Tailless aircraft

A tailless aircraft (often tail-less) traditionally has all its horizontal control surfaces on its main wing surface. It has no horizontal stabilizer - either tailplane or canard foreplane (nor does it have a second wing in tandem arrangement). A 'tailless' type usually still has a vertical stabilising fin (vertical stabilizer) and control surface (rudder). However, NASA has recently adopted the 'tailless' description for the novel [http://www.nasa.gov/centers/dryden/news/FactSheets/FS-065-DFRC.html X-36 research aircraft] which has a canard foreplane but no vertical fin.

The most successful tailless configuration has been the tailless delta, especially for combat aircraft.

Flying wings

Flying wings are tailless designs which also lack a distinct "fuselage", having the pilot, engines, etc. located directly in or on the wing.

Aerodynamics

Longitudinal stability

A tailless aeroplane has no separate horizontal stabiliser, either behind (Tailplane) or in front of (canard foreplane) the main lifting surface. Because of this the aerodynamic center of an ordinary wing would lie ahead of the aircraft's center of gravity, creating instability in pitch. Some other method must be used to move the aerodynamic center backward and make the aircraft stable. There are two main ways for the designer to achieve this:

*Sweep the wing leading edge back, either as a swept wing or delta wing, and reduce the angle of incidence of the outer wing section so that it acts rather like a conventional tailplane stabiliser. If this is done progressively along the span of the outer section, it is called tip washout. The outer section of the wing now acts as a conventional tailplane, and in level flight the aircraft should be trimmed so that the tips do not contribute any lift: they may even need to provide a small downthrust. This reduces the overall efficiency of the wing, but for many designs - especially for high speeds - this is outweighed by the reductions in drag, weight and cost over a conventional stabiliser. This method was developed by the English aeronaut J. W. Dunne in the early 20th century, but did not gain widespread use until the jet age. Since Dunne, this approach has been augmented by the use of low or null pitching moment airfoils, seen for example in the Horten series of sailplanes and fighters.

*Use a wing aerofoil section with reflex or reverse camber. With reflex camber the flatter side of the wing is on top, and the strongly curved side is on the bottom, so the front section presents a high angle of attack while the back section is more or less horizontal and contributes no lift, so acting like a tailplane or the washed-out tips of a swept wing. Reflex camber can be simulated by fitting large elevators to a conventional airfoil and trimming them noticeably upwards; the center of gravity must also be moved forward of the usual position. Due to the Bernoulli effect, reflex camber tends to create a small downthrust, so the angle of attack of the wing is increased to compensate. This in turn creates additional drag. This method allows a wider choice of wing planform than sweepback and washout, and designs have included circular (Arup) and straight wings. But the drag inherent in a high angle of attack is generally regarded as making the concept inefficient, and only a few types, such as the Fauvel and Marske Aircraft series of sailplanes, use it.

An alternative approach is to locate the main weight of the aircraft a significant distance below the wing center, so that gravity will tend to maintain the aircraft in a horizontal attitude and so counteract any aerodynamic instability. In practice this is not sufficient to provide stability on its own, and typically is augmented by sweepback and washout as described. A classic example is the Rogallo wing hang glider.

There is a trade-off between stability and maneuverability. A high level of maneuverability requires a low level of stability. Some modern hi-tech combat aircraft are aerodynamically unstable in pitch and rely on fly-by-wire computer control to provide stability. The Northrop B-2 "Spirit" flying wing is an example.

Pitch control

Many early designs failed to provide effective pitch control to compensate for the missing stabiliser. As a result, these aircraft could pitch up or down sharply and uncontrollably if they were not carefully handled. These gave tailless designs a reputation for instability. The original Dunne biplanes and the later success of the tailless delta configuration show that the problem was due as much to inadequate design, as to to any problem inherent in the tailless configuration.

The solution usually adopted is to provide large elevator and/or elevon (combined elevator and aileron) surfaces on the wing trailing edge. These must generate large control forces, as their distance from the aerodynamic center is small. Consequently, when maneuvring, a tailless type may suffer higher drag than the conventional equivalent, even though it has less drag in level flight. High maneuvrability demands high control moments (force times "lever arm" distance), and the short lever arm inherent in tailless types means they are not as manoeuvrable as their conventional equivalents.

Notable examples

The examples given here are in historical order.

J. W. Dunne

During and shortly after the First World War, the English engineer J. W. Dunne developed a series of tailless aircraft characterised by having swept wings. In his book "An Experiment with Time" he claims that one of these was the first aeroplane ever to achieve natural stability in flight. Certainly, Dunne designed the first practical tailless aeroplanes. Few records of these aircraft remain.

Most of Dunne's designs were biplanes, typically featuring a fuselage nacelle between the planes, with rear-mounted 'pusher' propeller, and twin rudders between each pair of wing tips.

The D.6 monoplane of 1910 was a pusher type high-wing monoplane which featured turned-down wingtips with pronounced wash-out.

Many of Dunne's ideas on stability remain valid, and he is known to have influenced later designers such as John K. Northrop (father of the B-2 spirit stealth bomber).

Lippisch deltas

The German designer Alexander Lippisch produced the first tailless delta design, the Delta I, in 1931. He went on to build a series of ever-more sophisticated designs, and after the Second World War went to America to continue his work.

Messerschmitt Me 163 "Komet"

During the Second World War, Lippisch worked for the German designer Willy Messerschmitt on the first tailless aircraft to go into production, the Me 163 "Komet". It was a rocket-powered interceptor, and was the fastest aircraft to reach operational service during the war. Its rocket propulsion system was highly unsafe, especially the early versions. Landing was hazardous not only because the Komet had no wheels, but because sparks from the metal landing skid often flew up and ignited fuel vapours escaping from the propulsion system. More pilots were killed in takeoff and landing incidents than in combat.

De Havilland DH 108 "Swallow"

In the 1940s, the English designer Geoffrey de Havilland made a few examples of a tailless jet-powered research aircraft called the DH108 "Swallow", based on the forward fuselage of the de Havilland Vampire jet fighter. One of these was the first aircraft ever to break the sound barrier - it did so during a shallow dive, and the sonic boom was heard by several witnesses.

Dassault "Mirage"

The French Mirage series of supersonic jet fighters were an example of the tailless delta configuration, and became one of the most widely produced of all Western jet aircraft. By contrast the Soviet Union's equivalent widely produced delta-winged fighter, the Mikoyan-Gurevich MiG-21, does have a tail stabiliser.

Convair F2Y "Sea Dart"

In the 1950s, the Convair F2Y Sea Dart prototype became the only seaplane ever to exceed the speed of sound. Convair built several other successful tailless delta types.

upersonic airliners

The Anglo-French Concorde SST and its Soviet counterpart the Tupolev Tu-144 were tailless supersonic jet airliners, with gracefully curved "ogival delta" wings. The grace and beauty of these aircraft in flight were often remarked upon.

Lockheed SR-71 "Blackbird"

The American Lockheed SR-71 Blackbird reconnaissance aircraft was the fastest known operational aircraft, achieving speeds above Mach 3.

Northrop B-2 "Spirit"

The most recent tailless type to see operational service is the Northrop B-2 Spirit flying wing. It is unstable in flight and has artificial stability provided by a fly-by-wire system.

Other tailless aircraft

*Avro CF-105 Arrow
*Avro 707
*Avro Vulcan
*Boulton Paul P.111
*Convair B-58 Hustler
*Convair F-102
*Convair F-106
*Dassault Mirage III
*Douglas F-4D Skyray
*General Dynamics F-16XL
*HAL Tejas
*Handley Page Manx
*Pterodactyl Pfledge — ultralight aircraft produced in large numbers
*Vought F-7 Cutlass
*Westland-Hill Pterodactyl
*X-44 MANTA

See also

*Movement of center of pressure
*Longitudinal static stability
*Neutral point

External links

* [http://www.desktopaero.com/appliedaero/configuration/tailless.html Tailless Aircraft] - discussion of design and stability.