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Convair F-102A Delta Dagger elevon.svg
US Air Force F-117 Nighthawk.jpg
Elevons at the wing trailing edge are used for pitch and roll control. Top: on the F-102A Delta Dagger of 1953, an early use. Bottom: on the F-117A Nighthawk of 1981.

Elevons or tailerons are aircraft control surfaces that combine the functions of the elevator (used for pitch control) and the aileron (used for roll control), hence the name. They are frequently used on tailless aircraft such as flying wings. An elevon that is not part of the main wing, but instead is a separate tail surface, is a stabilator (but stabilators are also used for pitch control only, with no roll function, as on the Piper Cherokee series of aircraft).


Elevons are installed on each side of the aircraft at the trailing edge of the wing. When moved in the same direction (up or down) they will cause a pitching force (nose up or nose down) to be applied to the airframe. When moved differentially, (one up, one down) they will cause a rolling force to be applied. These forces may be applied simultaneously by appropriate positioning of the elevons e.g. one wing's elevons completely down and the other wing's elevons partly down.

An aircraft with elevons is controlled as though the pilot still has separate aileron and elevator surfaces at their disposal, controlled by the yoke or stick. The inputs of the two controls are mixed either mechanically or electronically to provide the appropriate position for each elevon.


Operational aircraft

Avro Vulcan XH558 taking off at the 2008 Farnborough Airshow AvroVulcan2008.JPG
Avro Vulcan XH558 taking off at the 2008 Farnborough Airshow

One of the first operational aircraft to utilise elevons was the Avro Vulcan, a strategic bomber operated by the Royal Air Force's V-force. The original production variant of the Vulcan, designated as the B.1, did not have any elevons present; instead, it used an arrangement of four inboard elevators and four outboard ailerons along its delta wing for flight control. [1] The Vulcan received elevons on its extensively redesigned second variant, the B.2'; all of the elevators and ailerons were deleted in favour of eight elevons. [2] When flown at slow speeds, the elevons operated in close conjunction with the aircraft's six electrically-actuated three-position airbrakes. [3]

Another early aircraft to use elevons was the Convair F-102 Delta Dagger, an interceptor operated by the United States Air Force. [4] A few years after the F-102's introduction, Convair built the B-58 Hustler, an early supersonic bomber, which was also equipped with elevons. [5]

The first flight of Concorde 001 in 1969 02.03.69 1er vol de Concorde (1969) - 53Fi1931 - cropped.jpg
The first flight of Concorde 001 in 1969

Perhaps the most iconic aircraft fitted with elevons was the Aérospatiale/BAC Concorde, a British–French supersonic passenger airliner. In addition to the requirement to maintain precise directional control while flying at supersonic speeds, designers were also confronted by the need to appropriately address the substantial forces that were applied to the aircraft during banks and turns, which caused twisting and distortions of the aircraft's structure. The solution applied for both of these issues was via management of the elevons; specifically, as the aircraft speed varied, the active ratio between the inboard and outboard elevons was adjusted considerably. Only the innermost elevons, which are attached to the stiffest area of the wings, would be active while Concorde was flown at high speeds. [6]

The Space Shuttle Orbiter was furnished with elevons, although these were only operable during atmospheric flight, which would be encountered during the vehicle's controlled descent back to Earth. There were a total of four elevons affixed to the trailing edges of its delta wing. While flown outside of atmospheric flight, the Shuttle's attitude control was instead provided by the Reaction Control System (RCS), which consisted of 44 compact liquid-fueled rocket thrusters controlled via a sophisticated fly-by-wire flight control system. [7]

The Northrop Grumman B-2 Spirit, a large flying wing operated by the United States Air Force as a strategic stealth bomber, also used elevons in its control system. Northrop had opted to control the aircraft via a combination of split brake-rudders and differential thrust after assessing various different means of exercising directional control with minimal infringement on the aircraft's radar profile. [8] [9] Four pairs of control surfaces are positioned along the trailing edge of the wing's; while most surfaces are used throughout the aircraft's flight envelope, the inner elevons are normally only ever applied while being flown at slow speeds, such as on approach to landing. [10] To avoid potential contact damage during takeoff and to provide a nose-down pitching attitude, all of the elevons remain drooped during takeoff until a high enough airspeed has been attained. [10] The B-2's flight surfaces are automatically adjusted and repositioned without pilot input to do so, these changes being commanded by the aircraft's complex quadruplex computer-controlled fly-by-wire flight control system in order to counteract the inherent instability of the flying wing configuration. [11]

Research programmes

X-53 Active Aeroelastic Wing in flight X-53 Active Aeroelastic Wing NASA test aircraft EC03-0039-1.jpg
X-53 Active Aeroelastic Wing in flight

Several technology research and development efforts exist to integrate the functions of aircraft flight control systems such as ailerons, elevators, elevons and flaps into wings to perform the aerodynamic purpose with the advantages of less: mass, cost, drag, inertia (for faster, stronger control response), complexity (mechanically simpler, fewer moving parts or surfaces, less maintenance), and radar cross section for stealth. However, the main drawback is that when the elevons move up in unison to raise the pitch of the aircraft, generating additional lift, they reduce the camber, or downward curvature of the wing. Camber is desirable when generating high levels of lift, and so elevons reduce the maximum lift and efficiency of a wing. These may be used in many unmanned aerial vehicles (UAVs) and sixth generation fighter aircraft. Two promising approaches are flexible wings, and fluidics.

In flexible wings, much or all of a wing surface can change shape in flight to deflect air flow. The X-53 Active Aeroelastic Wing is a NASA effort. The Adaptive Compliant Wing is a military and commercial effort. [12] [13] [14]

In fluidics, forces in vehicles occur via circulation control, in which larger more complex mechanical parts are replaced by smaller simpler fluidic systems (slots which emit air flows) where larger forces in fluids are diverted by smaller jets or flows of fluid intermittently, to change the direction of vehicles. [15] [16] [17] In this use, fluidics promises lower mass, costs (up to 50% less), and very low inertia and response times, and simplicity.

See also

Related Research Articles

<span class="mw-page-title-main">Aileron</span> Aircraft control surface used to induce roll

An aileron is a hinged flight control surface usually forming part of the trailing edge of each wing of a fixed-wing aircraft. Ailerons are used in pairs to control the aircraft in roll, which normally results in a change in flight path due to the tilting of the lift vector. Movement around this axis is called 'rolling' or 'banking'.

<span class="mw-page-title-main">Delta wing</span> Triangle shaped aircraft wing configuration

A delta wing is a wing shaped in the form of a triangle. It is named for its similarity in shape to the Greek uppercase letter delta (Δ).

<span class="mw-page-title-main">Flying wing</span> Tailless fixed-wing aircraft that has no definite fuselage

A flying wing is a tailless fixed-wing aircraft that has no definite fuselage, with its crew, payload, fuel, and equipment housed inside the main wing structure. A flying wing may have various small protuberances such as pods, nacelles, blisters, booms, or vertical stabilizers.

<span class="mw-page-title-main">Stealth technology</span> Military technology to make personnel and material less visible

Stealth technology, also termed low observable technology, is a sub-discipline of military tactics and passive and active electronic countermeasures, which covers a range of methods used to make personnel, aircraft, ships, submarines, missiles, satellites, and ground vehicles less visible to radar, infrared, sonar and other detection methods. It corresponds to military camouflage for these parts of the electromagnetic spectrum.

<span class="mw-page-title-main">Flight control surfaces</span> Surface that allows a pilot to adjust and control an aircrafts flight attitude

Aircraft flight control surfaces are aerodynamic devices allowing a pilot to adjust and control the aircraft's flight attitude.

<span class="mw-page-title-main">Northrop X-4 Bantam</span> American experimental jet aircraft

The Northrop X-4 Bantam was a prototype small twinjet aircraft manufactured by Northrop Corporation in 1948. It had no horizontal tail surfaces, depending instead on combined elevator and aileron control surfaces for control in pitch and roll attitudes, almost exactly in the manner of the similar-format, rocket-powered Messerschmitt Me 163 of Nazi Germany's Luftwaffe. Some aerodynamicists had proposed that eliminating the horizontal tail would also do away with stability problems at fast speeds resulting from the interaction of supersonic shock waves from the wings and the horizontal stabilizers. The idea had merit, but the flight control systems of that time prevented the X-4 from achieving any success.

<span class="mw-page-title-main">Aircraft flight control system</span> How aircraft are controlled

A conventional fixed-wing aircraft flight control system (AFCS) consists of flight control surfaces, the respective cockpit controls, connecting linkages, and the necessary operating mechanisms to control an aircraft's direction in flight. Aircraft engine controls are also considered as flight controls as they change speed.

<span class="mw-page-title-main">Elevator (aeronautics)</span> Aircraft flight control surface

Elevators are flight control surfaces, usually at the rear of an aircraft, which control the aircraft's pitch, and therefore the angle of attack and the lift of the wing. The elevators are usually hinged to the tailplane or horizontal stabilizer. They may be the only pitch control surface present, and are sometimes located at the front of the aircraft or integrated into a rear "all-moving tailplane", also called a slab elevator or stabilator.

<span class="mw-page-title-main">Stabilator</span>

A stabilator is a fully movable aircraft horizontal stabilizer. It serves the usual functions of longitudinal stability, control and stick force requirements otherwise performed by the separate parts of a conventional horizontal stabilizer and elevator. Apart from reduced drag, particularly at high Mach numbers, it is a useful device for changing the aircraft balance within wide limits, and for reducing stick forces.

<span class="mw-page-title-main">Empennage</span> Tail section of an aircraft containing stabilizers

The empennage, also known as the tail or tail assembly, is a structure at the rear of an aircraft that provides stability during flight, in a way similar to the feathers on an arrow. The term derives from the French language verb empenner which means "to feather an arrow". Most aircraft feature an empennage incorporating vertical and horizontal stabilising surfaces which stabilise the flight dynamics of yaw and pitch, as well as housing control surfaces.

Aircraft flight mechanics are relevant to fixed wing and rotary wing (helicopters) aircraft. An aeroplane, is defined in ICAO Document 9110 as, "a power-driven heavier than air aircraft, deriving its lift chiefly from aerodynamic reactions on surface which remain fixed under given conditions of flight".

<span class="mw-page-title-main">Wing warping</span> Early system for lateral control of a fixed-wing aircraft

Wing warping was an early system for lateral (roll) control of a fixed-wing aircraft. The technique, used and patented by the Wright brothers, consisted of a system of pulleys and cables to twist the trailing edges of the wings in opposite directions. In many respects, this approach is similar to that used to trim the performance of a paper airplane by curling the paper at the back of its wings.

<span class="mw-page-title-main">Servo tab</span> Device on aircraft control surface

A servo tab is a small hinged device installed on an aircraft control surface to assist the movement of the control surfaces. Introduced by the German firm Flettner, servo tabs were formerly known as Flettner tabs. Servo tabs are not true servomechanisms, as they do not employ negative feedback to keep the control surfaces in a desired position; they only provide a mechanical advantage to the pilot.

<span class="mw-page-title-main">Flaperon</span> Type of aircraft control surface that combines the functions of both flaps and ailerons

A flaperon on an aircraft's wing is a type of control surface that combines the functions of both flaps and ailerons. Some smaller kitplanes have flaperons for reasons of simplicity of manufacture, while some large commercial aircraft such as the Boeing 747, 767, 777, and 787 may have a flaperon between the flaps and aileron. The 787 has a configuration known as a SpoileFlaperon that combines the action of spoilers, flaps and ailerons into one control surface.

<span class="mw-page-title-main">Stabilizer (aeronautics)</span> Aircraft component

An aircraft stabilizer is an aerodynamic surface, typically including one or more movable control surfaces, that provides longitudinal (pitch) and/or directional (yaw) stability and control. A stabilizer can feature a fixed or adjustable structure on which any movable control surfaces are hinged, or it can itself be a fully movable surface such as a stabilator. Depending on the context, "stabilizer" may sometimes describe only the front part of the overall surface.

In aeronautics, spoilerons are spoilers that can be used asymmetrically as flight control surfaces to provide roll control.

<span class="mw-page-title-main">Trailing edge</span> Rear edge of an aerodynamic surface

The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge meets. Essential flight control surfaces are attached here to control the direction of the departing air flow, and exert a controlling force on the aircraft. Such control surfaces include ailerons on the wings for roll control, elevators on the tailplane controlling pitch, and the rudder on the fin controlling yaw. Elevators and ailerons may be combined as elevons on tailless aircraft.

<span class="mw-page-title-main">Canard (aeronautics)</span> Aircraft configuration in which a small wing is placed in front of the main wing

In aeronautics, a canard is a wing configuration in which a small forewing or foreplane is placed forward of the main wing of a fixed-wing aircraft or a weapon. The term "canard" may be used to describe the aircraft itself, the wing configuration, or the foreplane. Canard wings are also extensively used in guided missiles and smart bombs.

<span class="mw-page-title-main">Tailless aircraft</span> Aircraft whose only horizontal aerodynamic surface is its main wing

In aeronautics, a tailless aircraft is an aircraft with no other horizontal aerodynamic surface besides its main wing. It may still have a fuselage, vertical tail fin, and/or vertical rudder.

Supermaneuverability is the capability of fighter aircraft to execute tactical maneuvers that are not possible with purely aerodynamic techniques. Such maneuvers can involve controlled side-slipping or angles of attack beyond maximum lift.



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