Spoiler (aeronautics)
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In aeronautics a spoiler (sometimes called a lift dumper) is a device intended to reduce lift in an aircraft. Commonly found in gliders, it is usually a plate which can be extended upward and/or downward from the wing, extending into the smooth airflow and spoiling it. Airliners too are usually fitted with extensive spoilers which are deployed on landing.
Spoilers are used by gliders in particular to control their rate of descent, and thus achieve a controlled landing at a desired spot. Spoilers are necessary because while an increased rate of descent can be achieved by angling the nose of an aircraft downwards, this may result in a significant increase in speed, possibly exceeding safe limits. Additionally, angling the nose downward may not result in an increase in descent angle.
Spoilers differ from airbrakes in that the latter are designed to increase drag while making little change to lift, spoilers greatly reduce lift while making little change to drag.
Often, both characteristics are desirable—most airliners for example feature combined spoiler and airbrake controls. On landing, the deployment of these spoilers causes 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. In addition, the form drag created by the spoilers directly assists the braking effect. Reverse thrust is also used to help slow the aircraft on landing.
Spoilers as control surfaces
Some aircraft use spoilers in combination with or in lieu of ailerons for roll control. The B-52 Stratofortress has no ailerons and achieves roll control entirely through spoilers. On the B-52 these spoilers are near the center of the wing in about the same place as most gliders. The Boeing 737 has fast-acting spoilers that assist the ailerons when the pilot commands a high roll rate. This can be readily seen when the pilot is fighting gusting crosswinds upon landing. The Wren 460 had no ailerons and instead had a series of spoilers on each wing. These spoilers twisted broadside to the wind to initiate roll control.de:Spoiler (Flugzeug) nl:Spoiler (luchtvaart)