THE 456th FIGHTER INTERCEPTOR SQUADRON
T PROTECTORS OF S. A. C.
The History Of Ejection Seats
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Ejection Seats Development
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Sgt. Lawrence Lambert (wearing parachute) lowers himself into the cockpit of of a P-61 prior to a test flight in which he was ejected from the aircraft. The purpose of the project was to develop a satisfactory means to escape from high speed aircraft in an emergency. (17 Aug. 1947)
Sgt. Lambert seconds after being literally blasted from the aircraft in an ejection seat. During WWII, Germany had pioneered in the development of ejection seats, but Lambert's ejection was the first such test in the United States.
Sgt. Lambert (right) following his successful ejection at Patterson Field, Dayton, Ohio.
A BRIEF HISTORY OF THE DEVELOPMENT
OF WESTERN AIRCRAFT EJECTION SEAT SYSTEMS
by Christopher T. Carey
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The destructive power of a modern military aircraft is an awesome concept to reflect upon. When one considers the weaponry, performance and powerplant parameters of just about any contemporary military fighter aircraft in use today, it quickly becomes apparent that by comparison, the performance envelope of the body of the human being flying the machine is a considerable number of magnitudes lower than that of his aircraft. One only has to take note of the grim aircraft accident investigation findings regarding disposition of aircrew and/or passengers involved in a catastrophic air crash to be all too aware of just how fragile the human body is when subjected to G-force stresses beyond even a modest level.
The science of aviation technology has progressed far, far beyond the state of development which in December of 1903 saw what is generally recognized as the first (fully documented) successful powered, manned flight--the Wright Flyers brief but historic launch from the sands of Kitty, Hawk, North Carolina. However, even in that earliest phase of mans pursuit of powered flight thoughts relating to human safety in this new and potentially dangerous environment were not unknown. Obscure references exist from that period (1910) regarding attempts to provide aircrew with escape from crippled flying machines (although of necessity, quite primitive).
The introduction of the new technology of air warfare into the hoary traditions of warfare etiquette resulted in no small amount of reactionary resistance to the phenomenon of aerial battle, let alone the startling concept of providing a safe operating environment for pilots of the early wood and fabric craft. Aviation was at that time an inherently hazardous undertaking, just as it still is today, but to a far greater extent due to the newness of the technology and operating environment. To a certain degree, resistance to early aviation safety concerns centered upon the ancient traditions of military honor and protocol. One did not wish to suffer the dishonor of retreat from battle, according to honorable custom, and therefore many felt that attempts to provide a safe exit from a crippled aircraft were somehow demeaning to the assumed bravery of aircrewmen.
Parachutes, the first practical aircrew safety device, were at first subjected to disdain by the higher echelons of English aviation command in World War One, who felt that their introduction would encourage a lack of firm resolve to 'stay the course' in aerial combat. This was apparently not the case in the the Imperial German High Command, for the Germans soon recognized the value of the new device and started equipping their balloon crews with this escape device; according to reports, some German pilots also adopted the parachute shortly before the war ended.
Although the development of parachute technology developed marginally in the years immediately following the First World War, the same cannot be said for the concept of ejecting an aircrew-man from a disabled aircraft. Perhaps this was due to the relatively low performance of the aircraft in use by the end of the war. To some degree, it must have been due to the general feeling that the successful resolution of the First World War had put the need for continued defense development on sustained hold. In any event, most defense technology activities experienced a significant slump immediately after the war, and it was not until Germanys military resurgence of the 30s renewed international anxieties that defense concerns (including aircrew safety) again became reestablished.
In most cases, if a pilot found himself in trouble in the 20s, it was relatively easy to simply disengage the seat harness and jump over the side of the machine so that the parachute could be deployed for a safe descent. However, as the power and performance of aircraft continued to increase, it quickly became apparent that the risks involved in simply jumping over the side of an aircraft were significant. Especially so if the aircraft were in any manner aerodynamically disabled or damaged in a way that created unusual airframe gyrations or G forces for the aircrew who were trying to exit. Furthermore, as the designs of aircraft became more sophisticated, especially as found in aircraft designs with placement of the propeller driven engine in the rear of the aircraft (behind the crew compartment), the need for a device to successfully extract the aircrew safely beyond the tail assembly (and/or rear-positioned power plant) became more fully focused in the minds of a few astute and enterprising individuals.
German Developments Through World War Two
As is the case with many innovations in technology, it was the Germans who were among the first to explore this area of aviation safety in a serious and innovative manner. Owing to the development of Germanys covert military capability in the 1930s, much work was being done in aeronautical engineering research for military aviation applications. As Germany explored and researched a new generation of higher performance military aircraft as part of Hitlers overall build-up of war materiel, the individuals concerned with aviation medicine in the new Luftwaffe recognized a coexistent, renewed need for aircrew safety. This was especially true, since much aeronautical flight testing of new designs was being undertaken, with all the implicit hazards pertaining to that area of technological investigation.
Many ideas occurred to German aeronautical engineers in the process of attempting to address this need for safe egress from crippled aircraft. One of the first was the "boom" concept, in which a pivoted fulcrum, attached to the pilots harness and powered by a compressed spring, pulls the pilot free of the cockpit in an emergency. Another of the early ideas was very simple--a compressed spring situated under the pilots seat which when released would eject the occupant (assuming that the canopy had been freed and cleared first, not always an easy thing to do using a manual technique and especially in a seriously disabled aircraft).
Interestingly, both these early ideas were also conceived and evaluated by counterparts in England, at the end of the Second World War and without knowledge of the original pre-war German research. In fact, back in 1930 an enterprising RAF Flight Officer, concerned with the increased performance of a new aircraft his squadron was transitioning into, formulated a design for an "escape seat." Consisting of a pilots seat mounted on two telescoping tubes, each containing a highly compressed spring, the seat would be pushed with its occupant up into the slipstream of the aircraft when the seats catch was released. While the seat was not actually ejected from the aircraft, the idea was that in this position it would be easier for the pilot to roll out of his seat and free himself of the stricken plane. The idea was submitted to the English Air Ministry, along with blueprints and a working model, but no further development was ever undertaken, and thus English innovations in aircrew escape would languish until immediately after the Second World War, when the captured German research and development would stimulate new interest in Allied aircrew escape technology.
In Germany, developments in aeronautical technology were accelerating with the introduction of the jet engine, while by 1939, the Luftwaffes Aviation Medicine branch was actively experimenting with ejection systems, using physiological testing devices that included instruments for measuring the forces of gravity and acceleration on the human body. Their tests has determined rough physiological parameters of human ability to withstand G force onset of about +20G for a duration of about 0.1 second. The German preference was at this time for a compressed gas system of ejecting the aircrew seat, although explosive cartridge propelled seats were also under development. The need for adequate aircrew escape from dive-bombing aircraft such as the Ju-87 Stuka, with its sustained high positive G loading during pull-out, significantly motivated investigations into use of high-pressure systems to eject aircrew. The German manufacturer Heinkel maintained chief engineering responsibility for development of all aircraft escape systems, throughout the war, and by late 1942 all German experimental aircraft being flight tested were equipped with some form of Heinkel ejection seat.
With aircraft development feverishly continuing in wartime Germany, Heinkel developed ejection seats finally started being installed in production aircraft, as radical new designs came into use. Although the singular Messerschmidt 262, twin-engined production jet fighter-bomber (Schwalb) did not feature such a schleudersitzaparat (the German term for 'ejection seat', which translates roughly to "seat catapult device"), reports suggest that at least a few versions (Sturmvogel) had what has been described as a catapult-seat (although it is not clear whether the seat was driven by an explosive charge or by a spring mechanism). Other aircraft, such as the Heinkel He-162 Volksjäger, were provided with a compressed air propelled ejection seat. Other aircraft to feature similar systems included the Dornier Do-335 Pfeil, the Arado Ar-234B Nachtigal, the Heinkel He-177, the Heinkel He-219 Uhu, the Dornier DFS-228, and the rocket-powered Messerschmidt Me-163 Komet (this last system was spring powered). Additionally, earlier research begun in the late 30s by Heinkel had resulted in the first recorded example of a completely ejectable crew compartment being developed. The rocket-powered Heinkel He-176 (the worlds first rocket propelled aircraft) featured a nose section which could be jettisoned in the event of an emergency. Development problems involving successful deployment of the main parachute designed to slow descent of the ejected crew compartment resulted in several innovative engineering designs, and subsequent testing demonstrated that in the event of the crew being disabled, the He-176s crew compartment would enable its occupant to survive a landing within the escape pod with only minor injuries.
The Heinkel explosively ejected seat consisted of a seat bucket assembly mounted on 4 rollers which moved in two parallel channels 42 inches long. The charge used in the two tube catapult consisted of 30 grams of powder, firing much like a conventional projectile cartridge, with the two part catapult tube fixed to the upper end of the seat and at the lower end to the aircraft frame. Ejection velocity achieved was 35 fps, with a stroke of 28 inches and an acceleration of about 12 Gs. Although an experimental compressed gas system achieved a ejection velocity of 57 fps and an acceleration of 27 Gs, the system was massively heavy and presented considerable field maintenance problems with over 1700 psig pressures required for successful operation.
On 13 January 1942, the first known emergency use of an ejection seat occurred during a test flight of the Heinkel He-280 jet fighter. The pilot, a man named Schenck, ejected from his iced-up aircraft after jettisoning his canopy, successfully achieving safe egress from the machine. Although Schencks was the first known use of an ejection seat for emergency egress, the Heinkel compressed air driven seat used by Schenck was purportedly tested in an experimental ejection from a test aircraft by a Heinkel employee named Busch, prior to Schencks 1942 ejection. (These facts was unknown outside of Germany until after the end of the Second World War, and for a while it was thought that the first successful emergency ejection was made by a Swedish pilot from his crippled SAAB J21-A1 aircraft--with "pusher" type propeller power-plant--on 29 July 1946).
By the end of the Second World War, more than 60 emergency ejections had been made by Luftwaffe personnel, and German Aviation Medicine branch research in aircrew egress technology had progressed substantially into areas of high-performance aircraft escape systems at proportionately high physiological limits of human endurance. Among the important facts that had became clear to German researchers, however, was that compressed gas driven systems were prohibitively heavy, requiring installation of heavy system components to contain the gas under high enough pressure to perform as required; they were furthermore quite difficult to maintain and keep operational under actual battlefield conditions. Ballistic (explosive) systems were lighter, but the requisite technology, while promising, was still in its infancy. These facts were not lost on American or British scientists going over the German research at war's end.
Sweden: Co-Pioneer In Evolving Egress Technology
While Americas interest in emergency aircrew egress languished for the most part until after the end of the war, Germany was not alone in recognizing the need for increased air crew safety during the 1940s. In Sweden, SAAB Aircraft was developing a pusher-type aircraft to be designated the SAAB J21, and with the attendant work came understandable concerns about how to effectively provide J21 aircrew with an effective emergency escape system. 1939 saw initiation of studies in ejection systems, and by 1941 primary design studies had been finished, with actual flight testing of the explosively deployed seat being carried out in 1942. Bryan Philpott, in his excellent book Eject! Eject!, remarks that Swedens egress program developed in the early 1940s, "...when war, so often the mother of invention, did not provide the spur to the Swedes that it did to the combatant nations..." In fact, Sweden was very much spurred on by the immense threat of being drawn into war against its will, and has long maintained a tradition, its political neutrality notwithstanding, of providing itself with innovative and advanced defense technology--a tradition it shares with Switzerland, and for similar reasons. Regardless of their motivations, with its excellent reputation for scientific and industrial excellence, Sweden enthusiastically went ahead with its initial research into aircrew egress systems. By the end of the war, Swedens technical and scientific database on emergency escape systems for aircraft was well advanced, although ostensibly entirely independent of any research undertaken by Germany in the same war-years period (this has not been verified, as Sweden, although technically neutral, had strong sympathies with Germany and maintained continuing diplomatic relations throughout the war--thus the possibility of exchange of technical or research information may not be entirely ruled out).
The Type 1/Type 21 seat ultimately evolved into their later Type 2 (Type 29) ejection seat. The Type 2 seat was intended for use in the SAAB J29 (known informally as the Flying Barrel), a post-war, swept-wing, barrel shaped aircraft of single engine design. Although substantially similar to the earlier Type 1 (or Type 21) seat, anticipating the highly touted modern McDonnell-Douglas ACES II seat concept as used three decades later in the F16 Viper, SAAB canted the seat back at a 30 degree angle to both reduce frontal area as well as improve pilot G-tolerance. At the onset of Swedish investigations into ejection seat design, a decision was made, as remarked earlier, to utilise an explosive cartridge type ejection gun. In the seat used on the SAAB J29, this took the form of 60 gm of explosive fired in a three-stage charge. A further preference of the SAAB designers was for a pilot worn back-type parachute configuration (not attached to the seat as on the Martin-Baker system), employing a seat-contained survival kit. Although seat ejection was originally to have been initiated through use of two strap-devices located at shoulder level, the design was changed to employ a face-curtain actuator similar to that used by the Martin-Baker system (English). A back-up, or secondary, seat actuating device was situated between the pilots knees, where it was conveniently at hand in the event unfavorable G forces made grasping the face blind actuator difficult (it is interesting to note that this innovation is now used almost uniformly by all current ejection seat systems). Further enhancements to the Type 29 seat were spring footrests intended to protect the pilots lower extremities and reduce flail injuries. On the whole, the philosophical approach of the SAAB seat was to eject the seat and occupant, thereafter immediately separating them. Successful man-seat separation was further provided for by the introduction of an apron device which was actuated by a separate power gun, actuated after the central harness unlocked after ejection. When man and seat had cleared each other, the idea was then for the pilot to either manually deploy his back-type parachute or rely on the automatic barometric chute deployment device.
Early American Efforts: The US Air Force and Navy Diverge
By the end of the war, captured German research came into the possession of the Allies. Although emergency egress concerns were not significant in the United States until later in the war, the US had made a few insubstantial efforts in this direction in the late 30s and 40s. Among them in 1937 was the establishment by a Dr. J.W. Heim of an impact facility in a hanger at Wright Field (later to become Wright-Patterson Air Force Base / Air Development Center) to investigate the forces of abrupt accelerations on human beings. A simple swing-device suspended on cables, the system could achieve parameters of about 16 Gs with a pulse of 0.15 seconds. There are further unsubstantiated reports of a late 1930s Army Air Corps experiment using a spring-driven, pivoted fulcrum arm to snatch the pilot out of a rear-engined aircraft under development to fling him to safety beyond the propeller arc. Beyond these examples, there is little to indicate a strong interest in emergency egress technology by American aviation medicine proponents until the later stages of the war, when German research and developments in this area came to light. With the acquisition of both German databases in egress research and actual examples of the German Heinkel explosive cartridge ejection seat by the US, immediately the war had ended, the US began to vigorously attempt to gain greater knowledge in this overlooked area of aviation technology.
The new American developmental research spurred on by acquisition of German wartime data branched off into two distinctly different approaches towards the same end, one taken by the US Air Force and one by the US Navy. With the political rivalry between these two services to attain ascendant aviation technology acting as a further goad, two schools of thought on military egress systems formed. The US Air Force researchers greatly favored many of the German findings, among which was the belief that the best manner of obtaining a favorable pilot posture that would minimize spinal injuries was having firing actuation controls built into armrests on the seat. The US Navy, on the other hand, tended to credit the British approach toward establishing correct spinal alignment to best absorb the punishing catapult forces; this school of thought advocated the use of a face-blind pull-handle firing actuator, the theory being that the act of reaching up to pull a blind down over the face automatically positioned the pilot for the most favorable spinal alignment. Neither of the two techniques were ultimately found to be completely perfect, but this resulted in initial US Air Force reliance upon arm-rest triggers and early US Navy adoption of the English Martin-Baker face-blind actuator system. This variance in developmental approach would remain a primary distinction between early US Air Force and US Navy ejection seat designs well into the 70s.
As regards the catapult itself, suffice it to say that, as in nearly every instance in which captured German research and technological innovations had been acquired, the cartridge-actuated Heinkel seat figured prominently in early US investigations into emergency egress systems; clearly, compressed gas systems (although functionally adequate) required far too great a compromise in terms of added airframe weight and loading. Along with actual examples of the German seats, associated equipment and physiological testing instrumentation (including a vertical seat-firing tower) were obtained and studied at Wright Field at war's end. With the first American jet fighter already in the air (Lockheed P-80 Shooting Star), some sort of ejection system was needed that would extract crew from these fast new machines under emergency conditions. Although the term 'bail-out' remained in use after the first ejection systems were installed in American fighters, the ballistically fired ejection seat provided far more positive results than a simple 'bail' over the side of the aircraft!
American concern with rapid development of ejection systems for US aircraft resulted in a formal policy of sharing the extant database on ejection systems technology among many different (US) aircraft manufacturers, once knowledge of the captured German developments in the field had been made available for analysis. The opinion has been offered and formally stated in Bryan Philpotts excellent book on the subject that this initially had the effect of creating more problems than it solved for the US Air Force. Whereas in Sweden, Germany and England, responsibility for ejection seat development had been given over to a single industrial concern, the proliferation of US corporate approaches to the problem ironically acted against the easy solution of common design obstacles. At least 6 or 7 aircraft manufacturers in the US designed and developed their own ejection seat systems, installing them in their own aircraft; thus design uniformity was largely absent, and attendant system and logistical complexities resulted which would later present technical and materiel problems for field maintenance. The obvious advantage obtained would be a proliferation of widely different researches that would provide a broader database upon which to draw in future egress R&D work.
As early as 1946, the US Navy had determined that England's Martin-Baker Company had satisfactorily pioneered the basic functional principles of pilot egress technology well enough that duplicate or redundant studies by Navy researchers would be both expensive and needless. Thus, the US Navy arranged with Martin-Baker to provide a seat somewhat tailored to US Navy requirements as well as technical support from that company to develop it. Photographs of this first M-B provided US Navy seat show it to be quite similar to that company's 'pre-Mk.I' seat. Along with the actual seat, a 105 foot tall test firing tower was also acquired and a converted Martin B-26 Invader (US Navy JD-1) was specially fitted for planned aerial test firings.
With at least 4 different companies working on US Navy jet aircraft designs in 1946, it was decided to issue an ejection seat specification and allow the individual Navy contractors to develop their own systems, as long as each stayed within specific general parameters. These parameters were based largely on the Martin-Baker seat and the standard features that characterized the English egress philosophy founded by Martin-Baker (face-curtain actuator, drogue gun, etc.) and mandated use of standard US Navy parachutes, survival kits, life-rafts, and other equipment. It is worth noting here that both the first US Navy and US Air Force seats were designed to use seat-type personal parachutes (this is evident in the use of characteristic rounded seat pans in all early US Navy seats), which followed the German example (Heinkel).
Initial US Air Force research showed that the Heinkel ballistic system was not powerful enough to use on anticipated Air Force jet aircraft, as the catapult velocity was insufficient for safe ejection at the new Lockheed P-80's maximum operating speed. However, a fairly simple redesign of the basic Heinkel seat by Wright Field resulted in a prototype US seat, which was tested by a live volunteer from a specially modified P-61B Black Widow on 17 August of 1946. A visual side-by-side comparison of the Heinkel seat and the American seat reveals distinct and clearly identifiable design concept sharing. Progress was made quickly in developing the concept, however, and the straight-winged Republic F-84 Thunderjet became the first production American jet fighter to be equipped with an ejection seat. As mentioned earlier, the USAF approach to ejection seat design called for armrest-actuating triggers (following the German example) which were first raised and then squeezed. Although a conventional seat-type chute was at first used in the original American seat (used in the P-80), a back-type parachute was later incorporated; these were not, of course, attached to the seat (similar to the Swedish approach, but contrary to the English design), but were worn by the pilot. Further, all early American seats were not automatic in that man-seat separation had to be achieved manually, and the pilot freed himself from the ejected seat first, then manually deployed his personal back-type chute after physically pushing himself away from the ejected seat. Only later did refinements come to be incorporated into the system, which included leg restraint provisions, correct separation sequencing, fully automatic seat-separations--all or most of these having been addressed or at least recognized as desirable early on by Englands Martin-Baker Company and quite soon thereafter by the US investigators.
Regardless of the rapid pace of American development in design and production of ejection seats for military aircraft, after the war, there was some small amount of resistance to the use of ejection seats on the part of American aircrew, who were somewhat reluctant to fly aircraft equipped with them. More than a few pilots likened the prospect of being seated directly upon a seat's live explosive charge akin to sitting on a powder keg with a short fuse. Purportedly, these anxieties were largely put to rest in 1949 by a series of demonstration ejections carried out by Air Force Captain Mazza from the aft cockpit of a specially modified TF-80C Shooting Star (later standardized as the T-33 jet trainer). The first US Navy emergency use of the new seat occurred later in the same year when the pilot of a McDonnell F2H-1 Banshee was forced to eject at 597 mph over South Carolina. After these events took place, acceptance of the new device was more readily forthcoming among US air crews. In August of 1949 the pilot of an Air Force F-86 Sabre also made a successful emergency escape using the new type seat (North American model T-4E-1 catapult seat), again demonstrating functional performance under adverse conditions.
Again, partly due to the broad approach taken towards development of ejection seat systems among US manufacturers, a number of unusual designs were produced. One in particular, developed for use on the pusher-engined XP-54 Swoose Goose featured a downward-accessed pilot seat, which would lower the aircrewman below the belly of the aircraft so as to clear the arc of the prop. While not strictly an ejection seat, the XP-54 design anticipated several future developments of a downward firing type seat on the Boeing B-47 Stratojet, and the Lockheed F104A Starfighter, as well as the downward firing cockpit system for the experimental XF108 supersonic interceptor (development discontinued after mockups were completed), and the Douglas X-3 Stiletto twin jet research aircraft. At the time, the official emphasis on development of a successful US system was on functional adequacy at high altitude and sustained high speed, as this was the envisioned performance area within which safe aircrew egress would be most critical; the obvious need for safe ejection at lower, slower speeds took a markedly subordinate priority in this overall Air Force conceptual view. Given the notable rate of engine failures and marginal reliability that characterized the early turbojet engines, this misplaced priority would subsequently have substantial consequences as well demonstrated in US Air Force aircrew survival statistics of the period.
Principal among the influences governing the US Air Force decision to continue developing downward ejecting systems was the fact that early catapult inertial acceleration velocities were not completely adequate to ensure clearance of jet aircraft vertical stabilizer assemblies. This, in combination with emergent awareness of the future importance of high altitude interception mission requirements, resulted in a failure to adequately address safety concerns related to 'low & slow' modes of flight performance. Unfortunately, the 'downward egress' concept was somewhat less than favorable for a number of reasons, not the least of them being its unsuitability for the critical low-altitude or zero/zero mode ejection. This fact was later sadly and graphically demonstrated when emergency use of a downward firing Stanley model C-1 seat on a test flight of the Lockheed F104A Starfighter resulted in the death of Captain Ivan Kincheloe in 1958.
As technical advances continued in seat design, it was quite clear that the problem of providing adequate clearance of fast moving aircraft tail structures presented collateral concerns in terms of increased rates of spinal compression injuries related to catapult inertial acceleration forces. Problems associated with having the catapult thrust force located behind the seat center of gravity included high multidirectional G loading due to aerodynamic tumbling forces, wind-flail injuries, wind-blast effects, man-seat separation problems, and parachute entanglements due to aerodynamic instability of the seats after ejection. The problems attending higher inertial acceleration rates to clear the aircraft were obviously not going to be easily solved with continued use of simple explosive pyrotechnic devices. Despite the statistical evidence of only marginal success in achieving safe ejections in the outermost corners of the flight performance envelope, explosively fired catapults of necessity remained in service until roughly 1958, at which time the first rocket catapults were introduced to American ejection seat design (the Convair F102 Delta Dart was the first aircraft fitted with a rocket catapult fired seat, designed by Weber Aircraft Company). [Of interest is the fact that the proof of concept design for the F102--the Convair XF-92A research aircraft--was fitted with an early explosively fired catapult ejection seat originally designed for the Convair XP-81. When the two examples of this combined prop and jet propelled prototype were retired from testing in 1947, this seat was fitted to the XF-92A. Perhaps fortunately, it was never put to 'test' use throughout the duration of that aircraft's flight test program.] Other innovations that were prompted by high rates of spinal injury associated with G-onset forces imposed upon the spine during ejection included the use of variable-density compressible foam in seat cushions, to help reduce or offset accelerative effects on the spinal column. (This same principle is employed today in crash helmet design, for the same end.)
Dr. Robert E. van Patten, former Chief of the Acceleration Effects Branch, Biodynamics and Bioengineering Division of Armstrong Aerospace Medical Research Laboratory (Dayton, Ohio), cites the rapid progress made by the United States in adopting emergency egress systems for its Air Force after the slow initial start at wars end with reference to the fact that in 1955 the first successful supersonic ejection was made by a pilot from his stricken North American F100A Super Sabre after the aircraft went into an uncontrollable dive. The ejection occurred at Mach 1.05 during a test flight, and while he was injured in the process, pilot George Smith survived the accident and fully recovered. This incident took place less than a decade after the first real investigations into egress systems had begun in America at wars end. Although the technology was improving rapidly, most US ejection systems were engineered to perform best under 'ideal' emergency situations. However, success in achieving a substantial safety record (and vindication of the new rocket powered catapult systems) is demonstrated by the fact that during the Vietnam conflict (1963 through 1975), more than 25% of the US Navys RA-5 (A3J) Vigilante combat ejections took place at speeds greater than Mach 1.0 (the system in use in that aircraft was the North American Aviation produced HS-1 rocket powered seat, with zero/zero to 700 knot IAS capability).
Certainly the Korean War provided much valuable information to the US Air Force and American aerospace manufacturers regarding egress design assessment. Philpott in his book cites the fact that in almost 2000 combat ejections experienced by the US Air Forces during the Korean conflict, 60% of the aircrew ejecting experienced no problems during egress. The other 31% experienced difficulties ranging from seat actuation, canopy release, maintenance failures, incorrect ejection posture, slipstream, through-canopy-ejection, premature seat actuation, and so forth. Similar difficulties, as well as ones unique to carrier operations, were reported by US Navy pilots. Although most of the problems were addressed, Philpott suggests that again the vast number of dissimilar ejection seat designs in use in various aircraft compounded quick resolution. A look at the official US Air Force statistics themselves shows a slightly different picture, with an overall (USAF) aircrew survival rate of 77% during the first 5 years of ejection seat operational experience (1949-1953) . In a recorded 4626 emergency ejections incurred under non-combat conditions, from 1949 through 1980, fatal injuries occurred in 838 (or 18%) of those ejections. With the refinements of automatic release restraint systems, automatic man-seat separators, variably-staged parachute deployment systems, and aerodynamic deployment stabilization devices such as the DART system, survival rates went up in the 1954-1958 period to 81%. Throughout the period of the mid 50s through mid 60s, most USAF aircraft egress systems received continual updating as operational experience provided new engineering understanding of optimal design features. The overall survival rate thereafter remained roughly at a plateau of about 80% until the 1975-1980 period, in which these values fell somewhat for USAF crews (introduction of the ACES II system, with enhanced ejection safety features).
England's Martin-Baker: Dedicated Commitment
With revelation of the early and substantial foundations in emergency aircraft egress technology developed by Germany and Sweden at the wars end, awareness was acute in England that the logarithmic increase in aeronautical performance parameters required a corresponding capability in aircrew protection and escape. The English Air Ministry sought assistance from Sir James Martin, founder of the Martin-Baker Aircraft Company. Baker was a brilliant self-made engineer and designer who had originally set up his company (in 1929) to manufacture machines and specialized vehicles. Development of his firm into the aircraft business in co-partnership with Capt. Valentine Baker (ex-RAF) had met with marginal success, although it was generally agreed that his abilities were quite substantial and his designs for three successive prototype aircraft had been innovative and progressive. In 1942, the third aircraft (designated the MB3) was lost on a test flight which also killed Capt. Baker. Profoundly affected by the loss of his flight testing partner, it is said that James Martin developed a keen interest in aircraft safety and aircrew survival from this experience.
During the war the company manufactured a variety of products ranging from ammunition feeder belt mechanisms to wing-mounted cable cutters and canopy quick-jettison equipment. During the Battle of Britain Martins canopy emergency release device quickly gained him recognition, and in 1944 the RAF Air Staff approached the Martin-Baker Company to develop a system whereby the pilot of a disabled aircraft could be safely ejected for a normal parachute recovery. An incident involving a pilot having been killed by colliding with the tail assembly of his aircraft (a jet powered Meteor prototype) on bailing out was the instigating cause.
The problem, considered from its medical and physiological standpoints, is a thorny one, and although the German studies of the 30s and 40s had produced a baseline database on the practical limits of human G tolerance, the critical principles of "jolt" and pulse pressure--in other words the rate at which accelerative force is applied--were not fully or completely fathomed. It was not until 1944 in studies carried out in Germany by one Dr. Weisehofer that this last factor became more adequately understood. In England, the concept was grasped more quickly and efforts began to determine how to devise a system which would achieve the required pilot extraction without exceeding the ability of the human body to withstand severe rates of accelerative force. One very early idea was the previously mentioned pivoted fulcrum principle, in which a beam attached to the pilots harness is actuated by a strongly compressed spring mechanism to pull him free of the cockpit and toss him away from the aircrafts tail assembly. The idea had a certain appeal in that it could conceivably be retrofitted to existing aircraft fuselages with a minimum of difficulty.
For various reasons, this idea was discarded and exploration into an ejectable seat system began in earnest. To develop a keen understanding of the limits of G force sustainable without injury by the human spine (which was the critical structure susceptible to damage) in vertical acceleration, it was necessary to develop a vertically inclined tower, up which a test seat could be shot at various rates of G. Both Sweden and Germany had constructed similar test equipment in their ejection seat programs. In the course of tests, it soon became apparent that it was not the peak gravity (or G) sustained which was the limiting factor in human tolerance, but the rate at which the acceleration occurred. Furthermore, onset of G ought not to exceed 300 G/sec, and proper body alignment during the application of force was critical to avoid spinal injury.
These insights led the English to the development of a two-cartridge gun, which met the physiological limitations while still providing peak G needed, and to various refinements in a seat which would assure proper posture (these included a face-blind actuation device and foot rests, both of which helped the ejectee to assume the desired anatomical alignment for a safe ejection). Still another consideration was revealed, after further study of the physiological function of the human spine while subjected to vertical compression forces. This was what is termed "acceleration overshoot," and is the amount of acceleration experienced by the seated person in excess to that of the seat, due to the construction of the bodys structure. It was found that spongy tissues of the bodys nether side tended to increase acceleration overshoot forces, just as did excessively soft seat cushions.
The earliest prototype Martin-Baker seats were configured with the parachute pack in the seat pan and the water-survival pack & inflatable raft fitted behind the back. This was also the configuration for the earliest production model, the Martin Baker Mk.I seat. This design allowed for increased possibility of acceleration overshoot injuries, as was discovered, and in subsequent Marks, the parachute was moved to a position behind the back, with the water-survival kit stowed in the seat-pan. In subsequent Mark developments, the parachute pack remained in the back stowed position, although with the present generation M-B seats (Mark IX and later), the chute has been moved to the seats head-support area.
In September of 1945, development of the prototype Martin-Baker ejection seat had proceeded far enough that a contract was placed for two experimental units which would be flight tested in a high-speed aircraft. The latter turned out to be a Meteor F3, and after a number of dummy ejections and corresponding modifications of such components as the drogue chute and its deployment device (a gun was incorporated in place of a spring deployment mechanism), the first English live ejection test was made by test subject Bernard Lynch on 24 July 1946.
It is interesting to note that only 5 days after Bernard Lynch conducted the first successful live test of the Martin-Baker prototype ejection seat in England, a Swedish pilot used the SAAB Type 1 (Type 21) ejection seat in his SAAB J21-A1 pusher-engine aircraft in an actual emergency. Furthermore, over 60 German Luftwaffe aircrew had previously used their Heinkel ejection seats for successful emergency wartime (WWII) ejections. Also at this time, the United States Army Air Force was still weighing the merits of ejection seat systems, investigating German wartime developments, and had not even a prototype of its own designed for possible American military aircraft use.
Egress Matures: Ejection Systems Develop Further
In June of 1947 the decision was made in England to fit the new Martin-Baker ejection seat (Mark I) to all British tactical military aircraft. A number of versions of the original Mk.I seat were produced for a variety of jet fighters and bombers. Various small changes in the Mark I application for each aircraft type reflected the unique requirements or constraints of that particular plane. The Meteor fighter was initially fitted with the M-B Mk.I, and later with the Mk.IE seat. The Attacker was fitted with the Mk.IA (it was later upgraded to the M-B Mk.IIA model). The Wyvern was fitted with the Mk.IB model (later upgraded to Mk.IIB). The Canberra bomber received the M-B Mk.IC seat, and the Seahawk aircraft was fitted with the M-B Mk.ID seat (later upgraded to M-B Mk.IID seat). The M-B Mk.IF seat went to the new Venom fighter (later upgraded to the M-B Mk.IIF seat).
Prior to full-scale production of the Martin-Baker Mk.I series, the Saunders-Roe Aviation Company placed an order for an ejection seat for use on its Saro A-1 jet flying boat/fighter. This seat lacked some of the more sophisticated features and detailing of the standard Mk.I production model, and was officially designated the Pre-Mark.I Seat. Altogether the Mk.I production seat weighed some 172 pounds (143 pounds of which was ejectable). A list of its innovations includes: 1) a two cartridge ejection gun; 2) gas-pressure release mechanism unlocking the ejection piston from the firing cylinder immediately upon firing of the first cartridge; 3) an adjustable seat pan; 4) spring-loaded footrests to facilitate foot placement for ejection; 5) a face-curtain seat actuation system, which assured proper ejection posture and which protected the pilots face from blast injury; 6) an explosive drogue gun method of deploying the seats stabilising drogue chute; 7) retractable seat-pan raising handle; 8) the Martin-Baker back-type water survival/dingy pack, and seat-cushion type personal parachute; 9) integral thigh restraining seat-pan extrusions. By 1950, the Mark I series seat was standard on all first line RAF and RN fighters.
It ought to be noted that there was considerable difference in the physical appearance of the various Mk.I models, and that not all of the dash variations featured a seat type chute. For example, the M-B Mk.IA variant (for Attacker aircraft) used a Mk.3A back-type parachute rather than a seat chute, and used a seat sea survival kit/inflatable raft--very much as later seats would. The Mk.IB, ID, IE, and IF seats all featured Type 3A M-B back-style parachute configurations. Only the Pre-Mk.I, Mk.I, and Mk.IC featured seat-mounted chute assemblies. In some cases, the seat style chute was used due to the constraints of the aircrafts cockpit, despite established awareness that acceleration overshoot problems were more of a concern with the seat-style chute design. All subsequent Mk.II series seats featured the back-style chute design.
As experienced in the US, there were initially some reservations about use of the new ejection systems on the part of both aircrew and aircraft manufacturers, who felt that the structural modifications required to fit the seats were costly and technically complex. Again, time and effort was needed to address the reluctance of aircrew to feel comfortable with the new safety devices, but it was not long before several actual in-flight emergency ejections proved the value of the Mk.I type system and these examples of its safe operational value put further hesitance to rest.
Within the first few years the results of about 70 successful ejections (50 of them successful) provided valuable information on much needed modifications to the original Martin-Baker design. The Mk.I system was, after all, a manual seat which did nothing more than successfully get the aircrewman out of his disabled aircraft safely. It was clear that further progress was needed in development, specifically in automating the man-seat separation process and in deploying the personal parachute. In instances where disorientation, confusion and/or disablement were factors in emergency ejections (as they frequently are, especially in aerial combat situations), automated systems would make the difference between saving a pilot or not.
The Mk.II seat addressed these problems. Among the modifications featured on the Mk.II series seats were 1) modification to the drogue shackle, and addition of a Time Release Unit (TRU) for deploying the drogue; 2) a mechanism for releasing the seat harness; 3) addition of an "apron" which would link the drogue chute to the pilots personal parachute and withdraw it after man-seat separation occurred; 4) a barostatic unit, which was fitted to the TRU so as to prevent deployment above 10,000 feet (oxygen deficit and hypothermia hazards); and 5) further modification of the drogue gun. By 1953 a retroactive modification program was carried out on all RAF and RN aircraft fitted with the original Mk.I series seats to bring them up to Mk.II standards. The effectiveness of the new design resulted in a reduction of ejection fatalities from the earlier, higher figure applicable to the Mk.I seats to about 10% of the Mk.II series ejections in 1954 14
Attention soon focused, however, on the parameters of emergency egress wherein the Mk.II series seats still fell short. Two of these were in high-speed and low altitude situations. Changes in the ejection gun ensued which increased ejection trajectory without significantly increasing peak acceleration. Additionally, the adoption of a two-stage drogue chute design resulted in faster, quicker and safer deployment of the pilots personal parachute at higher speeds. Finally, in order to prevent lower extremity flail injury, which frequently were a consequence of high-speed ejections, a system was devised using nylon strap restraints to secure the legs to the seat on actuation where they were secured until the man-seat separation occurred. These modifications resulted in a system which allowed successful ejection from altitudes of 50 feet altitude and 130 knots IAS. The new system was designated the Mk.III series seat.
Further modifications were carried out on the Mk.III series seat over the next few years to achieve a further refinement in the parachute deployment process (primarily a reduction in the drogue/main chute deployment sequence timing), which resulted in successful ejections from zero altitude and 90 knots IAS. The seat was also tested in ejections above 40,000 feet which proved that the seat was usable in both extreme polar limits of the possible performance parameters.
In the same time period (1954 through 1955), a system was devised whereby automatic explosive canopy jettison was incorporated as part of the seat actuation protocol, so that no time was wasted in clearing the canopy before egress was initiated. Owing to possible complications, however, the Martin-Baker seats were capable of ejecting through the canopy of aircraft if necessary, and in some RAF aircraft the egress drill was standardized to blast through the canopy routinely (an example in point was the Canberra B Mk.II aircraft).
By the time the mid-1950s had arrived, the continuing evolution of the standard British Martin-Baker emergency egress system had enabled the Martin-Baker seats to prove their sound and carefully considered design handsomely, and this fact was not overlooked by many of the other nations around the world who were growing increasingly interested in providing adequate emergency escape for their air force personnel flying high-performance machines.
Further Refinements And Improvements Outside The UK
Although Germanys involvement in aircraft egress systems had come to an end with the conclusion of the Second World War, the other early pioneering nation in ejection seat design--Sweden--continued to evolve their indigenous egress system engineering.
With development of the SAAB J32 Lanson interceptor/strike aircraft, a two-seat machine which flew for the first time in 1952, a new requirement arose for an ejectable seat system. This resulted in the 101 pound SAAB Type 3 (Type 32) ejection seat, powered by a two-stage explosive cartridge gun, and featuring the standard pilot-worn back-style personal parachute and seat-stowed survival kit as the in the previous seat (Type 29). Whereas the Type 29 seat had weighed about 66 pounds and was capable of being used at an altitude of 300 feet in level flight, minimum altitude for safe ejection using the SAAB Type 32 seat was reported to be about 150 feet in level flight. The Type 32 seat also featured separate guide rails (as in the Martin-Baker seat design) and a specially shaped parachute canopy; the seat survival kit incorporated a hard-shell container for the first time, instead of a soft-pack, thereby helping reduce acceleration overshoot potential. An inertia reel restraint system was also added, as was a modification from guide rail rollers to slide bars, an innovation that enhanced smoothness of operation. Seat actuation was again initiated by either use of the a face blind or a secondary "grab-loop" situated on the seat between the occupants knees.
In 1949 SAAB began studies which would result in the development of an entirely new design for a supersonic, delta-winged interceptor aircraft, capable of speeds in the vicinity of Mach 1.5 to Mach 2, to be designated the SAAB J35 Draken. In view of the rather small cross section selected for the new design so as to insure sufficiently favorable drag characteristics favorable for supersonic flight, the cockpits dimensions would have to be carefully considered in development of a suitable ejection seat system. [Interestingly, while the Swedish aeronautical engineers quickly focused on this critical concern--supersonic drag coefficients as related to cross section--their Convair colleagues in the United States who were developing the new delta-winged American interceptors (XF102) initially did not, and it was only after incorporation of Whitcombs "Area Rule" formula that the American delta design achieved a modicum of its anticipated performance capabilities. ]
In order to comply with the requirement for a low profile cross-section, it was decided that an entirely new seat would have to be developed. This new seat was again explosive cartridge driven and was installed on the first of the new SAAB J35 Draken delta-winged aircraft, which flew initially in October of 1955. The Type 35 seat featured a back-style parachute, again not integrated to the seat but worn by the pilot, and a seat-pan survival kit of rigid design. The seat was actuated either by the conventional head-blind device or a secondary actuator located on the lower seat, and had a dampening feature built in to help absorb crash-landing forces as well as an adjustable seat pan. Harness and deployment mechanisms were virtually the same as those used on the preceding Type 32 seat, and installation of the seat was made on a slight rearward cant (similar to the 30 degree rearward angle found on the SAAB J29 aircraft).
Sometime later, the SAAB J35 Draken F model was fitted with the new SAAB 35 Draken Rocket Seat Escape System. This new generation egress design replaced the conventional explosive catapult gun with a 5-nozzle cylindrical rocket motor fitted under the seat pan, as in the later Martin-Baker rocket seats. Firing of the 4.4 pound rocket charge was accomplished by generation of pressure in the catapult gun, and total burn time was about 0.2 seconds. While the original (non-rocket) Draken seat weighed about 176 pounds, the new rocket powered version totaled about 222 pounds (this included all components, chutes, kits, etc.), and substantial revisions of the rocket-equipped J35 seat included doing away with the face-blind actuation device in favor of a lower, pan-mounted ejection handle, and installation of automatic leg restraining straps. Additionally, the new rocket powered seat required installation of a new type of drogue for stabilisation control.
Fully automatic in egress sequencing from initial actuation, the rocket system allowed true zero/zero ejection capability for Draken fighter aircrewmen, and the new rocket seat was retrofitted to all earlier J35 Draken models. In 1967 the next generation SAAB J37 Viggen interceptor first flew, and a slightly improved version of the SAAB rocket seat was fitted to it. Understandably, use of the SAAB rocket seat in operational employment has provided much valuable data on the system, which has been constantly improved and evolved by SAAB.
Although the SAAB seat system was not selected for installation on the latest Swedish aircraft design, the JAS39 Gripen (The Martin-Baker Mk.XL system was chosen), there is no question concerning the excellence of Swedens past and present contributions to aircrew egress systems development, from its earliest products through the latest (and last). So well engineered and maintained are the now more than 40 year old Drakens, and their internal systems (including the egress system), that in Finland, one nation which uses the Draken, the Finnish Satakunta Air Wings Drakens have never had to use the SAAB egress system in an emergency. Unfortunately, the pioneering research accomplished by SAAB in the field of egress systems from the late 1930s onwards is many times not fully acknowledged or recognized as todays advances in system technology continue to overshadow previous standards of excellence. For those specialists in this critical area of aviation design, however, the facts peak loudly and eloquently for the engineering capabilities of the SAAB-Scania Aircraft Company, as they shall continue to in the years ahead.
Development Continues: In The United States
Work in the field of military aircraft emergency egress systems in the United States had begun in earnest, as previously referenced, with the revelation of captured German egress documentation painstakingly gathered by the Heinkel Company and the Luftwaffes Aviation Medicine branch since before the war. However, a complication in the process which was largely absent in the United Kingdom was the intensely political rivalry which existed between the US Air Force and the US Naval Aviation. Ever since the growing importance of US air power in the war had propelled the US Army Air Force further along on its avowed quest to become a fully separate and equal military service within the War Department, there had been corresponding exacerbation of the existing contest between the Army Air Force and the Navy to gain the upper hand in military aeronautical ascendancy. This intense inter-service struggle to surpass the efforts of the other was strongly in evidence in almost every aspect of operational development as well as in research and experimental areas of investigation. In brief, each service argued that it ought to be given the overall supreme authority to develop the nations potentially awesome aeronautical strength.
Nowhere was this rivalry more in evidence than in the field of aeronautical research and development, and both services maintained distinctly separate research and development commands (in 1947 the US Navys worst fears were realized when the US Armys Air Force was granted separate and autonomous peerage within the Defense Department as the US Air Force). The political battles which were continually being waged in the US Congress for funding of military projects were clearly polarized between Air Force and Naval Air Arm proponents in just about every category. This included ancillary but no less important areas such as air crew life support and egress. Fueled to a significant degree by this antagonistic atmosphere, it is not much of a mystery that egress research and development schools in both services inherently tended to diverge even more sharply from each other. Of further, and undoubtedly greater importance were the diverging performance criteria maintained by each service regarding ejection seat operational parameters. The US Navy insisted that naval aircraft needed a fully developed low-level ejection performance, reflecting safety concerns for the intrinsically hazardous nature of carrier operations. The US Air Force, by contrast, felt that safe ejection capability below 500 feet was unrealistic (not survivable, statistically speaking) and therefore unimportant as a procurement objective. Adding further impetus to this Air Force view was its awareness of the coming importance of the high-altitude interception role, which would increase with escalation of a Cold War hostile penetration treat posed by high and fast flying Soviet intercontinental bombers.
Immediately after the war had ended, the US Navy had shown a great interest in the work being carried out by the Martin-Baker Company on aircraft ejection systems. The US Army Air Force, in contrast, maintained the opinion that the development of ejection seat systems ought properly to be undertaken by American aviation companies in cooperation with the US Army Air Forces Air Research and Development Command (ARDC) at Wright Field (soon to become the Wright-Patterson AFB Air Development Center). The consequence of this veering away from each others inflexible contention was that US Air Force airplanes ultimately were developed with a range of different and proprietary US designed ejection systems, while the US Navys aircraft for the most part, initially used systems at least heavily influenced by the English designs and ultimately incorporating specially modified and uniformly adopted Martin-Baker systems after experience with US systems proved not fully suited to low-level ejection requirements (i.e. carrier operations) .
As previously mentioned, In October of 1945, US Naval officers J.J. Ide and R.B. Barnes had visited the Martin-Baker works at Denham to investigate the M-B test program and witness ejection seat trials. Subsequent to the visit, and after completing an assessment of suitable types of research equipment intended for ejection seat testing, the US Navy ordered a 105 foot seat testing tower to be installed at the Navy Yard in Philadelphia and for an actual example of the Martin-Baker Mk.I seat for purposes of testing it in a naval aircraft. Less than a year after the installation an initial test shot was undertaken, followed shortly thereafter by the first live seat test (August 1946). From that time forward, over the ensuing few years, a great deal of intensive physiological investigation was accomplished by the US Navy on ejection seat operational parameters and this was further advanced by numerous studies undertaken on Martin-Baker ejection seats installed in a modified Grumman F9F Cougar in 1957. Despite reluctance of the Grumman Company to participate in the tests, the results were quite satisfactory and the US Navy/Martin-Baker bond was further strengthened. The Navy approached the Martin-Baker Company in this matter of fitting a special Martin-Baker seat to replace the Grumman seat in the Cougar with a mind to adopting the English seat for all its carrier-based aircraft. The tests were quite successful and this resulted in the development of the Martin-Baker Mk.V seat specifically for US Navy use, which was widely used in variant applications in the F9F-6, the F-4, the A-6, and several other Navy aircraft. The Mk.V was produced alongside the Mk.IV, but differed in that it (the Mk.V) had been specially strengthened to decellerative G limits well beyond that engineered into the Mk.IV seat (40 Gs vs. 25 Gs). The Navy Mk. IV seat also incorporated a crotch loop pull handle actuator for the first time, as it had been found that in certain instances involving sustained high-G force, a pilot sometimes could not reach his arms above his head to grab the face-blind actuator to eject. The crotch level pull-loop provided ejection actuation capability for both possible scenarios.
Meanwhile, the US Air Forces Wright Air Development Center was developing a concern, in the mid-1950s, over how to best configure a suitable high-performance ejection system for the latest supersonic members of its new "Century Series" aircraft. American developed ejection seats had been produced by the North American, Douglas, Republic, Lockheed, Grumman, Weber, Stanley, and Stencil companies, and US Air Force aircraft had come into production in the early 50s with these seats. Most were actuated by arm-rest type triggers and were intended to work with the standard US Air Force back-type personal parachute, but none provided even a vestige of zero/zero capability and few indeed assured a safe ejection below the 500 foot altitude selected by the Air Force originally as the minimum safe low-level performance parameter. Of the many designs in use on Air Force aircraft, the Douglas ESCAPAC seat purportedly had the best reputation and would later almost match Martin-Baker performance standards, statistically speaking (the Douglas ESCAPAC 1A system was originally developed for use in the US Navy's A4 Skyhawk; it proved so effective that the Escapac 1A system served as the developmental basis for a whole collection of successive evolutions of this basic design that ultimately culminated in today's McD/D ACES II system).
One of the reasons the Air Force apparently initially abandoned study of low-level ejection systems was the opinion that extant seat catapult forces generated by systems in use on its planes could not generate the high forces needed to lift the aircrew high enough above the ground to allow full parachute deployment in low level egress situations.. The Air Force maintained that a limit of 22 Gs of vertical acceleration were the human physiological ceiling for safe ejection. Curiously, this figure seems to coincide with the final criteria developed by Germany in its early (WWII) studies of allowable vertical ejection acceleration forces, but it contrasted strongly to the vertical G limits of the Martin-Baker seats being tested at that time (about 32 Gs). Further, with Mach 2+ aircraft such as the Convair F106 Delta Dart under development, another concern expressed itself in how to engineer a high-performance seat that would allow routinely safe supersonic ejection. The development of a whole new generation of post-war, high performance jet aircraft (soon to be known as 'The Century Series'), would spur interest in the swift development of a functionally adequate USAF ejection seat with capability for safe ejection well in excess of the speed of sound.
These problems were soon to be investigated at Edwards Flight Test Center in California, Holloman AFB in New Mexico, and on Hurricane Mesa in Utah, using high speed rocket-powered sleds in a series of ongoing investigations which were ultimately intended to produce what the Air Force termed perhaps too simply the "Supersonic Seat".
It was recognized that one likely way of providing the necessary power to successfully meet the demanding parameters of human physiological limits, while simultaneously satisfying the ejection systems physics requirements, was through the use of staged rocket motors incorporated into the seats. In October of 1957 a requirement was specified by the US Air Force for a satisfactory supersonic-rated ejection seat system which would provide high-speed egress as well as adequate and reasonably safe low-level ejection (although this was still suborned to the high speed/high altitude capability requirement). This was termed the USAF / ICESC (Industry Crew Escape System Committee) program, and a committee of major US aviation firms was jointly established with the Air Force Systems Command to develop the system. Two proposals for a system meeting all requirements were considered, an "A" proposal and a "B" proposal. The Convair Company (formerly Consolidated Vultee) was finally given the go-ahead under the aegis of the ICESC to undertake primary project development of its "B Seat" design proposal, with the Stanley Aviation Company as a partner. The ICESC studies involved over 6 years of intensive testing (1 January 1956 through 30 June 1961) of the Convair / ICESC "B" Seat System on the high-speed rocket sled tracks at Edwards and Holloman. These rigorous and extensive tests ultimately culminated in the live ejection of volunteer TSgt. James A. Howell from the specially modified Convair F106B (two seater) aircraft at an altitude of 7113 meters and an IAS of 800 kph. The Convair / ICESC "B" Seat featured a unique, tilt-articulated design which upon actuation would first elevate the seat into a backwards-tilted horizontal plane (with pilot in supine position) above the aircrafts cockpit, before firing the seats rocket motor to blast the occupant clear of the plane. The seats appearance was distinctive in that, when deployed, the seat pans convex bottom extended beyond the feet of the aircrewman, which were first drawn up tightly towards his chest in a fetal position, so as to protect him from supersonic wind-blast effects.
The B Seat (other slang terms for the seat included the 'Tilt Seat', the 'Rotation Seat', and 'Supersonic Seat') was a strangely appearing design, with twin survival kit components sited bilaterally along the sides of the seat's occupant, and ejection actuator D-ring situated at crotch level. Featuring an integrated shoulder/lap harness, upward rotating 'sugar scoop' foot pans, powered foot retraction spurs, bilateral thigh guards that pulled the knees up towards the chest, aneroid controlled drag and recovery chutes, and two gas operated telescoping stabilization booms that projected aft on actuation, the seat not only looked strange but certainly must have presented the rider with a unique (possibly) terrifying prospect as he was first shot upwards into the wind at supersonic speed, then slammed back into a supine position before being fired away from his stricken aircraft with a powerful rocket blast. The seat was secured to the rotation frame with 4 explosive bolts that blew just before the rocket fired.
The B Seat ejection sequence was essentially as follows: A pull on the D-ring jettisoned the canopy, tripped the AFCWS (automatic flight control system) disconnect switch, retracted and locked the shoulder harness, retracted the occupant's feet via cable connected power reel spurs, raised the foot pans and elevated the occupant's knees and thigh guards. Feet retraction and canopy jettison safety locks release, allowing further pull on the D-ring, which disconnected the seat actuator and fired the seat's vertical thruster, moving the seat up the rails and out into the slip-stream. At this point the hose disconnect and personal-leads disconnect separated and at the end of the vertical thrust stroke, two rotational thrusters fired, slamming the pilot into a supine (horizontal) position above the aircraft's fuselage. During this rotation, the gas operated stabilization booms were extended and the four break-away bolts were fired. At this moment the primary escape rocket would fire the seat and occupant away from the aircraft. Two modes of chute deployment provided full deployment in low speed/low altitude mode at three and a half seconds, and full deployment at high speed in four and three quarters seconds. At extremely high altitudes, the pilot would stay with the seat until a safe lower altitude had been regained. The total weight of the seat and occupant, fitted with all normal personal equipment, was a substantial 607 pounds!
Although tested extensively in at least 15 rocket sled tests and 11 test flights (using an F106B two-seater), the single high altitude human 'live-fire' test was accomplished at 22,580 feet and only Mach .77 (at that altitude); flight performance parameters at the time of the test were far in excess of more realistic suboptimal conditions and did not come anywhere near the 'hard corners' of the seat's anticipated performance envelope. Rocket sled tests were exhaustively run on the test track with instrumented dummies at speeds simulating Mach 2.5 at a simulated altitude of 9,700 meters, with satisfactory results. Additionally, 35 human test subject rocket sled runs were reportedly concluded, verifying that ejections up to 900 knots IAS were within the range of human endurance.
As a result of the successful tests, the Convair / ICESC "B" Seat, or "Tilt-seat" as it became more commonly known by life support and human factors specialists, was installed in all production block Mach 2+ rated F106A & B aircraft--the most formidable and most high performance of the US Air Forces vaunted "Century Series" aircraft of the late 50s and 60s--from 1957 through 1959.
Unfortunately, and in spite of the years of exhaustive testing carried out in its development, the Convair / ICESC Tilt-seat did not prove satisfactory in actual Air Force operational use; this was especially true in the less favorable corners of the projected envelope. As might be predicted, the marginally assured low-level, low speed performance of the controversial seat simply did not meet minimal requirements...especially under anything less than optimal conditions. After several fatalities occurred during F-106 emergency ejections involving use of the Tilt-seat, a decision was made to remove the seat and replace it with a conventional, rocket-powered seat design made by the Weber Corporation. This retrofitting of the Delta Dart with the Weber seat was accomplished in 1963; thereafter, the Weber seat egress system remained in the delta-winged F106 for the rest of its 30 year service life and provided satisfactory high-speed ejection as well as adequate zero/zero capability.
Possibly as a consequence of the ultimate failure of the Air Forces ICESC supersonic seat program, the decision to use Martin-Baker designed seats in the Air Force version of the McDonnell-Douglas F4 Phantom II was a bit less objectionable in the years to come, and especially owing to its already proven performance. In any event, it is fascinating to speculate on this.
To return to the US Navys growing post-war association with the Martin-Baker Company, formerly alluded to, the Navy was by now also investigating the use of rocket engines as a satisfactory means of propelling a seat clear of a stricken naval aircraft without incurring unacceptable ejection injuries in its personnel. Studies conducted with the catapult gun then in use indicated that even significantly enhancing the conventional guns charge would not produce the desired Naval requirement for "dirty" low-level escape. Consequent to this, the Navy authorized the development of a rocket motor capable of being used on existing American egress system seats. A lengthy series of tests were conducted at the China Lake Naval Ordinance Test Station (NOTS, as it was then designated) on its high speed rocket sled track, and this eventually resulted in the production of the RAPEC (Rocket Assisted Personnel Ejection Catapult) system. Tests continued, concurrently, with the Martin-Baker ejection system at the US Naval Flight Test Facility in Patuxent River, Ohio.
By this time, the Douglas and Vought aircraft companies had devised rocket powered seats which were in the research and development phase. Both appeared to be capable of meeting Naval emergency ejection requirements at a lower limit of 150 feet altitude and 150 knots IAS--still not satisfactory parameters for the stringent zero/zero emergency requirements desired by the Navy. At this point, the political nuances of the competing systems manufacturers battles to secure Naval procurement contracts intensified considerably, and the result was a compromise in which the Douglas Escapac RAPEC system was selected for use in the Douglas A-4 Skyhawk, while Martin-Baker was selected to provide a uniform system for use in the remainder of US Navy aircraft. This final decision was still complicated further by an exception to the agreement which allowed North American Aviation to provide its own seat for use in the RA-5 (A3J) Vigilante and one other aircraft. Furthermore, a concurrent program authorized use of the Stanley built RAPEC seat in the Martin P6M jet-powered seaplane patrol bomber, due to inadequacies existing in the aircrafts original seat system. Subsequent emergency ejections involving an unmodified P6M and a later, RAPEC configured version, confirmed the effectiveness of the new RAPEC system.
In operational use, the Douglas Escapac HS-1 and LS-1 RAPEC seats used in the RA-5 (A3J) and T-2 aircraft proved their effectiveness in several incidents involving successful non-combat egress in the RA-5 (A3J) Vigilante at and above the speed of sound, and during the Vietnam conflict, Douglas HS-1 Escapac RAPEC type seats in the A-5 routinely allowed aircrew to successfully eject above the speed of sound in emergency combat ejections involving that type (25% of the combat RA-5/A3J ejections were undertaken above Mach I).
With the withdrawal of the RA-5 Vigilante from active operational use in the late 1970s, the only American rocket powered open (non-encapsulated) escape system proven in use for successful Mach 1+ recovery, and capable of zero/zero to 700 knots IAS performance, was also retired (this was a North American Aviation design), excluding the special X-15 seat system (also a North American design) and the Stanley/Lockheed S/R-1 system used in the Lockheed SR-71 Blackbird aircraft.
Meanwhile, development in both the US Air Force and the US Navy continued apace as new aircraft with different performance parameters came into service. One type of advanced concept ejection system which found its way into at least two supersonic, multi-engine designs was the fully encapsulated aircrew escape system. A version built by the Stanley company was installed on the Mach 2 Convair B-58 Hustler, a strategic nuclear bomber of amazingly high performance for its time (originally flown in the early 1960s). The 558 pound capsule, which unfortunately had a relatively high failure rate, was designed to provide flotation in the event of a water landing, and upon ejection streamed the half-open recovery parachute for 2 seconds to slow forward speed before reef cutting devices automatically allowed the 41 foot ring-sail type chute to fully open. The B-58 capsule featured upper and lower frontal clam-shell doors, which would close and seal in an emergency. The capsules featured self-contained individual oxygen and pressurization systems, much like another, later design, engineered by the North American Aviation company and installed in its Mach 3, advanced strategic bomber prototype, the XB-70 Valkyrie. The Valkyries encapsulated system was the only one of its general design to have been fully flight tested and approved prior to completion of the XB-70 aircraft itself. Another system, based upon the ejectable crew cockpit design (which harked back to the original ejectable crew-section concept used in both the WWII era Bachem Ba 349 Natter and Heinkel He-176), was developed for the controversial American TFX swing-wing aircraft. The TFX aircraft, after a prolonged and difficulty-laden initial development which called for its being adopted by both the US Air Force and the US Navy in slightly differing versions, would ultimately outgrow its teething problems and evolve into the excellent US Air Force F-111 Aardvark fighter-bomber.
Returning, for a moment to the early part of the 1950s, it is interesting to reflect for a moment on the concept of the American downward-firing ejection seat system. In particular, the Lockheed Company, in developing its powerful but lightweight F104 Starfighter in response to requirements provoked by experiences derived from aerial combat in the Korean War, elected to incorporate a downward firing pilots ejection system in the ultra-compact crew section of that post early 1950s design. As the inherent hazards of downward ejecting seat configuration are readily apparent, Lockheeds decision provokes speculation that the official US Air Forces consensus that ejections below 500 feet were not essentially survivable may have had inordinate impact on this aspect of the Starfighters development. There were Lockheed engineers who believed that, owing to the great speeds which the aircraft was designed to fly at, an upward firing system using the existing seat catapult technology would not be able to clear the F104s tail assembly in supersonic flight. There were certainly also numerous critics of the downward ejection scheme at that time, but the preponderant opinion that successful upward ejection was not absolutely attainable with existing technology managed to sweep these objections aside and work continued using the downward ejecting seat design.
Lockheed, in partly addressing critics of the system, suggested emergency procedures which would partly offset the hazards of egress situations occurring below 500 feet. Among these were the recommendation that in the event of a low-level emergency requiring ejection, the pilot of the Starfighter was to roll the aircraft 90 to 180 degrees or more to either side before ejecting. This would then yield, at least in theory, a horizontal or inverted vertical upwards ejection trajectory for pilot and seat, rather than a vertical descent. The suggestion was more euphemistic than practical, for in situations involving sudden loss of power, hydraulics or flight controls, such a maneuver would be near impossible to achieve. Further, the small cross section of the Starfighter allowed very little room for the crew compartment, and it was determined that there simply was not enough room in the by-then frozen design configuration to re-engineer a cockpit which would allow for installation of a conventional upward firing system without a major (and costly) redesign. Pilots, who could relate to such possibilities as low-level emergency bailout far more readily than could engineers, viewed the downwards firing system with obvious disapprobation.
The Starfighter prototype, as well as all developmental pre-production and initial production models, had the Lockheed downward firing seat installed. Egress was achieved through a large rectangular hatch located directly below the cockpit. In the event of an emergency requiring ejection, the between the knees actuator handle was pulled first, which set off the following sequential events: 1) the cabin was depressurized, and the control stick stowed forward, clear of the seat; 2) the pilots parachute harness tightened automatically, just as did the arm restraint net which secured his arms; 3) the pilots feet where drawn back into the seats footrests through use of cable attached spurs on his boots; 4) the hatch was blown off automatically, and the seat was ejected straight down with a conventional explosive catapult charge. For clear-thinking individuals, unencumbered by the policy constraints of a manufacturers cost projections, this system was purely and simply an accident waiting to happen; especially so, in view of the problems that early 1950s high-performance aircraft frequently had with power failure, compressor stalls and flame-outs, and the particular hazards normally implicit in landing and take-off portions of the flight envelope. Although adjudged satisfactory for medium to high altitude use, the original downward firing system was completely useless for low-level emergencies.
Unfortunately, it took the death of a high-profile and very popular flight test pilot to spur a major revision of the Starfighters egress design. Capt. Ivan C. Kincheloe, blonde, handsome and personable, as well as a highly regarded and high-profile flight test pilot, experienced an in-flight emergency in his production F104A Starfighter in 1958 shortly after takeoff at Edwards AFB in California. His ejection in the Stanley B-1 downward firing seat fitted to his aircraft successfully removed him from the stricken aircraft in a sideways, horizontal plane, as recommended by Lockheed; ironically, however, the aircraft banked and came down shortly after he ejected, exploding in a fireball on the ground which Captain Kincheloe was carried directly into by the ejection trajectory. Kincheloes death accomplished what a previous ground-swell of earlier protests had failed to do: shortly afterwards the F104 fleet was grounded, the old B, C, and C-1 seats removed, and quickly retrofitted with a Lockheed designed upward firing seat designated the C-2 Seat. Incorporation of the new C-2 seat increased aircrew confidence in the new fighter. At a later date (after 1966) the initial Lockheed designed upward firing seat was replaced by an improved upward firing version of the C-2 seat, designated the S/R-2 seat. This seat was reported to offer near zero/zero ejection capability. All European, export, and later generation Starfighter variants had their American upward-firing seat replaced with a Martin Baker Mk.VII series seat specially engineered for the Starfighter, designated the M-B Mk.DQ-7 model. The new Martin-Baker Starfighter seat unexpectedly experienced some initial problems, however, and several German Luftwaffe pilots were killed in Starfighter ejections using M-B Mk.DQ-7 seat. An investigation team was quickly brought into determine the source of the seat failure and found that frequently the pilots knees would not clear the forward canopy edge due to the fact that the parachute placement positioned the pilot too far forward. The seat was subsequently modified to address this problem and from then on the Martin-Baker Mk. GQ-7F seat performed quite well in Starfighter emergencies experienced by the German Luftwaffe. The same GQ-7F seat was installed in all export Starfighter seats the Danish Air Force and other NATO countries were taking delivery of and there were no further difficulties. It is indeed well that that was the case, since the F104 remained a demanding machine to fly throughout its long NATO service life owing to the peculiarities of its high wing-loading, high-performance design, and the training dissimilarities between the American west, where European pilots were trained to use the aircraft under typically excellent conditions and the European region with its usually marginal weather.
Among the refinements added to American-made seats of the mid-50s were inertial-locking harnesses and seat-pilot separation mechanisms (the seat-man separator on US Air Force seats consisted of a strap arrangement fitted between the seat and the pilots rear seat cushion, or parachute pack, which was sequenced to actuate after ejection had occurred and simultaneous with seat restraint release), after studies indicated that a more positive man-seat separation action was required to get the aircrewman away from the ejected seat. Thigh restraining guards were usually fitted and folded away in the down position until the seat was fired, being raised for use along with the armrest ejection triggers which were a standard American feature. In some cases, leg restraining mechanisms were also fitted, as in the original F-104 Starfighter seats.
In the early 1960s, North American Aviation experimented with a series of lightweight seat systems termed the "LW" series. This resulted in an LW-1, an LW-2 (developed for the XV-19 experimental aircraft), and a final LW-3 seat that was produced for use in its twin prop driven OV-10A Bronco forward air control / armed reconnaissance plane. The seat was designated the LW-3B model and two were fitted, fore and aft, in the Broncos cockpit. Uncharacteristic of the trend at that time, the LW-3B seat featured a seat-mounted pilot personal chute in an unusual configuration. The aircrewmans parachute was fitted to the side of the seat, housed in an elongated rectangular pack, and the system was capable of near zero/zero performance. In view of the fore and after seating arrangement of the OV-10A, the seats were angled to fire slightly to the side and away from each other, with the rear seat sequenced to eject first in the accustomed manner. The LW-3B type seat was later installed in the experimental prototype VTOL XV-15 tilt-rotor aircraft for flight testing of that machine in a tandem arrangement, and has also been installed more recently in civilian turbo-Mustang (F-51) conversions such as the Cavalier II, where it provides emergency ejection capability in a confined cockpit structure. The LW-3B seat featured a standard hard-shell seat type survival kit (RSSK 9) under the seat cushion. This was the first American seat to presage the future trend of installing the pilots personal parachute on the seat itself (although modern seats feature the chute assembly in the seats headrest area, not fitted to the side of the seat as was the case with the LW-3B). Reports of the Bronco system in use indicate it had a satisfactory success rate in combat situations (Vietnam), both for low level and medium level ejection.
It must be noted in passing that although American systems had originated from studies based upon the German escape technology of World War Two, there were several features incorporated in them which were thoughtfully conceived and engineered. One of these was the locking inertia-reel harness, which is to be found on nearly all American manufactured seats produced in the early 1950s (each of the 1950s Century Series fighters featured this device). Another is the life-support quick disconnect block, again incorporated in virtually every system produced by the US in this period. This latter device featured a module, frequently affixed securely to the seat, into which the aircraft and pilot connections were inserted for G-suit, breathing oxygen and communications use. Upon ejection, the aircraft connectors would pull free, leaving the seat-portion attached, from which the pilots connections would be released at the time of man-seat separation. Similar systems were not incorporated into Martin-Baker seats until the advent of later M-B Mk.IV models.
Several other systems were investigated that involved a pseudo-podded escape concept. One of these proposals was a design that featured inclusion of the aircraft's canopy as a sort of protective enclosure, with the pilot being drawn upwards into a supine position under it before actuation (this was researched for initial use on the Convair F102 Delta Dagger, but discarded in favor of a conventional Weber rocket seat). The canopy, with the pilot enclosed under it, would then be fired away from the aircraft. This concept was discarded after some initial exploration into its suitability.
Of passing interest is the fact that while the idea of the crew 'escape pod' was not entirely new, having been first actively explored in German designs of the early 40s (notably in the He-176 rocket powered aircraft), its possibilities were being closely studied in the late 40s and early 50s by US aeronautical and egress scientists. While US aircraft engineers subsequently designed several systems that would be incorporated into high performance aircraft of the 50s and 60s, in a curious footnote to this innovation, a little known Humphrey Bogart film titled 'CHAIN LIGHTNING' that came out in 1950 featured the escape pod idea with a central role in the plot (along with a primitive high altitude pressure suit). Although the technology represented was rude and almost laughable, by today's standards and in terms of what we now know about such highly sophisticated systems, the basic concept was amazingly all there. This old Bogy film is worth seeing for this and Hollywood's 1950s pressure suit representation, although the story line itself is considerably dated.
In the early to mid-1950s, a considerably advanced Mach 3.7 high altitude, point/area defense air interceptor aircraft design was proposed by Republic Aviation. This was what came to be known as the XF-103 (USAF Secret Project MX-1787), which never saw production (it was cancelled in 1957), but which took form in a completed full-scale engineering mock-up. This futuristic appearing interceptor featured an unusual 'boot-shaped' crew pod, in which the pilot of the XF-103 could encapsulate and eject downward. Preliminary studies showed the pod to be unusually aerodynamically stable, despite its odd appearance, but the system was never actually tested. The XF-103 pod promised to allow aircrew escape at the upper limits of the aircraft's performance envelope, although data was never released concerning its low altitude, low speed characteristics (presumable very poor, given experience with other downward firing systems in use at the time in similar operating conditions). This concept did, however, pioneer certain parameters shared with later upward firing podded escape systems that would be used successfully in the B-58 Hustler and XB-70 Valkyrie .
One instance of a very satisfactory American escape system having been developed is found in the ejectable crew compartment concept employed in the General Dynamics F-111 Aardvark. Although a controversial design from its very onset, the F-111 (neé TFX), with its swept-wing features and technical innovations, featured an egress system which was one of the most reliable component systems found on the plane. Borrowing from pioneering studies conducted by the Heinkel company and use of the concept in its He-176 rocket-powered airplane of WWII vintage, the General Dynamics Corporation (formerly Convair) incorporated an ejectable crew compartment egress system in the final pre-production TFX prototypes. Although the original prototype had flown using two conventional ejection seats, the ejectable crew compartment became a standard feature of the F-111, and throughout its service life provided Aardvark crews with reliable, safe egress--both in non-combat emergencies as well as in wartime combat situations (Vietnam). As might be imagine, the ejection sequence involved actuation of an explosive disconnect system which separated the crew compartment from the nose section and fired a rocket system which shot the crew section away from the crippled aircraft. A high-speed drogue system then deployed, which in turn actuated a recovery parachute attached to the compartment. Crew members had the choice of either staying in the capsule until it came down to earth or opening the canopy and manually parachuting from the compartment while it was still descending. Statistically, the success rate of F-111 ejections was remarkably high, testifying to the engineering concept and development underlying the design.
It is worth noting, in passing, that the Bell X-2 rocket research aircraft that was being flight tested in the mid 1950s at the Edwards Flight Test Center in California featured a jettisonable crew compartment. The plane was designed to exceed Mach 2 at a time when such extreme speeds by manned aircraft were still challenging, and as yet un-reached, aeronautical objectives beckoning to aviation engineers. Interestingly, on September 27, 1956, Captain Milburn Apt was flying the 13th test flight of the Bell X-2 when he encountered a particularly severe roll-coupling situation in flight testing at a speed of Mach 3, after beginning a descent from 72,000 feet. So unusual was the situation, and so severe the buffeting which resulted that the decision was made by Apt to eject, and he did do, actuating separation of the entire nose section of the research aircraft which contained the small cockpit. The capsule was designed to be separated, then stabilized by a drogue chute after adequate deceleration had occurred. Once the capsules recovery chute had been deployed, the plan was for the occupant to release the canopy, un-strap his harness and manually bail out using the capsules seat-type personal parachute.
Documentation of the accident shows that the capsule separation was achieved as planned for and that the drogue system worked as anticipated. Unfortunately, Apt appears to have been disabled through some sort of injury sustained, either in the violent buffeting before ejection occurred or after the capsule separation took place, and was unable to leave the capsule before it plummeted into the desert floor at about 120 mph. The G forces sustained in the impact, estimated to be about 90 G (plus or minus 40 G), resulted in Apts death. The Bell X-2s recovery capsule was not intended to land with the pilot in it, unlike other systems (such as the F-111) in which emergency descents might be survived while still contained within the capsules crew compartment. Evidence was found at the site which indicated that Apt had succeeded in jettisoning the capsules canopy, and also had been able to release his restraint harness prior to impact, but had not been able to leave the capsule to bail out of it for reasons which are still uncertain.
Although the North American XB-70 supersonic advanced strategic bomber program never progressed beyond the production of two prototypes, the crew escape system that consisted of fully encapsulating individual crew modules was inadvertently put to the test in an unfortunate mid-air accident which destroyed the number two XB-70 prototype (XB-70A-2) on 8 June 1966. As designed, the individual capsule-type crew ejection system allowed for safe ejection from near zero/zero conditions (90 knots IAS, zero altitude) through Mach 3 and its 80,000 feet operating ceiling. Each module consisted of a central seat unit which employed upper and lower clam-shell type doors to cocoon the crew member when the escape system was actuated. Each contained its own environmental support system and allowed for pressurization and crew oxygen so that in addition to serving as a rocket powered escape vehicle, the capsules could also protect against emergency high-altitude decompression in flight.
A window in the upper clamshell door allowed observation of instruments while the crewman was encapsulated, and provision was made for minimal encapsulated control of the aircraft thusly configured. Ejection sequencing consisted of manual actuation of the arm-rest triggers, immediately whereupon the capsule tilted 20 degrees to the rear before encapsulation by the clam-shell doors was accomplished. Further, the crewmans heels had to be properly emplaced before the process would begin. After the capsule had closed and sealed, the crewman had to activate a further actuator to jettison the upper and lower fuselage before firing the capsule out and away with its integral rocket motor. Main recovery chute was automatically deployed by a complex biostatic system and capsule descent rate was reported to be about 28 feet per second. Twin, rear projecting booms served to stabilize the capsule during ejection and an inflatable cushion automatically deployed (with a manual inflation option) under the capsule to help the occupant withstand landing forces. The crewman remained within the capsule throughout the entire recovery process, from ejection to landing, and included in the capsule were survival equipment, life-raft and other items. On a water entry, the capsule would remain afloat in an upright position automatically.
The prototype XB-70A-1 and A-2 aircraft undergoing flight testing from 1964 through 1969 were configured with two such crew capsules (pilot & copilot), although the intended production B-70 bomber was to have two additional crew positions in routine operational use.
On 8 June of 1966, during a media fly-by flight of several types of aircraft using GE engines (the XB-70 included), an inadvertent mid-air collision occurred involving a Lockheed F104 Starfighter and the number two XB-70 prototype. The cause of the F104s veering into the starboard outer wing section of the XB-70 was never to be learned, although the consequence of the collision was the immediate destruction of the Starfighter and the smashing of the two vertical fins of the XB-70, which the F104 slashed through after hitting the bombers wingtip.
The XB-70A-2, traveling at about 300 knots IAS, remained in a state of stable horizontal flight for about 16 seconds after the collision before suddenly going into a nose-down roll, with subsequent violent yawing that ended up with the aircraft entering a final, unrecoverable flat-spin before impacting in the desert, 25,000 feet below. The two crew, test pilots White and Cross, immediately upon experiencing the roll over, began to realize that ejection was mandated. Pilot White was successful in ejecting himself by pulling the ring to begin encapsulation, which he estimates he accomplished about 60 seconds after the XB-70A-2 became violently unstable. His copilot, Cross, was apparently unable to do so. It is speculated that possibly G-forces or a head-injury may have prevented him from taking the initial step to initiate ejection. White, meanwhile, caught his arm between the clam-shell closure seals and suffered a dislocated shoulder attempting to free the arm, but managed to get free and was safely lowered to earth in his capsule. Despite the fact that the impact cushion beneath his seat failed to inflate, he survived the 43 G impact, albeit with severe internal injuries that were partly lessened by collapse of the capsules internal seat structure.
Crosss capsule was never ejected, and its remains were recovered in situ at the site where the XB-70A-2 hit the earth in a flat spinning attitude and burned. The incident was thoroughly investigated from all angles, including performance of the life support/escape system, and Whites survival contributed greatly to knowledge of how such an encapsulated escape system could be further engineered to deliver an even higher level of protection. The mere fact of his survival vindicated, at least in part, the integrity of the encapsulation escape system concept.
In still other areas of US military flight operations--particularly in the area of flight test--various escape seat systems were developed for special applications. One of these was the North American Aviation escape seat designed for their X-15 high-altitude, Mach 6 rocket research vehicle. The seat employed was designed and extensively tested--again on the Air Forces rocket sled track at Edwards in California--to allow for escape at extremely high altitude and extreme speed. Considering the performance parameters of the X-15--maximum altitude of more than 50 miles and maximum speeds exceeding 6 times the speed of sound--the challenge was formidable. Once more, a rocket powered, open-seat design was employed, which would allow recoverable egress up to a speed of Mach 4 in any attitude and any altitude up to 120,000 feet. During ground testing on rocket sleds at Edwards Air Force Base, the seat was demonstrated to give good ground-level escape at speeds as low as 90 knots IAS. A ballistic rocket-type catapult system provided the basic propulsion force, and the seat featured side-mounted folding stabilizing fins and extendible booms that would deploy upon ejection to maintain proper escape attitude during initial boost phase of about 0.5 seconds and subsequent recovery deceleration, until the seat drogue system and main recovery chute could release satisfactorily.
Amazingly, despite many years of often quite dangerous flight testing at the very limits of known aerospace performance parameters for manned vehicles, the X-15 ejection seat system was never needed, and hence no documentation exists as to its actual performance in the event of a genuine flight emergency requiring ejection, as none occurred.
Among the more unusual egress systems developed in the US was the Stanley "Yankee" System, in which a tractor rocket was integrated to the pilots harness which would be fired off to literally haul him out of the aircrafts cockpit. This system, which was fitted to some aircraft in which it would have been impossible install conventional ejection seats, was in use in the mid 1960s and was fitted to the Douglas A-1D Skyraider, among others. The system provided for aircrew extraction by rocket first, after which a second rocket deployed and spread the pilots personal back-style parachute; the Yankee System was successfully employed in a real emergency situation in Vietnam in 1967, when a Skyraider piloted by Maj. J.E. Holler sustained engine failure at low level in combat. It is interesting to note that this system provided true zero/zero capability at a time when no other conventional systems did.
Still other innovative egress systems under investigation during the Vietnam conflict were the Karmen Aircraft SAVER System, and the Goodyear Aerospace PARD System. The first design consisted of an ejection seat which after deployment functioned like an autogyro. The Karmen Stowable Aircrew Vehicle Escape Rotoseat (SAVER) contained a small turbojet and folding rotors and tailplane, which would allow the pilot to remain airborne and travel about 50 miles at speeds of about 100 knots. Its development was incomplete when the war ended, thereby ending investigation into its possible use in combat aircraft.
The second egress system mentioned above was the Goodyear Pilot Airborne Recovery Device (PARD), and this system featured an unusual balloon-parachute hybrid design (called a BALUTE) which would fill with heated air provided by a small LPG burner above the pilots conventional parachute, after ejection in a standard ejection system seat. The heated air would allow the pilot to remain airborne for about 30 minutes, during which time a mid-air recovery attempt could be effected with an aircraft equipped with appropriate snaring apparatus. The system was tested and demonstrated to work successfully in tests performed in Southern California, but again the project was discontinued when Americas Vietnam involvement ended in 1975.
Refining The Original Concept: The United Kingdom
As research and development of seat technology gained momentum in the decade following the end of the Second World War, there were at least two other companies involved in production of ejection seat systems for high performance aircraft, in addition to the well established Martin-Baker Aircraft Company. These were the ML Aviation Company and the Folland Aircraft Company, Ltd.
ML Aviation, under the direction of Belgian engineer Marcel Lobelle, produced a series of seats from the ML Mk.I through the ML Mk.IV. The first two seats were fitted into production aircraft in use by the RAF and were manual (not automatic) systems very much like the M-B Mk.I. The Mk.III and Mk.IV were automatic seat designs (fully automated sequencing, with man-seat separation and deployment of personal parachute), but according to B. Philpott were not installed in active service airplanes. The earlier two seats were used experimentally in several aircraft types (including Meteor and Wyvern types) but in 1951 an experimental Hawker fitted with an ML seat crashed, and there was speculation that the pilots seat had somehow failed. Shortly thereafter the company ceased production of egress systems and focused on other aircraft sub-component manufacturing.
The Folland Aircraft Company of the UK acquired licensing rights to produce the Swedish SAAB Type 29 seat (as fitted to the SAAB J29 aircraft), but modified the system to provide for automatic release before incorporating it into their Folland Gnat, a lightweight, swept wing fighter/trainer used by India, Finland and a few other nations with some success. Folland was not interested in continuing the production of egress systems, beyond that of the Gnat, and it wasnt long before the only UK egress system manufacturer was the Martin-Baker Aircraft Company.
The Folland Gnat egress seat was a lightweight, simplified system, which suited the perceived need at that time for use of lighter ejection systems for aircraft which were becoming increasingly more complex and much heavier. Englands Martin-Baker also felt the need to reduce the weight and bulk of its seat design (the Mk.III) in keeping with this philosophy, and consequently this led to the development of the M-B Mk.IV seat. Naturally, it was important to achieve this weight reduction without significantly altering the level of egress effectiveness which the Martin-Baker systems provided. This was achieved by incorporating a redesign of several key components in the guide-rail/track system and seat framework support structure. The seat pan and parachute pan units were retained with slight modifications, as were the twin-drogue system and the 80 ft/sec ejection gun. The Mk.IV seat incorporated for the first time a between the legs ejection handle as a secondary means of actuation ejection, since it had been determined that in certain situations the effects of adverse inertia and G loading made it difficult to use the conventional face-curtain actuator. (This began subsequent engineering conjecture over the question of whether or not to focus on use of one actuator only, for a number of years, which seems to have ultimately led to final selection of the between-the-legs actuator design as found in the most recent M-B systems).
The parachute and sea-survival/inflatable raft kits were redesigned for use on the new Mk.IV seat, and this was prompted in part by the need to improve pilot comfort as well as fit the overall seat modification requirements. Further improvements consisted of an integrated seat and parachute harness system, eliminating two separate harness systems; the system was controlled by the M-B Timed Release Unit (TRU) and was so effective that it was retrofitted in some cases to older Mk.III seats. The new inverted U-shaped personal chute assembly was placed higher up in the seat back, just under the drogue/head-box container, which positioned it more efficiently for simplified deployment. Sea-survival /inflatable raft--usually made to order by Martin-Baker for the specific requirement of the contracting nation--was stowed in the seat pan, under the pilot, and a specially designed, high-density, slow-acting foam rubber material was used in the seat cushion over the kit to reduce the possibility of spinal injury due to effects of acceleration overshoot. One final refinement was the addition of a G sensing switching unit in the TRU which permitted either standard drogue deployment delay of 1½ seconds (at low speed, low altitude), or delayed drogue deployment appropriate to the negative G force loading imposed by deceleration. The M-B "guillotine" device for cutting the drogue withdrawal line to the seat was also used for the first time in the Mk.IV seat, a feature which has remained an important component of M-B automatic seat systems. Modification was also made to the leg restraint strap system. The idea of incorporating built-in rigid foot rests had been long since discarded on M-B seats (most American seats built in the early 1950s also used the rigid footrest feature, although this was also discarded by US seat manufacturers in the mid 1950s, in favor of the leg restraint strap concept).
The next step in M-B seat development, the production of the Mk.V seat, was substantially influenced by the M-B/US Navy ties referenced in the previous chapter. Largely due to the requirements of the Navy, the basic Mk.IV seat was structurally modified to withstand greater deceleration loads (40 negative G, instead of 25), as was the seat harness system. Featuring the 80 foot per second ejection catapult and most of the features of the Mk.IV seat, the new US Navy specification Mk.V family seat began service in the late 50s and early 60s, and was eventually installed in over 20 different American aircraft types (this includes the later Mk.VII rocket powered version, which was markedly similar to the Mk.V but featured the installation of a rocket unit under the seat-pan). Most of the US Navy Mark.V seats were upgraded to the later, rocket-powered Mk.VII version at a later date. The Mk.VII seat featured a prominent change in the personal parachute container component, which was manufactured in an inverted U-shape of fiberglass (in contrast to the shaped metal parachute fitment shroud and U-shaped fabric parachute pack in use on the Mk.V), and had two compressed springs situated between the seat structure and the container to help fling the container somewhat out and clear of the seat on chute deployment (it remained tethered to the seat, however). There were also minor changes in the thigh portion of the seat pan. Suffice it to say that the addition of a rocket power unit to the Mk.IV and Mk.V seats resulted in the Mk.VI and Mk.VII seats, although that is considerably oversimplifying the process.
In the early 60s, many American aircraft purchased by NATO nations began to be fitted with Martin-Baker Mk.V seats. Norway was the first nation to have the American manufactured ejection seats in its F-86 and F-84 type aircraft replaced by Mk.V units, and Germany and others shortly followed suit; Denmark had much earlier (in 1950) placed an order for a number of UK Meteor fighters fitted with the Mk.I seats, demonstrating the design effectively to the rest of Europes allies.
Several other specially designed seats produced by Martin-Baker were their rear-facing ejection seat design (first live-fired in 1960, proving the concept) for UK "V-bombers," and a Mark.V based egress system configured to fire underwater, eject the pilot from his ditched aircraft, inflate his life-vest and bring him to the surface automatically, even if he is unconscious.
As mentioned earlier, the purpose of the rocket-seat development program at Martin-Baker was principally to provide enhanced low-level escape. The original Martin-Baker rocket unit was a twin-tube design with an adjoining nozzle chamber, fitted under the seat and firing downwards. This system was first successfully tested with a "live ejection" in April of 1961. M-B rocket seat systems strive to ensure a near vertical trajectory away from the disabled aircraft. This is allowed owing to the fact that the M-B seat uses a conventional ejection gun and separate rocket propulsion system which are sequentially actuated by the egress systems automation. This stands in marked contrast to other systems, such as that routinely employed by most US manufactured ejection seats of the 1960s, which combined the ejection catapult and rocket charge in a single gun. The combined gun system functions as a standard explosive charge ejection catapult until the automatic sequencing device allows it to discharge the rocket charge rearwards at a 45 degree downward angle, thereby achieving a slightly less vertical, 45 degree upwards and forwards trajectory.
The combined gun concept is less desirable for low level and "unfavorable aircraft attitude" situations (nose down, low level, low speed), while the separate rocket pack approach allows, in theory, more altitude to be gained in a vertical plane for safe chute deployment and recovery. Martin-Baker was a pioneer in developing this system at a time (1960s) when most other seat manufacturers retained and used the less ideal, although somewhat simpler, combined gun system.
Mentioned earlier, one important modification of the UK's Mk. VII series was specifically designed and fitted to the Lockheed F104G Starfighter (export version for NATO, particularly used by West Germany in extensive numbers). This seat was the M-B Mk. DQ-7 seat. After a series of severe pilot injuries were experienced by aircrew upon emergency ejection using this seat, an investigation showed the cause to be due to the pilot's knees fouling on the forward instrument panel of the Starfighter cockpit. Resulting modification of the seat's main chute containment system, which allowed placing the pilot further aft in the seat, resolved the difficulty. This and subsequent seat modifications led to adoption of the M-B Mk. GQ-7F in Starfighters, with the final modification designated the Mk. GQ-7W. This seat is still in service with the Italian Air Force's Starfighters, as Italy acquired the remainder of former German F104Gs when that nation replaced its Starfighters with newer aircraft. The photograph to the right shows a Luftwaffe F104G egress display at the Munich Museum of Science's Aviation Section, in which a pilot is shown in mid-ejection from a stricken Starfighter.
Another very important seat used extensively by the USN in The F14 Tomcat , and also a derivative of the Mk. VII series seats, was the M-B Mk GRU-7A seat. This seat featured enhanced features, updated system components, and weighed slightly less than the earlier Mk H7AF type seat. This seat has seen extensive service with the US Navy's Tomcat squadrons and has an exemplary survival rate in emergency egress situations--many of which have taken place on or just off of carrier decks.
From the US inspired Mk.VII seat, the next step up for Martin-Baker was development of the Mk.VIII seat; this unit was specifically produced to meet the requirements of the high-performance, experimental TSR-2 aircraft. Although the TSR-2 never flew, the developmental work accomplished by Martin-Baker on the seat formed the basis for a whole new generation of ejection seats that would shortly result in the Mk.IX, Mk.X series, and the latest, high technology Mk.XIV seat.
The entirely redesigned Mk.VIII seat was the first major departure taken from the previous generation of M-B seats and set the style for the current Mk.X and Mk.XIV seats. Among the refinements of the Mk.VIII seat was the elimination of the face-blind ejection actuation feature, a between the legs grab-handle being used exclusively. Also featured was a multi-tube rocket powered unit with twin chamber nozzles and use of the head-rest/drogue containment area for placement of the personal parachute. A special power retraction system was installed which acted to pull the pilot into a favorable ejection position, very much as an earlier unit mounted on the US Navy Mk.VII seats did. Additionally, a remotely actuated rocket firing system was fitted which was a considerable improvement over the previously used rocket actuation device.
The new Mk.IX seat of the mid-to-late 70s benefited from the Mk.VIII development, and with this unit Martin-Baker seats underwent a major reconfiguring. One result, aside from significantly enhanced function, was considerable aesthetic improvement in appearance. Most components of the Mk.IX seat were reworked and advanced features found on the experimental TSR-2 seat were incorporated in the new Mk.IX series seats. These included an entirely new gas actuated seat firing system replacing the previous cable linkages. The face-blind actuator system was discarded in favor a between-the-knees grab handle since studies indicated that such a system was faster to use than a face-blind design (additionally, modern crash helmets provide considerably improved wind-blast protection, making that former function largely redundant). The power retraction system was further improved, and the personal parachute containment area was placed lower in the seat-back, behind a contoured back-rest. Additionally, the seat and back pan assembly was fitted so that it could be quickly removed from the central seat structural members for ease of cockpit maintenance. The Mark IX series seats were installed in Harrier and Jaguar aircraft, for the most part, and their design trends were reflected in the development of the even more improved Mk.X series seats which followed.
Perhaps the most significant improvement found in the M-B Mk.X seat is the incorporation of the pilots personal parachute into the head-rest structure containing the drogue system. This is a concept which now appears to be adopted almost universally by egress seat manufacturers; it is now used successfully by the American Stencil Aero Engineering Corporation in their AV-8A (US spec Harrier) Stencil SIIIS seat, as well as by McDonnell-Douglas in the ACESII system. The head-rest container appears to be advantageously sited for optimal deployment of the main (pilots) recovery chute and permits simplified, efficient automatic deployment operation. Other improvements found on the Mk.X seats are an extended gas-actuation system, a simplified two-point aircrew harness system, an arm restraint system (in use on the SAAB Gripen and the UKs Tornado aircraft), and complete design of the drogue gun and barostatic time-release mechanism. The pilots personal chute uses a GQ Aeroconical canopy design which permits rapid deployment with reduced susceptibility to severe deceleration forces, and the combined drogue and main chute placement concept allows greater ease in servicing by ground personnel in that the entire combined chute system is removable as a unit. The Mk.X series seats are specified to permit zero/zero operation and safe ejection at speeds up to 630 knots IAS.
Mk.X type seats are used in a variety of aircraft, including the MiG-19 (Pakistan), the Hawk, Tornado, Macchi MB339, CSA 101, Sea Harrier, Northrop F5, SAAB JAS 39, Nanchang A5, K8/L8, the Lavi, and a number of other types in use around the world. Variations belonging to the Mk.X family are the Mk.X-L Lightweight ejection seat and the Mk.X-LF (Northrop F5 upgrade seat); all feature similar systems and specifications / performance capabilities.
The Mk.X-LF is a special retrofit for the Northrop F5 Freedom Fighter which is in use my many nations using that aircraft. The original Northrop seat proved ineffective for low level safe pilot recovery, and therefore selection was made of the Mk.X-L lightweight version of the Mk.X for use in it. (By example, the original Northrop seat provided safe recovery at 1720 feet AGL, at an IAS of 400 knots and a dive angle of 45 degrees. The figure for the M-B seat in identical speed and dive is only 625 feet AGL).
Another more recent Martin-Baker seat is the Mk.XI seat, based upon the successful lightweight seat used on the T-27 Tucano turboprop trainer. The Mk.XI is designed for use in medium performance propeller-driven aircraft and does away with the rocket pack while still providing ground level/60-400 KIAS performance. It features all the advancements of the Mk.XIII (TSR-2) seat, but with substantially less weight.
The Martin-Baker Mk.XII seat is a development of the Mk.X, and very similar to it, but employs pitot-type air and motion sensors to actuate the appropriate safe egress sequencing. Two extendible pitot sensors (one mechanical and the other electrical) on the side of upper seat structure are part of a three component system which determines a variety of parameters to facilitate egress actuation in any of three modes: low level/low speed, low level/high speed, and high level (speed is not factored in in this mode). Furthermore, the seat sensors permit control of parachute deployment in such a manner as to minimize damage which may occur due to severe high-speed ejection forces. The Mk.XII also features a much reduced maintenance requirements which permits a one minute daily inspection for functional readiness, and a three-year servicing schedule.
In 1985 M-B received a contract to produce the Mk.XIV seat for use in the US Navys F-14 Tomcat, F/A-18 Hornet, and T-45 Hawk aircraft. This was designated the high-technology NACES, or Naval Aircrew Common Ejection Seat. Utilising the latest in micro processing technology, the Mk.XIV seat features enhanced operational sensors which permit much greater levels of safe operation in a wide variety of speeds, combat attitudes and altitudes.
Yet another M-B seat is the Mk.XV seat, which was originally developed for use in the Pilatus PC-7 aircraft. An ultra light seat design with a rocket power pack, the very compact Mk.XV seat permits ground-level and 60 KIAS, to 350 KIAS operation in medium performance propeller-driven aircraft. Through canopy ejection is provided as a contingency. Total weight of the seat is only 80 pounds.
The latest and most advanced Martin-Baker ejection seat available at this writing is the lightweight, high-technology Mk.XVI seat. This seat, designed specifically for the latest generation, high-performance lightweight aircraft such as the European Eurofighter and Rafael, features advanced 2nd generation state-of-the-art electronic & microprocessor controlled systems to assure the highest optimal survival margin for aircrew operating the most recently developed aircraft. Offering zero/zero operation and up to 600 KIAS and 50,000 feet operation, the Mk.XVI seat features a weight/mass reduction of 30% over previous seats by combining the twin-catapult gun tubes with the seat structure itself as structural members. Developed as a variant, the Mk.US-XVI-L seat is a special model designed to meet the US JPAT (Joint Primary Aircraft Trainer System) requirement for a lightweight, advanced egress system. Featuring similar specifications to the Mk.XVI, the variant weighs only 125 pounds with full kit and components, and performs safely from zero/zero to 450 KIAS and 40,000 feet altitude. Important also is the seats reduced maintenance requirement, which improves on previous late-generation M-B seat standards.
Modern American Advancements : ACES and ACES II
The development of American Air Force ejection seat research continued in the late 60s period with refinements of the Douglas Escapac IC system that led to a new phase of work, conducted under the aegis of the Douglas Aircraft Division of the McDonnell-Douglas Corporation, and based on enhancements to the proven & successful Douglas Escapac system. With Air force use of aircraft originally developed for use by the US Navy (F-4 Phantom II and the A-7, most notably), the merits of the excellent Escapac family of seats became clear and McDonnell-Douglas was charged with principal responsibility for a new, substantially improved system Air Force egress system termed the ACES, or Advanced Concept Ejection Seat.
While work continued on the McDonnell-Douglas ACES program, Stencil Aero Engineering Corporation (Formerly a division of Talley Industries that is now owned by Universal Propulsion Co., Inc.), which had been actively designing and testing aircraft escape systems for military use at both China Lake NOTS and its privately owned Utah rocket sled facility at Hurricane Mesa for years, fielded the other major American seat system recognized as being in the forefront of US seat technology. Stencil innovations included the DART seat stabilization package that was retrofitted to most older USAF ejection seats, a line of highly engineered and reliable seat initiation and actuation components, and several well conceived and innovative ejection seats that were noted for their structural integrity, light weight, and reliability.
The Stencil SIIIS-3 series of seats was designed to meet the US Navy's requirement for the American AV-8A Harrier and ended up being used in the German Luftwaffe's Alpha Jet aircraft. It was also used at some time in the early F-117 Stealth production aircraft, the Navy F-18 prototype, and the early F-16 FSD aircraft. The Stencil seats departed from prior American designs in incorporating a fiberglass seat pan that covered a soft nylon seat survival package (much like the early USAD MD-1 survival seat kit concept), replacing the entirely "hard" seat kit that was used extensively in the Century Series era aircraft (this return to a previously explored concept was also a feature of the McDonnell-Douglas ACES technology). Stencil was acutely aware of the tendency of ejection seats, both American and foreign, to become excessively ponderous and heavily constructed and favored early development of so-called "lightweight" designs (such as the NAA LW series seats). Stencil seats incorporated a rotating seat kit feature that aided in man-seat separation and used leg restraints and used a series of fail-safed ballistic chute deployment devices. Original SIIIS-3 seats featured a US Navy type face-blind actuation system as well as a between the thigh grab handle actuator, but this was later deleted in favor of the grab handle system. A version of the seat also was produced using standard USAF arm rest grip actuators, which was flown in the early F-117 stealth aircraft. Another Stencil innovation was the RANGER rocket extraction system that was similar in concept to the Stanley YANKEE system (used in the A-1D "Spad") and employed a rocket boosted device that pulled a crew member from a stricken aircraft (this concept was further explored in the aftermath of the NASA Challenger disaster, as a possible egress system usable on the space shuttle).
Other seats designed and produced by Stencil included the SIIIS-3RW "reduced weight" seat, featuring all of the original SIIIS-3 performance, but with a 20% further reduction in overall weight, and the S4S system for use in advanced, high performance jet aircraft. Stencil seats have been used in the US AV-8A & AV-8B Harrier aircraft, several nation's ALPHA jets, the Argentine AF's IA-63, the Japanese Self Defense Air Force's T-4 trainer, and several other types of aircraft, both jet and propeller driven. Although somewhat eclipsed by the USAF's choice of the McDonnell-Douglas ACES system, the Stencil seats remain examples of the finest American egress technology in recent decades.
Meanwhile, the US Air Force adopted the Escape system, but made basic improvements to the US Navy system to enhance low-level, low speed performance characteristics. This included replacing the Navy's RAPEC I rocket catapult with a higher rated rocket impulse unit (RPI-2174-16) and adding a zero-delay parachute lanyard to increase escape capabilities. The higher energy rocket increased trajectory height and the zero-delay lanyard improved early chute deployment performance to give true zero-zero operation. The high speed capabilities of the Escapac IC system remained unchanged, allowing excellent survival margins at the upper reaches of the operational envelope. Thus modified, the IC-2 seat (used in the USAF A-7D), permitted escape from ground level and zero knots through 600 (or more) knots at altitude. However, despite additional refinements that led to development of the IC-7 seat (used in the early F15A and F-16), it was clear that much work remained to ensure the greatest level of safety for emergency escape by aircrewmen from all corners of the envelope--not just in the specific zero-zero and high performance modes.
A study of emergency Air Force crew ejections over the previous years indicated certain inadequacies of design concepts that were established standards in existing systems. Chief among these problem areas were recovery parachute deployment timing, rocket-burn stability problems, and man-seat separation issues.
The ACES attempted to address all of these areas of concern and it was well noted by US designers that attempts had already been made to correct similar problems in several European seat systems by that date (1970). In an effort to improve system ejection timing sequences, the ACES adopted a refined three stage approach that attempted to reduce the inherent tolerances in the timing sequences through use of more sophisticated electro-explosive actuators (previous actuator components had been largely explosively driven and mechanically timed). Low level/low speed considerations were given higher priorities than had been previously accorded. The matter of rocket burn stability, which had previously been adjusted via aerodynamic devices such as projecting booms, vanes, and parachutes, was corrected to a great degree through use of a gyro-controlled vernier rocket unit (STAPAC). Man seat separation concerns, which in past American seats had been addressed through such devices as rotary actuated straps (Weber and others), inflatable bladders (Escapac), and snubber systems (Stencil DART system--Directional Automatic Realignment of Trajectory), were broached through adoption of a European system in which the deployment of the main recovery chute pulled the occupant from the seat. It was determined that this last approach satisfied concerns over man-seat collisions, additionally. Automatic ejection responses conformed to one of the following three general conditions, to assure the best response consistent with physiological limitations: 1) Low-speed mode (below 275 KEAS, Below 15,000 ft altitude); 2) High-speed mode (Above 275 KEAS, Below 15,000 ft altitude); 3) High-altitude mode (above 15,000 ft altitude).
The ACES seat's physical structure followed lines established by the NAA LW-3B design and the M-B Mk. 15 concept, which optimized lightweight design characteristics, and upper structures were somewhat lessened so as to increase rearward/lateral visibility. The ACES seat fired through actuation of conventional hand-grip control handles, located at the forward bilateral edges of the lower front seat pan (much in the manner of the Weber seats). Catapult values of 18 Gs and 250 gps rate of onset were established as a practical upper limit across the whole range of temperatures and ejected weights. High sink-rate and unfavorable attitude situations were factored into the staging of the catapult main thrust rocket. A pitch control subsystem, linked to the STAPAC components, was configured that offset to a great degree previous thrust centerline sensitivities peculiar to rocket powered systems. Finally, a mortar deployed main recovery chute system was adopted that would most adequately address all points along the anticipated deployment curve (zero/zero to high speed/high altitude); this ejected the 28 foot flat circular main canopy, the inflation of which was also adjusted to ejection parameters by a controlled reefing system.
Additional refinements involved a new configuration for survival kit construction, as the previous all-rigid seat kit design had certain inertial characteristics that were less than desirable in many weapons delivery and ACM profiles. In the ACES system the walls and bottom of the seat's bucket provided the rigid containment needed for the kit contents, allowing a soft (non-rigid) kit configuration to be employed. The non-rigid kit contained two subsection containers, one of which contained items needed quickly (termed the "hit & run" kit) that could be scooped up and carried quickly off to a position of cover. Emergency oxygen capability came from a seat mounted bottle/regulator assembly.
Additional work with the ACES system led to a further improved McDonnell-Douglas ACES II rocket propelled ejection seat system, which has since been installed on most modern American combat aircraft. The Advanced Concept Escape System II (ACES II) followed the years of research and investigation spanning the 1968 through 1975 period that produced the original ACES system just referred to. Chief advances on the ACES II Seat are a gyro-stabilized vernier pitch-control rocket, a sustainer rocket, and a controlled force catapult, which together ensure a much greater range of safe ejection attitudes and situations. The system actively monitors (or senses) environmental conditions such as airspeed, temperature, and altitude, and uses a microprocessor controlled electro-explosive system to properly sequence ejection events so as to safely slow, stabilize and recover the crewman from any point within its performance envelope (which is from zero/zero to over 600 knots IAS). The system is claimed to be so effective that it permits escape from an inverted position 155 feet off the ground and from ground level up to 50,000 feet altitude. As might be imagined, much of the earlier Douglas Escapac RAPEC work helped in laying the groundwork for the ACES I and II systems. The ACES II system utilizes an upper seat mounted main parachute configuration, similar to but significantly different from the latest Martin-Baker seats, and is specifically designed to minimize adverse ejection forces such as tumbling and excessive parachute opening shocks. An under-seat non-rigid survival kit is employed in the conventional manner, similarly as was the ACES I counterpart. In 1977 McDonnell-Douglas was awarded a contract to produce the ACES II High Technology Ejection Seat for use in A-10 Thunderbolt, F-15 Eagle and F-16 Fighting Falcon aircraft, following what the company terms a "fly before buy" competition. This culminates the production of more than 6800 ejection seats by the company, according to their statistics. The ACES II system was also installed in the Lockheed F-117 stealth fighter, as well as the Rockwell B-1B and Northrop B-2 stealth bomber. Each application has a slightly customized configuration (for instance, the F16 seat is actuated with a between the legs D-ring, while the B-1B seat has the original bilateral front seat pan control grip actuators first employed by the ACES I seat.
While the ACES II system was until recently arguably the best system American had to provide aircrew escape (the Stencil systems providing much the same capability), the latest American egress technology program is currently underway at this time, being conducted by Boeing in cooperation with the US Air Force. Designated the CREST program (CRew EScape Technology), the purpose of the research is to produce a new generation egress system for the next wave of advanced combat aircraft. Performance criteria for the new open-seat system are reputed to be zero/zero to 70,000 feet and up to Mach 3 speeds, with an "adverse flight configuration" low of 100 feet altitude. The CREST rocket propulsion system will feature 6 to 8 propellant chambers, containing about 60 pounds of propellant, with twin-omni directional thrust nozzles under the control of a microprocessor command unit which has been programmed to recover the pilot from all possible attitudes.
Additionally, the three-part seat program will result in a seat which also provides aircrew protection against high G forces and unusual physical effects while in the aircraft. This is partly required by emerging technologies that include use of what are termed "inherently unstable aerodynamic aircraft" (or aircraft which must be flown with the assistance of computers to maintain aerodynamic stability in flight), and thrust vectoring systems that allow for a far broader range of maneuvering capability with resultant new and unconventional G forces.
It is interesting to note that most recently, a program was also underway in the United States to study the effectiveness of Russian egress systems, the exceptional capabilities of which were most dramatically demonstrated to the whole world by an almost miraculous pilot recovery at the Paris Air Show several years ago, when the Russian pilot's MiG-29 aircraft was literally within a few dozen feet of impacting the ground in a semi-inverted, extremely disadvantageous attitude. Of note are the many advanced features of the Russian seats, and their exceptionally favorable recovery rates, which have been until recently all but ignored by Western egress systems researchers. Much work remains to be done on this but there was at least one cooperative study has been completed investigating the possibility of integrating Russian seats (and/or their technology) into modern high-performance American aircraft--something that would have been inconceivable prior to 1989.
At this time (3/2002) , the decision has been made to continue developing and using US egress technology in the latest US combat aircraft (F-22 Raptor and XF-35 Strke Fighter) programs.
(Permission to use this copyrighted article is granted, provided it is presented as written here and with full author's credit to: Christopher T Carey).
COURTESY OF AEOLUS AEROSPACE
Bailout For The Other Guy
by Phil Rowe
Much has been written over the years about ejection seats and escape systems for pilots. But what about the other guys? How did the navigators, radio operators, flight engineers, crew chiefs, gunners and others get out? That's what we'll look at here in this historical perspective.
The problem of bailing out of airplanes hasn't gotten easier over the years. As planes flew faster and higher, the complications increased as well. Things were much simpler back in the early days.
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In the combat airplanes of World War II, getting out for all crew members was a matter of jumping out of the nearest hatch, window or even the open bomb bay doors. If you had a parachute and could struggle to an opening, you had a chance. Airspeeds were relatively slow, few multi-place planes went faster than 350 knots.
Then came the high speed jet airplanes of the post-WWII period. Speeds increased markedly and altitudes reached 40,000 feet and higher. Getting out of planes in trouble became a real problem. If you could get to an open hatch and manage to jump, you ran the risk of being slammed against the fuselage or other part of the plane by the wind blast. It was difficult.
Jet fighter pilots were getting ejection seats to help them survive. Even bomber pilots found themselves sitting on similar upward firing seats that could clear the aircraft and then parachute them safely to ground. The story was different for the other crew members.
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Among the early airplanes with ejection capabilities for navigators were the B-45 and B-47 medium bombers. The former, a straight-wing 450 mile-per-hour jet, featured a sideways ejection seat for the navigator sitting in the nose. When it was time to bail out, the B-45 navigator left via the port-side hatch as his seat threw him clear of the craft. Of course there was some danger of hitting the engine pod, but when it's time to leave, it's time to leave.
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The B-47, Strategic Air Command's proud swept-wing wonder, offered the navigator a downward ejection seat as the primary escape. Of course that was of concern at low altitudes, but otherwise it gave him a chance of surviving. Spare crew members, like an Instructor Pilot or Instructor Navigator, didn't fare quite as well. Their options included dropping down the entry hatchway or jumping out of the navigator's hatch after he ejected clear.
The enormous B-52 Stratofortress heavy bombers came along and didn't offer a whole lot of improvement. The upper ejection seats for pilots and the electronic warfare officer were pretty good, but still the two navigators faced the prospect of ejecting downward. The low altitude bailout problems persisted. And spare crew members were no better off. The tail gunner had his own unique escape option. He merely severed the tail gun and jumped aft out the resulting hole in the rear. Actually, tail gunners had a good survival record.
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Speed kept increasing. The hazards of getting clear of the airplane and surviving the wind blasts, which could break flailing arms and legs, grew worse. Improvements were needed.
Interim measures were taken. Some ejection seats featured pull-down curtains to protect the head and face against the terrific wind blasts. Restraints were added to keep arms and legs from flailing wildly. But those measures only helped the primary crew members who sat in ejection seats. The spare crew or other passengers were still on their own, hoping they could reach an open hatchway and jump to safety.
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Bailing out at ever higher altitudes posed the additional problem of enduring the extreme cold aloft and the thin air which would not support breathing. Oxygen bottles solved the latter problem, while delaying parachute opening until lower altitudes were reached by free-fall helped the former. Automatic, aneroid-operated parachute opening mechanisms were a significant development.
Before we talk about supersonic bombers and the most advanced aircraft, we need to consider the crew members in large tanker and transport airplanes. Neither pilots nor other members of those crews were provided with ejection seats, up or down. Bailing out of many of these planes just wasn't a high priority matter, for being comparable to jet airliners and not as likely to suffer battle damage as bomber as fighters, they were deemed safer. Hence, no ejection systems were added. And besides, commercial airline passengers don't have any bailout options. Do they?
They, the designers and decision-makers, did make minimal provision for bailing crew members out, after a fashion. They adopted the tried and true approaches of telling people to jump from open hatches, doors and open aft cargo ramps. Some planes, like the KC-135 were still considered dangerous. Those flying gas stations, loaded with jet fuel, for themselves and planes they were to refuel in flight, were dangerous. And getting out was not easy.
Jet and turboprop cargo planes like C-130's, C-141's and C-5's relied on the bailout techniques of their earlier prop-driven ancestors. Crew members were expected to get to an available door or hatch and simply jump clear. Not a whole lot of progress has been made for these aviators. But then there was no discrimination between pilots and non-pilots either.
The greatest advances in crew escape systems for both pilots and others came with the B-58, F/FB-111 and the B-1. Supersonic craft, all, they incorporated escape and bailout systems that greatly improved survivability, all that is save for the B-1. The first two craft featured fully enclosed capsules or modules for single or grouped crew members.
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The Mach 2 supersonic B-58 bomber originally came with upward ejection seats for each of the three tandem seated crewmen. There was no room for carrying spare crew members or passengers. The navigator and Defensive System Operator both had the same chance of surviving as did their pilot. But at the extreme speeds of 1400 miles per hour at Mach 2, something was needed. That came in the form of the Stanley Aviation capsule, a clamshell-like enclosed ejection system. All B-58's ( though not the two-pilot trainer versions ) were upgraded with escape capsules.
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Supersonic F\FB-111 fighter-bombers featured an escape module to protect both of the crew members. Like the B-58, F\FB-111's had no room for spare crew members. On ejection, the entire cockpit unit or module separated from the fuselage and rocketed to safety. A parachute system gently lowered the module to earth.
The B-1 developers originally considered an escape module. It failed qualification tests and was dropped in favor of proven upward ejection seats, for both pilots and the two others of the primary crew. Spare crew members were left to their own devices in finding open hatches or doorways.
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It's fair to say that many modern airplanes do provide bailout and escape systems for non-pilots, those on the primary crew. Spare crew and passengers are still left to fend for themselves. On cargo and tanker aircraft, all crew members must rely on decades-old bailout and escape methods. They must find an opening and jump.
Of course fighter pilots and members of one and two-man crew high performance craft are pretty well off, by comparison.
It's all a matter of trade-offs. Don't you think?
Ejection Seat Development
Introduction and Early History
As many of you have read, initially it was considered very "un-manly" to even consider wearing a parachute in an airplane. Several countries made a concerted effort to warn their pilots not to even think about anything other than their assigned mission to think about getting out of the airplane was out of the question. In this country pilot safety was always of some concern, following the first fatality in a military aircraft accident. Through most of WW II it was considered an even bet that should something happen to the aircraft you could use your parachute. Most aircrew members wore them all of the time, usually sitting on the chute that doubled as a seat cushion and merely jumped from the airplane, time and altitude permitting. With the arrival of modern, jet and other types of high performance aircraft, the pilots sought more of an advantage in getting away from the aircraft, often when the pilot was incapacitated or unconscious and the plane crippled. Both the British and American aerospace worked toward enhancing pilot survivability leading to what we have known as the modern ejection seat and its related equipment. Most of the modern seats are known simply as "0-0" (zero-zero) seats, meaning that they are fully capable of ejection of the aircrewmen from "0" feet altitude and without any forward airspeed (as opposed to earlier seats which required a predetermined altitude and speed for safe deployment of the seat and its parachute). As an added note, since I began these notes, Bill Johnson was kind enough to lend me a copy of a book published by the Martin-Baker company in England, in which they very clearly illustrate their early efforts to design and build ejection seats. From all that I have seen, the Martin-Baker company is clearly one of, if not the world's leader in these efforts over the last 45+ years.
Basic Ejection Seat Design and Features:
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|Early U.S. Ejection Seat|
1. Initiating Cable
2. Shoulder Strap (riser)(with inertial reel system)
3. Arm Rest
4. Oxygen & Radio Connections
6. Vertical Seat Adjustment
7. Right Hand Grip
8. Safety Belt
|It appears to me that the greatest interest in modern ejection seats was the direct result of the Navy's interest in their carrier based pilots. For the most part, the other services felt the need was largely one of getting the pilot or crew member out of an aircraft that was at least at altitude. The Navy was confronted with a need to insure the survival of a pilot who was often sitting still or best in the early throws of preflight and may be only a few feet above the deck surface.|
Martin B-57 Ejection Seat (about 1955)
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Key Seat Features
1. Face Curtain Ejection Handle
2. Canopy Breaker
3. Ejection Controls Safety Handle
4. Emergency Release Handle
5. Lower Ejection Handle
6. Shoulder Harness Lock Lever
7. Shoulder Harness Straps
8. Koch Fittings
9. Lap Belts/Harness Straps
10. Personal Services Connector
11. Survival Kit (RSSK-8)
12. Parachute Rip Cord Handle
13. "Remove Before Flight" Safety Pin
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ESCAPAC 1G-2 Seat (with pilot)
The ejection seat is quite an engineering feat in itself. It is usually light weight, yet very strong material, able to withstand the high g-load of the rocket's ejection (from the aircraft), contains the parachute for the crewman, the survival kit (usually in a rigid seat kit, containing the material I mentioned in an earlier article), a separate booster rocket to "right" the seat, some type of stabilizing equipment, separate oxygen supplies for a the crewman (though some of the newer seats like the Martin-Baker SJU series actually contain their own self-contained oxygen generation systems) and the pilot's attachments for the seat, the parachute, survival kit, and communications connectors. These modern seats are really marvels of aerospace engineering.
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Martin-Baker MK H7 Ejection Seat from F-4 Phantom
Large scale models of such a seat would be a very interesting modeling subject in itself. The seat is usually mounted onto or into to the aircraft using a "rail" type of system and often attached to the back of the bulkhead itself, rather than the floor of the aircraft (which appears to be the way most model kits depict them). One should also note that there are still a few "pod" types of ejection systems in operation, such as in the EF-111 and B-1 aircraft, where the entire area around the aircrew is ejected from the aircraft and leaves with the aircrew inside for it's ascent. For the most part however, the basic ejection seats are similar to those described in this article.
Another facet of this story is that until the U.S. started using the Martin-Baker and ESCAPAC style of seats (about the early 60's), most of the early ejection seats were largely "in house" products of the aircraft companies themselves. When one bought a B-52, an F-106 or an F-11, one acquired whatever type of seat the manufacturer provided. These were usually the very basic types of seats. A look at the basic B-57 seat (see page 3) built by the Martin Company in 1955 illustrates this point well I believe.
Ejection Seat Parts and Features:
- High strength, lightweight seat structure of monocoque-type aluminum sheet construction
- An integral ground safety device for ejection controls (this allows for the seat to be "safed" whenever the aircraft is not in service)
- A two-stage rocket catapult (allowing for both the actual "ejection" of the seat and pilot from the aircraft and the "righting" of the seat)
- Flip-up or fixed canopy breakers to allow safe ejection through the canopy (hence the height restrictions on some pilots today)
- Two ejection controls: a face curtain ejection handle and a lower ejection handle located on the forward or side edge of the seat bucket
- An MA-2 integrated torso harness which provides positive torso restraint during the flight, crash, and parachute opening loads
- A rigid seat survival kit contains the emergency oxygen supply and survival equipment. Two hooks on the front of the survival kit cause the survival kit to rotate straight forward out of the seat during pilot/seat separation. A survival kit release handle is located on the right side of the seat which will release the life raft and survival equipment (attached by a 25-foot lanyard)
- An actuator cable is attached to radio beacon in the survival kit so that automatic actuation of the beacon occurs upon seat separation from the aircraft.
- A seat stabilization consisting of two braking devices attached to the bottom of the seat
- Pilot's services (anti-g, exposure suit ventilation, and oxygen/communication) which plug into the aft portion of the left console. These lines pull free at their disconnects upon ejection.
Modern ejection seats are highly developed technological wonders! One could imagine what would happen if a modern techno-thriller author like Tom Clancy were to learn about these seats and include this type of knowledge into a book of his fiction!
These parts are the major components only. Believe me, I am skimming the surface. When you look into the individual seats, one will quickly find many added subsystems and functional parts. In the case of the ESCAPAC 1G-2 seat illustrated throughout this article, the seat manual alone runs over 400 pages of parts and instructions. The rigid seat survival kit, without its contents, is over 40 pages of diagrams and instructions. It is very easy to understand why the current generation of ejection seats are no longer a simple aluminum frame, but rather a million dollar plus engineering facet of the aircraft itself.
Another limiting factor which demonstrates the cost of these seats is that the government has apparently stopped the practice of providing an ejection seat to each pilot who has survived their ejection from a modern jet. The cost of a modern ejection seat prohibits it from being removed from inventory unless damaged beyond repair.
Pilot Chute Canopy Suspension Lines Harness Pack
It is also appropriate that we concern ourselves briefly with the parachute itself and its basic nomenclature. This will permit you to have a better understanding of the complexity of the ejection seat, the firing sequence and the pilots eventual ascent. The basic parachute is comprised of several major parts, as illustrated in the drawing below.
It is important to understand the pilot is attached to the seat, which is turn attached to the aircraft. The pilot's attachment is intended to be a strong one and designed to carry him with the seat should it or he become separated from the aircraft. Much of this attachment system is intended to act and or perform independent of the pilot himself (I'll use the old fashioned "him" but should point out that there are both men and women flying in military aircraft today). The way this is done is through the basic torso harness (which is usually separate from the pilots "G-suit" and survival vest or equipment, but not always, some pilots chose to have their survival vest or "suit" sewn onto the torso harness. In modern U.S. equipment this is usually the MA-2 lightweight harness (which is lightweight only when considered next to the aircraft itself). It is very constricting and if worn properly may not allow the pilot to walk fully erect while on the ground. Such a harness is shown below, both with the harness' nylon covering cut away (the way most pilots choose to use it), with the nylon "body" in place and as it might appear on a pilot (with the balance of the survival vest and oxygen mask attached).
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Pilot's Attachment to the seat:
MA-2 Harness (without nylon enclosure) MA-2 Harness on aviator (with nylon enclosure)
Typical Koch Fittings
Attaching oneself to the seat isn't always as easy as you might think. The actual attachment of the pilot (already safely buckled into his harness) is usually a matter of attaching only four location points (two at the waist or lap belt and two on the shoulder harnesses) and usually done using Koch release fittings. These are spring loaded devices which contain two openings and are designed to prevent accidental openings (as one moves about in or out of the cockpit). The shoulder strap Koch fittings also now commonly contain a small cylinder device called SEAWARS release fittings (automatic sea water actuated release system). These automatically release the parachute risers from these Koch fittings whenever submerged in sea water.
There are also usually leg garters worn by the crewman to prevent his legs from moving away from the seat during the ejection sequence (and often employ a device to pull the legs back and down against the seat front). Keeping ones hands, arms and legs close to the seat is of great importance as the pilot and seat are ejected from the aircraft. It is also the reason that the preferred method of ejection initiation is for the crewmen to use both hands and pull the face curtain down over their helmet. When done properly, this keeps the pilots' arms and hands in a safe position and greatly reduces the traumatic effects which usually accompany automatic or involuntary departures from the aircraft. As you can see from the M-B MK 7 drawing, there are often two sets of garters, an upper and lower, which provide even greater support for the pilot's legs.
The pilot is also "plugged into" the aircraft, normally at their left side using a simple (and uniform) connector, which supplies him with oxygen, air for his g-suit and communications connections for his helmet and mask (to the aircraft). After these connections are made, normally the pilot's seat safety pins are removed and the seat is ready for full operation. This final step is normally not taken until the final moments before the aircraft is about to be started, for the simple reasons that the operation of the seat may result in ejection when not necessary. Many of you will remember the sad story of the small child who was killed during his ejection from an S-3 about 15 years ago during an airshow demonstration. The crew had left a seat in the "unsafe" configuration and the seat was fired while the child was sitting in it. For these reasons, the "insertion" of the air crewman is usually done (like almost every aspect of aviation) using two critical tools: a crew chief and a checklist.
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Attachment points to shoulder straps
MA-2 Harness with survival vest and seat attachments
(without nylon enclosure)
MA-2 Harness on dashing
Ejection Initiation, Sequence and Timing:
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Two-handed grip on lower handle Both hands grip face curtain Both hands pull face curtain down and over helmet
One would think it might be easy to "just get out of the airplane" and "hit the silk." You've seen it the Flying Tigers and many other Hollywood epics. The pilots pull back the canopy, stand up (often not even taking the time to undo their seat belts...I'm telling you, those were when men were real men....), stand out on the wing and jump into the mattresses carefully laid out for them. I've spoken with two members of the Caterpillar Club (both Navy pilots) who, during WW II, jumped and survived. Neither thought it was such a neat deal at the time and both thanked their stars and God to be alive after the experience. Two other acquaintances related their experiences in "leaving" an F-4 and F-8; both said they never really wanted to go through it again, their ejection seats both "worked as advertised" and they say "it was the most thrilling ride they did not want to take." They each sustained some minor physical damage. One lost his rear seat RIO. As a direct result of the all to numerous ejections encountered in our Viet Nam efforts, the current seats are much more highly automated than earlier seats and have built-in features which will hopefully greatly increase the pilots survival, even when unaware of the ejection. Current U.S. military studies point to about a 90% survival rate when the ejection suit is properly deployed.
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|Step 1: Ejection initiated by pilot using face curtain||Step 2: Canopy blown||
Step 3: Ejection seat departs a/c
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Step 4: Seat leaves a/c, pilot is separated from seat, pilot and main chute deploy with survival kit and raft deployed beneath pilot
Beginning the initiation process (assuming the pilot is capable of doing so under his own power) is normally handled in one of two methods: (1) using the lower handle (between the legs and in front of the seat) or (2) using the face curtain. Both methods are best illustrated above.
For the best understanding, I have "borrowed" several drawings, which I hope will better illustrate the ejection sequence itself. The first of these shows the sequence in the order of ejection (from an A-7), the second set, to give a bit more detail to the major steps as the pilot is ejected (again from an A-7) and the third, the actual times involved in the full ejection sequence. As you will see from the time-line graph, the entire time, from initiation of the pilot's ejection sequence in only about 5 seconds! The timing is quite precise and very quick as you will notice. In an aircraft such as the F-14, F/A-18 or EA-6B (which has four ejection seats and aircrew positions) the timing is even more critical and there are built-in time lapse sequences between the various seats as they are fired and ejected from the aircraft
In an EA-6B, for example the timing sequence is even more critical, when you realize there are often a full crew of 3 or 4 pilots and NFOs (or ECMO: electronic counter measures officer) in the aircraft, each of which has to have his precise departure from the aircraft in a very exact position and apart from the others.
Their sequence is (following the ejection initiation):
ECMO 3 (left rear position) 0 sec's
ECMO 2 (right rear position) 0.40 sec's
ECMO 1 (right front position) 0.80 sec's
Pilot (left front position) 1.20 sec's
There are a few other small details incorporated into modern seats. One is the ability for the seat to work effectively underwater (should the aircraft be submerged), with full oxygen supply to the pilot (assuming his oxygen mask is in place) and the ability of the pilot's parachute and harness to separate while in the water. One was mentioned earlier in these notes. The Navy (and subsequently all services) have incorporated this unique device in the parachute harnesses called "SEAWARS" releases. It automatically releases the chute from the pilot's harness as it senses salt water, thereby relieving them of the often fatal drag of water into the parachute. While it may seem like fun to be in the water, apparently drowning in the sea is one of the most common problems encountered by pilots downed at sea.
History Of Aircraft Escape System Propulsion
This information is provided by the courtesy of R. F. Sadler, of B. F. Goodrich Areospace.
R. F., Sadler
Universal Propulsion Company, Inc.
E. B. Skinner
Talley Industries of Arizona, Inc.
A brief history of the use of propulsive elements in aircrew escape systems is presented. For the purposes of this history, both closed propulsion elements (catapults), as well as rocket motors are considered since early ejector seats depended solely on catapults for their motive source. Applications of rocket motors other than for providing the main impetus to the escape system are also considered in more recent systems. Information contained in this history was obtained from all types of literature both published and unpublished, as well as from discussions with individuals who have been involved in the escape system arena from its infancy.
Almost since the first days of flight man has been concerned with the safe escape from an aircraft which was no longer flyable. Early escape equipment consisted of a recovery parachute only. As aircraft performance rapidly increased during World War II, it became necessary to assist the crewmen in gaining clear safe separation from the aircraft. This was accomplished with an ejector seat which was powered by a propellant driven catapult - the first use of a propulsive element in aircrew escape. Since then, this collection of component has evolved through several generations into today's relatively complex systems which are highly dependent upon propulsive elements. Today, propulsive elements (rocket motors, specifically) are used to stabilize the ejected mass, provide trajectory steering, jettison aircraft canopies, provide positive separation of the ejected seat from the crew member, generate the force necessary to rapidly extract a parachute from its container, all in addition to the basic function of providing clear safe separation from the aircraft. Since the first operational ejections from aircraft, nearly 6,800 successful non-combat ejections have taken place from US Navy and US Air Force aircraft alone. In savings to the taxpayer, that amounts to over 8 billion dollars, based on the current average training cost of 1.2 million dollars per aircrew member,
THE EARLY DAYS
The first operational use of a propulsive element to assist an aircrew to escape from an aircraft apparently occurred during World War II. It appears that the country to receive credit for the first operational system was Germany, as it is known that approximately 60 successful ejections were made from German aircraft during World War II. It is interesting to note, however, that the first aircraft ejection seat was designed and tested (successfully) with a dummy in 1910 by J. S. Zerbe in Los Angeles, California, apparently using bungee cords for propulsion. This was one year before the first parachutist successfully, jumped from an aircraft.
German tests of escape systems started as early as 1938. Initial designs used compressed air for propulsion, but this approach was abandoned due to high weight, low performance, and maintenance problems. Their next step was apparently to investigate propellant powered seats. A parachutist by the name of Busse made the first live ejection from a propellant powered seat. Propellant powered seats were operational in German aircraft by 1944.
As an example of the degree of development of escape system propulsion in Germany during World War II, the Dornier DO335 presented both a unique aircraft from an aerodynamic view, as well as from the escape system propulsion point of view. The aircraft having both a tractor and pusher airscrew, as well as dorsal and ventral centerline fins, presented a unique challenge to the aircrew who needed to escape in flight. To that end, this aircraft utilized explosive bolts and other propellant driven devices to jettison the dorsal tail and the pusher airscrew, as well as the ejector seat. It is not known if this system was ever used. Other German aircraft fitted with the propellant driven ejector seats included the ME-163B, ME-262, Heinkel HE-162, HE-219 (with the two seats), and HE-280.
Another country involved in early ejection seat work was Sweden. Initial experiments were made by SAAB in 1942 using propellant powered seats. The first successful dummy in-flight ejection was on 8 January 1942. A successful live ejection was made on 29 July 1946.
In the US, the Army Air Corps picked up in 1936 where Mr. Zerbe left off when they began considering experimentation with high performance pusher prop aircraft. A funded study was conducted in 1940 to investigate escape from such aircraft. In June of 1944 a contract was let to Vultee for the XP-54 aircraft which had a pusher propeller behind the cockpit. This aircraft (only two of which were built) became the first US aircraft to have a positive ejection device. In this ease, the seat was pivoted downwards through a hatch in the belly of the aircraft. A spring was used as the propulsive mechanism.
In England Martin-Baker had begun evaluating methods of positive escape from an aircraft in the early summer of 1944 for the Ministry of Aircraft Production. In order to provide a system that could be retrofitted to existing aircraft which had insufficient clearance in their cockpits to allow ejection of the seat, Martin-Baker proposed a spring powered swinging arm concept. The aft end of the arm pivoted at a point near the base of the vertical tail and the forward end attached to the aircrew's parachute harness. At actuation, the arm effectively extracted the crewmember from the cockpit. This approach was dropped when it became obvious that retrofit was not practical. The next approach presented was that of ejecting the seat using a propellant powered catapult. The first live Martin-Baker ejection took place on 24 January 1945, on a 16 foot vertical ejection test tower using a propellant powered seat.
At the end of World War II both the British and Americans acquired German and Swedish ejection seats and data. This information and equipment added impetus to their efforts. The first live flight test in England occurred on 24 July 1946 when Mr. Bernard Lynch ejected from a Meteor III aircraft at 320 mph IAS at 8,000 feet, using a prototype propellant powered Martin-Baker MK I seat. On 17 August 1946 First Sergeant Larry Lambert ejected from a P61B at 300 mph IAS at 7,800 feet to become the first live in-flight US ejection test.
All of these early seats were a collection of component including a parachute, a seat structure to which the aircrew and parachute were firmly attached, and a propulsive element which forcibly separated the seat and its contents from the aircraft. This early propulsive element has been called a gun or catapult and, is in essence, a closed telescoping tube arrangement containing a propellant charge to forcibly extend the tubes, thereby imparting the necessary separation velocity to the "ejector seat" and its contents.
All of this effort culminated in ejection seats being fitted to early operational jet aircraft in both the US and Britain. The first British emergency ejection occurred from an out-of-control flying wing on 30 May 1949. The first operational British aircraft with a propellant driven ejector seat was the Meteor. The first operational ejection from it occurred on 11 November 1951 over Korea. Meanwhile, in the US the first US Navy operational ejection occurred on 9 August 1949, while the first operational USAF ejection occurred from an F-86 fighter on 29 August 1949.
To this point in time, then the development of escape propulsion consisted of refining the propellant driven catapult or gun. While many different catapults were designed, developed, qualified, and produced, they all basically fell into two design categories: the short-stroke catapult, and telescoping tube catapult. The former is a two-tube device, one of which is attached to the aircraft, and the other attached to the seat. The two tubes are nested one inside the other and are attached to each other by some type of locking device. A propellant charge is contained in one of the tubes which when fired, unlocks the two tubes from each other and then provides the necessary gas pressure to accelerate and separate the two tubes, thereby ejecting the seat from the aircraft. Typical stroke to separation of the tubes was about 30 inches, and separation velocity was as high as 50 feet per second. The factor limiting separation velocity was acceleration and rate of acceleration change or onset rate as seen by the aircrew's spinal column.
The second category of catapults utilized three tubes nested one inside the other to achieve separation velocities as high as 83 feet per second from a total of 72 inches of stroke Typically, the US catapults of this type used a single propellant cartridge and provided separation velocities closer to 60 feet per second, while the British catapults (Martin-Baker) utilized a primary and two subsequently staged cartridges to achieve the higher velocity.
APPLICATION OF ROCKET MOTORS
The jet engine continued to increase the performance of post World War II aircraft, and it was not long before the limitations of the simple ejector seat become apparent. Two such areas of limitations were: (1) Inability of the ejected seat to clear the aircraft's vertical tail at high speed, and (2) The potential for windblast injury to the aircrew forced to eject under high "Q" conditions. Propulsive elements were involved in the solutions to these problem areas.
The problem of achieving tail clearance was approached in several ways. As indicated earlier, the German approach was to jettison the vertical or dorsal surface. One approach taken in the US was to eject the seat downwards, rather than upwards. This approach had serious shortcomings when the ejection occurred at low altitudes. Another approach was to increase the catapult output sufficiently to provide adequate tail clearance. While successful in clearing the tail, this approach was also very successful in inducing spinal injury to the aircrew.
The problem was finally addressed successfully by combining a rocket motor with the catapult to form a two-stage propulsion system for the seat. The catapult remained as the initial booster to get the seat/man mass clear of the cockpit, while the rocket motor came on line, once clear of the cockpit, to act in a sustainer mode. When combined into a single unit, this propulsive element was termed the rocket catapult. The first USAF rocket catapult, the TALCO Engineering Co. 1057, was installed in the F-102 in 1958. Shortly after this, the first USN rocket catapults, the RAPEC I for the A-4 and the TALCO Engineering Co. 1192 for the T-2, became operational. Propellants used in the RAPEC were double base, as were most previous escape propulsion units. The 1057 and 1192 units were unique in that they used a composite propellant. This basic rocket catapult configured seat is illustrated in Figure 1.
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A slightly different approach was taken by Martin-Baker in England. The catapult was maintained as separate component, and the rocket motor was located separately under the seat bottom. This configuration is illustrated in figure 2, and is, if not unique, certainly rare in its use of multiple propellant tubes feeding into a single nozzled manifold. Propellant is double base. This propulsion concept was extensively tested, culminating in a live static (zero airspeed and zero altitude) test on 1 April 1961. The test was repeated at the Paris Air Show of the same year.
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The Stencel Aero Engineering Company of Asheville, North Carolina, likewise utilizes separate catapult and rocket motors. However, their system consists of twin catapult tubes which also do duty as the main seat structural beams. Rocket motors are located on both sides of the seat at the aft extremity, and they are termed "SBR's" for "Seat Back Rockets." Figure 3 illustrates this variation. Composite propellant is used.
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In summary, then, the next major step in escape propulsion evolution was the addition of the rocket motor to the ejection seat to compliment the catapult. In general, the first rocket catapults were categorized as "low impulse" units, indicating that the rocket motor delivered from 800-1,000 pound-seconds of impulse, in addition to that provided by the catapult. This additional impulse was sufficient to provide tail clearance at high speed and to provide recovery from ground level at speed, when used in conjunction with other ejection seat improvements.
Emphasis was initially placed, however, on high speed recovery. As time progressed it became obvious that many ejection fatalities were occurring at low speed close to the ground. Hence, in the mid-1960's, the "high impulse" rocket/catapult system was put into service to provide static (zero airspeed, zero altitude) recovery capability in conjunction with the current seats. High impulse generally designated that the rocket motor portion of the system provided approximately 2,000 pound-seconds of impulse. function time of the rocket was .5-.6 seconds, and the increase in impulse compared to the low impulse unit generally provided additional trajectory height which translated into additional time available for all of the automatic ejection seat functions to occur.
Today the advent of high performance aircraft operating at very high speed and very close to the ground have necessitated that the escape system designer reduce the total time from ejection initiation to full parachute to the absolute minimum consistent with human physiological tolerances. This has necessitated shortening rocket function time and hence impulse. Current generation rocket propulsion units are again sized to deliver 1,000-1,100 pound-seconds of impulse. When combined with much faster parachute systems, the low impulse units can still provide zero-zero recovery capability while at the same time provide greatly improved adverse attitude recovery capability.
Another interesting escape system propulsion concept Is that of the Stanley Aviation Yankee (now produced by Stencel Aero engineering and called the Ranger extraction System. This system utilizes a tractor rocket which Is ejected or catapulted away from the aircraft above the cockpit. It is attached to the crewmember by a pendant. When the rocket motor reaches pendant line stretch, It Is fired and tows or extracts the crewmember clear of the aircraft. This concept is illustrated in Figure 4.
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High speed windblast protection was originally addressed by providing some type of encapsulation for the aircrew. This approach was heavier than the open seat, necessitating larger propulsion systems. The first such capsule was developed by Douglas Aircraft Company under contract to the US Navy for the F-4D Skyray. While this capsule never was installed in the aircraft, it was tested at China Lake. The propulsion system was developed by AeroJet Engineering and provided approximately 9,000 pounds of thrust for .3 seconds. It also provided bleed gas for drogue parachute deployment and fin extension. Testing was accomplished in 1951 - 1952. Other capsules, encapsulated seats, etc., were designed and tested, including a separable nose section for the F-104. Rocket motor impulses ranged from under 1,000 pound-seconds, all the way to 40,800 pound-seconds for the proposed Boeing ADO-12 airplane nose capsule.
Other propellant powered devices evolved during post World War II to assist the aircrew in achieving safe escape. Their functions included limb positioning and restraint, torso positioning and restraint, seat positioning, canopy jettison, seat/man release and separation, and aerodynamic stabilization.
RECENT APPLICATION OF ROCKETS TO ESCAPE SYSTEMS
The open ejection seat, as well as the escape capsule have gone through a continuous evolution to the point where today they have become "systems" by providing all or nearly all of the functions necessary for the aircrew to complete a safe escape end recovery. A typical ejection sequence includes the following functions which occur generally in the order listed, following initiation by the crewmember .
1. Canopy or hatch jettison
2. Crewmember torso positioning and restraint
3. Clearance of work station equipment from ejection path
4. Seat ejection/crewmember extraction .
5. Seat stabilization
6. Seat trajectory control
7. Drogue parachute deployment
8. Seat man separation
9. Recovery parachute deployment and inflation
10. Survival gear deployment
11. Parachute release upon water entry.
Many of these functions are provided by rocket motors, as shown in Table 1.
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Many powered escape capsule configurations have been conceptualized, designed, and even fabricated and tested since the early days of escape systems. However, of the many, only four made it into flying aircraft, and of these four, only two made It into production aircraft. The four are: 1) B-58 Encapsulated Seat, 2) B-70 Encapsulated Seat, 3) F-111 Escape Capsule, and 4) B-1 Escape Capsule. Other capsules of note include the Mercury and Apollo Command Modules, which could be towed away in total from the launch vehicle by large solid propellant motors.
Both the B-58 and B-70 Encapsulated Seats used rocket catapults for their main propulsive elements. The B-58 system utilized twin rocket catapults, each delivering approximately 1,475 pound-seconds of impulse from the rocket portion. The B-70 system utilized a single rocket catapult delivering, approximately 3,500 pound-seconds of impulse from the rocket portion.
The B-1 and F-111 Capsule departed from the catapult boost/rocket motor sustainer approach and evolved around the rocket motor only.
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The B-1 capsule which is fitted to the first three prototype aircraft uses two identical spherical rocket motors for propulsion. One motor is mounted so that it can be gimbaled In the pitch plane of the capsule and the second In the roll plane. Both motors are, therefore, used for propulsion, as well as for capsule stabilization and trajectory control, in accordance with an inboard control system. Figure 5 illustrates the B-1 configuration.
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The basic motor configuration is a 20 inch sphere. Nominal delivered impulse Is 34,000 pound-seconds which is delivered in two phases: an initial boost phase followed immediately by a sustain phase. Nominal thrust for the boost and sustain phases are 44,270 pounds and 15,260 pounds respectively. Boost burn time nominal is .369 seconds and sustain burn time nominal is 1.075 seconds.
The F-111 motor is a cylindrical unit with three separate nozzles, one at the lower end (as mounted In the capsule) called the primary nozzle and secondary and auxiliary nozzles located at the opposite or upper end. In ejection below 300 knots, the motor thrusts through the primary nozzle and through the auxiliary nozzle. Above 300 knots the secondary nozzle replaces the auxiliary nozzle after about .15 seconds of motor burn. The purpose of the secondary and auxiliary nozzles is to produce a nose-down moment to counteract an aerodynamic pitch-up moment Inherent in the capsule. Total impulse for the motor varies between 21,400 and 23,600 pound-seconds ambient. Figure 6 illustrates the F-111 configuration.
CURRENT ESCAPE SYSTEM PROPULSION APPLICATIONS
With very few exceptions, the escape systems in use today all use at least one rocket motor. Several use more than one motor and two operational systems use four different motors. Table II lists the aircraft, the ejection seat, and the specific rocket motor applications of some typical systems.
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Other specific/representative current state-of-the-art open escape systems (ejector seats) using rocket motors include the USN/Stencel Aero Engineering SIIIS seat system, the USAF/Lockheed SR-71 seat system (which was also used in the Space Shuttle Test Orbiters), the Stencel Aero Engineering Ranger Extraction System, and the USN/McDonnell Douglas ESCAPAC IG seat system series. Other open escape systems included those used in the X-15 and the Gemini space vehicles.
The ESCAPAC IE-1 seat holds the current record for the number of separate rocket motors per seat (four) each performing a different function. These functions are: seat ejection by MK 16 Mod 1 rocket catapult (1,100 pound-second rocket phase), trajectory divergence by MK 83/MK 85 yaw motors (11 and 22 pound-seconds respectively), seat stabilization by MK 84 vernier motor (250 pound-seconds), and seat-man-separation by MK 82 motor (100 pound-seconds).
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The ESCAPAC IE-1 is used in the Lockheed/US Navy S-3A aircraft, which is equipped with four seats per aircraft. In a normal escape system sequence, the rear side-by-side pair of seats are ejected simultaneously followed by the front pair of seats approximately .75 seconds later. A typical function sequence of a single IE-1 seat system is presented to illustrate the rapidity of a typical escape sequence, as well as the short function time of the rocket motors:
T=0 Catapult portion of MK 16 rocket catapult fires and begins to move seat up the rails.
T= + 150 ms. Seat clears the ejection rails at approximately 50 feet per second and is essentially clear of surrounding cockpit structure.
Rocket portion of MK 16 rocket catapult ignites. MK 84 vernier motor fires, and commences to gimbals in response to gyro inputs to counteract any adverse pitch changes.
MK 83/MK 85 yaw motor fires to induce slight yaw moment into seat to assure separation from adjacent ejection seat. Burn time is approximately 100 milliseconds. (Rear seats are equipped with MK 85 motors, while front seats use MK 83 motors . This assures that the rear seats yaw more than the front seats to provide four separate trajectories.)
T= + 500 ms. MK 16, MK 83/MK 85, and MK 84 rocket motors, all have burned out. Seat is between 100 and 200 feet above ejection altitude. depending upon conditions.
T= + 520 ms. MK 82 seat-man-separator motor fires at the same time the cartridge fires to release crewmember and his equipment from seat. Seat is positively separated from crewmember. Parachute pack is opened by cartridge-actuated opener and parachute deployment commences.
T= + 2.5 - 4.0 sec. Parachute fully inflated.
The rocket motor has proven to be the only stored energy source which can provide the needed force versus time output consistent with both the human physiological limitations and the necessity to decrease escape system total functioning time to the absolute minimum.
Since the human physiological limits are not likely to change as rapidly as the performance envelope of the next generation of combat aircraft, it seems likely that the rocket motor will continue to be a key part of future escape systems.
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