of the machine could not be conveniently varied in order to rise or to descend; but it is probable that Mr. Phillips has long since remedied this defect, for he is understood to have been continuously experimenting, although the results attained have not as yet been published.

He apparently concluded that he had not developed the best shape in 1884, for he patented, in 1891, the form shown at the bottom of fig. 65. In this, the upper side A of the blade was made convex, as formerly, but the after portion of the lower side of the blade was made concave, as shown at B, while the curvature of the forward portion of this lower side was in the form of a reverse curve consisting of a convex curve, C, at the forward edge, followed by a concave curve, D He states in his patent:

"The particles of air struck by the convex upper surface 4 at the point E are deflected upward, as indicated by the dotted lines, thereby causing a partial vacuum over the greater portion of the upper surface. The particles of air under the point E follow the lower convex and concave surface C D until they arrive at about the point G, where they are brought to rest. From this point G the particles of air are gradually put into motion in a downward direction, the motion being an accelerating one until the after edge Fof the blade is passed. In this way a greater pressure than the atmospheric pressure is produced on the under surface of the blade."

Mr. Phillips indicates that such blades may be of wood, 12 ft. in length and 6 in. in width, from the leading edge E to the rearward edge F, but further experiment led him to make these blades still narrower, and he finally constructed an experimental machine which was tested in the early part of 1893, and has been described in various English journals, notably in Engineering of March 10 and May 5, 1893 the latter issue containing four illustrations, which were reproduced in the AMERICAN ENGINEER for June, 1893. From these various publications the following description of the Phillips experimental machine is compiled.

Instead of providing two series of curved blades, one behind the other, there was but one set, approximately as shown in fig. 64. The apparatus looks like a huge Venetian blind with the slats open. There are 50 of these slats or "sustainers" I 1/2 in. wide and 22 ft. long, fitted 2 in. apart in a frame 22 ft. broad and 9 1/2 ft. high. The sustainers have a combined area of 136 sq. ft.; they are Convex on the upper surface and concave below, the hollow being about 1/16 in. deep. The frame holding the sustainers is set up on a light canoe-shaped carriage, composed principally of two bent planks like the two top streaks of a whale boat, and being 25 ft. long and 18 in. wide, mounted on three wheels I ft. in diameter, one in front and two at the rear. This vehicle carries a small boiler with compound engine, which works a two-bladed aerial screw propeller revolving about 400 times per minute. The fuel used is Welsh coal. There is said to have been no attempt to provide exceptionally light machinery. The weights of the various parts of the machine are, approximately: carriage and wheels, 60 lbs.; machinery with water in boiler and fire on grate, 200 lbs.; sustainers, 70 lbs.; total weight, 330 lbs. The machine was run on a circular path of wood with a circumference of 628 ft. (zoo ft. diameter), and to keep it in position (preventing erratic flight) wires were carried from various parts of the machine to a central pole, as in the Tatin experiments heretofore described. Still further to control the flight, which there is no means of guiding, as the machine is not of sufficient size to carry a man, the forward wheel is so balanced that it never leaves the track, and therefore serves as a guide, carrying some 17 lbs. of the weight, the remainder being on the hind wheels.

On the first run 72 lbs. dead weight were added, making the total lift 402 lbs. As soon as speed was got up, and when the machine faced the wind, the hind wheels rose some 2 or 3 ft. clear of the track, thus showing that the weight was carried by the air upon the Venetian blind sustainers. A second trial was made with the dead weight reduced to 16 lbs. and the circuit was made at a speed of about 28 miles per hour (2,464 ft. per minute), and with the wheels clear of the ground for about three-fourths of the distance That the machine can not only sustain itself, but an added weight, was demonstrated beyond all doubt, even under the disadvantages of proceeding in a circle, with the wind blowing pretty stiffly.

It is stated in the journal Iron that the boiler is a cylindrical phosphor-bronze vessel 12 in. in diameter and 16 in. long. The fire grate area is 70 sq. in., and the fuel Welsh coal. The engine is compound, having cylinders 1 3/4 in. X 3 5/8 in. X 6 in. stroke, fitted with ordinary slide valves. The working pressure of steam is 180 lbs. per square inch, The propeller is 6 ft. in diameter and 8 ft. pitch, with a projected blade surface of 4 sq. ft. The machine was also moored by a stern rope in which a dynamometer was inserted, and on the engine being run at full speed the dead pull was 75 lbs.

If the latter figures be correct, then the power developed was 75 X 2,464 ÷ 33,000 = 5.6 horse power, and the weight carried per horse power was 402 ÷ 5.6, or 72 lbs. per horse power, which is inferior to the 110 lbs. per horse power carried by M. Tatin's apparatus, and probably due to the increased resistance produced by the frame which holds the sustainers.

Mr. Phillips's experimental machine neglects any provisions for maintaining equilibrium in full flight, or for rising and alighting safely. Those he may add later; but whether he does or not, he is entitled to great credit for having been among the first experimenters who have tested concavo-convex surfaces instead of adhering to plane surfaces, and who have thus drawn attention to what may prove to be a very important line of inquiry.

Almost all scientific experiments in air have hitherto been tried with planes, and such few formula as have been proposed are based upon the effect on flat surfaces. It is probable that such formulae--those of Smeaton, Duchemin, Joessel and others-will be found to need modification, either in form or in constants, when applied to curved surfaces. In such case the tables of "lift" and "drift" heretofore given herein will either need recalculation for each specific curved shape, or require the application of a variable coefficient, as exemplified in the calculations of the power expended by the pigeon as heretofore given. In any case it seems very desirable that further scientific experiments be made on concavo-convex surfaces of varying shapes, for it is not impossible that the difference between success and failure of a proposed flying machine will depend upon the sustaining effect (with a given motor) between a plane surface and one properly curved to get a maximum of "lift."

Fig. 66 represents a kite-like aeroplane proposed by M. de Graffigny a French aeronaut, and the author of several works upon aerial navigation, This apparatus was to consist of a kite 46 ft. across, with its fabric surface capable of bagging to a certain extent, and attached to a longitudinal frame, as shown, which was to be trussed both above and below. In front, a stiff triangular head was to be affixed, and an adjustable horizontal tail was to be placed in the rear. Between these, a boat-shaped body containing the machinery and aviators was to be swung on trunnions and attached to the frame. In front of this car a two-armed screw was to rotate, and behind the car a vertical steering rudder was to be placed, above the surface of the kite.

M. de Graffigny estimated that the power required to drive the apparatus we. in the proportion of one horse power for every 110 lbs., and he proposed the use of liquefied carbonic acid gas, which he states to weigh but 55 lbs. per horse power, including the motor, the recipient and a supply for several hours. This, of course, was a mere makeshift, a reservoir of power for experiment, and not a prime mover; inasmuch as the whole apparatus was to weigh but 396 lbs. and to have sufficient sustaining surface (some 1,300 sq. ft.) to come down like a parachute, should the motor break down while in the air. The screw was to be 6 ft. in diameter and 10 ft. pitch, and its shaft was to remain constantly horizontal (this being the object of hanging the car on trunnions), so that the position of the propeller should be independent of the angle of incidence of the sustaining surface, in accordance with the theory of the designer.

M. de Graffigny states that he experimented with a model of this apparatus in 1890. The screw was rotated some 300 turns per minute by a skein of twisted rubber threads weighing, in the aggregate, I.l lbs., and producing 1,085 foot-pounds in 2 1/2 minutes, or at the rate of 7.23 foot-pounds per second, which proved quite insufficient to give to the apparatus (mounted on three wheels, the foremost of which was adjustable) the velocity necessary to cause it to rise upon the air. The designer expresses himself as unable to state what would be the result with a full-sized apparatus.

It will be noted that this proposal resembles a number of others which have already been described. It is probable enough that the best form for sustaining a given weight and for propelling it with a minimum of surface and of power, or for maintaining equilibrium, were not selected. but M. de Graffigny in the book³¹ in which this design is incidentally described, strongly advocates the kite principle generally, as the one most likely to lead to success in devising a flying machine, and in learning how to manage it in the air.

This will have occurred to many readers, and it may be interesting to them to inquire as to what has been published upon past experiments with kites, a subject upon which the writer has found distressingly little on record.

Among the first, if not the very first, to call attention to the fact that the study of the kite as a means of obtaining unlimited lifting and tractive power had been unduly neglected was Mr. Wenham, who, in his celebrated paper on "Aerial Locomotion," published in 1866, described briefly some very interesting experiments with kites, and who has kindly furnished the writer with some additional particulars. Mr. Wenham states that his principal summary of facts was taken from a little book, styled the "History of the Charvolant, or kite Carriage," by Mr. George Pocock, of Bristol, England, who also published a small work on "Aeroplastics," both of them, unfortunately, now having become very rare.

The experiments described took place more than half a century ago, and the purpose of the inventor was not to evolve a flying machine, but to provide a floating observatory to serve in warfare, or to drag wheeled vehicles over land.

The apparatus was, in fact, a huge kite, of suitable size to carry the intended weight, with a chair swung just below and so rigged that by tightening or slackening the different cords which held it, the wind would meet it at an>, angle desired, and the apparatus would rise or fall, or could be made to swing a considerable distance to one side or the other. It was so arranged that in case the cords broke, it would act like a parachute, and thus insure safety.

The following quotation, descriptive of the experiments, was given by Mr. Wenham in his paper:

"While on this subject we must not omit to observe that the first person who soared aloft in the air by this invention was a lady, whose courage would not be denied this test of its strength. An arm-chair was brought on the ground; then, lowering the cordage of the kite by slackening the lower brace, the chair was firmly lashed to the main line, and the lady took her seat. The main brace being hauled taut, the huge buoyant sail rose aloft with its fair burden, continuing to ascend to the height of 1000 yards. On descending she expressed herself much pleased with the easy motion of the kite and the delightful prospect she had enjoyed. Soon after this another experiment of a similar nature took place, when the inventor's son successfully carried out a design not less safe than bold--that of scaling, by this powerful aerial machine, the brow of a cliff coo ft. in perpendicular height. Here, after safely landing, he again took his seat in a chair expressly prepared for the purpose, and, detaching the swivel line, which kept it at its elevation, glided gently down the cordage Lo the hand of the director. The buoyant sail employed on this occasion was 30 ft. in height, with a proportional spread of canvas. The rise of the machine was most majestic, and nothing could surpass the steadiness with which it was maneuvered; the certainty with which it answered the action of the braces, and the ease with which its power was lessened or increased.... Subsequently to this an experiment of a very bold and novel character was made upon an extensive down, where a wagon with a considerable load was drawn along, while this huge machine, at the same time, carried an observer aloft in the air, realizing almost the romance of flying.

"It may be remarked (continues Mr. Wenham) that the brace lines here referred to were conveyed down the main line and managed below; but it is evident that the same lines could be managed with equal facility by the person seated in the car above; and if the main line were attached to a water-drag instead of a wheeled car, the adventurer could cross rivers, lakes, or bays with considerable latitude for steering and selecting the point of landing, by hauling on the port or starboard brace lines as required. And from the uniformity of the resistance offered by the water-drag, this experiment could not be attended with any greater amount of risk than a land flight by the same means.

The reader may perhaps inquire whether there was not some risk that the kite should run away with the wagon when the wind freshened; but Mr. Wenham further explains that the kite attached to the "charvolant" or chariot was provided with a smaller "pilot," or upper kite, which was sufficient to support the "draft," or lower kite, when it was relaxed or allowed to float edgewise, on the wind. The "draft" kite had two cords, one attached well forward, and the other attached well aft, running through rings to keep the cords together. I! the aft cord was slacked off by the driver of the chariot, the "draft" kite floated edgewise on the wind, and the wagon stopped; but by pulling on the aft cord the kite could be made to face the wind absolutely, and to produce the maximum of draft.

Mr. Wenham also mentions in his paper Captain Dansey's kite, for communicating with a lee shore, as described in Vol. XLI. of the "Transactions of the Society of Arts." This was made of a sheet of Holland fabric exactly 9 ft. square, and, as stretched by two spars placed diagonally, spread a surface of 55 sq. ft., the remarkable fact about its performance being that in the experiment about to be quoted this surface of 55 sq. ft. sustained no less than 92 1/4 lbs. The quotation is as follows:

"The kite, in a strong breeze, extended I,100 yards of line in. in circumference, and would have extended more had it been at hand. It also extended 360 yards of line I) in. in circumference, weighing 60 lbs. The Holland weighed 3 1/2 lbs., the spars, one of which was armed at the head with iron spikes for the purpose of mooring it, weighed 6 3/4 lbs., and the tail was five times its length, composed of 8 lbs. of rope and 14 lbs. of elm plank, weighing together 22 lbs."

This latter kite seems to have been provided with a tail to steady it in the air, and in considering the bearing of such experiments upon possible flying machines, it is preferable to select those upon tailless kites, sailed with one single line, for it is easy to maintain the stability if several restraining cords be used. Mr. Wenham has kindly furnished to the writer the particulars concerning a tailless kite, or, rather, series of superposed kites, patented in Great Britain in 1859 by E. J. Cordner, an Irish Catholic priest, who designed the apparatus to save life in shipwrecks, and who preferred to arrange hexagonal disks of fabric (stretched upon three sticks), above each other on the same line, so that they would all pull together. The operation was to be as follows:

When a sailing-vessel had struck, which almost in every case occurs by the ship being blown on a lee shore, a common kite was to be elevated in the usual way from on board the vessel. When enough cord had been paid out to keep the kite well suspended, the end of the cord on board was to be attached in a peculiar manner to the back of another and larger kite (without tail), and the second kite was then to be suffered to ascend. The end of the suspending rope was to be attached in a similar manner to the back of another and still larger kite, and the process to be repeated until enough elevating and tractate power was obtained, when a light boat or basket with one occupant was to be fastened to the kite line, the latter being paid out until the occupant reached the shore and alighted, when by means of a light running line, extending from the ship to the person ashore, it was deemed easy to haul the basket back and forth as many times as necessary to rescue the passengers and crew.

It is not known whether this ingenious method of saving life without extraneous aid was ever used in a case of actual shipwreck, but it was tested by transporting a number of persons purposely assembled on a rock off the Irish coast, one at a time, through the air to the main land, quite above the waves, and it was claimed that the invention of thus superposing kites so as to obtain great tractate power was applicable to various other purposes, such as towing vessels, etc.

Many proposals have been made at various times and in various countries to utilize kites in life saving, but none seem to have come into practical use. Such attempts may have suggested to Mr. Simmons (the English aeronaut) the experiments which he is said to have tried, in 1876, of gliding downward under such buoyant sails.

The only accounts which the writer has found of these experiments are given in the Aéronaute for April, and for November, 1876 The apparatus of Mr. Simmons is described as consisting of a huge "pilot" kite 49 ft. high and 49 ft. wide, with another kite below, still larger. The pilot kite was first to be raised, and to carry up the second the two were to be adjusted to the breeze, and the aeronaut was to be suspended in a car, and allowed to ascend 200 or 300 yards. Then by adjusting his weight by means of guy lines, so as to obtain a proper angle of incidence, the apparatus was said to glide downward to the ground, being slightly dirigible through the guy lines, and to be arrested by the bystanders seizing a dragging guide rope.

Mr. Simmons is said to have been fairly successful with his experiments in England, but to have failed to repeat the feat at Brussels, Belgium. In the latter case it was claimed that there was not sufficient wind, but steadiness of breeze would be more important. The surfaces operated with seem to have been very large--some two to three square feet per pound in order to alight gently; but such extent of surface is so unmanageable in a gusty wind as probably to have led to the abandonment of the experiments.

The exploit is feasible, and would prove useful in-experimenting with various shapes and extent of surfaces, but such experiments should be tried with areas more nearly corresponding to the proportions which exist in soaring birds, and the operator should invariably alight in water until he has learned how to manage his apparatus.

³¹ "Traite d'Aerostation." H. de Graffigny 1891, p. 189.

 

Aeroplanes  Part XI

by O. Chanute

May 1893.

In July, 1880 M. Biot exhibited to the French Society for Aerial Navigation an ingenious kite, invented by himself, which sailed without a tail and possessed great stability under all conditions of wind.

At the top of a flat plane of elongated elliptical shape two hollow cones were affixed, one on each side. The base or large end of these cones faced the wind, and the other end or point was slightly truncated, so as to leave an opening through which the wind could blow, and, by the action of the streams or columns of compressed air thus created, counteract any tendency of the plane to tip to one side or to the other. This provided for the lateral stability on the same principle as in the well-known Japanese kite, in which the side-pockets catch the wind and maintain the equipoise.

The fore and aft equilibrium was provided for by affixing a rotating screw at the lower end of the plane, pivoted on its central line. This screw had two vanes of coarse pitch and was free to rotate under the impulse received from the wind. It spun around with great speed when the kite was raised, and obviated any need of the usual tail by performing the same steadying office. It prevented any oscillations, without impeding the rising of the kite, and maintained it perfectly steady in all winds.

It was not agreed between the French aviators whether this effect was due to the action of the vanes, making an angle with the sustaining plane, as in the case of Pénaud's "planophore," or to "gyroscopic" action, but when the screw was omitted the kite swayed about, while when the screw was rotating, its twirling and tremor could be felt through half a mile of string, and the kite remained perfectly upright and steady,

M, Biot carried on quite a series of experiments with this apparatus. In the kite which he used the elliptical plane was 15 in. high, the two cones at the side were each 8 in. in diameter at the base by a height of 8 in., while the screw was 12 in. in diameter, its two vanes being each 1 3/8 in. broad.

The experiments were carried on in winds varying from 13 to 33 miles per hour, and the kite was found to be steady under all conditions, the only difference being in the height to which it would rise. When the wind blew from 13 to 18 miles per hour, 4,900 ft. of cord were paid out, the kite remaining at this distance during two hours. On other occasions, with stronger wind, as much as 6,500 and 8200 lineal feet of cord were paid out, and the kite mounted so high that it passed through several strata or currents of wind of varying direction, as was conclusively proved by the fact that the restraining cord as-timed a sinuous attitude when the full height was gained, and instead of approximating to a straight line or a regular curve, as usual, the line became serpentine in form, thus indicating that different trends existed in the various strata of air.

In one instance the kite, with 2,600 ft. of cord paid out, advanced against the wind and mounted directly over the head of the operator. This was attributed to an ascending trend in the wind, for the kite still tended to rise vertically and to advance against the wind, although the plane was horizontal, and the cord, now greatly bowed by the wind, tended to drag the apparatus backward. This attitude continued but a short time, when, the trend of the wind having apparently changed, the kite settled back to its original position, flying at an angle of 40 to 60 with the horizon,

M. Biot, who was an old experimenter with kites (having as early as 1868 been lifted up from the ground by a large apparatus of this kind), found the groscopic stability of the arrangement which has just been described so satisfactory, that he thereupon designed, in connection with M. Dandrieux, a full-sized aeroplane on the same principle, calculated to carry up a man. This design was submitted early in 1881 to a special committee of the French Society for Aerial Navigation, but this committee seems to have hesitated in recommending its construction, and no record has been found by the writer of its having been built or experimented with about that time.

When, however, the publication and discussion of M. Mouillard s "L'Empire de L'Air" had directed fresh attention to the soaring of birds on rigid wings, and given grounds for the belief that man could utilize the wind in the same way, M. Biot constructed in 1887 a soaring apparatus in the shape of an artificial bird 27 ft. across, and weighing 55 lbs., with which he hoped to reproduce the maneuvers of the sailing birds.

It is known that a number of very interesting experiments were tried with this apparatus, but the writer has been quite unable to find in print, or to obtain from correspondents, a description of the machine or a record of its trials. He merely knows that these triads were many, and that on one occasion M. Biot suffered a tumble which was not encouraging to further experiment, but no account of them is to be found in the Aéronaute.

It is to be hoped that a full narrative may yet be given to the public of the results of experiments which must have been most instructive for other aviators who contemplate imitating the birds.

In 1882 M. Jobert exhibited before the French Society for Aerial Navigation the model of a proposed apparatus designed by himself, in order to test the possibility of imitating the manoeuvres of the soaring birds, as described by M. Mouillard. This aeroplane was to be hinged and jointed, so that it might be folded up like an umbrella for convenience in transportation, or opened out and stiffened by sliding bars in order to make the wing rigid. With this M. Jobert proposed to experiment on various areas of surfaces in proportion to the weight, and to test the efficacy of both fixed and adjustable sustaining surfaces. He does not seem to have met sufficient encouragement to carry out his design, for the writer has been quite unable to learn that he ever completed a full-sized aeroplane capable of sustaining a man.

Having begun where M. Biot terminated--ie., with the design for a soaring apparatus--M. Jobert next turned his attention to kites, and proposed in 1887 the apparatus shown in fig. 67, which he termed a "rope bearing kite," designed for establishing communication with wrecked vessels. It consisted of a hollow truncated cone C, under which was rigidly connected a kit e P, from which depended two light lines terminating in a ring, the latter carrying a light cord steadied by the drag 0. The object of this arrangement was to ensure a rapid and certain connection with the shipwrecked mariners, who, by seizing the light cord, could at once haul down the kite and thus gain access to the main carrying rope, with which to haul aboard the usual life-saving cable. This carrying rope was fastened to a bridle attached to the top cross-stick of the kite, and to the top of the cone at V, which arrangement was claimed to produce perfect stability, and to ensure that the apparatus should travel straight back in the line of the wind without rising to any great elevation. In order to regulate the height, the angle of the plane could be varied by means of a light string (not shown), extending from the lower cross-stick to the carrying rope and fastened by a hook in one of a series of loops.

The sustaining plane was, like the cone, formed of calico, in which hems were turned at the top and at the two sides, in order to form cases for the sticks of the frame, the lower edge of the kite being left uncaged, in order to produce bagging and consequent increase of lifting power. At the small end of the cone a couple of thin metallic tongues were fastened, which, thrown into vibration by the wind rushing through the cone, produced a howling sound which might notify the shipwrecked sailors of the approach of the apparatus, and the whole arrangement, as will readily be perceived, was quite cheap and readily rigged up or folded away, no matter how large it might be.

The writer does not know whether this apparatus ever came into practical use. It has here been figured in order to show how a cone can be applied to a kite in order to impart stability to the latter, but the arrangement would need to be greatly modified in order to admit of its utilization in an aeroplane, so as not unduly to increase the resistance to forward motion.

In 1886 and 1887 M. Maillot a French rope-maker, tried quite a series of experiments with the kite represented in fig. 68. This was constructed of poles and canvas, in the shape of a regular octagon; it measured 775 sq. ft. in area, about 32 ft. across, and weighed 165 lbs. It had neither balancing head nor tail, and was so poised by the bridle of attachment that the center of pull corresponded to a point only one-third of the distance back from the front edge, or to a spot, therefore, decidedly forward of the center of pressure, at the comparatively coarse angle; (30 to 60 ) usually assumed by kites. This angle of incidence it was intended to regulate by a cord, attached to the rear edge and carried to the seat swung beneath the kite for the operator, who might then, by hauling in or paying out this cord. regulate the angle of incidence and cause the kite to rise or to fall. This was intended to furnish the longitudinal stability, while (there being no provision for automatic lateral equilibrium) the side oscillations caused by the varying intensity and directions of the wind were restrained by side ropes attached to the kite and handled by men standing on the ground.

In the first experiments (May, 1886) M. Maillot was dissuaded from ascending beneath the kite, and he therefore substituted for his person a bag of ballast weighing 150 lbs., tied just below the seat. The kite was raised by first securely anchoring the main rope, which was 800 ft. Iong. and then lifting up the front edge so that the wind might sweep under the surface; upon which the kite rose to such height that the bag of ballast swung some 30 ft. above the ground, where M. Maillot and two assistants managed the two side ropes and the tail cord (not shown in the figure), which latter regulated the angle of incidence by depressing or raising the rear of the kite.

Allowing 33 lbs. for half the weight of the main rope, it was estimated that the apparatus sustained, on this occasion, an aggregate weight of 348 lbs., or in the proportion of 2.32 sq. ft. per pound. The wind was variously estimated at 15 to 22 miles per hour; but as this speed was not measured, nor the pull upon the various ropes ascertained, while the angle of maximum incidence was merely guessed at, as about 45 no accurate computation can be made of the various reactions. The kite was easily controlled by the three men, hauling or paying out the two side ropes and the tail cord, but it plunged about with the varying intensity of the wind, and in one of the oscillations so produced the bag of ballast was whipped about and broke the rope by which it was suspended.

M. Maillot repeatedly experimented with this and other kites (but smaller) on the same principle during the year 1887. He states that he succeeded in sustaining as much as 594 lbs., but whether he ever went up himself beneath the kite the writer has been unable to ascertain. There would have been little or no risk in doing so, provided the wind was steady and strong, for it is evident that the three lines carried to the ground would give almost complete command over the apparatus, but then such a performance would have taught very little toward the management of an aeroplane free in the air. Changes were made from time to time in the modes and points of attachment of the various ropes, and the endeavor seems to have been directed to the discovery of some arrangement by which automatic equilibrium could be secured, under all conditions and varying velocities of wind, without the use of a tail. From the discontinuance of the experiments it is interred that they did not succeed, and the writer attributes this failure (if failure it was) to the employment of a single rigid plane;; for it will be remembered that M. Pénaud obtained a stable kite, on the principle of his "planophore," by adding to the upper pair of planes a second set, inclined at a slight angle to the first, the effect of which was to regulate the incidence.

On the same principle, M. Barrett, whose proposed aeroplane has already been noticed, obtained stability with a tailless kite many years ago, by shaping the plane like a laundry "flat-iron," cutting out a portion of this from the rear or broad end, and adjusting the band so obtained at an angle with the rest of the surface, so that the kite would fly steadily.

M. Copie, on the other hand, obtained partly the same effect by inserting a hemispherical pocket in the body of the kite, but this did not prove quite satisfactory until an opening was cut in the apex, on the same principle as the hole which is provided in the top of a parachute, after which the wind, rushing through the pocket, produced much the same effect as in the Jobert regulating cone; but the device is not one which can be profitably applied to an aeroplane in forward motion.

Upon the whole, M. Maillot's kite was rather crude, and decidedly inferior to Pocock's "charvolant," heretofore described, in which the pilot kite might be used to regulate the carrying kite. The stability of the Maillot arrangement could probably have been improved, and the side ropes dispensed with, by breaking up the surface into two planes, forming a dihedral angle with each other, like the attitude of a bird gliding downward, or the same effect might have been partially produced by providing the plane with a keel

Very good results with central keels have been obtained by M. Boynton with his various forms of "Fin" kites, which are now sold in the shops. They consist of a plane, to which is affixed at right angles a "fin" or keel located in the lower part of the kite, and raised slightly above its surface. They fly without a tail, with a steadiness depending somewhat upon the form of the main bearing surface, and seem to afford a good opportunity for further experiment as to the shape of greatest stability; for keels have been frequently proposed for aeroplanes, in which they will produce less resistance to forward motion than obtains with other arrangements, but few seem to have tested how such keels should be applied.

These remarks chiefly apply to plane rigid kites, and to the various adjuncts and forms which have been tried in order to confer stability upon a main plane surface sustaining the weight; but still better results have been obtained with flexible surfaces, and it seems not improbable that this is the arrangement which will give the greatest amount of stability to a kite, by producing automatic adjustment to the wind's varying intensity.

As an example of such action may be mentioned the "Bi-Polar" kite of M. Bazin, who experimented with it in 1888. It consists of a main sustaining surface like a boy's "bow" kite, or practically the same in shape as the kite surface in fig. 66. The frame is composed of two sticks, one of them a flexible rod at the head, bent to a bow. and the other a main central spine at right angles, to which the bow-strings are fastened. The peculiarity of the "Bi-Polar" kite is that this central spine is also made flexible, and that to its lower end (projecting some distance below the supporting surface of the kite) three triangular fins are attached, just like the tail of a dart, omitting one fin. This arrangement obviates any necessity for a tail and confers automatic stability, for the lateral equilibrium is obtained through the elasticity sideways of the main surface or head, which is blown back by the pressure to a convex surface with a dihedral angle, which angle varies in accordance to the violence of the wind, while the longitudinal equipoise is likewise maintained by the balancing pressures on the head and on the fins, as the flexible spine yields more or less to the breeze. The kite is thus made stable in both directions, and flies steadily without a balancing tail. M. Basin sailed it with two strings, one attached at the top and the other at the bottom of the main sustaining surface; these strings were both carried to the ground, and attached at each end of a stick of equal length with the vertical distance which they spanned at the kite, and with this stick in his hand the operator could vary the angle of incidence. This was intended to secure measurements of this angle of incidence in connection with the pull, but the results thus obtained have not as yet, to the writer's knowledge, been published.

Even better results can be attained with the "Malay" kite, which is in shape a lozenge, composed of two flexible sticks crossing each other at right angles. The cross or horizontal stick is the longest, being preferably 1.14 times the length of the upright stick, and fastened to the latter at a point 0.18 of its length below the top; a string is then carried (in notches at the ends of the sticks) around the periphery of the resulting lozenge, and this is covered with paper or with muslin in the usual way. This surface, when impinged upon by the wind and restrained by the bridle, is bent back by the pressure and adjusts itself to the varying irregularities of the breeze, the kite flying without a tail with great steadiness and rising to great elevations.

M. Eddy, of Bayonne, N. J., who has been constantly experimenting with kites during the last few years, and who is recognized as an expert in such matters, prefers the "Malay" kite to all others. He has improved it by so fastening the cross-stick and tying its outer ends as to produce a slight initial convexity, which is further increased by the action of the wind, and which materially adds to the steadiness of the flight. With this arrangement M. Eddy has succeeded in causing a single kite to ascend to a height of 2400 ft, with 3000 ft. of line, and then bringing it to the zenith directly over his head, or even a little back of his hand, where its attitude strongly suggested the advance of the soaring bird against the wind. Upon a previous occasion he had succeeded in attaining a height of 4,coo ft., with a string of five kites flying in "tandem"--that is to say, each kite attached by a string of its own to the string of the preceding kite already raised, so as to take up the slack or sagging of the line, and thus enable the upper kite to rise to an altitude otherwise unattainable. This performance seems to suggest an easy way for the exploration of the upper air by the Weather Bureau, for by affixing to the upper kite self registering instruments (thermometer, barometer, hygrometer, etc.), or, preferably, by connecting such. instruments (and an anemometer besides) electrically with recording instruments on the ground (through a series of fine wires insulated in the kite string), observations of the conditions prevailing aloft can be easily obtained. The French have lately been making such observations by means of "free balloons" of medium size, and they are said to be of material assistance in forecasting the weather; the records obtained from the top of the Eiffel Tower showing that even at that moderate height coming changes in wind and in temperature are indicated several hours in advance of their prevalence at the ground.

The same principle of obtaining stability without a tail, by means of an elastic frame, can be applied to other forms than the "Malay" or the "Bi-polar" kites but it requires a good deal of delicate adjustment and balancing. It has been done with the common hexagonal form of kite by M. C. E. Myers of Frankfort, N. Y., the aeronautical engineer who furnished and operated the balloons and kites by means of which the recent (1891) rain-compelling experiments were tried in Texas.

It will be remembered that the explosions intended to produce rain were in some cases produced by exploding dynamite suspended below kites, and fired by electricity. In providing for this, M. Myers, who has for several years been conducting systematic experiments with kites, evolved some very interesting facts, and he has published part of his experience in the Scientific American Supplement (No. 835) for January 2 1892 from which the following is extracted:

The originating cause of my interest in kite flying is aerial navigation, and by successive steps I have adapted kites to fly without tails, to fly with considerable weight attached, and, finally, to fly without the restraint of the usual kite-string; and, rising higher and higher, finally to disappear miles in height and miles away on the verge of the distant horizon.

Theoretically, there should be no difficulty in attaining these results. Practically, there is as much difficulty as with a child learning to walk or a youth learning to manage a bicycle. In a word, it is the art of balancing....

Theoretically, the kite should be light or possess much surface with little comparative weight. It should balance at the flattest possible angle, nearly horizontal, and its surface should be widespread, like the wings of a soaring bird. As a fact. I have obtained the best results with this model, but had great difficulty at first to induce it to fly at all, and was finally forced to attach a compromise tail--not a kite tail, but a bird-like tail, which, being flexible, vibrated or undulated with the vertical oscillations of the kite, and thus acted as a propeller, so that this kite actually moved against the wind....

The most practical form of kite for general purposes seems, however, to be the six sided. Those created by me as part of my apparatus for the Government rainfall expedition in Texas were composed of an X, formed of two spruce sticks, each 6 ft. long, tapering, with a top section of 1/4 in. X 1/4 in. and bottom section of 1/4 in. X 1/2 in. tacked flat wise together with a very small pin-nail, and bound with hemp cord at the joining. Five in. below this crossing (which was about 2 ft. from the top) was a similar piece of timber, but 14 in. shorter, and tapering each way, placed crosswise of the X, horizontally, so as to form a 5-in. triangle, which stiffened the frame more than if all crossed at one point. The outer end of each stick was creased with a knife and notched around, so that a hemp cord passed first through the crease and was "half-hitched' around each stick to prevent splitting. The kites were covered with red calico, pasted on tight, and bits of cloth were also pasted across the sticks where the kite-strings attached. These strings were attached as long loops--one loop to the top sticks about 6 in. from their tips, one loop to the two bottom sticks about 30 in. from the bottom, and one loop to the cross-bar about a foot from each end. All these loops were then gathered together and drawn through one hand as the kite lay on the ground, held in place by one foot on its crossing, and being adjusted carefully and equally to draw from a point somewhere midway between the cross-stick and top, best attained by trial, were then tied together.

The kite was thus rather stiff and light at top, elastic and heavier at the bottom, and suspended at a point above its center of gravity and center of surface. To the loop at the bottom was usually hung a narrow strip of cloth to afford greater steadiness in supporting the kite's burden of dynamite to be exploded. I have been thus particular to describe minutely this construction because many have written me for this information.

The first trial kite flown at Midland Tex., escaped. I had built it all myself, as a model, and it had drawn up one ball of hemp twine, and an assistant was holding the string preparatory to running out another ball when the cord parted at a flaw, and the kite flew into space. When last seen with a glass, it was estimated to be about 3 miles high and 8 or 10 miles away, a fading red dot in the distance....

In ordinary light winds this kite floats well, is steadier than many other kinds I have tried, and would seem to be well adapted for photography. If hung very near its top, it is prone to advance upward and forward against the wind till over and beyond the party holding the string, and literally floats on the air as if propelled by its fluttering triangular section at or near the bottom of the kite.

The accidental escape of this kite exhibited a very interesting example of partial "aspiration," and it is understood from additional information, kindly furnished by M. Myers, that he succeeded in reproducing this effect on several occasions. The kites were hung, after considerable experiment, so that they floated nearly flat on the air, with as little tail as possible, and sometimes none at all. They rose upon a light breeze, and drew away as long as the string was let out. When checked or pulled, they rose higher and higher until quite overhead, when the string had to be released. If suitably balanced the kite then rose still higher and drifted back, but not as fast as the wind blew, its rearward flap vibrating more or less, and making its action a progressive one relative to the wind thus producing "aspiration" with respect to the breeze. A long string, or small weight at the end of a shorter string, was sufficient to keep it balanced, so that it might remain up for hours and go floating out of sight.

The possibility of this progressive action against the wind without loss of height (or of "aspiration") has been strenuously denied, and yet it is easily explained if, instead of assuming the wind to blow horizontally, as we generally do, we consider that it has at times a more or less ascending trend, this being a not unusual condition over the sun broiled plains of Texas. It is clear, from the description of the mode of attachment of the string, that its weight when released would tilt the kite forward, so that the plane would point below instead of above the horizon, In this position the direction in which the "drift" is exerted would be reversed--that is to say, the horizontal component of the pressure, instead of pushing backward, would be pulling forward, and thus become a propelling force against the wind, provided, of course, that the latter still exerted its pressure on the under side of the kite. Thus an upward trend in the breeze of but 3° or 5°, operating against a kite inclined forward 2° below the horizon, would be sufficient to cause it to advance relatively to the wind, somewhat as a vessel "close hauled" advances against the breeze which furnishes its motive power. In point of fact, therefore, that which has herein been termed the "drift" may act upon a plane surface, as a force pushing backward or propelling forward, according as that plane is inclined to the front above or below the horizon; but in the latter case there needs be an ascending trend in the wind in order to produce a sustaining pressure on the under side, for otherwise the horizontal wind would strike the upper surface of the plane and press it downward instead of upward. The effect may be quite otherwise with concavo-convex surfaces.

 

 

Aeroplanes  Part XII

by O. Chanute

June 1893.

Ascending trends of wind are by no means rare, as abundantly proved by published observations since M. Pénaud called attention to the many causes which must produce such trends. This was shown in a very able paper on "Sailing Flight," which was published in part in the Aéronaute for March and April, 1875 but which, unfortunately, was left unfinished. M. Pénaud demonstrated that such winds must necessarily result from even moderate undulations of the ground (and therefore a fortiori from mountains or deep valleys), from natural or artificial objects acting as wind breaks, from the meeting of air currents flowing in different directions, or even from the heating effect of the sun. He doubtless expected to show, in the portion of the paper remaining unpublished, that an upward trend of 1/9 to 1/6 (from 6° to 10° in the wind was quite sufficient to enable a sailing bird to progress against the breeze by inclining his aeroplane so that the horizontal component of the pressure would have a forward direction, while the wind still acted on the under side; for we have already seen in computing the foot-pounds expended by a 1-lb. pigeon in gliding, that with a speed of 40 miles per hour and an angle of incidence of 3 the "drift" will be 0.05647 lbs., while the body resistance and that of the edges of the wings together will be 0.05555 lbs., and that at 5 (30 miles per hour) the "drift" will be 0.08892 lbs., and the resistance of the body and edge of wings will be 0.03124 lbs., so that in both these cases the "drift" (calculated even with the coefficients which have been obtained with planes, and which are known to be inferior to those to be expected from concavo-convex surfaces) is sufficient, if directed forward, to overcome the resistances and to give to the sailing bird a forward impulse; this reversal in direction of the "drift," as previously explained, occurring when the plane becomes inclined so as to point forward below the horizon.

Since Pénaud's day a great many observations have confirmed the frequent prevalence of both ascending and descending currents. Aeronauts, more particularly, have noted that the atmospheric currents follow the undulations of the ground, causing their balloons to subside upon approaching a valley, or to rise when nearing a cliff or a mountain. They have also inferred, from the fact that they have found butterflies a mile or more above the earth while sailing over table lands, that these trends are frequent in such regions, although their effect upon the balloon is less immediately noticeable than in mountainous countries, where the angle of ascent often is 45 or more. In such broken countries very curious observations have been made as to the invariable prevalence of steeply ascending winds in certain well-defined localities when the wind blows from a particular quarter; such, for instance, as the observations of M. Mouillard in the Lybian chain near Cairo, and those of M. Bretonniere in the vicinity of Constantine, Algeria, where certain zones or gaps of ascending winds seem to exist, which the sailing birds utilize to gain elevation by circling. There they congregate in crowds, forsaking the rest of the sky, and spirally mount on rigid wings, until they have gained sufficient altitude to carry them toward any point which they may want to reach in descending.

It is probably in sub-tropical regions that such phenomena are most numerous and permanent; but the reader, who is accustomed to thinking of the wind as blowing horizontally, may be quickly edified by watching the smoke issuing from a tall chimney even in northerly climates. This smoke will be seen at various hours, or on various days, to trend either upward or downward or with exact horizontality, as may depend upon the undulations of the great atmospheric waves which are produced by the impinging upon each other of the currents flowing and crossing at various altitudes; or if the observer have the good fortune to be in the regions inhabited by the sailing birds, he may satisfy himself as to the similar atmospheric undulations which are constantly taking place, even in a perfectly flat country, such as the plains of Texas or the sea beaches of Florida, by liberating bits of down or threads of smoke fro rn the same spot at various times or days. He will also-observe the local ascending currents permanently produced by a mere wind break, such as a belt of trees facing the in flowing sea breeze. He may satisfy himself (by attaching light strips of bunting or bright-colored threads to the tops of those trees) that the breeze is deflected upward just over their upper branches, and he will then understand why these spots constitute the favorite haunts of the sailing birds when the breeze is light. He will see the soarers for hours gliding back and forth and back and forth on pulseless wings just above the top of the wind break formed by these belts of trees, evidently utilizing the ascending current to patrol the adjoining beach while awaiting, with no labor, whatever food may be brought by the incoming tide, or an opportunity of eating it undisturbed.

It is not intended here to convey the impression that ascending trends of wind are absolutely necessary for sailing flight. The writer has seen the feat performed many times, when every test seemed to prove that the current was absolutely horizontal; but it then seemed to him that on such occasions the equilibrium was more difficult to maintain, and that the bird had to bestow greater attention upon the nice adjustments required to preserve his balance and to produce "aspiration" when the wind varied in intensity and direction; just as an acrobat experiences greater fatigue in walking a tight rope, through the attention and care expended to avoid falling, than in walking many times the same distance on the ground, where no particular care is required to preserve the balance. It is probably because of such relief from all cerebral strain that the soaring birds seem to sail with less care and with far greater steadiness whenever they are utilizing an ascending current. They are then easily and safely sustained, and so mechanical does the performance seem that some observers have expressed the opinion that they then sleep on the wing. There is no doubt, moreover, that ascending trends of wind enable the creatures to soar in lighter breezes than would otherwise be possible, and when the faint morning wind first begins to blow, many of the sailing birds will be seen congregated just above wind breaks, while the other parts of the sky are vacant,

But to return from this digression, occasioned by the feat of "aspiration" performed by M. Myers kites, it will be discerned that the principle of flexibility alluded to confers stability upon the well-known Japanese kite specimens of which are now to be found in almost all toy shops. This kite flies without a tail, the frame being so light and elastic that the surface adjusts itself constantly to the irregularities of the breeze. The side pockets catch the wind, and by springing back of the medial line form a diedral angle which confers lateral balance, while the flexibility up and down confers longitudinal equilibrium. The same principle is exemplified in the upward bending of the extremities of the feathers of birds in flight, which doubtless adds much to their stability, and, indeed' so universally is this principle illustrated by all creatures which navigate fluids, that Dr. Amans, in a work upon the locomotive organs of fishes,³² lays it down as an axiom derived from physiological considerations, that an aeroplane of rigid form is contre nature, or in direct antagonism with all the inferences to be drawn from the observation of creation.

The Japanese are expert kite-flyers, and have produced many shapes besides that which has been above alluded to. They are said to use kites as weather vanes, and to have hitching posts in their gardens to which the device is almost permanently affixed. Indeed, it is said that these kites sometimes remain 8 or 10 consecutive days up in the air--an astonishing achievement to European and American kite fanciers, who seldom succeed in keeping their apparatus up more than a few hours. The explanation is probably to be found in the greater regularity and permanence of the air currents in the regions of trade winds, and these too are the regions where the soaring birds are most numerously found, probably because they are there sure of a sustaining breeze every day, through the use of which they may evade the fatigue of flapping flight.

The various forms of the Chinese kites are even more numerous than those of the Japanese, and most of the tailless kind are said to depend upon the same principle of flexibility for their equilibrium. It would not at all be surprising to find, should a stable aeroplane be hereafter produced, that it has its prototype in a Chinese kite; but the writer has discovered very little information in print upon the subject; the following article, translated from La Nature by the Scientific American and published in its issue of March 24th 1888, being perhaps the best available:

One of our correspondents in China, Mr. Huchet, at present in Paris, has had the kindness to have made for our purposes, by a skillful Chinese manufacturer, a series of models representing the different types of kites used everywhere in China, Annam, and Tonkin, and which the same gentleman has been obliging enough to bring to us in person.

Fig. 69 represents the simplest form of these kites. Its frame is formed solely of a stiff bamboo stick, A B, and two slightly curved side rods, C D and E F. To this frame is pasted a sheet of paper, which is somewhat loose at the extremities C E and D F where, under the action of the wind, pockets are formed that keep the affair bellied and in an excellent position of equilibrium. Our engraving shows the mode of attaching the strings that serve to hold it. Kites of this kind are usually about 3 ft. in width.

Fig. 70 shows the appearance of the musical kite, so called because it is provided with a bamboo resonator, R containing three apertures, one in the center, and one at each extremity. When the kite is flying the air, in rushing into the resonator, produces a somewhat intense and plaintive sound, which can be heard at a great distance. This kite is somewhat like the preceding, but the transverse rods of its frame are connected at the extremities and give the kite the aspect of two birds' wings affixed to a central axis. This kite sometimes reaches large dimensions--say TO ft. in width. There are often three or four resonators placed one above another over the kite, and in this case a very pronounced grave sound is produced. Mr. Huchet informs us that the musical kite is very common in China and Tonkin. Hundreds of them are sometimes seen hovering in the air in the vicinity of Hanoi. This kite is the object of certain superstitious beliefs, and is thought to charm evil spirits away. To this effect it is often, during the prevalence of winds, tied to the roofs of houses, where, during the whole night, it emits plaintive murmurs after the manner of Eolian harps.

Among ingenious fancies of the Chinese is their bird kite, fig. 71, the frame of which is made elastic. The thin paper attached to the wings moves under the action of the wind and simulates the flapping of the wings. This kite is sometimes 3 ft. in length.

The most curious style of Chinese kite is the dragon kite, fig. 72. It consists of a series of small elliptic, very light disks formed of a bamboo frame covered with India paper. These disks are connected by two cords which keep them equidistant. A transverse bamboo rod is fixed in the long axis of the ellipse, and extends a little beyond each disk. To each extremity of this is fixed a sprig of grass which forms a balancing plume on each side. The surface of the foremost disk is slightly convex, and a fantastic face is drawn upon it, having two eyes made of small mirrors. The disks gradually decrease in size from head to tail, and are inclined about 45 in the wind. As a whole, they assume an adulatory form, and give the kite the appearance of a crawling serpent. The rear disk is provided with two little streamers that form the tail of the kite. It requires great skill to raise this device.

This last device resembles in arrangement the multiple disk kites for life saving of the Rev. Mr. Cordner, already described, and suggests that the superposition of kites affords a good field for experiment, There is a limit in size beyond which the increasing leverage will so add to the required strength and weight of the frame as to make a kite unduly heavy as well as unwieldy,³³ and superposition naturally suggests itself for experiments intended to test the efficacy and equilibrium of kite aeroplanes. There will be many practical details to work out in devising the best mode of attachment of such aeroplanes with each other, so that all surfaces may pull together and yet counteract the effects of wind gusts, so that experiments with kites seem to offer the readiest, quickest, and least expensive method of working out this part of the problem.

The attention of experimenters is specially called to the form of kite shown in fig. 70. It resembles in shape and attitude those of the soaring birds, which, as already remarked, perform their maneuvers with peculiarly curved and warped surfaces, and it will be seen hereafter that the nearest success in compassing gliding flight hitherto obtained--that of M. Lilienthal--has been achieved with just such surfaces.

Inventors seem to have bestowed but little attention upon kites, less than a score of such devices having thus far been patented in the United States. These patents chiefly cover various methods of making the frames to fold, so that the kite may be more portable, while but few inventors seem to have considered how the stability may be increased. Among these latter may be mentioned Mr. Clarke (No. 96,550), who proposes the insertion of a spring on one of the three cords which compose the bridle. By the yielding of this spring the angle of incidence of the kite may vary somewhat with the varying velocities of the wind, and thus diminish the perturbations.

Mr. Maddans (No. 121,056) proposes a kite with a convex surface, this being obtained by providing a stick across the top, which stick is sprung into a bow by attaching its ends to each other; but this bowing seems to have been chiefly devised to attach a flapping tongue, rotating on the bowstring, and so making a drumming noise, while there is no doubt that the convexity of the kite must add to its stability.

Mr. Thompson (No. 225,306) patents a reversible convex or concave kite, with a frame like that of an umbrella; but nothing is said of the equilibrium or of dispensing with a tail, the object being, apparently, to provide for convenience in carrying.

Mr. Coldly (No. 354,098)) provides for the stability by inserting in the middle surface of a kite a wind bag rearward projecting, which is distended by the breeze and prevents the kite from darting. This is virtually the same device as that of Mr. Copie, already mentioned, which was found to require a central opening to allow the escape of the air when experimented in large dimensions. It is evident that such a device, if applied to a navigable aeroplane, would largely increase the resistance to forward motion; but this might be minimized by making such wind pockets very shallow, and inserting a large number in the aeroplane. The experiment may be worth trying by kite fanciers.

While several forms of folding frames for kites have been patented by inventors, few seem to have been designed to act as parachutes also. This has been accomplished recently by Mr. Moy in a very simple way (British patent No. 1.916, A.D. 1892) by providing the folding frame with a central hub, to which a trapeze bar may be suspended when such a kite is used for conveying passengers or for exploration. By using two lines, the angle of incidence may be controlled, and the kite be made either to raise a weight or to descend slowly to the ground as a parachute.

As already intimated, the writer has found singularly little on record concerning kites, and that little bears but slightly upon the important question of the stability of aeroplanes. It may be for lack of more thorough search that only fragmentary information has been gathered. Kites are supposed to have been invented 400 years before the Christian era by Archytas, a resident of Smyrna (where the flying of kites remains a national sport to this day), and the Asiatics have always been and are now the great kite experts of the world. It is, therefore, not improbable that search in books of travel or inquiries addressed to Orientals might elicit information bearing directly upon the flying machine problem; and it is much to be desired that some competent person shall undertake to write a critical account of kite experiments as well as of the kites of all nations, and of the influence of form as to stability and sustaining power. There is a large collection of Chinese kites in the National Museum at Washington, and it would certainly be interesting to have an account of the various principles exemplified and of the behavior of the various shapes in the air.

³² Comparaison des organes de la locomotion aquatique, P. C. Amans.
³³The largest kite on record is said to belong to a Japanese gentleman, and is 50 ft. X 45 ft., weighing 1,700 lbs. Its frame is composed of 350 pieces of wood.
 

 

Aeroplanes  Part XIII

by O. Chanute

July 1893.

At the annual meeting of the American Association for the Advancement of Science, held in Buffalo, N. Y., in 1886, a paper on The Soaring Birds was read by Mr. Lancaster, then of Chicago, which paper attracted great interest and attention.

Mr. Lancaster, in the hope of surprising the secret of the birds, had the pluck, in 1876, to exile himself to the wilderness of Southwestern Florida, on the Gulf coast, near the Everglades, and there to remain for five consecutive years watching the sailing of the master soarers. He published some of his observations and deductions in the London Engineer, in the reports of the Aeronautical Society of Great Britain, and in the American Naturalist but the subject was by no means exhausted, and his description of the phenomena observed was so interesting to the members of the association, few of whom had ever seen a soaring bird at close range, that they demanded to hear more upon a subsequent day.

Unfortunately for Mr. Lancaster, upon the latter occasion he attempted to give a mechanical and mathematical explanation of the performances which he had previously so well described, and his theory was so plainly erroneous that he was subjected to harsh ridicule and criticism. He had witnessed some remarkable feats of "Aspiration," he had attempted to reproduce them artificially, but he was clearly wrong in his expounding of the mystery, and his critics did not properly discriminate between the statements of observed facts and the attempted explanation.

The principal issue, however, was made concerning some attempts to imitate soaring action, which Mr. Lancaster claimed to have successfully made in Florida, and which he unwisely declined to exhibit at Buffalo. He had described them in his paper as follows:

I constructed floating planes which, for lack of a better name, I have termed "effigies," and which are an example in point. I have made scores of them. They would draw into the breeze from the hand and simulate the soaring birds perfectly, moving on horizontal lines or on an inclination to a vertical. They would float in the best winds with neither ledge, rough front surface nor rear curve if very nicely adjusted; but one of this construction I never induced to pass beyond the limits of vision, as the equilibrium was so very delicate that a little inequality in the wind current would capsize it.

There is every probability that such an experiment would invariably fail if tried in any but a perfectly steady sea breeze, an inflowing current of air with peculiar conditions; but it does not follow that the action described is impossible, for if we presume that current to have an upward trend (and the writer knows, of his own knowledge, that such upward trends are not rare in sea breezes), we can readily see that an aeroplane, tipped forward so as to point below the horizon, may be both sustained and "aspirated," or possess a forward component of pressure, so that it may advance against the wind, and rise at the same time, like the kite of M. Myers.

The equilibrium is, of course, excessively delicate, and hence the requirement for a sea breeze, for a local homogeneous mass of air flowing from the water over the land to replace the rising quantity heated by the sun; but it is erroneous to suppose that the experiment described by Mr. Lancaster involves a mechanical impossibility. It is, doubtless, difficult to repeat it successfully, because it requires a combination of peculiar conditions; but the soaring birds are daily performing the feat, and apparently in horizontal winds.

In order that those who are favorably circumstanced may test the matter experimentally, the following description of the device is copied from a paper of Mr. Lancaster, published in 1882.

Take a stick of wood 1 in. square and 18 in. long, and point one end. Slit the other end 3 or 4 in., and insert a piece of stiff cardboard 6 in. wide and I ft. long. This will represent the body and tail of the bird. Fasten on both sides near the pointed end a tapering stick 2 ft. long, with the outer ends slightly elevated, and fasten to these and the body a piece of cardboard 10 in. wide and 2 ft. Iong. Have the tail vertical instead of horizontal, as in the bird. Round off the outer rear corners of the wings for 3 or 4 in. The imitation of the natural bird is now complete. There is no need of exactness, as the air you are to try it in will be an unknown quantity, and it may just suit the shape you make. An indispensable part is now to be added, which is to preserve the equilibrium and is not used by the natural bird. A tapering stick, say Ii in. wide, 3/8 in. thick at the top, 3/8 in. square at the other end, and 18 in. long is used. This piece is to be securely fastened by a small bolt through the upper end of the body piece, about 5 in. from the from end. It must be capable of adjustment by allowing the lower end to swing front and back through say 4o . To the lower end is fastened a muslin bag which will hold 2 lbs. of shot. Expose the effigy to a breeze of from 3 to 20 miles an hour, from as high a situation as it is possible for you to obtain, by holding it by the pendant stick near the body. Adjust the weighted stick forward or back, and add or subtract shot until the effigy has a tendency to spring from your hand against the current of air, when it may be released at a moment of greatest steadiness of breeze.

I have made hundreds of these toys, with all kinds of success, but have never yet succeeded in getting one to travel beyond the limits of vision. They have proceeded directly against the breeze for 500 yards, and obliquely, up or down, or to right or left, within those limits, when they would dose their balance and come down Sometimes almost any kind of one that was presented to the air would float creditably, while at others none would succeed. The pendant weight for maintaining equilibrium, though the best I have ever devised, is far too sluggish for perfect work. The momentum of this weight prevents the best results, for, if a succession of puffs of wind upon the same wing should occur quickly together, the weight would swing far enough, in obedience to the impulse given, to capsize the effigy. Such a succession of puffs is sure to occur, sooner or later, at each trial. These toys operate long enough, however, to prove the purely mechanical character of flight, and serve to materially strengthen the theory.

The writer may confess that he has tried this experiment several times under special instructions furnished by Mr. Lancaster, but that he has never succeeded in floating one of these "effigies" so that they would advance against the wind. Others have, to his knowledge, tested the matter, and had no better success, yet it is not rational to say that the feat is impossible, for it is very clear that if the wind have an ascending trend, and the "effigy" be slightly tipped toward the front, the horizontal component of air pressure will drag it forward, while the vertical component will sustain or elevate it, as already explained. It is probably because of the uncertain prevalence of ascending trends that Mr. Lancaster complains that sometimes almost all these toys would succeed in simulating soaring, and sometimes none at all.

In 1888 Mr. Lancaster moved to Colorado, where he has been experimenting with a view to the solution of the problem of soaring flight; and in the American Naturalist for September, 1891, he gave an account of some of his experiments, with the conclusions which he deduced there from. The following extract contains an account of a remarkable occurrence. He says:

I can produce true soaring flight in natural wind, with a plane exceeding 2 lbs. to a square foot of surface, whenever I wish to do so and can obtain wind strong enough for the purpose. During the past three years I have made about 50 planes [aeroplanes ?] of various shapes and sizes, and from 25 lbs. to 400 lbs. in weight. These planes are not set free in wind, but used in the experimental cases above described, but with rigid rods in place of the parallel wires. These rods run in large rings and have a cross-head at their outer ends allowing the plane to run to the front until its edge rests against the rings. In the best trial the parallel [with the plane ?]] component is neutralized at 10 from horizontal, far exceeding my expectations derived from observations of the birds, their angle of obliquity being rarely over 5°.

On a few occasions these planes accidentally escaped me in time of highest wind, and were ruined at once for all purposes excepting firewood, in each case being a loss of two or three months' work, and playing havoc with my finances. One that I valued particularly plunged to the front in a violent blast of wind with force sufficient to tear out the rings. It rose into the air. gradually higher and higher, until an elevation of at least 3,000 ft. was attained, when some part of the device giving away, it lost equilibrium and plunged through the air, striking the earth about 21 miles from the 2 1/2 and 1,000 ft. higher than that locality. Another mile would have carried it to the summit of the Flat Top Mountains. It was in the air about three hours, and I walked beneath it during its flight. Its course was directly against the highest wind I have experienced during my residence here. At times it did not progress, bat went higher. It weighed 110 lbs., and had been well balanced for experimenting on surface manipulation. There was no lesson taught in this flight, the birds having been doing the same thing for a long time. It was an interesting spectacle to look at: so is a large bird in the same act. I presume Mr. Darwin's provisional solution would apply to this plane as well as to the condors; but I am trying to explain the actual mechanical activity of both.

The best effects produced were with a plane of 400 lbs. weight and 80 sq. ft. of surface. In a wind that would be rightly termed a gale, arising about midnight, this plane was thrown about 7° from horizontal. It ran to the front against the rings at 10°, where the entire parallel component was neutralized, and at 7° it hugged the rings with a force that required a backward pull of 15 lbs. to detach it.

This plane would make a splendid navigator, and I would have no hesitation in trusting myself to it, when steering. equilibrium and alighting or stopping items had been worked out. I mean to say that it would navigate wind. I am now just entering on a course of experiments in calm air.

This very interesting case of "aspiration" may have been produced by the same cause as in the case of M. Myers's kite--i.e., an ascending trend of wind; but certainty concerning this depends upon the shape of the surface. Mr. Lancaster writes of it as a "plane ;" but as he mentions also the "front ledge" and the "rear curve," the surface operated upon by the wind was probably a more or less compound surface, for which there is no specific name, but which may be described as an aeroplane. If it was shaped like those of the soaring birds, then "aspiration" might occur with a horizontal wind, but the equilibrium would be very unstable, and, as Mr. Lancaster points out, the steering, alighting, and stopping would be the important points to work out.

Among the most systematic and carefully conducted series of experiments that have ever been made in the direction of artificial flight are those of Herr Otto Lilienthal, of Berlin, Germany, a mechanical engineer and constructor, and a prominent member of the German Society for the Advancement of Aerial Navigation.

The general position that he maintains, and in pursuance of which he has made his more recent experiments. is that bird flight should be made the basis of artificial flight. Dexterity alone, as he maintains, invests with superiority the native denizens of the air, and, therefore, man, if he possessed sufficient skill, might participate in flight. He evidently believes, like M. Mouillard, that for the soaring birds ascension is the result of the skillful use of the power of the wind, and that no other force is required; and, therefore, that to imitate them no engines or other external sources of power are needed, but that all the necessary apparatus consists of properly constructed sustaining surfaces skillfully operated.

Herr Lilienthal, instead of first flying at conclusions, began by a systematic analysis of the problem, verified by experiments, which latter were carried on by himself and his brother, G. Lilienthal, during a period covering nearly 25 years, and he published in 1889 a book on "Bird-Flight as the Basis of the Flying Art,"³⁴ in which he gave the result of his investigations.

From a review of this remarkable book in the Aéronaute for January, 1892 the following account of its contents has been prepared.

Herr Lilienthal seems to have begun by observing the sailing of various sea birds following vessels at sea, and of the stork, an expert sourer, which inhabits Germany; he drew the conclusion that plane surfaces present undue resistance, and that success in artificial flight is only to be expected from concavo-convex sustaining surfaces; a belief which, as we have already seen, was also entertained by Le Bris, Beeson, Goupil Phillips , and others.

He declares that the laws of air resistances and reactions which, unfortunately, are as yet but imperfectly known, form the whole basis for the "technique" or actual performance of flight, and that the shapes and methods of birds so completely utilize these laws and offer such appropriate mechanical movements that failure must follow if they be discarded.

Herr Lilienthal's experiments were in great part directed toward an investigation of the resistances and reactions of air, and the power necessary for flight. One of these consisted in suspending himself from a spar projecting from a house and operating a set of six wings opening and closing like concave Venetian blinds, through which he measured the lifting effects of wing strokes performed with the muscles of the legs, so that the step of each foot would produce a double stroke of the wing. The weight of the operator and wings combined was 176 lbs., and they were counterweighted with 88 lbs. suspended to a rope passing over two pulleys. With some practice he was enabled, by operating the wings with the pedals, to lift himself 30 ft. from the earth, thus proving that he obtained, through his mechanism, wing power sufficient to lift the remaining 88 lbs.--a very excellent performance, and much in excess of most of those hitherto described in this review of Progress in Flying Machines.

This and other experiments, together with a consideration of the power to be obtained from the wind, convinced him that artificial flight was accessible to man, aided by considerably weaker motors than have generally been thought indispensable, and, indeed, under favorable circumstances of wind, with no motor at all.

Herr Lilienthal therefore, carefully analyzed the shapes and methods of the living birds and the exact proportions of their concavo-convex surfaces. He went into this in detail, and finally formulated in his book the following conclusions:

1. The construction of machines for practical operation in nowise depends upon the discovery of light and powerful motors.

2. Hovering or stationary flight without forward motion cannot be compassed by man's unaided strength. This mode of flight would require him to develop, under the most favorable circumstances, at least 1.5 horse power.

3. With an ordinary wind man's strength is sufficient to worn efficiently an appropriate flying apparatus.

4. With a wind of more than 22 miles per hour, man can perform soaring or sailing flight by means of adequate and appropriate sustaining surfaces.

5. A flying apparatus, in order to operate with the greatest possible economy, must be based, both in shape and proportion, upon the wings of the large, high-flying birds.

6. The sustaining wing surface may be from 0.49 to 0.61 sq. ft. per pound of weight.

7. Sufficiently strong apparatus can be built of willow frame and stretched fabric, so as to provide a sustaining surface of 107 sq ft., with a weight of about 33 lbs.

8. A man provided with such an apparatus would have an aggregate weight of 198 lbs., and would then have 0 55 sq. ft. Of sustaining surface per pound, or about the proportions of large birds.

9. Experiment must determine whether the most advantageous shape be that of birds of prey and of waders, with broad wings and spread out primary feathers, or that of sea birds, with narrow wings tapering to a point.

10. If the broad wing be adopted, the wings of an apparatus with 107 sq. ft. of sustaining surface would needs be of 26.25 ft. spread, with a maximum width of 5.25 ft.

11. If the narrow wing be adopted, a surface of 107 sq. ft. would need a spread of 36 ft. with a maximum width of 4.60 ft.

12. The application of an additional bearing surface, as a tail, is of minor importance.

13. The wings must be curved in transverse section so as to be concave on the under side.

14. The depth of flexure should be one-twelfth of the width, in order to correspond with that of birds' wings.

15. Experiment must determine whether greater or lesser flexure will prove preferable for larger wing surfaces.

16. The framing and spars of the wings should be at the front edge so far as possible.

17. A sharp cutting edge should terminate this framed front edge if possible.

18. The flexure should be parabolic, the greater curvature being to the front and flatter to the rear.

19. The best shape of flexure for large surfaces must be determined by experiment; also what preference is to be given to those shapes which produce the least resistance to forward motion at flat angles of incidence.

20. Construction must be such as to admit of the rotation of the wing upon its longitudinal axis, which rotation will best be obtained, in whole or in part, by the pressure of impinging air.

21. In flapping flight the inner wide portion of the wing should oscillate as little as possible, and serve exclusively in sustaining weight.

22. The propulsion to maintain speed should be obtained by up-and-down beats of the wing tips or of the primary feathers, the forward edge being depressed.

23. In flapping flight the widest portion of the wing must also co operate in the up stroke in order to sustain weight.

24. The wing tips should encounter as little resistance as possible on the up stroke.

25. The down stroke should be in duration at least six-tenths of the time occupied by the double stroke.

26. The wing-tips alone need oscillate; that portion of the wing which merely sustains may remain rigid, as in soaring flight.

27. If only the wing tips oscillate they should not be articulated, as this would dislocate them; moreover,-the transition to the up stroke should be as gentle as possible.

28. In order to beat a pair of wings, man must employ his extensor muscles, and this not simultaneously, but alternating each side, so that each stroke of the foot shall produce a double stroke of the wings.

29. The up stroke may be produced by the pressure of the air under the wings.

30. The energy of the air pressure under the wings may be partly stored in a spring so as to restore the power on the down stroke, and thus produce economy in work done.

Such are the principal considerations which must be observed in the application of the theories herein expounded.

Governed by these considerations, equipped with much preliminary experiment and analysis, Herr Lilienthal put his theories and conclusions to practical test, in the Lilienthal of 1891 by undertaking a series of experiments with a pair of curved wings designed for soaring alone--that is, to serve as sustaining surfaces and not for flapping or propulsion.

The following account of these experiments has been furnished by Mr. George E. Curtis, of Washington, D. C., who has also obtained from Dr. C. Kassner, of the Meteorological Institute at Berlin, the very graphic photographs from which the engravings have been made.

The Lilienthal apparatus is shown in fig. 73, and consists of a pair of extended bird-like wings, incurvated from front to back on parabolic lines, and sinuous in the direction of their lengths. The area of sustaining surface, as at first constructed, was 107 sq. ft., but it was diminished in the course of numerous changes and remodeling to 86 sq. ft. There was, as will be observed, a horizontal tail and a vertical rudder or keel. The framework was made of willow, and covered with sheeting fabric. The weight of the whole apparatus, without the operator, was 39.6 lbs.

In order to become accustomed to the management of these artificial wings, Herr Lilienthal first practiced in his garden. Here he had a spring-board, toward which he ran for a distance of about 26 ft.; and with the velocity thus acquired, together with the reaction of the springboard, he launched himself into the air, where he could learn to operate and to manage the wings.

After these preliminary experiments had given him dexterity and facility in the management of the apparatus, he betook himself to a hilly region in the suburbs of Berlin, and there practiced soaring flight in natural winds of moderate velocities. The plan, of course, consisted in first running against the wind, and thus deriving there from the necessary sustaining air pressure.

Having selected a hill whose downward inclination faced the prevailing wind, he ran along the summit straight toward the wind, until a sufficient velocity was attained at the brow, where he was carried into the air and landed safely at the foot of the hill, having sailed a distance of 65 to 82 ft.

When the wind velocity became greater than 11 to 13 miles per hour. the management of the apparatus became exceedingly difficult, and Herr Lilienthal advises an experimenter not to venture to leave the ground under such circumstances, unless he has attained, through long practice, a considerable degree of dexterity in maneuver

The results attained in the practice of the season of 1891 were sufficiently encouraging to warrant the further prosecution of these experiments in the following year; but they disclosed a number of points to which additional attention needed to be given in order to overcome the practical difficulties in imitating the birds. These points related to a better adjustment of the center of gravity, to methods for obtaining greater stability, and to the mode of management of the apparatus when the wind blew more rapidly than 11 to 13 miles per hour.

In the issue of the Zeitschrift für Luftschiffahrt for November, 1892 Herr Lilienthal published an article on "Soaring and its Imitation, "in which he gives a brief account of his experiments in the summer of 1892 from which the following abstract has been prepared:

Many theories have been proposed to explain soaring. My own explanation is based upon the advantageous relations of air resistances incident to the use of slightly curved wing surfaces (as I have demonstrated) and upon the gently rising trend of alr current which I have found to prevail.

A flying apparatus which has the same proportions as those of a good soaring bird and is of sufficient size to carry a man, can scarcely be held fast by three or four men together when exposed to a brisk wind. When we look at the safe and quiet sailing of the birds, it almost seems as if some undiscovered mechanical principle were at work, some feature in the elastic

properties of air or in the elastic curvature of the feathers which accounts for the mystery of sailing flight; but my experiments have taught me that there is no mystery, and that the same mechanical science which has explained the theory of the steam engine and followed the orbits of the planets is adequate to explaining the operations of soaring flight.

Dexterity alone, in my opinion, invests the native inhabitants of the air with superiority over man in that element.... Inasmuch as continuous soaring with large wings in high winds can terminate in scarcely anything but the destruction of the foolhardy fellow who may first attempt the experiment without previous practice, I first undertook last year to gain some expertness with a smaller apparatus and in moderate winds. In spite of my caution the wind several times played the mischief with me. Even with only 86 sq. ft. of sustaining surface, I was several times tossed up into the air by unexpected gusts of wind, and but for the circumstance that I was able to release myself quickly from my apparatus, I might have had a broken neck instead of the sprains in feet or arms which always healed in a few weeks.

Almost every Sunday, and sometimes on week days, I went out to practice on the hill between Grosshreutz and Werder. A mechanic, Herr Hugo Eulitz, the maker of my apparatus, went with me, and each practiced alternately while the other rested. Thus we obtained dexterity in gliding down on the air and in landing at the foot of the hill without mishap.

Herr Kassner, of the Meteorological Institute, was so kind as to photograph me in the air, and has thus enabled me to exhibit to the members of the society how I sailed right over the head of the miller of Derwitz (in whose barn I stored my apparatus) and of his esteemed poodle dog.

Equipped with the experience gained in 1891, I this year attempted to soar with wings measuring 172 sq. ft. in surface. My apparatus weighed 53 lbs., and my own weight is 176 lbs., so that the whole was 229 lbs. Each Square foot of surface, therefore, sustained 229/172 = 1.33 lbs.

The up-thrust of the wind (the lift) upon the wing surface is perhaps half as much as the pressure of the same wind upon the same surface if turned perpendicular thereto.³⁵ Now, as the apparatus therefore needs to sustain it a wind producing a pressure of 1.33 X 2 = 2.66 lbs. per square foot we see that (by ordinary tables of wind pressures) it must blow at a velocity of about 23 miles per hour.

I have, however, been very cautious about exposing myself to such a wind with this large apparatus; and in such high winds have used smaller surfaces for my sailing practice.

This year I selected a locality between Stegiitz and Südende. It had, however, the disadvantage that only westerly starts were possible. Herr Kassner has again taken instantaneous photographs of my apparatus, which have been laid before the society (fig. 74) The strongest winds in which I practiced had a velocity which I estimated at between 15 and 16 miles per hour. By running I obtained an additional velocity of 7 miles an hour, making the total relative velocity 23 miles an hour, which was required for soaring. Under these circumstances the first part of my flight was almost horizontal, and the alighting was always a gentle one.... Each apparatus had a vertical and horizontal tall, without which it is impracticable to practice in the wind. In conclusion, I will remark that sailing flight near the earth's surface must be much more difficult than at greater heights, where the wind blows more regularly, while every irregularity of the ground at lower levels starts whirls in the air.

³⁴"Der Vogelflug als Grundlage der Fliegekunst," Von Otto Lilienthal, Berlin, 1889.
³⁵Lilienthal, "Der Vogelflug als Grundlage der Fliegekunst," Tafel VII.

 

 

Aeroplanes  Part XIV

by O. Chanute

August 1893.

 

In the opinion of the writer of these lines Herr Lilienthal has attacked the most difficult, and perhaps the most important, of the many problems which must be solved before success can be hoped for in navigating the air with flying machines. He has engaged in the effort to work out the maintenance of equilibrium in flight, and to learn the science of the bird. He has made a good beginning and seems to be in a fair way to accomplish some success in riding on the wind.

We have already seen that this has been tried before, and that (to say nothing of ancient myths) F. B. Dante, Paul Guidotti, Francisco Orujo, and Captain Le Bris, all met with partial success in soaring. Singularly enough all four met also with the same accident--i.e., a broken leg, in consequence of the loss of equipoise. Herr Lilienthal has greater chances of success, not only because he seems to have set about his experiments only after thorough investigation and consideration, but also because mechanical knowledge as well as constructive methods and workmanship have greatly improved since even Le Bris's time. Besides this, we have the gliding exploit of M. Mouillard, whose experiment has already been related, and that of M. Ader, which is yet to be mentioned.

Most of the capable inventors who have undertaken to solve the problem of flight have first concerned themselves with the question of motive power, and we shall see hereafter that very great progress has been achieved in this direction since 1890 but no amount of motive power will avail unless the apparatus to which it is applied is stable in the air--unless it can rise, sail, and come down again without danger of losing its equipoise. As has already been said, safety is the first requisite, and until this is assured, all the other elements of success will be unavailable.

Herr l Lilienthal has eliminated for the present the question of motive power, by undertaking to utilize ascending trends of wind, like a sailing bird, and if he succeeds in gliding up as well as down, and to the right or left, and in maintaining at all times the coincidence of the center of gravity with the center of pressure at all angles of incidence, he may not only apply an artificial power hereafter, for use when great speed is required or when there is no wind, but he will also probably have evolved a method of gratuitous transportation through the air when the wind blows under proper conditions; for there seems to be no good reason why a soaring apparatus for one man should cost more than twice as much as a first-class bicycle, or half as much as a city carriage; and when the wind is in the right direction, a good many miles could be sailed over in a day with no expenditure of force save for the evolutions necessary to maintain the equilibrium, although this can only be done under peculiar circumstances, and the commercial use must be very much less than that of bicycles.

That this expectation is not altogether absurd will appear from a brief consideration of the power of the wind; and to make the matter plain we will suppose it to have an upward trend of 15 or 26 per cent. or a very moderate inclination, which must be frequently exceeded. Under that circumstance a horizontal aeroplane will, as previously explained, have the horizontal component of the normal pressure directed to the front and acting as a forward propelling force. We may now calculate what the effect of this would be upon Herr Lilienthal's aeroplane.

This was proportioned in the ratio of 0.75 sq. ft. of surface to the pound of weight; but as the surfaces were concavo-convex, we may assume that the coefficient of efficiency would be about the same as that which we have assumed heretofore for the pigeon, or 1.3 per cent. of the actual surface, and we may further simplify the calculations by assuming the equivalent plane surface as equal to 1 sq. ft. per pound to be sustained. Now if this be exposed to a wind blowing at the rate of 25 miles per hour, at which the rectangular pressure, as given by Smeaton's table, is 3.125 lbs. per square foot, and if we suppose the plane to be inclined forward, so as to point 5 below the horizon, then the wind will make an angle of 10 with the plane, at which the normal pressure, by our tables, will be 0.337 of the rectangular pressure. As the effect upon the plane is in the ratio of the angle which the latter makes with the direction in which we desire to calculate it ie., the horizon, and this angle is 5 , the sine of which is 0.087, then we have for the propelling force for each square foot of sustaining surface:

Drift = 1. X 3.125 X 0.337 X 0.087 = 0.0916 lbs per square foot.

But as the speed is 2200 ft. per minute, we have for the power:

Power = 0.0916 X 2200 . 33000 = 0.00611 horse power per square foot,

which for an apparatus with 172 sq. ft. of sustaining surface furnishes a motive power of 0.00611 X 172 = 1.05 horse power, which is the power at the disposal of Herr Lilienthal when the wind blows 25 miles per hour, with an upward trend of 15.

This, of course, varies with the trend and the strength of the wind; but it will be noticed that with the data assumed it will amount to some 6 horse power for an aeroplane with 1000 sq. ft. of sustaining surface--an amount which will probably be surprisingly great to those who have not considered the subject.

It will doubtless be objected that these calculations are all based upon the assumption that the wind has an ascending trend, and that this condition does not uniformly obtain, particularly at sailing heights above the earth, where the wind may be horizontal at the very time that experiment shows an ascending trend near the surface. This is granted; it is acknowledged that the calculations of power to be obtained from the wind are predicated upon an assumption which may be untrue part of the time; but the answer to the main objection is that the birds soar at all times when there is wind enough (not too much), and that while we cannot yet explain how they do it, man ought to be able to avail himself of the same circumstances as the birds, if only he can maintain his equilibrium.

This is what Herr Lilienthal has undertaken; he has done so with great prudence and good sense, and so far as the results of his experiments have been published they teach several valuable lessons, which may be summed up as follows:

1. The upright position for the body of the aviator is the most favorable, as being most natural to man.

2. Safety while learning the management of an apparatus is promoted by beginning with comparatively small surfaces, because wind gusts are liable to destroy the balance. It is best to glide downward in initial experiments until practice has conferred the skill requisite to maintain the equilibrium, in case the apparatus is tossed up in the air by the wind. This is a lesson which was not obvious, and it should be heeded by experimenters, some of whom have assumed that safety was best promoted by large surfaces.

3. The aviator must be so affixed to his apparatus that he can detach himself instantly should the machine take a sheer.

4. It is not safe to experiment in winds blowing more than 23 miles per hour until skill has been acquired in the management of the apparatus, or until the latter has been so improved as to minimize the danger.

5. It seems now reasonably possible for designers of soaring machines (and the writer knows several) to experiment with their apparatus without further search for some hidden secret, for Herr Lilienthal says that his experiments have taught him that there is no mystery about sailing flight; that the wind is sufficient to account for it. Inventors need not look for some new mysterious force, some "negative gravity,"³⁶ like that in Mr. Stockton's tale, to take them up into the air; nor need they be afraid that if they propose to experiment with soaring machines they will be considered lunatics, The main question for them to consider is that of the equilibrium.

Of course, even if this be worked out, the practical usefulness of a soaring machine would be very limited. It could only be availed of when the wind blew with about the favorable velocity (neither too slow nor too fast), and its field of daily use would probably be limited to the trade wind latitudes, or, in other words, to those regions inhabited by the sailing birds; but if the equipoise be worked out, if man succeeds in devising an adequate soaring apparatus and in learning how to use it, unhampered by the necessity for looking after a motor at the same time, it will not probably be long before some motor is added to confer upon him command of space at all times.

In June, 1891, the quidnuncs in Paris were interested in the rumored success of some experiments with a flying machine carried on near Paris, in the private park of Mr. E. Pereire, the banker, by M. Clement Ader, who was said to have succeeded in rising to a height of about 60 ft., and in flying a distance variously estimated at 100 to 400 yds.

M. Ader is a well-known French electrician, the inventor of a telephone, and has long been interested in the flying-machine problem. In 1872 he constructed an artificial bird 26 ft. across and weighing some 53 lbs., with beating wings actuated by the muscular force of the operator's legs, aided by elastic auxiliary pectorals. In high winds, and restrained by ropes in order to guard against accidents, it would lift up a man, but it was found, as many times before, that man has not the requisite energy to sustain his weight in calm air. Subsequently the same apparatus, or a modification of it (for the accounts are not quite clear), was set up under a shed at Passy and visited by M. de la Landelle,³⁷ who states that the operator was stretched horizontally (a bad position) between the wings, and worked with his feet and hands the organism of transmission to the parts that acted upon the air. A certain lifting effect was produced, but not enough to sustain the whole weight. I his apparatus was never photographed, but its inventor now contemplates unboxing it and setting it up again as a curiosity.

In 1891 as already mentioned, M. Ader built another artificial bird 54 ft. across, with which he experimented in the open air with such close privacy as he could secure; but the details are being kept secret, as the inventor states that he believes that it is destined to play an important part in the national defense of his country. He merely mentions the fact that the motor and the man who works it are placed in the interior of the machine, which is shaped like a huge bat; that the motor is actuated by a "mixture of a combination of vapors," and that the instrument of propulsion is a screw (of which he tried some eight patterns) placed at the head; that the whole apparatus rests upon skates or upon wheels, and that he needs a long smooth, flat space to gather headway by sliding or rolling some 20 or 30 yds. or more. He stated that he had already expended some $120,000 in his aerial experiments during the 15 years that he had been working at the problem, and that he contemplated exhibiting his machine in the air, if he could secure the use of the great machinery hall built for the Paris Exposition of 1889.

The above data are extracted from an account of an interview with M. Ader, published in the Paris Temps of July 9, 1891, in which he gave an interesting account of the preliminary studies that led to his last conception, the result, as he says, of a private theory of the resistances of air, which he proposes to publish some day.

Moved, probably, by the accounts of the sailing of large birds published by M. Mouillard as witnessed by him in Africa, M. Ader first obtained from the zoological gardens some eagles and some large bats, and observed their flight in his workshop. Judging this to be insufficient, he next went to Algeria, but could find none of the large vultures near Constantine; so, disguising himself as an Arab, he went into the interior with two Arab guides, and by enticing the birds with pieces of meat left in secluded places, he succeeded in obtaining ample observations.

M. Ader states that he became fully convinced that these vultures, some of them measuring 10 ft. across, do not beat their wings when rising on the air; that they flap them at most two or three times when first rising from the ground, and then hold them rigidly spread out to the current of wind upon which they ride, and upon which they rise in great circling sweeps by merely adjusting their aeroplane to the varying conditions of incidence and force of wind.

Starting from his theory and observations, M. Ader next built the machine which he has been experimenting with near Paris, in the presence, it is said, of only three or four persons, and with many precautions to avoid divulging his secret. He has even announced that he intends, from patriotic motives, to take no patents in foreign countries, so as not to divulge the design of his apparatus, and that all he can say at present is that the problem is an exceedingly difficult one, involving enormous mechanical difficulties, which increase rapidly with the size of the apparatus.

Naturally this reticence excited curiosity, and the French paper L'Illustration, in its issue of June 20, 1891, published a picture from which fig. 75 is reproduced, and it also made the following comments:

Nobody has seen anything, nobody knows anything, but L'Illustration has its friends everywhere. One of them was hunting rarely in the environs of Paris, when he caught a glimpse through the leaves of a strange object resembling an enormous bird of bluish hue. It was impossible to approach close to it; an enclosure surrounded the private park shut in by the forest in which the aforesaid machine was situated. Assuredly it could only be a flying machine. Our friend is something of a limner as well as an engineer, and he communicates to us the sketch which he made from a distance, and which is as correct as it was practicable to make it. Upon making due inquiry it turns out to be the invention of M. Ader the electrician, well known for his telephone apparatus, and it seems that the machine has really flown several hundred yards, rising some so to 65 ft., and holding a course through space.

The name of the inventor of this machine should be a guarantee of its possible success; still we have our doubts. It is said to have glided a certain distance in the air--100 or 200 or, say, 400 yds. But can it continue to do so for several hours, without having recourse to some fixed supply of power to recharge the motor actuating it ? For this is the vital point: what is the motor? As the inventor is an eminent electrician, thoroughly understanding this new science, he must have selected his favorite motor, the dynamo.

But electric accumulators are impracticable on account of their weight, while primary batteries act for only a short time, and they, too, are heavy.

Therefore, for the present, and until we have witnessed a convincing experiment, at which we shall have seen with our own eyes the generator of the power employed, we shall remain skeptics, and we shall believe (and this only because of the high scientific standing of the inventor) that it the machine sketched by our friend can really fly, it is only for a very brief period of time.

In point of fact, it is surmised by the writer of these lines that M. Ader has really been experimenting with a soaring machine, using a motor only to get under way, and (if the sketch of the apparatus is correct) that the principal difficulty he has met with has been to maintain the equilibrium. He may have had a few good flights under favorable circumstances, but he must have had many mishaps.

It is probable that one of his errors lies in adopting too large a sustaining surface, under the mistaken belief that this would promote safety. It would probably do just the reverse, by enabling little wind gusts and ground currents to upset the equipoise. The machine is 54 ft. across, and must spread to the breeze twice the surface employed by Herr Lilienthal, which we have already seen is found by the latter to be dangerous in winds of more than 23 miles per hour.

In August, 1891 M. Trouvé, whose mechanical bird with flapping wings actuated by explosions within a Bourdon tube, and whose hovering screw machine, worked by a dynamo connected by a wire to a source of electrical energy remaining on the ground, have already been noticed, deposited with the French Academy of Sciences a sealed letter, containing descriptions and drawings of an aeroplane, which he believes to be destined to solve successfully the problem of aerial navigation.

This method of depositing sealed descriptions of inchoate inventions with the Academy of Sciences is a favorite one in France, and answers generally much as the filing of a caveat does in the United States.

Nothing is known, of course, concerning the designs for this aeroplane, but M. Trouvé says that he has made great strides toward developing his aerial apparatus since 1870, and especially since 1884 that his laboratory experiments have convinced him that while his explosion motor is satisfactory as to the power exerted in proportion to weight, wings are less efficient than screws as instruments of propulsion. He has therefore designed an aeroplane propelled by two screws, rotating in contrary directions, which he believes to be superior to the former arrangement of beating wings.

The arrangement of this aeroplane is said to be such that the surface may always be proportioned to the weight to be carried, no matter what that weight may be.

The method of obtaining initial velocity is ingenious and effective. The apparatus is to be placed upon a railway car, and this is to be towed by a locomotive upon an ordinary railway, until the speed is sufficient to furnish the required reactive support from the air; when, the machine rises, and is thenceforth supported by its sustaining surfaces, driven by the two screws moved by the explosion motor.

M. Trouve believes that success is now a simple question of money expenditure, and that the daring man, favored by fortune, who first navigates the air will reap the glory of that success with less title thereto than his predecessors, who have pointed out the way.

In 1891 Gustav Koch, an aeronaut of Munich, published a pamphlet entitled "Free Human Flying, as the Preliminary Condition of Dynamic Aeronautics,"³⁸ which contains the plan and description of an apparatus designed by him, in order to endeavor to imitate the soaring of the birds, and which also gives an account of the experiments which he had tried with models. This design has been thought worthy of trial, and the Bavarian Ministers of the Interior and of Education in May, I893, granted 1,600 marks ($400) to Herr Koch to enable him to make experiments. This he is about to do (with an assistant) over the lake of Constance near Lindau, and while the results may not prove satisfactory, they cannot but prove interesting.

The aeroplane designed by Herr Koch consists in a pair of rigid wings, approximately shaped like those of the dragon fly each about 27 ft. long and 6 ft. broad, back of which there is a triangular tail, some 7 ft. long and about 8 ft. wide at the rear end. The wings are to be constructed of bamboo, covered with unbleached silk slightly oiled, and pivoted to the back of the operator. The latter is to lie horizontally, face downward, in a sort of hammock suspended from a frame which attaches to the wings, and the latter can thus be swung forward or back within small limits, so as to change their position with respect to the center of gravity, but they have no flapping action whatever. The operator is to swing the wings and to elevate or depress the tail by means of pedals on which his feet rest, and of lines leading to his hands.

It will thus be seen that the action of the apparatus, which is some 57 ft. across, consists in altering the position of the center of pressure, with respect to the center of gravity, by swinging the wings forward or back, and thus changing the angle of incidence which the apparatus makes with the course, while still further changes can be produced by the action of the tail.

The weight of the aeroplane. including the mechanism which works it, is estimated at 99 lbs., and that of the operator at 176 lbs., making a total of 275 lbs., to be sustained by about 325 sq. ft. of surface.

Herr Koch proposes to test the apparatus by taking it up beneath a balloon and cutting it loose when about 3,000 ft. in the air. The first experiments, of course, are to be tried with a dummy instead of a man, and if these indicate sufficient strength and stability, the operator is to take the place of the dummy. He expects the machine to descend like a stone for the first second or two, and then, when air pressure has gathered under the wings, to gradually right itself, and to glide downward upon an easy slope, which would bring it down to the water in about 8 minutes and a distance of some 2 1/2 miles, thus being a dirigible parachute. Meanwhile, however, the operator is expected to bring the apparatus under control; by swinging the wings forward he expects to tilt the planes so as to glide upward again, by virtue of the acquired momentum, and by movements of the tail and of his own

body, which has a certain latitude of motion in the hammock, he expects to tack and to sail upon the wind like a soaring bird, sweeping in circles or making a series of zigzag glances, during which elevation might be gained by utilizing the force of the wind.

Such is the scheme; it is not wholly devoid of merit, because the soaring birds perform those very maneuvers, and they do it much in the way which Herr Koch has indicated, hut it may be questioned whether his apparatus is properly designed to accomplish the results desired. In the first place, the sustaining surface and the spread across are too great, and will terribly strain the strength of materials. It would be better to shorten the wings and to make them broader in order to reduce the length of leverage. 1 in the second place, the horizontal position selected for the operator, probably to reduce horizontal resistance, is decidedly bad, because it is unnatural to man, and gives him inadequate control over the apparatus. The man should be placed vertically, and instead of maneuvering, as planned, to cause the back part of the tail to strike the ground first and roll along, while the aeroplane settles forward slowly, the operator should alight on his feet and stop his impetus while running if he alights on land. In the third place, the mode of experimenting proposed is exceedingly dangerous. Herr Koch says, quite properly, that the first step toward success in artificial flight consists in acquiring the skill to manage an apparatus, but until that skill has been acquired it will evidently be little short of suicide to cut himself loose high in air, even if over a bed of water.

Perhaps, however, these various elements of failure have already been eliminated. The design was published in 1891 and may by this time have been so remodeled as to lead, not to an absolute success, for this is not to be expected, but to such partial control over the apparatus as to warrant further experiments.

In the Cosmopolitan Magazine for November, 1892 and in Cassier's Magazine for February, 1893 appeared two analytic articles by M. J. P. Holland, in which he takes the ground that mechanical flight has already been proved to be attainable, that what remains to be done is merely to combine things already tried and proved by other experimenters; and in which articles he advances three proposals or designs for flying machines.

In the Cosmopolitan article M. Holland proposes to place two aerial screws, superposed and rotating in contrary directions, above a spindle-shaped body containing the machinery, with a pair of wings or aeroplanes attached. This may be termed his first design, as indicated by his figs. 2, 3 and 4. In his second design the spindle and the superposed screws are retained, but the supporting surface consists of lo narrow, superposed, concavo-convex aeroplanes, somewhat like a Venetian blind, and they as well as the screws are mounted upon a frame pivoted to the spindle-shaped body, so that the screws may first be used to raise the apparatus from the ground, and then to drive it forward when the frame is raised to the vertical; support being then derived from the aeroplanes. This is indicated in M. Holland s figs. 5, 6 and 7.

In the Cassier's Magazine article the design is further modified by placing the aerial screws side by side in the frame instead of superposing them. The superposed aeroplanes are retained, but the number is increased to 16, and the mode of operation is much the same.

The design is somewhat similar to that which Mr. Phillips experimented in England, which was illustrated in Engineering of May 5, 1893, but is an improvement upon the latter design in the provision for pivoting the Venetian-blind aeroplanes to the body, and in the employment of two screws instead of one for the propelling instrument.

³⁶One theorist expounds his ideas as follows: "One point I have studied, and that is, How can a twenty pound wild goose carry itself so easily? Weigh every feather you can pick off from a wild goose, and they will not weigh one pound. Now if the feathers be picked off from the goose he can come no nearer flying than we can.

"So there we have it clearly demonstrated that one pound of goose feathers can pick up nineteen pounds of goose and carry this nineteen pounds and its one pound of feathers through space at about half a mile a minute, if in a a hurry.

"Now my theory is this, and it applies to all birds. Notice any bird when he suddenly starts to fly, and you will notice a lightning-like quiver of his feathers. I believe that this quiver causes the production of a negative force of magnetism, or some kind of force which pushes the bird from the earth- just the reverse of the loadstone. He then has only to use his wings to propel the body, for the magnetic negative earth-force does the lifting, and that is all produced by the feathers. If it were not, then the bird ought to fly when divested of his feathers. This is the force which should be looked for; whoever discovers it will make a fortune."
³⁷ Dans les airs, G. de la Landelle, pp. 236 237
³⁸ Der freie Menschliche Flug als Vorbedingung dynarnischer Luftschiffahrt. Müatnchen, 1891.

 

 

Aeroplanes  Part XV

by O. Chanute

September 1893.

If there be one man, more than another, who deserves to succeed in flying through the air, that man is Mr. Laurence Hargrave, of Sydney, New South Wales. He has now constructed with his own hands no less than 18 flying machines of increasing size, all of which fly, and as a result of his many experiments (of which ,an account is about to be given) he now says, in a private letter to the writer, that: "I know that success is dead sure to come."

M. Hargrave takes out no patents for any of his aerial inventions, and he publishes from time to time full accounts of them, in order that a mutual interchange of ideas may take place with other inventors working in the same field, so as to expedite joint progress. He says: "Workers must root out the idea that by keeping the results of their labors to themselves a fortune will be assured to them. Patent fees are so much wasted money. The flying machine of the future will not be born fully fledged and capable of a flight for 1000 miles or so. Like everything else it must be evolved gradually. The first difficulty is to get a thing that will fly at all. When this is made, a full description should be published as an aid to others. Excellence of design and workmanship will always defy competition."

M. Hargrave is probably correct in his reasoning; for the history of all new methods of transportation teaches that the original inventor seldom receives pecuniary reward for the contrivance which is the first to succeed, but nevertheless he is certainly broadly liberal in giving to

the world gratuitously the results of his constant studies and labors. He uses exceeding care in determining the different elements which compose the flight of his models. He has carefully registered the sizes of all the parts, the power consumed in each performance, and the length of the flight, together with its trajectory. He states that he has always kept his work in such shape that it could be taken up and continued by any person at any time; so that a stranger, if an expert, could come into his shop, study his notes and drawings, pick up his tools and continue his work, and thus no portion of it would be lost.

M. Hargrave reports regularly the progress of his work to the Royal Society of New South Wales, of which he is a member. Thus far 13 such papers have been published, the latest having been read June 7, 1893.

He first devoted his attention to the motions performed by the propelling surfaces of birds and fishes, the waves which these created in the fluids on which they acted, and the counteraction of these waves upon the forms of the propelling surfaces themselves. The first paper, therefore, presented in August, 1884, was on the Trochoided plune which M. Hargrave defines as"a Hat surface, the center of which moves at a uniform speed in a circle, the plane being kept normal to the surface of a trochoidal wave, having a period equal to the time occupied by the center of the plane in completing one revolution." This was illustrated by working models, and the motions of wings and of fishes in swimming were artificially reproduced.

Starting from these data, M. Hargrave next experimented with nearly 50 models intended to reproduce horizontal flight, and in exhibiting some of these and reading his second paper, June, 1885, he said: " If the ,notion is not that used by birds, it is at all events very like it, and its acceptance or rejection as a scientific truth is of no further interest, as it only remains for practical mechanics to step in and adjust the details to suit the material and the motive power which they may think best for the purpose they have in view; or, in other words, that the solution of the problem of just how a bird flies is of very trifling importance from a practical standpoint, as compared with the judicious variations of the parts of the machine that will have to be made before any return can he expected for money invested in such undertakings."

Some of these models seem to have been driven by clock-work, and the motions were those of the "trochoided planes," as applied to flapping wings; then selecting the best of these models, and making their mean dimensions a standard from which to take a fresh departure, M. Hargrave next built a series of experimental flying machines actuated by indict-rubber in tension.

The French experimenters, as we have seen, have preferred to use rubber in torsion in order to diminish the strains upon the central spine or backbone of the model

but they thus obtained less energy per pound of weight than if they had used it in tension. M. Hargrave stretched the rubber so that its elongation was multiplied by pulley tackle, and that, as the rubber contracted, its center of gravity moved forward, thus advancing the center of gravity of the entire machine, and consequently diminishing the angle of flight as the force of the rubber decreased.

No less than 10 different flying machines of various types were thus built and experimented with, all moved by rubber in tension In the first models the cord proceeding from the rubber was wound around a cylindrical drum on the crank-shaft, but owing to the variable resistance natural to a crank-shaft, it was found better to replace the cylindrical drum by a flat winder, so adjusted on the shaft that the moment of the cord varied with the resistance of the crank, and thus communicated a more uniform movement to the wings.

Seven of these machines seem to have been propelled by flapping wings--i.e., "trochoided planes"--but in order that a comparison might be made, three varieties of models were made with screw propulsion--namely, with double and with single screws in the bow, and with a single screw in the stern, which latter was concluded to be the most practicable and serviceable form.

From these experiments M. Hargrave concluded that the screw and the flapping wings are about equally effective as instruments of propulsion, although he rather prefers the latter, as the wings possess several marked advantages. Any currents, he says, initiated during the upstroke are utilized in giving increased efficiency to the down-stroke, if the machine has not progressed far enough to be acting upon entirely undisturbed air. Moreover, when steam-engines come to be used, there will be only one cylinder needed for both wings, there will be no conversion of reciprocating into rotary motion, and no variable listing moment to be counteracted, while, finally there is less liability that wings shall be damaged in alighting than screw blades

Fig. 76 shows the last one (1889) of the indict-rubber driven machines described by M. Hargrave. He calls it the "48 band-screw." The screw is at the stern, and the machine weighs exactly 2 lbs. Its sustaining area is 14.51 sq. ft. (7.26 sq. ft. per pound), and it flew 120 lineal feet with the expenditure of 196 foot-pounds of energy, while the preceding machine, weighing 2.09 lbs., with flapping wings, had flown 270 ft. with 470 foot-pounds, thus showing respectively 0.61 and 0.57 lineal feet flown per footpounds of power.

The framework of these machines was of pine, the larger piece (main spine) being a hollow box-girder, to secure strength and lightness. The sustaining surfaces were of paper, pasted on, and after the gum was dry rendered as tight as a drum by blowing a light spray of water over the paper and allowing it to dry. Thus with small, light, simple, and inexpensive models many experiments were made. and great advance realized in the distance flown over any previous experiments of others.

Having progressed thus far with india-rubber as a motive power, and gathered most valuable data and experience: as to the best arrangement and proportion of parts, the equipoise and the power required, M. Hargrave next undertook the construction of a flying machine actuated by compressed air, and, in 1890. he produced the machine illustrated by fig. 77, which he calls his "No. 10 40 5 oz. compressed air," and which marked a very considerable advance in design by a great simplification of the propelling arrangement.

In presenting it to the Royal Society, June 4, 1890, M. Hargrave said:

The principle embodied in this experiment is that of Borelli, published in 1680, and it doubtless has had many stanch advocates in later times; but the writer maintains that this is the first practical demonstration that a machine can and does fly by the simple (vertical) flapping of wings; the feathering, tilting, twisting, trochoiding, or whatever it may be called, being solely effected by torsional stress on the wing arms.

The combination of Borelli's views with the results of work recorded in your proceedings (Royal Society) has swept away such a mass of tackle from the machine that its construction becomes a ridiculously simple matter. The engine of the model, of course, retains its precedence as the most important part, and by continuous effort the number of pieces and the difficulties of construction have been so reduced that it is possible to make them by the gross at a cost that cannot exceed five shillings each ($1.25). For instance, the cylinder, usually the most expensive portion of an engine, can be produced with the ease and celerity of a tin can.

It might be said that this flying machine is not on the principle enunciated by Borelli, because the wings are not continuous from their tip to the body. But this arrangement is only a device to enable the wing tips to act on the required quantity of air with less spread; it may possibly be one of those variations which make all the difference between success and failure. These wings are also distinctly double-acting, and it is not quite clear that birds' wings thrust during the up-stroke; but, as previously stated, the question as to the exact movement of a bird's wing is merely straw-splitting, when We have a mechanism that actually flies and is manifestly imperfect in its present mechanical details.

This machine flew 368 ft., with the expenditure (as corrected by M. Hargrave of 870 foot-pounds of energy. It weighed 2.53 lbs., and the sustaining body plane measured 14.78 sq. ft., while the two wings measured 1.50 sq. ft. in area, making a total of 16.28 sq. ft., or, say, 6 .43 sq. ft. per pound.

London Engineering, in its issue of December 26 1890, gives the following description of the machine:

The compressed air is stored in a tube which forms the backbone of the whole construction. This tube is 2 in. in diameter, 48 1/4 in. long, and has a capacity of 144.6 cub. in. Its weight is 19.5 OZ., and the working pressure is 230 lbs. per square inch. The engine cylinder has a diameter of I! in. and a stroke of II in., while the total weight of the engine is only 6 1/2 oz. The piston-rod is made fast to the end of the backbone, and the cylinder moves up and down over the piston. Two links connect the cylinder to the Canadian red pine rods which carry the wings. The air is admitted to the cylinder and exhausted by means of a valve worked by tappets. The period of admission continues through the entire stroke. The cylinder and receiver ends are pressed, and the piston is made of vulcanite, with a leather cup ring for packing.

The wings are made of paper, and have no canting or feathering motion other than that due to the springing of the material of which they are made. The weight of the wings is 3 oz. To find how much the wings deflected, one was held by the butt and a weight of 71 oz. was put on the membrane 24 in. from the fixed point, and I! in. abaft the wing arm. The deflection produced due to torsional stress, was 3 1/2 By moving the weight half way across the wing it was twisted 8 1/4 The area of the body is 2.128 sq in.; the area of the wings 216 Sq. in., and the total area 2.344 sq. in.

When first made, the machine had its center of gravity so placed that the percentage of area in advance of it was 30 per cent. of the whole area, but continued disaster caused its reduction to 23.3 per cent. In a dead calm the machine flew 368 ft. horizontally.

It will be noted that the engine is a marvel of simplicity and lightness. Its cylinder is made like a common tin can, the cylinder covers are cut from sheet tin and pressed into shape in a vice, the piston and junk-ring are made of vulcanite, and the cup leather packing does away with the necessity for the cylinder being either round or parallel.

Beside the engine, a marked advance consisted in securing the torsion of the wings through no special mechanism, as formerly, but simply by the elasticity of the material composing them. This throws a new light upon the part performed in the flight of birds by the elasticity of their feathers, and promises great simplicity and efficiency in the future designing of artificial wings.

By looking at the figure, a bowsprit will be noticed. This was a so-called safety stick, which was added to break the fall of the machine when alighting, and it has proved quite successful in accomplishing that object.

A noticeable feature of this and subsequent machines exhibited by M. Hargrave consists in the extraordinary length of its supporting body plane, The same surface would carry a far greater load if it were driven broadside instead of lengthwise; but M. Hargrave explains that the plane was purposely so designed in order to insure longitudinal stability. This quality might also be secured by placing a tail far in the rear of a narrow supporting plane, as practiced by Pénaud and others. He states, moreover, that the plane is rendered more effective per unit of surface by being cut away in the middle portion, or by being formed in two parts, separated by a gap.

As regards the lateral equilibrium, he seems to have met with but little difficulty a slight diedral angle of the two halves of the body plane with each other providing the necessary stability, and preventing any swerving, so long as the center of gravity was at all below the center of effort; but he had great trouble in working out the longitudinal stability. This he did upon the "cut and try" principle--a method doubtless the most thorough, the surest, and the most convincing, but also the most tedious. He found that the direction up or down of the machines in flight was entirely due to the distance of the center of gravity from the forward edge of the body plane, and therefore to the coincidence or otherwise of the center of gravity with the center of pressure. He measured the percentage of area in advance of the center of gravity in his three most successful machines, and found it respectively 19.3, 20 and 23.3 per cent. of the length of the plane, while subsequently he came to the general conclusion that the true position for the center of gravity for a continuous rectangular surface is situated between 0.25 and 0.2 of the length from the forward end, these positions being arrived at "by experience gained by repeated wrecks when groping in comparative darkness."

This independent working out of a complex question well illustrates the perseverance and ingenuity of this experimenter. At this juncture, however, he would have been saved much groping, time, and annoyance had he been aware of the formula of Joessel for determining the center of pressure:

C = (0.2 + 0.3 sin. a) L,

in which C is the distance from the forward edge of a rectangular plane to its center of pressure, when inclined at the angle of incidence a with the course, and L is the length of the plane along the line of motion.

In the same year (1890) M. Hargrave built another flying machine, actuated by compressed air and propelled by beating wings. This is shown by fig. 78. It was of the increased weight of 4.63 lbs., with sustaining body plane of different shape, measuring 29.63 sq. ft., or in the proportion of 6.40 sq ft. per pound. It flew 343 ft., with an expenditure of 789 foot-pounds of energy, and therefore showed better results than the previous machine (No. 10), inasmuch as more pounds were transported on the air approximately the same distance, with a somewhat smaller expend ture of energy.

Having apparently found some advantage by shortening the body plane, M.. Hargrave next built his flying machine No. 13, which shown in fig. 79, with a body plane still shorter, and he provided it with a two-bladed aerial screw, set in the bow and actuated by a three-cylinder compressed-air engine of the Brotherhood type. This drove it 128 ft. in eight seconds, with an expenditure of 143 foot-pounds of energy. The apparatus weighed 46.86 oz. (2. 93 lbs.), and exposed 2952 sq. in. or 20.5 ft. of floating surface, being in the ratio of 7.00 sq. ft. per pound.

This is the first time (paper 10, July 1, 1891) that M. Hargrave gives us the time of flight of his machines, so that we may calculate the number of pounds of weight transported in ratio to the horse power. He says:

The time of flight is taken with a sandglass which has a ]orp of string at each end of it. The loop at the sand end is put round the right wrist, and the other loop is held between the right thumb and the receiver, so that the glass is turned the moment that the machine is let go. On the machine taking the ground the glass is put horizontal, and the sand which has fallen is timed at leisure. This seems an obvious enough method of finding the speed, but a practical way to do it was not devised previously.

This showed for No. 13 machine a speed of 10.34 miles per hour which is about what we should have expected from the ;large proportional surface, it being about in the ratio of the slowest flying birds. This low speed M. Hargrave adopts on purpose, the better to observe the motions of the machines and to save breakage, and he adds quaintly that he sees no objection to this course, so long as the atmosphere is not crowded with flying machines. As No. 13 machine (fig. 79) is reported as having expended 143 foot-pounds in eight seconds, we have:

Power = 143 ˜ 8 = 18 foot-pounds per second,

nearly, and, as it weighed (as reported) 2.93 lbs., we have for the weight sustained per horse power:

2.93 X 550 ˜ 18 = 89.53 lbs. per horse power;

while it will be recollected that M. Tatin sustained 110 lbs. per horse power and that M. Phillips in his recent (1893) experiments floated 72 lbs. per horse power We will see by the analysis of subsequent performances that M. Hargrave did not obtain quite as good results with subsequent flying machines.

He next built his No. 14 flying machine, with much the same shape of body surface, but propelled by beating wings instead of a screw. It weighed 3.69 lbs. and exposed 22.84 sq. ft. of surface, being in the proportion of 6.19 sq. ft, per pound. It flew 312 ft. in 19 seconds, with an expenditure of 509 foot-pounds, and thus we have:

Power = 509 ˜ 19 = 26.79 foot-pounds per second,

and for the weight floated per horse power:

3.69 X 550 ˜ 26.79 = 75.75 lbs. per horse power.

This apparatus (No. 14) M. Hargrave has generously offered to present to some American institution which will take proper care of it, believing it to be one in which "the increased skill in construction acquired by practice is thought to have resulted in an apparatus that, for its weight, it will be hard to excel." He says in his paper to the Royal Society:

It may be said that it is a waste of time to make machines of such small capabilities, and that no practical good can come of them. But we must not try too much at first; we must remember that all our inventions are but developments of crude ideas; that a commercially successful result in a, practically unexplored field cannot possibly be got without an enormous amount of unremunerative work. It is the piled-up and recorded experience of many busy brains that has produced the luxurious traveling conveniences of to-day, which in no way astonish us, and there is no good reason for supposing that we shall always be content to keep on the agitated surface of the sea and air, when it is possible to travel in a superior plane, unimpeded by frictional disturbances.

No 16 was another compressed-air flying machine with beating wings and somewhat differently shaped body plane. It weighed 4.66 lbs., spread 26.06 sq. ft. of surface, and flew 343 ft. in 23 seconds, with an expenditure of 742 foot-pounds. The power was therefore:

Power = 742 ˜ 23 = 32.26 foot pounds per second,

and the weight floated per horse power:

4.66 X 550 ˜ 32.26 = 79.45 lbs. per horse power.

Several forms of body plane seem to have been tested in this machine and no less than 12 trials were recorded, trial No. 10 being the successful one, from which the above data have been taken.

Having now constructed 10 flying machines of different types and proportions actuated by mafia-rubber in tension, and six actuated by compressed air, of increasing size and weight, M. Hargrave then turned his attention to producing a steam motor which should equal in lightness and surpass in power the best compressed-air motors thus far constructed by him, and which should furnish driving power for a longer time.

But first he endeavored to work out an idea which he seems to have entertained for some years, of testing an explosion motor. His engine No. 15 consisted of a turbine to be worked by the gases resulting from the explosion of a mixture of nitrate of ammonia, charcoal, and sulphur; but a considerable expenditure of time only resulted in a failure.

He also experimented upon a method of utilizing sea waves in propelling vessels, which he believes to be the germ of the solution of the soaring problem, and he succeeded in securing such automatic action that a 12 1/2 lb. mode advanced in the winds eye at five-eighths of a mile per hour.

He also made some experiments upon pure aluminum, but found that it presented no advantages for flying machine construction.

 

 

Aeroplanes  Part XVI

by O. Chanute

October 1893.

No. 17 flying machine of M. Hargrave is described in his twelfth communication to the Royal Society of New South Wales, read August 3, 1892. The total weight of the apparatus is 64.5 oz, or 4.03 lbs., including 12 3/4 oz. for the strut and body plane, so that the engine and boiler, including 5 oz. for spirit fuel and water, weighs 3.25 lbs., and develops 0.169 horse power, or at the rate of 1 H.P. per 19.2 lbs.--a very remarkable achievement.

The boiler is of the "Serpollet" type, made of 12 lineal feet of 1/4 in. copper tubing (steel pipe could not be got in Sydney), in the form of a double-stranded coil, encased in asbestos, and placed just over the backbone of the apparatus. The fuel is methylated spirits of wine, drawn from a tank placed above the boiler, vaporized, mixed with air and spurted into the furnace. As much as 6 .9 cub. in. of water have been evaporated by 1.7 cub. in. of spirit in 80 seconds, making 182 double vibrations of the propelling wings, say, 2.35 per second, and developing 0.169 horse power.

It was estimated that if the apparatus were loaded with 10 oz. more of spirit and water, and thus made to weigh the same as the compressed-air machine No. 12, which flew 343 ft., then the steam apparatus No. 17 would possess a sufficient store of energy to fly 1640 yds., or nearly 1 mile.

But M. Hargrave has done still better, for in March 1893, he prepared a paper, which was presented to the Conference on Aerial Navigation at Chicago, August 2 1893 in which he gave data concerning his No. 18 flying machine. This apparatus is also driven by a steam-engine which weighs, with 21 oz. of fuel and water, an aggregate of 7 lbs, and indicates 0.653 horse power, or at the rate of 10.7 lbs. per horse power; so that, roughly speaking, the weight of the motor has been doubled, and the power has been increased fourfold.

Four boilers were constructed. The final one was made of 21 lineal feet of 1/4 in. copper pipe, with an internal diameter of 0.18 in., and arranged in three concentric vertical coils whose diameters were 1.6 in., 2.6 in., and 3.6 in. respectively. It weighed 37 oz., but it is now known "that a coil of equal capacity can be made weighing only 8 oz, and still excessively strong." The cylinder is 2 in. diameter with a stroke of 2.52 in. The feed-pump ram is 0.266 in. diameter, and the piston valves 0.3 in. diameter. On one occasion this motor evaporated 147 cub. in. of water with 4.13 cub. in. of spirit in 40 seconds. During a portion of the time it was working at a speed of double vibrations per minute.

M. Hargrave gives no data concerning the flight of his last two (steam) machines. He states that 11 different burners have been tried, and that the flame striking the water boiler first has a tendency to vary the supply of heat to the spirit holder. From this it is inferred that he is struggling with the same difficulties already encountered by Stringfellow, by Moy, and by Maxim in regulating and keeping alight spirit burners when the apparatus gets under forward head-way; but this difficulty, while a serious one, will doubtless be eventually overcome by persistent experiment, and we may then expect flights of astonishing lengths.

Seeing now his way to an adequate motor and to extensive flights in the near future, M. Hargarve recently turned his attention to experiments upon curved surfaces, and to the seeking for a better disposition of the sustaining surfaces or body planes. He had described the eccentricities of a curved strip in the form of a segment of a hollow cylinder, when exposed to the wind, in his paper No. 12 to the Royal Society of New South Wales, read August 3, 1892 and he describes some of his experiments with "cellular kites," in his paper read in the Aerial Navigation at Chicago, August 2 1893.

The "cellular kites" constitute quite a new departure, and practically consist of superposed aeroplanes connected together in pairs. B, in fig. 80, shows the simplest form. This consisted of two hollow cylinders of aluminum, each 13 in. diameter by 4 1/2 in. deep, mounted 30 in. apart upon a connecting stick, and weighing 14 3/4 lbs. The kite-string was attached 11 in. back from the forward section, and as a consequence of the angle of incidence thus produced, the apparatus mounted upon the wind. Its particular behavior is not described in the paper. C, in fig. 80, shows a kite with 16 cells, the length of each being 3 in., by a height of 3 in., and a breadth of 3 in. It was made of cardboard, and the two sections were 22 in. apart, the point of attachment of the kite-string being 6 1/2 in. distant from the forward section, while the weight was 10.5 lbs. This seems to indicate that this kite flew at a steeper angle than the preceding, although we should expect the reverse, in consequence of the greater proportion of sustaining surface. M. Hargrave says, "These kites have a fine angle of incidence, so that they correspond with the flying machines they are meant to represent, and differ from the kites of our youth, which we recollect floating at an angle of about 45 , in which position the lift and the drift are about equal. The fine angle makes the lift largely exceed the drift, and brings the kite so that the upper part of the string is nearly vertical."

Kites E and F, fig. 81, are of exactly the same size and weight, consisting of one cell, 4 in. long, 10.7 in. broad by 6.25 in. high, constructed of wood and paper, and weighing 3.25 lbs.; the two sections are 21.25 in. apart, and the string is fastened 7.25 in. back of the forward section. The only difference is that kite E has its horizontal (top and bottom) surfaces curved to a radius of 4.5 in. while all the surfaces of kite F are true planes, The result is that when kite E is flown with the convex sides up it pulls about twice as hard on the string as kite F, so that, as M. Hargrave says: "A flying machine with curved surfaces would be better than one with a net body plane, if the form could be made with the same weight of material."

M. Hargrave, in this last paper, figures and describes two other forms of cellular kites with which he has experimented, and points out that the rectangular form of cell is collapsible when one diagonal tie is disconnected. so as to make it easy of transportation. He says: "Theoretically, if the kite is perfect in construction and the wind steady, the string could be attached infinitely near the center of the connecting stick, and the kite would fly very near the zenith. It is obvious that any number of kites may be strung together on the same line, and that these is no limit to the weight that may be buoyed up in a breeze by means of light and handy tackle. The next step is clear enough--namely, that a flying machine with acres of surface can be safely got under way, or anchored and hauled to the ground by means of the string of kites."

He duly gives credit to M. Wenham for suggesting the superposition of planes in 1866 and it is an interesting circumstance to note that at the same Chicago Conference, a paper from M. Wenham was read suggesting a course of experiments with kites, to determine the best arrangement of superposed aeroplanes and the conditions of equipoise.

Such are the labors of M. Hargrave up to the present time. He no longer troubles himself about the general problem of man's eventual success in navigating the air, but he says: "The people of Sydney who can speak of my work without a smile are very scarce; it is doubtless the same with American workers. I know that success is dead sure to come, and therefore do not waste time and words in trying to convince unbelievers."

Instead of this, he constructs machines and reports the results in detail, so that others may repeat his experiments. He e says that the record of unsuccessful experiments takes up a considerable portion of kits notes, and further, that "there is no use in the mind's conceiving an idea, if the hands are not ready to carry out the work skillfully, in the absence of reliable assistance, and if the design be found faulty, the whole thing should be begun again without trying to use up old machines. The question of intricate workmanship and costliness is being continually battled with; my constant endeavors are directed to making the machines simple and cheap, so that any one who doubts can verify my work, provided his hands are as skillful as mine, and I am sure that the photographs show clearly that the workmanship is anything but first-rate.

He began with small, cheap models, and has gradually enlarged their size, and obtained flights longer than any heretofore accomplished. It is noticeable that the heavier the model, and the smaller the sustaining area in proportion to the weight, the more successful has been the flight. He may not be the first man to ride at will upon the air, but he deserves to succeed.

In November, 1890, M. Hiram S. Maxim the celebrated American inventor of a writing telegraph, of several systems of electric lighting, and of the "Maxim automatic machine gun," addressed a letter to the New York Times in which he stated that, before sailing back to England, he thought it would be well to state what he was doing toward constructing a flying machine which had been alluded to lately by the American press. Among other things he said:

I would say that among the large number of societies to which I belong in England, the Aeronautical Society is one, and need I say that I am the most active member? At the present moment experiments are being conducted by me at Baldwin's Park, Bexley, Kent, England, with a view of finding out exactly what the supporting power of a plane is when driven through the air at a slight angle from the horizontal. For this purpose I constructed a very elaborate apparatus, provided with a great number of instruments, and arranged in such a manner that I can ascertain accurately the 'efficiency of a screw working in air. the amount of power required to drive a screw, the amount of push developed by a screw, the amount of slip, and also the power required for propelling planes through the air when placed at different angles, as well as to ascertain the friction and all other phenomena connected with the subject. I have been experimenting with motors and have succeeded in making them so that they will develop I horse power for every 6 lbs. My experiments show that as much as 133 lbs. may be sustained in the air by the expenditure of 1 horse power; of course. it is premature now to express any opinion; still, if I am not very much mistaken, and if some new phenomenon, which I do not understand, does not prevent it, I think I stand a fair chance of solving the problem, and I think I can assert that within a very few years some one--if not myself, somebody else--will have made a machine which can be guided through the air, will travel with considerable velocity and will be sufficiently under control to be used for military purposes. I have found in my experiments that it is necessary to have a speed of at least 30 miles per hour, that 50 miles is still more favorable, and that 100 miles would seem to be attainable. Everything seems to be in favor of high speed.

Whether I succeed or not, the results of my experiments will be published, and as I am the only man who has ever tried the experiments in a thorough manner with delicate and accurate apparatus, the data which I shall be able to furnish will be of much greater value to experimenters hereafter than all that has ever been published before.

In May 1891 M. Maxim again visited the United States, and he gave to various newspaper reporters, notably to one from the New York Sun, some particulars concerning the flying machine, or "first kite of war," which he was building in England, and upon which he had spent up to that time (including the preliminary experiments) some $45,000.

He described the apparatus with which he had made his preliminary experiments, to ascertain accurately the supporting power and resistance of air to aeroplanes at small angles of incidence, and then continued as follows:

My large apparatus is provided with a plane 110 ft. long and 40 ft. wide, made of a frame of steel tubes covered with silk. Other smaller planes attached to this mane up a surface of 5500 sq. ft. There is one great central plane, and to this are hinged various other planes, very much smaller, which are used for keeping the equilibrium correct, and for keeping the flying machine at a fixed angle in the air. The whole apparatus, including the steering gear, is 145 ft. long. . . . A part of the aeroplane, or actual kite, is made of very thin metal, and serves as a very efficient condenser for the steam.

It is ready and awaiting my return. It is now resting on a track 8 ft. wide and half a mile long. in my park. The first quarter of a mile of the track is double--that is to say, the upper track is 3 in. above the lower. By that means I am able to observe and measure the lift of the machine when it starts, because the upper track will hold it down when it lifts off the lower one. When completed the machine will weigh, with water tanks and fuel, somewhere between 5,000 lbs. and 6,000 lbs., and the power at my disposal will be 300 horse power in case I wish to use it; but it is expected that about 40 horse power will suffice after the machine has once been started, and that the consumption of fuel will be from 40 lbs. to 50 lbs. per hour. The machine is made with its present great length so as to give a man time to think; its length makes it easier to steer and to change its angle in the air. Its quantity of power is so enormously "real in proportion to its weight that it will quickly get its speed It will rise in the air like a sea-gull if the engine begun at full speed while the machine is held fast 10 the track, and if it is then suddenly loosened and let go.

M. Maxim very judiciously refrained from furnishing drawings or detailed descriptions of an apparatus which was still in process of evolution, and which he might want to modify as he proceeded in erection and trial. Indeed, it is probable that he has varied considerably from the various arrangements which he has patented from time to time,³⁹ so that drawings and descriptions made from these might be wide of the mark.

The important, the vital feature, however, he recognized to be the motor, and to perfecting this he gave kits first attention. In steam motors he seems to have accomplished wonderful results, hitherto quite unreached, and in an article published in the Century Magazine for October, 1891 after describing and illustrating the experimental whirling machine with which he had gathered his preliminary data, he gives the following account of what he had accomplished up to that time with the motor:

I have come to the conclusion that the greatest amount of force with the minimum amount of weight can be obtained from a high-pressure compound steam engine, using steam at a pressure of from 200 lbs to 350 lbs. to the square inch, and lately I have constructed two such engines, each weighing 300 lbs. These engines, when working under a pressure of 200 lbs. to the square inch, and with a piston speed of only 400 it. per minute, develop in useful effect in push of screws over 100 horse power, the push of the screws collectively being over 1000 lbs. By increasing the number of turns, and also the steam pressure. I believe it will be possible to obtain from 200 horse power to 300 horse power from the same engines, and with a piston speed no greater than 850 ft per minute.⁴⁰ These engines are made throughout of tempered steel, and are of great strength and lightness. The new feature about my motors however is the manner of generating steam. The steam generator itself, without the casing about it, weighs only 350 lbs.; the engine, generator, casing, pumps, cranks, screw shaft, and screws weight 1,800 lbs., and the rest of the machine as much more. With a supply of fuel, water, and three men the weight will not be far from 5,000 lbs. As the foregoing experiments have shown that the load may be 14 times the push of the screw, it would appear that this machine ought to carry a burden, including its own weight, of 14,000 lbs., thus leaving a margin of 9000 lbs, provided that the steam pressure is maintained at 200 lbs. to the square inch. The steam generator is sell-regulating, has 48,000 brazed joints and is heated by 45,000 gas jets, gas being made by a simple process from petroleum. When the machine is finished the exhaust steam will be condensed by an atmospheric condenser made of a great number of very thin metallic tubes, arranged in each a manner that they form a considerable portion of the lifting surface of the aeroplane. The greater part of the machine is constructed from thin steel tubes. I found that these were much more suitable for the purpose than the much-talked aluminum; still I believe that if I should succeed in constructing a successful machine, it would lead to such improvements in the manufacture of aluminum products that it will be possible to reduce greatly the weight of the machine.

The question of keeping the machine on an "even keel," of steering, and of landing, has been duly considered and provided for, hut a description of these would be premature before the machine has actually been tried.

When it is remembered that locomotives weigh some 200 lbs. per horse power, that the lightest marine (launch) engines in 1889 weighed about 60 tbs. per horse power, and that the largest steam-engines previously built for aerial navigation purposes were those of Giffard and of Moy each of 3 horse power and weighing (with their boilers) 110 lbs. and 27 lbs. per horse power respectively, then the importance of M. Maxim's achievement as above set forth, may be partially realized, particularly when it is considered the! the relative weight tends to increase with the size, and that M. Maxine's expectations of obtaining 300 horse power from the same engines have been fully confirmed, as will be seen hereafter.

Moreover, as exhausting the steam into the air would involve carrying a supply of water amounting to some 20 or 25 lbs. per horse power per hour, and this would have been simply prohibitory, M. Maxim's plans included a surface aero-condenser. in order that the same water might be used over and over again. This was a wholly unsolved problem. such tentative experiments as had been tried previously by others having indicated weights of 50 lbs. to 150 lbs. per horse power, as necessary for efficient aero-condensers, and. this would also have been prohibitory.

M. Maxim proposes to solve this problem by making all the frames of his apparatus of hollow tubes, and connecting therewith a condenser consisting of a large number of wide, flat, or film tubes--that is to say, of tubes of thin metal having a flat bore, through which the steam will pass in thin films of considerable width, these film tubes being so arranged that in the forward motion of the machine the air will impinge upon them, thus effectually cooling them and condensing the steam therein. This aero-condenser is utilized as a part or the whole of the sustaining surface, or there may be substituted there for a large flexible bag or chamber, connected at the forward part with the exhaust steam-pipe, and at the rear end with the hot well, or directly with the suction pipe of the feed pump. He relies, of course, upon the increased condensation produced by air currents due to the forward motion of the machine, and the extent of the condenser is therefore a matter for experiment, so that its exact weight cannot be settled in advance.

The horizontal angle of incidence in flight is to be maintained by a "Gyrostat," which consists in a gyroscopic wheel rotating rapidly, suspended by universal joints and connected with two horizontal rudders, one at the front and the other at the back of the apparatus, so as to act upon them instantly (through the well-known property of the gyroscope to continue rotating in the same plane), in case any tendency occurs to deviate from the angle of incidence with the horizon.

The whole of the apparatus is to be thoroughly stayed by diagonal wire ties, so as to make every part rigid and prevent deformations under varying wind pressures.

Fig. 82 engraved from a photograph kindly furnished by M. Maxim, exhibits the main features of the apparatus. It does not show the front or back rudders, which have been removed, nor the side wings, set at a dihedral angle, to preserve the transverse stability nor sundry possible keel-cloths or auxiliary planes intended to promote the same object. It exhibits the central or principal aeroplane, with the forward end facing the observer. This main aeroplane is understood to be 50 ft. wide, about 58 ft. long, and slightly concave in the direction of its length, while it is trussed and stiffened in every direction by wire stays. The condenser is indicated by the dark shading at the front of the main plane, and, as will readily be seen, can be largely increased in surface, but, however, at the expense of added weight. The driving screws are placed at the rear, and are understood to be 17 ft. 10 in. in diameter, the speed of rotation varying, of course, with the power exerted.

The whole apparatus is mounted upon wheels, running over a railway track, so as to acquire sufficient speed to rise upon the air, and the three men who are grouped about the front may enable the reader to gather by comparison some general conception of the colossal dimensions of this flying machine.

³⁹ British patents Nos. 10,359 and 16.883 A.D. 1889 No. 19.228 A.D. 1891
⁴⁰ The piston speed of an express locomotive is about 1000 ft. per minute.

 

Aeroplanes  Part XVII

by O. Chanute

November 1893.

Having thus designed and built his apparatus, the next point for M. Maxim to consider was how to get it up into the air, how to control it while sailing. and how to alight with it safely. To this he has evidently given much thought, and in an article published by him in the Cosmopolitan Magazine for June, 1892 he thus describes what course he would pursue if a sum of $100,000 were placed at his disposal, for constructing and experimenting a successful flying machine; which course seems to be so carefully planned that we may fairly assume that it is the one determined upon by M. Maxim for experiments with his own actual machine.

"The machine should be run around the one-mile track at all speeds, from 20 miles per hour to 100 miles per hour, and the power actually required should be carefully noted. These runs would enable us to ascertain how our pumps worked at high speed. and how much our screws pushed, and if we put a brake to the wheels we should find out the slip of the screws. We could also ascertain the efficiency of our condenser at various speeds, and the temperature of the water could be taken. In order to run on a railway track, the machine, of course, must be provided with wheels, and two sets of these would be necessary; one set should be of great weight, so as to hold the machine down when running on the track. and the other set should be light, for actual flying. Springs should be interposed between the axle trees and the machine, after the manner of railway carriages, and there should be attached above each wheel some sort of an index or indicator to show the exact load resting on each wheel. When all the parts of the machine had been made to operate smoothly and satisfactorily, the silk could be placed on the aeroplanes, and then our serious experiments might be said to commence.

"We should first begin by running slowly--say at the rate of 20 miles per hour--and carefully note the lift on the indexes over each wheel. If we found that with a speed of 20 miles an hour, three fourths of the load was lifted off the forward axletree, and only one-fourth off the hind one, then we should change the center of weight further forward, so as to bring it as near as possible under the center of effort or lift. We should then make another trial and if we found that the lift was equal both fore and aft we should increase the speed very carefully, gradually observing the lift at the four corners of the machine, until the whole weight of the machine was supported by the aeroplane, and the whole weight of the wheels (about one ton) by the railway track. Then, when there was neither lift nor load on either wheel, we might consider that we had arrived at a stage in our experiments where we could turn our attention to the subject of steering.

"A boat has to be steered in only one direction--namely, a horizontal direction, to the right or to the left. A locomotive torpedo or a flying machine must be steered in two directions--right or left, or up or down. We should experiment with the more difficult one at first--namely, the up and down or vertical direction. We should attach two long arms to our aeroplane in such a manner that they would project a considerable distance in she rear of the machine. To these arms we should pivot a very large and light silk-covered rudder and connect it with ropes, so that it could be turned up or down by a small windlass from the machine. We should then take a run on the track and see it the changing the angle of this rudder would increase or diminish the load on the forward or hind wheels. If we found that it would do this, but not sufficiently so, we should attach another rudder in exactly the same manner to the forward end of the machine. Suppose that, at a speed of 35 miles per hour, with both rudders set at the same angle as the aeroplane, we should find that the whole weight of the machine was carried by the aeroplane and the whole weight of the wheels (2,000 lbs.) by the track, we could then consider that the adjustment of our load was correct, and that the center of weight was directly under the center of effort for a speed of 35 miles an hour. We should then elevate the front edge of the forward rudder and depress the front edge of the rear rudder; this would cause the machine to lift on the forward axletree and the rear end of the machine to press on the hind axletree. If we found by changing the angle of the rudders that the load could be increased or diminished on either axle tree to the extent of 15 5 per cent. of our whole load we could consider that this phase of the problem was solved.

"For horizontal steering we should try first the effect of the screws. There should be a three-way valve in the steam pipe connected with a lever, so that we should be able to partly close off the steam from the engine of one screw, and turn more steam on to the other. This would probably be all that would be found necessary; if not, we should try rudders.

"To prevent the machine from swaying in the air, the aeroplane should so be constructed that no matter in which direction it tilted it would diminish the lifting power of the lifted part and increase the lifting power of the depressed part. This (diedral side wings) would be simple and automatic; moreover, the stability of the machine could be still further increased by having the center of gravity much below the center of lift.

"Having all things in readiness, the heavy wheels should be removed and the light ones put on; and taking one man with us to attend to the two horizontal rudder and to keep the machine on an even keel,⁴¹ we should take our first fly, running the engines and doing the right and left steering ourselves. A day should be selected when there was a fresh breeze of about 10 miles per hour. We should first travel slowly around the circular railway until we came near that part of the track in which we should face the wind. The speed should then be increased until it attained a velocity of 38 or 40 miles an hour. This would lift the machine off the track and probably would slightly change the center of effort. This, however, would be quickly corrected by the man at the wheel. While the machine was still in the air careful experiments should be tried in regard to the action of the rudders; it should be ascertained to what degree they had to be tilted in order to produce the desired effect on the machine. The machine should also be run at a speed less than 35 miles per hour in order to allow it to approach the earth gradually; then the speed should be increased again to more than 35 miles an hour in order to rise, at the same time trying the effect of running one propeller faster than the other, to ascertain to what extent this would have to be done in order to cause the machine to turn to the right or to the left. If the machine should be constructed so that each particular foot of its surface carried a load of 1 lb. 2 oz., and if we should stop the engine dead and allow the machine to fall, it would approach the earth at a speed of 15 miles an hour. or one mile in four minutes. This evidently would cause a considerable shock, and unless there was a good deal of elasticity to the parts and a good deal of travel between the axletrees and the machine, the shock would probably be sufficient to distort or injure. some part of the light structure. But it is not necessary to approach the earth directly. Professor Langley found in his experiments that when a horizontal plane was traveling rapidly through the air, it approached the earth as though it were 'settling through jelly.'

"A large field as near our railway as possible should be selected for alighting, and having approached the field so as to be facing the wind, we should gradually descend by slowing up the engines, and finally alight while the machine was still advancing at the rate of 20 miles an hour. If the wind should be blowing at the rate of to miles an hour the machine would approach the earth very gradually indeed, so that all shock would he avoided. It would only require a few yards of comparatively smooth ground to run on after alighting, in order that there should be no disagreeable shock or danger.

"The cost of these experiments would be from $50,000 to $100,000, and the time required would be two years."

It will be noted how complicated and delicate these various adjustments must necessarily be, and how many different parts must be made to do their work perfectly before it can be safe to venture into the air. The aeroplane surfaces must be prevented from altering their shapes at varying speeds, the rudders must be made to maintain the course automatically, the engine must be governed as to speed, the boiler and gas-jet flames must be regulated by the consumption of steam, and the condenser must be efficient at all temperatures of the air, as well as at all speeds. Moreover, and most important, no part must break under varying strains, and the equilibrium must be maintained.

These are formidable and yet indispensable requirements, well calculated to appall the boldest inventor; for while with an experimental model an accident is of little consequence and is easily repaired, with an actual flying machine an accident will probably prove disastrous, even if the inventor does not lose his life.

M. Maxim, therefore, has acted most wisely in taking plenty of time and in testing his apparatus in every way before venturing to leave tile ground with it. Having completed it so that it was ready for the hazard of actual trial, he next experimented with it under conditions of comparative safety, and opened up the chapter of accidents.

The first difficulty he met with occurred through the breaking of some of the wire stays. These had been made of steel high in carbon in order to secure great tensile strength, and they proved brittle. From a private letter from M. Maxim dated October 6, 1892 the writer is permitted to give the following extract, which gives also a most interesting and hitherto unpublished description of the steam-engine and boiler, which constitute thus far the great achievement of M. Maxim:

The steam generator is constructed somewhat on the Thorneycroft principle, except that the tubes are much lighter and thinner and have a greater number of sinusitis in them. In the Thorneycroft boiler the distributing water tubes at the bottom are of considerable size and of great weight. In my engine they are only 2 1/2 in. in diameter and Ii mm. in thickness. The down take for the water is only 3 in. in diameter, and instead of having two, as with the Thorneycroft boiler, there is one, which branches off like the inverted letter Y. In the Thorneycroft boiler the difference in gravity of the water in the hot interior tubes and in the two external ones, which are not heated. is the only means of keeping up the circulation; but as all the passage-ways for water are very large, this is sufficient.

Suppose that in my system I am using steam at 300 lbs. pressure to the square inch; I have my water at a pressure of 335 lbs. to the square inch, and the water escapes through a species of automatic injector, and in falling 35 lbs. in pressure does a certain amount of work on the surrounding water The cold water going in from the pump is therefore made to combine with the hot water in the down take. This increases the gravity of the water and at the same time causes a very rapid forced circulation. No matter to what extent the fire may be forced, the water has to go through in any event. All the water that is coming in from the pump, as well as all of the water that it takes along with it from the top separating drum, from which the steam is taken, is forced through the hot tubes. The nozzle through which the incoming water escapes from the higher to the lower pressure is provided with a spring, which always keeps a difference in pressure of about 35 Ib .; whether the quantity of water pressing in is large or small, the difference is always the same. A very convenient apparatus is attached to the teed water pipe, by which it is possible to see at a glance exactly how many pounds of water per hour are entering the boiler. Directly over the boiler proper there is another series of very small copper tubes through which the water passes before entering the boiler proper, therefore products of combustion, after passing between the tubes of the boiler. are brought in contact with the incoming water before escaping. This so reduces the temperature of the escaping products of combustion that Brunswick black or linseed-oil are not burned off the smoke-stack.

For a fuel I employ naphtha of 72° Beaume. This naphtha is pumped into a small vertical boiler heated with a part of its own contents.

The vapors from the boiler are led directly to an air injector, where they escape under a pressure of 35 lbs. to the square inch. The mixture of air and gas is then burned through rather more than 6,ooo gas jets under the boiler. Steam might be also mixed if required. The distributing of the flame is very even, and it is possible to fill the whole fire-box with a purple flame. The regulating of the supply of naphtha is controlled by the weight of the gas generator; if the weight of the generator is too great, it operates upon a ratchet, which shortens the stroke of the pump; if it is too light, a spring raises the generator and its contents, when the ratchet operates in a contrary direction and increases the stroke of the pump. In this way the quantity of naphtha in the boiler is kept constant. The fire is regulated not only by the pressure in the boiler, but by a thermostatic regulator also. The feed-water pump is also regulated by changing the length of the stroke.

The engines are compound, and have a peculiar arrangement placed in a connection between the high and low-pressure cylinders in such a manner that if the pressure in the boiler rises above 300 lbs. to the square inch the steam is shunted past the high-pressure cylinder and enters the low-pressure cylinder, and it is arranged in such a manner that the pressure of steam falling from 300 lbs. to 100 lbs. does a certain amount of work on the exhaust steam that is passing through the high-pressure cylinder after the manner of an injector-that is to say, the escaping force of the steam reduces the back pressure on the high-pressure cylinder and increases the pressure on the low pressure piston.

With two screws, each 17 ft. 10 in. in diameter, and with 300 lbs. pressure to the square inch, the machine has been made to pull on a dynamometer 1,960 lbs. If we multiply this pull by the number of lures per minute that the engine makes, and by the pitch of the screws, we find that the engines develop 300 horse power.

The complete weight of engines, boilers, pumps, generators, condensers, and the weight of water in the complete circulation. amounts to 8 lbs to the horse power, and this of itself I consider quite an achievement.

The spread of the wings of the machine is 107 ft., and the total length from the point of the forward rudder to the rear end of the after rudder is about zoo ft. Beneath the main aeroplane there is a considerable number of narrow planes superposed, which extend outward to nearly the full width of the machine. So far, trials have only commenced with the main aeroplane, which is 50 ft. wide and 45 ft. long in the direction of the length of the machine.

The whole machine is mounted on steel wheels 8-ft. gauge, and springs are interposed between the machine and the axletrees, both forward and back axletrees are attached to a diagraph, which makes a diagram of the lift of the machine as it advances upon the track. The drum which holds the paper turns once round in 1,800 ft., and whatever the machine lifts either forward or back is recorded upon the paper drum. One of the drums is also provided with a pencil, which makes a diagram of the speed at which the machine is traveling.

I am very much hampered, however, for room; there is very little clear space between the trees, and to obtain adjoining premises without trees costs a prohibitive sum. What I should have is a circular or oval track, which would be a mile long. When the experiments are tried with a side wind blowing five miles an hour, a lift of one ton has been recorded on one side of the machine while the other side would not lift over 100 lbs.

The whole machine, when loaded, will weigh about 7000 lbs., so you will see if the machine will lift anything like as much, per pound of push. as I succeeded in lifting with my first apparatus, it will be sure to go.

However, I find that a great number of steel stays are necessary in order to hold the machine in shape, and while these do not weigh much, they appear to offer a considerable resistance to the passage of the machine through the air. If I were to build another machine I should aim more at getting less atmosphere resistance, because I can see now that everything else is assured except this single factor. If the machine does not go it will simply be because too much force is expended in driving the framework through the air.

Work has been greatly delayed, in the first place, because I was absent from England a great deal, and, in the second place, we have had several serious accidents. The high-class steel wires-plow rope--which are used for stays are not always reliable. On two occasions these wires have broken, and becoming entangled in the wheels, have made a complete wreck of the wheels and everything about them. The last breakdown will take about a month to repair, and I shall put in a lower class of steel in all the stays that are near the wheels.

This damage was duly repaired, and the experiments were resumed early in 1893. In one of these, with a spread of somewhat more than half of the sustaining surface which the apparatus is designed to carry in full flight, M. Maxim succeeded in obtaining, at a speed of 25 miles per hour and with a thrust of the screws of 1,000 lbs, a lift over the front wheels of 2,300 lbs., and over the hind wheels of 1,900 lbs., as recorded by the dynagraphs. On a subsequent run, after making some alterations, he succeeded in obtaining, at a speed of 27 miles per hour and with a thrust of screws of only 700 lbs., a lift over the front wheels of 2500 lbs., or quite all the weight resting on them and of 2,800 lbs. over the hind wheels; thus showing a total lift of 7 57 lbs. per pound of thrust, as against 4.20 lbs. lifted per pound of thrust on the former occasion.

M. Maxim published the diagrams illustrating both these runs (and still another subsequently made) in the London Engineer for March 17, 1893 and gave a description in which he stated that the principal lift was obtained from the large aeroplane of 2894 sq. ft. in area.

The run last above described was made on February 16 1893 and on the same day two more runs were made until stopped by an accident.

First, an additional pair of wheels was attached under the front end of the machine, connected in such a manner that the small and lighter wheels could lift 3 in. from the track. Three men were also placed over the forward axletree. and a run was then made with 900 lbs. pull on the dynamometer. After the machine had run about 400 ft. the light wheels lifted clear of the track, and when the engines were stopped they came back to the track all right. The machine was then run again with 1000 lbs. pull on the dynamometer, with the following result, described in a letter to the writer from M. Maxim dated February 21 1893:

I have had another accident with my apparatus.

My main aeroplane is 50 ft. wide and 47 ft. long in the direction in which the machine travels. I had another aeroplane directly in front of the engine, which was about 18 ft. long and 4 ft. wide. On the first runs which I had been making I found a great deal of atmospheric resistance which I could not account for except that it resulted from the bagging of the main aeroplane and the resistance offered by the numerous struts and wires which I used in my attempts to keep it approximately flat. With the engines running at a sufficient speed to give a push of 1325 lbs., it was found that the lift on the aeroplane did not much exceed the push of the screws.

I then made a radical change in the manner of holding the plane flat and tried my first experiments after this with a push of 800 lbs., when it was found that the lift was a great deal more than it was with the 1.325 lbs. in the previous experiments; in fact, the lift on the front pair of wheels was equal to the weight resting on these wheels, and the machine was only kept from leaving the track by the weight of three men whom I carried directly over the front axletree. This I regarded as dangerous. I then attached two very large cast-iron wheels in such a manner that the light wheels could lift some inches from the track before the heavy wheels were lifted at all, the weight of the heavy wheels and their axletree being about 1,400 lbs. Three men were also added to this load.

In making the run the gas was carefully turned on until the engines gave a push of 1000 lbs. I had noticed that as the machine advanced and the engine ran faster, the boiler pressure was diminished. I therefore, upon starting, turned on a little more gas, so that the pressure, instead of falling, increased slightly during the run. When about 400 ft. had been covered, the two front wheels lifted off the track, leaving the heavy wheels still on the track; but just before stopping the heavy iron wheels also lifted from the track, and when the engines were' slopped one of the wheels got into the soft earth, sinking down and tilting the machine over to one side. A gust of wind then tipped the machine on its side; but the breaking, which was confined almost entirely to the framework for holding the cloth. was caused by the impetuosity of a lot of men who tugged away at my ropes, and putting a strain downward instead of upward on the ropes, succeeded in completely destroying the framework.

The speed was 27 miles an hour, and the pressure of steam about 200 lbs. The lift recorded was nearly 6,000 lbs., as shown by the diagrams taken from the dynographs. The incline of the main aeroplane was, however, very steep, being about 1 in 9.

The lift was more than I expected. I did not think that a plane so very large, especially in the direction in which it was traveling, would be so efficient. I thought I should have to depend more on the narrow planes which extend beyond the main plane. This more than expected lift, however, may have been due to the wind, during the last end of the run, being contrary to the direction in which the machine was traveling.

I think that these experiments demonstrate that an aeroplane may be made to carry a considerable load.

It will take some time to repair the damage. None of the expensive machinery was damaged in the least. I shall take greater care in the future not to experiment when there is a liability to squalls, and shall have a fender so that if the machine gets off the track it will not topple over.

It is understood that at the time this run was made about half of all the sails were in position--namely, 3160 sq. ft. The power which the engines developed was about half of their full power, so that it will be realized that there will be ample lifting power when free flight is attempted.

Since then the apparatus has been repaired, and in an article which has been extensively published in American newspapers, a correspondent, writing under date of London, September 12 1893 gives an account of a ride which he took on the machine. After describing it and the house in which it is sheltered, he says:

I mounted the platform, made of light matched boards so thin that they seemed scarcely able to bear a man's weight. Prior to the start a rope running to a dynamometer and pose was attached behind, to measure the forward impulse or push of the screws. . . . The action of the screws caused very little shaking through the whole machine, and this was a surprise to me, comparing the tremendous force with the delicate framework. Behind the ship, 10 ft. away, two men were shouting from the dynamometer and indicating the degree of push on a large board for the engineer to read. The index quickly marked in succession 400, 500, 600, 700, and finally 1200 lbs. of push, and then the commander yelled, "Let go!" A rope was pulled, and then the machine shot forward like a railway locomotive, and with the big wheels whirling, the steam hissing, and the waste pipes puffing and gurgling, flew over the 1,800 ft. of track. It was stopped by a couple of ropes stretched across the track working on capstans fitted with reverse fans. The stoppage was quite gentle. The ship was then pushed back over the track by the men, it not being built, any more than a bird, to fly backward.

M. Maxim is quoted by the correspondent as saying, among other things, concerning his apparatus:

Propulsion and lifting are solved problems; the rest is a mere matter of time. . . . Haste in such a venture is the worst of policies. Weak points must be thoroughly sought for, and everything made completely safe before the public is invited to consider the air-ship as a practical means of transit. I am looking for a location with more room for me to experiment in I can find in England. I am cramped here for want of space.

Such is the present status (1893) of this bold and costly attempt to solve the problem of aviation with an aeroplane. M. Maxim as he says himself, may not achieve final success; but he has, in the opinion of the writer, very greatly advanced the chances of eventual success. He has constructed, it may be said invented, a steam engine with its adjunct developing 300 horse power, and weighing only 8 lbs. to the horse power--an achievement hitherto unparalleled, and probably the most important problem to solve before man can hope to succeed in navigating the air at will.

There doubtless remain other problems to be worked out practically, notably that of effectually controlling a flying machine while in the air, both in the vertical and the horizontal direction; that of maintaining the equilibrium under all circumstances of speed and angles of incidence, and also those of devising methods of starting up and of alighting safely anywhere; for in practical operation, even for war purposes, M. Maxim's machine cannot always be brought back to get a start upon its initial railway track.

There probably also remain some questions to be settled as to the best forms, extent and texture of the supporting surfaces; and it is not impossible that his experiments will eventually lead M. Maxim to a complete remodeling of his aeroplanes; but, as has been pointed out in discussing "screws to lift and propel," it is already within his power, by reason of his marvelously light steam-engine, to go up into the air with an aerial screw, and to perform therein various evolutions.

In any event, the name of M. Maxim must ever remain as that of one of the men who have hitherto done most to advance the solution of the problem of aviation.

⁴¹ M. Maxim has since added the gyrostat.

 

 

Aeroplanes  Part XVIII

by O. Chanute

December 1893.

The Conference on Aerial Navigation in Chicago in August, 1893 brought out a number of experimenters whose ventures had theretofore been unpublished.

One of these, Mr. E. C. Huffaker of Tennessee, had been experimenting with a model somewhat resembling the "effigy" of Mr. Lancaster. It consisted in a rectangular surface of fabric made concavo-convex by a rigid front spar with curved ribs at right angles thereto, so as to resemble the cross-section of a soaring bird s wing A cross stick attached thereto carried a balancing horizontal tail, the center of gravity being determined at the front by loading with lead. The area of sustaining surface was 2 sq. ft., and when held by the cross stick at arm's length overhead, vibrating between two fingers and

facing a wind of 35 miles per hour (6 lbs. pressure at right angles), the weight sustained (or lift) was estimated at 2 lbs. to the square foot, or that corresponding to an angle of 10° upon a flat plane, while in point of fact the model seemed to be horizontal, and the force required to hold it in the wind was very small.

When the model was let go in a steady breeze it would rise to a height of 12 or 15 ft., slowly retreating from the wind but always facing it; then, tipping slightly forward it would descend into the face of the wind, all these effects being easily explained in a horizontal current.

When projected forward by hand, the model would sail away in steady flight with a velocity of about 17 miles per hour, and then descend on a gradient of about 1 in 15. If thrust rapidly forward it would rise some 8 or 10 ft.. and then, hanging suspended for a moment, it sailed forward to the ground.

These experiments are interesting as confirming what has hitherto been said concerning the greater lift appertaining to concavo-convex surfaces, and it is to be hoped that they will be continued.

The other experimenter was Mr. J. J. Montgomery, of California. He had, some years previously, constructed a soaring apparatus, consisting of two wings, each 10 ft. long by an average width of 4 1/2 ft., united together by a framework to which a seat was suspended, and provided with a horizontal tail which could be elevated or depressed by pulleys. The wings were arched beneath, like those of a gull, and afforded a sustaining area of about 90 sq. ft. The weight of the apparatus was 40 lbs., and that of the experimenter some 130 lbs. more.

Mr. Montgomery took this apparatus to the top of a hill nearly a mile long, which gradually sloped at an angle of about 10°, and placing himself within the central framework, the rods of which he grasped with each hand, ready to sit down, he faced a sea breeze steadily blowing from 8 to 12 miles an hour, and gave a jump into the air without previous running.

He found himself at once launched upon the wind, and glided gently forward, almost horizontally at first, and then descended to the ground, finding that he could mean while direct his course by leaning to one side or the other. The total distance glided was about 100 ft., and the sensation was that of firm yet yielding and soft support, being quite similar to the experience of M. Mouillard, as already described, except that there was no apprehension of disaster.

Mr. Montgomery carried his machine back to the top of the hill and prepared to repeat the experiment but as soon as he got into position the apparatus began to sway and to twist about in the wind; one side dipped downward, caught on a small shrub, and, as quick as a flash, the operator was tossed some 8 or 10 ft. into the air, overturned, and thrown down headlong. He fortunately fell without serious injury, and found, as soon as he recovered himself, that one side of his machine was smashed past mending.

This experience led him to design and build a second soaring apparatus, in which he endeavored to relieve undue pressure upon either side by providing a diagonal hinge in each wing, along which the rear triangle might fold back (it was restrained by a spring) and yield to a wind gust. This apparatus measured some 132 sq. ft. of sustaining surface, and weighed 45 lbs. It was not successful; several trials were made, but no effective lift could be obtained with it. This was attributed to the fact that the wings had been made true planes (flat) instead of being arched underneath as in the first machine.

So a third apparatus was designed and built. The wings were each 12 ft. long by an average width of 6 ft., and were given the cross-section and front sinuosity of those of a soaring vulture. They were so built and braced as to allow rotation in a socket at the front of the frame which supported the seat. A hinged tail was added, as in the two previous trials, and the machine weighed 50 lbs.

This last apparatus proved an entire failure, as no lifting effect could be obtained from the wind sufficient to carry the 180 lbs. it was designed to bear. Mr. Montgomery then turned his attention to other matters, but he has since made a more careful and complete study of the principles involved, and he expects to resume his experiments.

The foregoing pages comprise all the experiments, the result of which has been published, which the writer has been able to collate, and which he has considered of sufficient importance to be described in this account of ÏProgress in Flying Machines." Other important experiments are pending or in partial progress; but the designers of these have as yet given out no information for publication, and indeed could scarcely do so concerning tentative plans, subject to constant modifications.

The writer has gathered from the newspapers, accounts of some other experiments, but these seem to be so erroneously or vaguely described that no instruction could be obtained by republishing them. It has been the aim of the writer throughout to gather all the information possible but only to publish that which was reliable and instructive.

 

Conclusion