Spoiler (aeronautics)

Spoiler (aeronautics)

In aeronautics, a spoiler (sometimes called a lift dumper) is a device intended to reduce lift in an aircraft. Spoilers are plates on the top surface of a wing which can be extended upward into the airflow and spoil it. By doing so, the spoiler creates a carefully controlled stall over the portion of the wing behind it, greatly reducing the lift of that wing section. Spoilers differ from airbrakes in that airbrakes are designed to increase drag making little change to lift, while spoilers reduce lift as well as increasing drag.

Spoilers fall into two categories: relatively small spoilers that are deployed at controlled angles during flight to increase descent rate, and much larger spoilers that are fully deployed immediately on landing to greatly reduce lift ("lift dumpers") and increase drag.

Spoilers are used by nearly every glider (sailplane) to control their rate of descent and thus achieve a controlled landing at a desired spot. An increased rate of descent could also be achieved by lowering the nose of an aircraft, but this would result in an excessive landing speed. Spoilers enable the approach to be made at a safe speed for landing.

Airliners are almost always fitted with spoilers. Spoilers are used to assist descent to lower altitudes without picking up speed. Their use is often limited, however, as turbulent airflow which develops behind them causes noticeable noise and vibration, which may cause discomfort to passengers. Spoilers may also be differentially operated to provide roll control. Martin Aircraft was the first to develop spoilers to help with roll control in 1948. On landing, however, the spoilers are nearly always used at full effect to assist in slowing the aircraft. The increase in form drag created by the spoilers directly assists the braking effect. However, the real gain comes as the spoilers cause a dramatic loss of lift and hence the weight of the aircraft is transferred from the wings to the undercarriage, allowing the wheels to be mechanically braked with much less chance of skidding. Reverse thrust is also often further used to help slow the aircraft on landing.

In air-cooled piston engine aircraft, spoilers may be needed to avoid shock cooling the engines. In a descent without spoilers, air speed is increased and the engine will be at low power, producing less heat than normal. The engine may cool too rapidly, resulting in stuck valves, cracked cylinders or other problems. Spoilers alleviate the situation by allowing the aircraft to descend at a desired rate while letting the engine run at a power setting that keeps it from cooling too quickly. (This is particularly true for turbocharged piston engines, which generate higher temperatures than normally aspirated engines.)