Inaeronautics, aspoiler (sometimes called alift spoiler orlift dumper) is a device which increases thedrag and decreases thelift of anairfoil in a controlled way. Most often, spoilers are hinged plates on the top surface of a wing that can be extended upward into the airflow tospoil the streamline flow. By so doing, the spoiler creates a controlledstall over the portion of the wing behind it, greatly reducing the lift of that wing section.
Spoilers differ fromairbrakes in that airbrakes are designed to increase drag without disrupting the lift distribution across the wing span, while spoilers disrupt the lift distribution as well as increasing drag. However, flight spoilers are routinely referred to as "speed brakes" on transport aircraft by pilots and manufacturers, despite significantly reducing lift.[1]
Spoilers fall into two categories: those that are deployed at controlled angles during flight to increase descent rate ("flight spoilers") or control roll ("spoilerons"), and those that are fully deployed immediately on landing to greatly reduce lift and increase drag ("ground spoilers"). In modern fly-by-wire aircraft, the same set of control surfaces can serve both functions ("multifunction spoilers").
Spoilers were used by mostgliders (sailplanes) until the 1960s to control their rate of descent and thus achieve a controlled landing. Since then, spoilers on gliders have almost entirely been replaced by airbrakes, usually of theSchempp-Hirth type. Spoilers and airbrakes enable the glide angle to be altered during the approach while leaving the speed unchanged.
Airliners are commonly fitted with spoilers. Spoilers are used to increase descent rate without increasing speed. Spoilers may also be differentially operated for roll control as spoilerons in place ofailerons; Martin Aircraft was the first company to develop such spoilers in 1948.[2] Onlanding the spoilers are usually fully deployed to help slow the aircraft: the increase inform drag created by the spoilers provides a braking effect. The spoilers also cause a significant loss of lift so that there is more weight acting on the landing gear, allowing more braking to be used without skidding.
In air-cooledpiston engine aircraft, spoilers may be needed to avoidshock 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 (especially true forturbocharged piston engines, which generate higher temperatures thannormally aspirated engines).
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 ofailerons for roll control, primarily to reduceadverse yaw when rudder input is limited by higher speeds. For such spoilers the termspoileron 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. Eliminating dedicated ailerons also avoids the problem ofcontrol reversal and allowsflaps to occupy a greater portion of the wing trailing edge.
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 theDouglas 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). TheLockheed Tristar was fitted with a system calledDirect Lift Control that used the spoilers on landing approach to control descent.
Airbus aircraft withfly-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.
Ground spoilers, sometimes called lift dumpers informally, are a special type of spoiler designed to reduce wing lift on landing, differentiated from flight spoilers by having only two positions: deployed and retracted. The spoilers have three main functions: increasing the weight acting thelanding gear for maximum braking effect, increasingform drag, and preventing aircraft "bounce" on landing.[3]
Ground spoilers usually deploy automatically on touch down, with the flight spoilers also raised to increase the effect.
Virtually all modern jet aircraft are fitted with ground spoilers. TheBritish Aerospace 146 is fitted with particularly wide-span spoilers to generate additional drag and makereverse thrust unnecessary.
A number of accidents have been caused either by inadvertently deploying ground spoilers on landing approach, or forgetting to set them to "automatic".
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