Ailerons and spoilers1 have a considerable amount in common; both are wing-mounted panels, hinged at their leading edges, that move up and/or down to alter the aircraft’s aerodynamic characteristics.
- Ailerons are mounted on the wing’s trailing edge, are useful only during flight, and move up on one side and down on the other to increase the lift of one wing, decrease it on the other, and roll the aircraft to one side.
- Spoilerons (also known as “roll spoilers”) are mounted on the wing’s upper surface, are useful only during flight, and move up on one side to decrease the lift and increase the drag of that wing, rolling and yawing the aircraft towards that side. They are more useful than ailerons at low speed, as (unlike ailerons) they do not increase the angle of attack of any part of either wing, create proverse rather than adverse yaw, and, thus, are immune to the crossover-airspeed phenomenon inherent to ailerons.2
- Lift/drag spoilers move up symmetrically to decrease the lift and increase the drag of both wings simultaneously, either in flight (when they are called “flight spoilers”; this enables the aircraft to descend more quickly, or to use a higher power setting on approach,3 without excessively increasing its speed) or on the ground (in which case they are known as “ground spoilers”; this enables the aircraft to slow down more quickly during a landing or rejected takeoff, both by increasing the aircraft’s drag and by dropping its weight onto the wheelbrake-equipped main landing gear); they can be (and almost always are) combined with spoilerons, to provide a single spoiler system with both spoileron and flight/ground spoiler functions.
As ailerons are useful only during flight (since an aircraft generally can’t roll left or right on the ground,4 due to said ground being in the way), the aileron panels on most aircraft don’t do much of anything useful on the ground. It isn’t too hard to visualise a system in which the ailerons, when on the ground, deflect upwards to decrease lift and increase drag, acting as additional ground spoilers, but I’ve no idea what these combined ailerons/ground spoilers would be called; “spoileron”, as noted above, is already taken by a different type of system (one using asymmetrical spoiler deflection in flight to roll and yaw the aircraft).
What would be the term used for a control surface that functions as an aileron in flight, and as a ground spoiler on the ground?
1: (and flaps)
2: Additional advantages of spoilerons over ailerons are that, being located on the wing’s upper surface rather than at the trailing edge, they do not interfere with flap placement, and are much less prone to causing the wings to twist when deflected; as a result, some aircraft use only spoilerons (and no ailerons), either to allow flaps to be placed along the full span of the wings (thus reducing takeoff and landing distances and speeds) or to allow the use of thin, flexible wings at high speeds without encountering wing-twist-induced control reversal. Disadvantages of spoilerons are their lower maximum control authority at intermediate speeds and their greater total drag penalty.
3: A higher approach power setting makes go-arounds safer by reducing the time needed for the engines to spool up to full power; this is especially important for jets, as jet engines are slow to accelerate, and accelerate ever more slowly from lower and lower initial power settings.
4: Barring a collapse of one or more of the main landing gear, which is not generally a planned, or desired, occurrence.
