Dedicated to all those who served with or supported the 456th Fighter Squadron or 456th Fighter Interceptor Squadron or the UNITED STATES AIR FORCE
In Memory of ROBERT 'BOB' JUSTUS, original creator of
Definitions and Use
Awing is a surface used to produce an aerodynamic force normal to the direction of motion by traveling in air or another gaseous medium. The first use of the word was for the foremost limbs of birds, but has been extended to include other animal limbs and man-made devices. 

The commonest use of wings is to flyby deflecting air downwards to produce lift, but wings are also commonly used as a way to produce down force and hold objects to the ground (for example racing cars) Artificial Wings

Terms used to describe aeroplane wings

  • Leading edge: the front edge of the wing
  • Trailing edge: the back edge of the wing
  • Span: distance from wing tip to wing tip
  • Chord: distance from wing leading edge to wing trailing edge, usually measured parallel to the long axis of the fuselage
  • Aspect ratio: ratio of span to standard mean chord
Design Features
Aeroplane wings may feature some of the following:
  • A rounded leading edge cross-section
  • A sharp trailing edge cross-section
  • Leading-edge devices such as slats or slots
  • Trailing-edge devices such as flaps
  • Ailerons (usually near the wingtips) to provide roll control
  • Spoilers on the upper surface to disrupt lift
Wing Types
  • Dihedral wings, which have an angle between them, have inherent stability in roll. As the aircraft rolls, one wing generates more lift, rolling the aircraft back into position.
  • Swept wings are good for fast aircraft. They present the wing at an angle to the airflow, so that the wing "sees" a slower airflow.
  • Elliptical wings are theoretically optimum for efficiency at subsonic speeds.
  • Delta wings: have reasonable performance at subsonic and supersonic speeds.
  • Wave-Riders: are efficient supersonic wings.
  • Rogallo wings are two hollow half-cones of fabric, one of the simplest wings to construct.
  • Swing-wings (or variable geometry wings) are able to move in flight to give the benefits of dihedral and delta wing. Although they were originally proposed for the un-built Boeing 2707, they are currently only found on some military fighter aircraft.

The Science of Wings
The amount of lift produced by a wing increases with the angle of attack (the angle between the onset flow and the chord line) but this relationship ends once the stall angle is reached. At this angle the airflow starts to separate from the upper surface, and any further increase in angle of attack gives no more lift (it may actually reduce) and gives a large increase in drag. Wing design is complicated and very tightly associated with the science of aerodynamics.
  • A helicopter uses a rotating wing with a variable pitch or angle to provide a directional force.
  • The space shuttle uses its wings only for lift during its descent.
Delta Wing
The delta-wing is a wing planform in the form of a large triangle. Its use was pioneered by Alexander Lippisch prior to WWII in Germany, but none of his designs entered service. After the war the delta became the favored design for high-speed use, and was used almost to exclusion of other planforms by Convair  [ The Consolidated Vultee Aircraft Corporation, universally known as Convair, was the result of a 1943 merger between Consolidated Aircraft and Vultee Aircraft, resulting in a leading aircraft manufacturer of the United States. In 1954, Convair merged with Electric Boat to form General Dynamics, and the aircraft operation became the Convair Division of the merged company. It produced aircraft until 1965 then shifted to space and airframe projects, continuing until 1996, when the division was entirely shut down. ]  in the United States and Dassault in France. In early use delta-winged aircraft were often found with no other horizontal control surfaces, creating a tailless design, but most modern versions use a canard [ In aeronautics, canard (French for duck is a type of fixed-wing aircraft in which the tailplane is ahead of the main lifting surfaces, rather than behind them as in conventional aircraft. The earliest models, were seen by observers to resemble a flying duck — hence the name.  The term canard has also come to mean the tail surface itself, when mounted in that configuration. ]  in front of the wing to modify the airflow over it, most notably during lower altitude flight.

The primary advantage of the design is that the wing's leading edge remains behind the shock wave generated by the nose of the aircraft when flying at supersonic speeds, which was a distinct improvement on traditional wing designs. Another advantage is that as the angle of attack increases the leading edge of the wing generates a huge vortex  [  vortex is a spinning turbulent flow which resembles a tornado. Or, maybe it is better to say that a tornado is a well known example of a large vortex. ]  which remains attached to the upper surface of the wing, making the delta have very high stall points. The combination of these two features is a dream come true, a normal wing built for high speed use is typically dangerous at low speeds, but in this regime the delta transitions to a mode of lift based on the vortex it generates.

Angle of Attack is a term used in aerodynamics to describe the angle between the wing's chord and the direction of the relative wing, effectively the direction in which the aircraft is currently moving. The amount of lift generated by a wing is directly related to the angle of attack, with greater angles generating more lift. This remains true up to the stall point, where lift starts to decrease again because of airflow separation. Planes flying at high angles of attack can suddenly enter a stall if, for example, a strong wind gust changes the direction of the relative wind, an effect that is seen primarily in low-speed aircraft.

In military terminology, angle of attack is often referred to as alpha (α), the symbol used to denote it on most diagrams. Using a variety of additional aerodynamic surfaces (a.k.a. high-lift devices) like leading edge extensions, fighter aircraft have increased the potential flyable alpha from about 20 degrees to over 45, and in some designs, 90 degrees or more. That is, the plane remains flyable when the wing's chord is at right angles to the direction of motion.

Lippisch studied a number of ramjet powered (sometimes coal-fueled!) delta-wing interceptor aircraft   [ An interceptor aircraft (or simply interceptor) is a type of  fight aircraft designed specifically to intercept and destroy enemy air craftt, particularly bombers. A number of such aircraft were built in the period starting just prior to World War II and ending in the late 1960's, when they became less important due to the shifting of the strategic bombing role to ICBMs. ] during the war, one progressing as far as a glider prototype. After the war Lippisch was taken to the United States, where he ended up working at Convair. Here the other engineers became very interested in his interceptor designs, and started work on a larger version known as the F-92. This project was eventually cancelled as impractical, but a prototype flying test bed was almost complete by that point, and was later flown widely as the XF-92. The design generated intense interest around the world. Soon almost every aircraft design, notably interceptors, were designed around a delta-wing.  Examples include the Convair F-102, F106 & B-58 Hustler, the Avro- Arrow and the MiG-21

Deltas fell out of favor due to some undesirable characteristics, notably flow-separation at high angles of attack (swept-wings have similar problems), and high drag at low altitudes. This limited them primarily to the high-speed, high-altitude interceptor roles. A modification, the compound delta, added another much more highly swept delta wing in front of the main one, to create the vortex in a more controlled fashion and thereby reduce the low-speed drag.

As the performance of jet engines grew, fighters with more traditional planforms found they could perform almost as well as the deltas, but do so while maneuvering much harder and at a wider range of altitudes. Today a remnant of the compound delta can be found on most fighter aircraft, in the form of leading edge extensions. These are effectively very small delta wings placed so they remain out of the airflow in cruising flight, but start to generate a vortex at high angles of attack. The vortex is then captured on the top of the wing to provide additional lift, thereby combining the delta's high-alpha "trick" with a conventional highly efficient wing planform.

Sometimes, a technology persists despite its problems and eventually is rescued by other technologies. The delta wing story provides an excellent example.

A delta wing is a wing whose shape when viewed from above looks like a triangle, often with its tip cut off. It sweeps sharply back from the fuselage with the angle between the leading edge (the front) of the wing often as high as 60 degrees and the angle between the fuselage and the trailing edge of the wing at around 90 degrees. Often delta-wing airplanes lack horizontal stabilizers. Despite the fact that paper airplanes have delta wings and appear to fly quite well when launched from a height, delta wings actually perform poorly at low speeds and often are unstable (i.e., they do not stay in level flight on their own). Their primary advantage is efficiency in high-speed flight.

The first patent for a delta-wing aircraft design was granted to Englishmen J.W. Butler and E. Edwards in 1867. Their aircraft design would have used a jet-propulsion system, with thrust provided by rockets, compressed air jets, steam, or gunpowder, had it ever flown. Like many advanced concepts, not until the combatants in World War II conducted actual wind tunnel tests did large numbers of aircraft designers start to take the delta wing seriously. Professor Alexander M. Lippisch of Germany, best known for developing the Messerschmitt Me 163 Komet rocket fighter, began thinking about supersonic airplanes during the 1940s. He chose the delta shape and constructed a wooden glider to be launched from high altitude by a transport plane. The Allies captured the unflown glider at the end of the war and sent it to the United States for study. Lippisch also came to the United States where he worked on supersonic flight for the U.S. Army Air Forces, the predecessor to the U.S. Air Force.

Soon after the end of the war, Convair, a U.S. manufacturer of bombers, began work on a supersonic interceptor aircraft with a delta wing. The company's engineers began testing models in wind tunnels before building a full-size aircraft. The XF-92A first flew from Muroc Air Base (later Edwards Air Force Base) in 1948. Its designers gave it an extremely large vertical tail, thought necessary because of fears that the large delta wing might block airflow to the tail and make the plane impossible to control. Flight tests with the XF-92 proved that a large tail was unnecessary.

By 1953, Convair's engineers had developed the YF-102 Delta Dagger, a radical design that lacked a horizontal tail and featured a large, sharply swept delta wing. Wind tunnel tests of small-scale models indicated that the aircraft could accelerate through Mach 1 (the speed of sound) with relative ease, rather than "punching" through it like earlier experimental planes that had to burn a lot of fuel to go faster than Mach 1. However, the first prototype unexpectedly encountered immense drag as it approached Mach 1. This so-called "transonic" region presented a major problem for the aircraft.
To overcome high drag loads at transonic speeds, Convair engineers redesigned the fuselage and wing. The fuselage design used the "area-rule" which resulted in the characteristic "coke bottle" shape.
Near the same time, Richard T. Whitcomb, an aeronautical scientist at the National Advisory Committee for Aeronautics (NACA), was studying transonic drag. Whitcomb developed what he called the "supersonic area rule." This theory stated that aircraft that would fly at supersonic speed should increase in cross-sectional area from a pointed nose. Anything that protruded into the air stream, such as the canopy over the cockpit, wings, or tail, should be accompanied by a reduction in cross-section elsewhere. In 1954, Whitcomb, who was then only 33-years old, was awarded the prestigious Collier Trophy for this contribution to aeronautics.

Convair's designers quickly applied the supersonic area rule to a new aircraft, the YF-102A, pinching the fuselage near its mid-point to give it a slightly hourglass (or Coke-bottle) appearance. This was a compromise for an existing aircraft; later airplanes included the area rule in their designs in much less obvious ways. When the first YF-102A with this new design took flight, it easily accelerated through Mach 1.

During the 1950s the delta wing was used on several aircraft that had a need for speed, including the B-58 Hustler and the cancelled XB-70 Valkyrie bomber. The Soviet Union used a delta wing for its failed Tu-144 supersonic passenger jet, and for its famed MiG-21, one of the most widely-used fighter jets of the Cold War. The French also adopted the delta for its successful Dassault Mirage III.

The two most famous current aircraft to use the delta wing are the Concorde and the Space Shuttle. The Concorde's delta wing made the plane's sustained cruising speed of Mach 2 possible. The Space Shuttle's wing, known as a "cranked delta" because the leading edge of the wing has a slight bend near its midpoint, is used for a different purpose. The Space Shuttle originally had what was known as a "high cross-range" requirement, which was the ability to glide for thousands of miles to either side of its flight path when landing. Conventional straight wings did not provide enough lift at high speeds and altitudes to achieve this type of range, and so the large delta wing was necessary.
The delta wings can easily be seen on this photograph of the Shuttle orbiter Columbia.
While delta wings are critical to achieving high lift for supersonic flight, they also have a number of disadvantages for less high-performing aircraft. They require high landing and takeoff speeds and long takeoff and landing runs, are unstable at high angles of attack, and produce tremendous drag when "trimmed" to keep the plane level. Of these disadvantages, pilots and designers usually consider the high landing and takeoff speeds the most important because they make flying the plane dangerous. Indeed, when the Concorde had its first ever crash in 2000, after two decades of safe operations, the high-speed takeoff was a factor in this terrible accident, for the plane's high ground speed before becoming airborne placed major stress upon the aircraft's tires, which exploded upon striking an object on the runway.

By the 1980s, except for the Concorde and Space Shuttle, the delta wing appeared headed for obsolescence. Its drawbacks made it unattractive and changes in fighter warfare reduced the requirement for sustained supersonic speed. Few aircraft spend much time traveling at high supersonic speeds because it burns so much fuel, rendering the delta wing, which is primarily useful for supersonic flight, less attractive. But the computer and an additional flight control device called the canard have rescued the delta wing from obsolescence.
Computer-controlled "fly-by-wire" flight control systems have allowed designers to compensate for some of the delta wing's poor control qualities. Canards are small horizontal fins (or small wings) mounted on the fuselage in front of an aircraft's main wings to provide greater control, particularly during high angles of attack. When they are part of a delta-wing aircraft, they improve its stability and maneuverability.

Several aircraft appeared in the 1980s and 1990s that incorporated both delta wings and canards. The latest delta-wing aircraft are the Swedish JAS 39 Grippen, the Dassault Rafale naval fighter (designed to be launched from the French aircraft carrier Charles de Gaulle), the Indian Light Combat Aircraft, or LCA, and the Eurofighter Typhoon. The Typhoon, which had its first flight in the mid-1990s, is a joint European effort (Britain, Germany, Italy and Spain, with France withdrawing early) to develop an advanced fighter to replace a number of different aging aircraft in their air forces. Thus, the delta wing, which seemed destined for obsolescence, has gained a new lease on life.

Certainly Concorde flies better than a lot of deltas, but one fact of life is that deltas come in on the back side of the drag curve, and you've got to remember it... B. Trubshaw, Director of Concorde Flight Test, 1969
Delta wings (Deltas) are symmetrical triangular wings designed to fly at subsonic or supersonic speeds. At supersonic speeds the leading-edge can be subsonic, sonic or supersonic, depending on the relation between sweep angle and speed (see below).

Leading edges are generally linear, although there are cases of more complex geometries, such as the ogive delta (Concorde SST), the gothic delta, the cranked delta (Lockheed CL-823), the double delta (SAAB Viggen), delta + canards (North American XB-70 and others).

Almost all delta wings fall into the category of low aspect-ratio wings. Their aspect-ratio is defined by AR = 4/tan(D), where D is the leading edge sweep angle (this lead to AR less than 3 in most cases; about 1.8 in the case of Concorde). Wing thickness is generally small.

The problem is to find the aerodynamic properties of the wing (CL, Cd, Cm, Cp distribution, etc.), along with the lateral and longitudinal stability characteristics of the wings at different operation points.

The technical literature on deltas is huge, and it is safe to say that all speeds and sweep angles have been investigated (experimental, theoretical and computational research).

Delta Wing in Subsonic Flow

Flows past delta wings are severely compounded by the leading edge separation, by the roll-up structure of the concentrated vortices, and by the lateral and longitudinal instability that is consequent to large sweeps, high-angle of attack, and sharp maneuvers.

Although the aerodynamics of the delta wing is non-linear, most of the research has relied for a long time on liberalized small perturbation theory (shortly reviewed below).

Computational methods (ex. vortex lattice methods, panel codes) have proved tremendously effective at low speeds and unsteady flows (Katz, 1984, among others).

Linearized Theory

Linearized theory for the slender body with small angle of attack (Munk, 1924; RT Jones, 1945) leads to a very simple conclusion: lift is produced in the conical flow created by the stream-wise variation of span b(x). There is one singularity at the apex of the delta, where the theoretical pressure would be infinite.

The expression for the lift coefficient is CL=2 , that is correct only for very low aspect-ratios (AR=1). The corresponding induced drag coefficient is   , that is just half the value that is expected at angle of attack . The center of pressure is found at 2/3 chord from the pointed leading-edge, where the pressure is also singular.

Fuselage Effects

The effect of a fuselage can also be estimated by a more general formulation (Ashley-Landhal, 1965) that gives a lift coefficient in the wing-body configuration is lower that the wing-alone.

Lifting surface theory (for ex., vortex lattice method) is a better approach to the prediction of the basic coefficients. There are also methods for arrowhead wings (Mangler, 1955) and wings in yawed flow (Carafoli, 1969).

Delta Wings in Supersonic Flow

Delta wings are appropriate plan forms to fly at supersonic and hypersonic speeds, therefore there has been a long time interest in investigating the effects of high Mach numbers.

The principle of independence (Buseman, 1935) allows to investigate separately wings with subsonic and supersonic leading edges (e.g. for which the normal Mach number is below or above the speed of sound).

Separation Characteristics

In general, wings with subsonic leading edges are characterized by leading edge separation; wings with supersonic leading edge are characterized a Prandtl-Meyer expansion.

The main parameters of the wing problem are sweep, free stream Mach number, angle of attack and wing thickness. The effects of all these parameters can be collapsed in one single plane alfan-Machn, where the occurrence of subsonic or supersonic flow can be diagnosed as function of the parameters (Stanbrook- Squire, 1964).

Delta Wing with Subsonic Leading-Edge

The wing is inside the Mach cone if the sweep angle is greater than the Mach angle, thus yielding leading-edges that are fully subsonic, Fig. 1. Linearized theory leads again to simplified expressions for the main aerodynamic characteristics, which are quite powerful to describe the operation of the wing.

The lift coefficient depends on the aspect-ratio, according to en expression that is fairly approximate for incidences less than 5 degrees (Ashley-Landhal, 1965). According to the theory, the strong leading edge suction gives rise to a leading edge thrust that decreases the amount of drag (in practice only a small amount of this suction can be realized.) 

Delta Wing with Supersonic Leading-Edge

Figure 1: Delta wing with subsonic leading-edge

Figure 2: Delta wing with supersonic leading-edge

The leading-edge is inside the Mach cone, by virtue of the comparatively larger sweep angle (Fig. 2). In such a case there is no interaction of flows between upper and lower surface.

The pressure jump at any given point on the wind surface has a definite expression, which is constant along lines through the wing vertex (conical flow). By integration of the pressure jump one finds that the lift coefficient is independent from the sweep angle, and the lift-curve slope is also independent from the angle of attack for as long as the leading edge is supersonic.

Carafoli (1969) report analytical studies of a wide array of delta wings, polygonal wings, and T-wings, also in yawed flow.

Flow Separation on Highly Swept Wings

Real cases of flow past slender delta wings (wings of small aspect-ratios) are almost certainly separated, and to a great extent. Separation starts from the leading-edge and produces a series of vertical regions that have a conical shape growing stream wise. The angle of attack at which these vortices appear depends on the slenderness.

Separation is at the leading-edge when the leading edge is sharp, and leads to performances largely independent from the Reynolds number. The presence of the leading-edge vortices is the cause of a number of phenomena:
  • The lift coefficient is larger than that predicted with linearized theory (see below). This is due to the suction effect of the separation vortices. The difference between the linear value of the lift and its actual value is called vortex lift.
  • The leading-edge vortices induce a field of low pressure on the suction side of the wing. The increased suction is a reason for increased lift (point above).
  • Stall occurs at a large angle of attack, because of the vortex instability, leading to vortex burst. When the vortex core bursts the suction effect disappears. A a vortex burst far behind the trailing edge, the burst has little or no effect; vortex burst on the wing itself will reduce the vortex lift.
  • The vortex pattern behind the delta wing depends on the slenderness, because slenderness, together with angle of attack, is what decides the vortex burst.
  • Vortex asymmetry appears on very slender wings at lower and lower angles of attack, because the vortex finds less physical limits for development, therefore becoming soon unstable.
Flow separation characteristics depend on speed (Mach number), wing sweep, angle of attack and wing thickness.

Wings with subsonic leading edge are dominated by leading edge separation. Secondary separation appears at moderate to high angles of attack, Fig. 3.

Wings with supersonic leading edges are characterized by a Prandtl-Meyer expansion behind the bow shock and by an attached leading edge flow Fig. 4.

Figure 3: Flow separation on delta wing with subsonic leading edge.
A = attachment; S = separation; V = vortex.

Figure 4: Flow separation on delta wing with supersonic leading edge.
SW = shock wave

Alexander Lippisch
Dr. Alexander M. Lippisch, Aviation Pioneer, 1894-1976
Dr. Alexander Martin Lippisch (November 2, 1894 - February 11, 1976) was a German pioneer of aerodynamics who made important contributions to the understanding of flying wings and ground effect craft. His most famous design was the Messerschmitt Me 163 rocket-powered interceptor.

Lippisch was born in Munich, Germany. He later recalled that his interest in aviation was first kindled by watching a demonstration by Orville Wright in September 1909 in Berlin. He was, however, planning to follow in his father’s footsteps and enter art school when World War I  intervened. During his service with the German Army from 1915 – 1918, Lippisch had the chance to fly as an aerial photographer and mapper.

Following the war, Lippisch worked for a while with the Zeppelin Company, and it was at this time that he first became interested in tail-less aircraft. In 1921 the first such design of his would reach fruition in the form of the Lippisch-Espenlaub E-2 glider, built by Gottlob Espenlaub. This was the beginning of a research program that would result in some fifty designs throughout the 1920s and 30s. Lippisch’s growing reputation saw him appointed the director of Rhon-Rossitten Gesellschaft (RRG), a glider research group.

Lippisch’s work led to a series of tail-less designs numbered Storch I – Storch IX between 1927 and 1933. These were greeted with almost complete indifference by both government and private industry. During this time, one of Lippisch’s designs, the Ente (Duck), would enter history as the first aircraft to fly under rocket power. It was a sign of things to come.

Experience with the Storch series led Lippisch to concentrate increasingly on delta-winged designs. These would find expression in five aircraft (simply numbered Delta I – Delta V) built between 1931 and 1939. In 1933, RGG had been reorganized into the Deutsche Forschungsanstalt für Segelflug (DFS - German Institute for Sailplane Flight) and the Delta IV and Delta V were designated as the DFS 39 and DFS 40 respectively.

In early 1939, the Reichsluftfahrtsministerium (RLM) – (Reich Aviation Ministry) transferred Lippisch and his team to work at the Messerschmitt factory to design a high-speed fighter aircraft around the rocket engines then under development by Hellmuth Walter. They quickly adapted their then-current design, the DFS 194 to rocket power, successfully flying in early 1940. This was the direct ancestor of the Messerschmitt Me 163 Komet.

Although technically brilliant, the Komet did not prove to be a successful weapon, and friction between Lippisch and Messerschmitt was frequent. In 1943, Lippisch transferred to Vienna’s Luftfahrtforschungsanstalt Wien (LFW), to concentrate on the problems of high-speed flight. That same year, he was awarded a doctoral degree in engineering by the University of Heidelberg.

Wind tunnel research in 1939 had suggested that the delta wing was a good choice for supersonic flight and Lippisch set to work designing a supersonic, ramjet-powered fighter, the Lippisch P-13. By the time the war ended, however, the project had only advanced as far as a development glider, the DM-1.

Like many German scientists, Lippisch was taken to the United states after the war under Project Paper Clip.

[Originally called Operation Overcast, Operation Paperclip was the code name for the operation by the government of the USA to extract rockets (e.g. V-1, V-2), chemical weapons (e.g. Zyklon-B) and medical scientists from Germany, after the collapse of the Nazi government during World War II.

Scientists were deployed at White Sands Proving Ground, New Mexico and Fort Bliss, Texas to work on guided missile and ballistic missile technology, and led to the foundation of NASA and the US ICBM program.

Over 700 members of the Nazi scientific community were brought to the US as a direct result of Operation Paperclip, many of whom were still ardent Nazi supporters

Although President Harry S. Truman gave explicit orders not to allow any scientists who were thought to have strong Nazi leanings to enter the US under Operation Paperclip, many dossiers were re-written to "clean-up" the histories of many of the scientists involved, to avoid their knowledge falling into the hands of another power.

Much of the information surrounding Operation Paperclip is still classified. ] Advances in jet engines were making his original interceptor designs more practical, and Convair became interested in a hybrid jet/rocket design that they proposed as the F-92. In order to gain experience with the delta wing, they first built a jet powered test aircraft, the 7003, which became the first powered delta-wing aircraft to fly. Although the USAF lost interest in the F-92, Convair's experience with the delta-wing design led them to proposing it for most of their projects through the 1950s and into the 1960s, including the F-102 Delta Dagger, F-106 Delta Dart and B-58 Hustler.

From 1950 - 1964 Lippisch worked for the Collins Radio Company in Iowa, which had an aeronautical division. It was during this time that his interest shifted toward ground effect craft. The results were an unconventional VTOL [Vertical Take-Off and Landing] describes airplanes that can lift off vertically. This classification includes only a very few aircraft; helicopters are not considered VTOL.

In 1928, Nikola Tesla received patents for an apparatus for aerial transportation. It is one of the earliest example of VTOL aircraft. In the late 1950's and early 1960's almost all fighter aircraft designed included some VTOL features. This was a response to the worrying possibility that a first-strike against airfields by nuclear armed bombers would leave a country open to attack by following bombers. The "solution" was to use VTOL fighters that could be moved to open fields around the countryside, making them immune to widespread destruction.

In reality the costs of VTOL performance were huge, and while it turned out to be fairly easy to move the plane, moving the support equipment and fuel was not so easy. By the mid-1960s interest in VTOL had faded, perhaps due much to the widespread introduction of ICBMs as the main nuclear delivery system.

Currently there are believed to be two types of practical VTOL aircraft in operation:
  • Bell Boeing V-22 Osprey "tilt-rotor" and the
  • British Aerospace Hawker Harrier "Jump jet" ]
aircraft (an aerodyne) and an aerofoil boat. Lippisch resigned from Collins because of ill health caused by cancer.

When he recovered in 1996, he formed his own research company, Lippisch Research Corporation, and attracted the interest of the West German government. Prototypes for both the aerodyne and the ground-effect craft were built, but no further development was undertaken. The Kiekhaefer Mercury company was also interested in his ground-effect craft and successfully tested one of his designs as the Aeroskimmer, but also eventually lost interest.

Lippisch died at Cedar Rapids, Iowa.