Elevator (aeronautics)

Elevators' effect on pitch

Elevator and pitch trim tab of a light aircraft

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, sometimes located at front (early airplanes) or integrated into a rear "all-moving tailplane" also called a slab elevator or stabilator.

Elevators' effect

The horizontal stabilizer usually creates a downward force which balances the nose down moment created by the wing lift force, which typically applies at a point (the wing center of lift) situated aft of the airplane's center of gravity. The effects of drag and engine thrust may also result in pitch moments that need to be compensated with the horizontal stabilizer.

Both the horizontal stabilizer and the elevator contribute to pitch stability, but only the elevators provide pitch control.^[1] They do so by decreasing or increasing the downward force created by the stabilizer :

• an increased downward force, produced by up elevator, forces the tail down and the nose up. At constant speed, the increased wing angle of attack causes a greater lift to be produced by the wing, accelerating the aircraft upwards. The drag and power demand also increase;
• a decreased downward force at the tail, produced by down elevator, allows the tail to rise and the nose to sink. At constant speed, the decrease in angle of attack reduces the lift, accelerating the aircraft downwards.

On many low-speed aircraft, a trim tab is present at the rear of the elevator, which the pilot can adjust to eliminate forces on the control column at the desired attitude and airspeed.^[2] Supersonic aircraft have all-moving tailplanes (stabilators), because shock waves generated on the horizontal stabilizer greatly reduced the effectiveness of hinged elevators. Delta winged aircraft combine ailerons and elevators –and their respective control inputs– into one control surface called elevon.

Elevators' location

Elevators are usually part of the tail, at the rear of an aircraft. In some aircraft, pitch-control surfaces are in the front, ahead of the wing ; in a two-surface aircraft, this type of configuration is called a canard (the French word for duck) or a tandem wing. The Wright Brothers' early aircraft were of canard type ; Mignet Pou-du-Ciel and Rutan Quickie are of tandem type. Some early three surface aircraft had front elevators (Curtiss/AEA June Bug) ; modern three surface aircraft may have both front (canard) and rear elevators (Grumman X-29).

Research

Several technology research and development efforts exist to integrate the functions of aircraft flight control systems such as ailerons, elevators, elevons, flaps and flaperons 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. These may be used in many unmanned aerial vehicles (UAVs) and 6th 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.^[3][4][5]

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.^[6][7][8] In this use, fluidics promises lower mass, costs (up to 50% less), and very low inertia and response times, and simplicity.

Gallery

• 

  A drooped elevator, nearly touching the grass, on the horizontal stabilizer of this Currie Wot biplane .

• 

  The tail of an Airbus A380, showing the elevators at the rear of the horizontal stabilizer

• 

  Pre-installed elevators for a small Airbus. The elevator is the silver surface on the right hand side of the picture, immediately below the red pipes on the factory wall

See also

• Rudder
• Aileron

References

1. Phillips, Warren F. (2010). Mechanics of Flight (2nd ed.). Hoboken, New Jersey: Wiley & Sons. p. 385. ISBN 978-0-470-53975-0.
2. "3 - Basic Flight Maneuvers". Airplane Flying Handbook. U.S. Government Printing Office, Washington D.C.: U.S. Federal Aviation Administration. 2004. FAA-8083-3A.
3. Scott, William B. (27 November 2006), "Morphing Wings", Aviation Week & Space Technology
4. "FlexSys Inc.: Aerospace". Retrieved 26 April 2011.
5. Kota, Sridhar; Osborn, Russell; Ervin, Gregory; Maric, Dragan; Flick, Peter; Paul, Donald. "Mission Adaptive Compliant Wing – Design, Fabrication and Flight Test" (PDF). Ann Arbor, MI; Dayton, OH, U.S.A.: FlexSys Inc., Air Force Research Laboratory. Retrieved 26 April 2011.
6. P John (2010). "The flapless air vehicle integrated industrial research (FLAVIIR) programme in aeronautical engineering". Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering (London: Mechanical Engineering Publications) 224 (4): 355–363. doi:10.1243/09544100JAERO580. ISSN 0954-4100.
7. "Showcase UAV Demonstrates Flapless Flight". BAE Systems. 2010. Retrieved 2010-12-22.
8. "Demon UAV jets into history by flying without flaps". Metro.co.uk (London: Associated Newspapers Limited). 28 September 2010.

External links

• Aircraft Pitch Motion (elevator function explanation, NASA website)