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An elevon is a combination pitch and roll aircraft control surface in delta wing aircraft with no horizontal stabilizers and elevators. An elevon supplies roll inputs by moving the controls on either side of the aircraft the same distance in opposite directions. Pitch control is achieved by equally moving both elevons either up or down. Combined pitch and roll control is achieved by moving both elevons either up or down to pitch the aircraft; one control is extended further than the other to induce roll. Pilot controls in elevon equipped aircraft remain the same as conventional aircraft with the combination inputs facilitated by sophisticated flight control systems.
Conventional aircraft designs feature an empennage or tail section consisting of a vertical stabilizer and two smaller, wing-like horizontal stabilizers. Mounted on the horizontal stabilizers are a set of movable control surfaces known as elevators which control the pitch or nose up and down attitude of the aircraft. These pitch controls make the aircraft descend or climb. Mounted on the ends of the wings are a similar set of controls known as ailerons which, when moved in opposite directions, roll the aircraft around its axis. Many aircraft such as delta or flying wing designs lack horizontal stabilizers or elevators and an alternate method of pitch control has to be used.
The answer to this dilemma is additional aileron functionality to induce both rolling and pitch motion. This combined function control surface is known as an elevon. Generally ailerons only move in opposite directions in equal increments. In elevon designs, they can also move in the same direction and to differing degrees. The result of this additional range of movement is a multipurpose control surface that can both roll the aircraft and cause it to climb or descend.
The theory and operation of the elevon is fairly simple and capable of producing very accurate flight control. When the elevons are moved equally in opposite directions as conventional ailerons, the air traveling over and under the wing will push one wing down and the other up, thus causing the aircraft to roll about its axis. If they are both moved up or down equally, the air moving either over or under the wing will cause the aircraft's nose to rise or dip to climb or descend. Combinations of roll and pitch are a little more complex and require compound movement. Both elevons move either up or down to induce pitch motion with one control extended further than the other to induce rolling motion.
This departure from control surface norms does not affect the way the pilot controls the aircraft. Inputs are still achieved using familiar control column or side stick controls; the unique elevon combination movements are controlled by the aircraft's flight control systems. The elevon system is typically employed in high performance, delta wing military aircraft such as the F-117 Nighthawk and F-102 Delta Dagger. Delta wing civilian aircraft utilizing elevons are not as common, the best known example being the Concord.
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