Spoiler Controls
Spoiler controls can be used for roll control (outboard or mid-span spoilers) or descent control (inboard spoilers).
Some aircraft use spoilers in combination with or in lieu of ailerons for roll control, primarily to reduce adverse yaw when rudder input is limited by higher speeds. For such spoilers the term spoileron has been coined. In the case of a spoileron, in order for it to be used as a control surface, it is raised on one wing only, thus decreasing lift and increasing drag, causing roll and yaw. Spoilerons also avoid the problem of control reversal that affects ailerons.
Almost all modern jet airliners are fitted with inboard lift spoilers which are used together during descent to increase the rate of descent and control speed. Some aircraft use lift spoilers on landing approach to control descent without changing the aircraft's attitude.
One jet airliner not fitted with lift spoilers was the Douglas DC-8 which used reverse thrust in flight on the two inboard engines to control descent speed (however the aircraft was fitted with lift dumpers). The Lockheed Tristar was fitted with a system called Direct Lift Control using the spoilers on landing approach to control descent.
Airbus aircraft with fly-by-wire control utilise wide span spoilers for descent control, spoilerons, gust alleviation, and lift dumpers. Especially on landing approach the full width of spoilers can be seen controlling the aircraft's descent rate and bank.
Read more about this topic: Spoiler (aeronautics)
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