A spoileron is a control surface on an aircraft's wing that aids in turning, descent, and braking operations. These are typically sets of small flaps which sit flush along the upper surface of the wing when not operational and raise up into the flow of air over the wing when activated. This has the effect of destroying or “spoiling” a certain amount of the wing's lift potential. This effect provides a supplementary input to the primary roll control surfaces when turning the aircraft. The spoileron also increases descent rates and reduces lift potential on the runway when landing, thereby increasing braking potential.
More commonly known as spoilers, the spoileron is a wing mounted control surface found on all heavy commercial aircraft and many smaller aircraft. It typically consists of sets of hinged, oblong flaps situated towards the center of the upper wing surface. They are hinged in such a way that they lift towards the rear or trailing edge of the wing presenting an obstruction to the air flowing over the wing. Spoileron sets in heavy commercial aircraft may be manually deployed via a lever on the flight deck or automatically as part of the aircraft's banking or braking actions.
Level flight relies on a balanced relationship of lift on both wings which is a product of the relationship of air flowing over and under the wing. When banking or turning, one wing dips towards the inside of the turn radius and the outer wing lifts. The primary control surfaces responsible for this action are the ailerons situated on the trailing edge of the wings towards their ends. When banking, the inner wing aileron raises above the surface of the wing so that air traveling over the top can push against it and force the wing down. The outer wing aileron will move down so that air traveling under the wing can push against it and lift it.
Although this may seem to be an efficient way of getting the aircraft to roll, there is one problem with using ailerons alone. During the roll maneuver, both wings continue to produce almost equal amounts of lift so the wing being deflected down fights against the aileron input. To counteract this effect, the spoilers on the inside wing raise up at the same time. This has the effect of disturbing the flow of air over the top of the wing and reducing its lift potential. This makes it a lot easier for the aileron to deflect the inside wing down, improving the aircraft's roll response time, and placing less stress on the wing.
Spoilerons are also used when aircraft start to descend. An aircraft typically climbs or descends by using the elevator controls on the tail to pitch the nose up or down. Planes often have to descend fairly briskly to maintain their flight plan descent profiles. This normally requires a pronounced nose down attitude which would generally be upsetting to passengers. To expedite the descent, spoilers are deployed, usually manually from the flight deck, on both wings to knock some of the wings' lift potential off; this causes the aircraft to drop vertically as well as along its glide path. This also allows for descent rates of several thousand feet per minute with minimal nose down pitch; although it may induce some buffeting, it increases passenger comfort.
The last use of the spoileron is a braking aid when landing. This is typically an automated process initiated by the aircraft's auto flight system. As soon as the plane's main gear contacts the runway the spoilers deploy fully which kills the lift of the wings. This causes the aircraft to settle fully on the runway, thus allowing for maximum braking efficiency.