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 while making little change to lift, while spoilers greatly reduce lift while making only a moderate increase in drag.

Spoilers are used by gliders 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. However spoilers enable the approach to be made at a safe speed for landing.

Airliners too are usually fitted with spoilers. Spoilers are sometimes used when descending from cruise altitudes to assist the aircraft in descending 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 extra-sensitive passengers. The spoilers may also be differentially operated to provide roll control. 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 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 in turbocharged piston engines, which generate higher temperatures than normally aspirated engines.)

poilers as control surfaces

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, thus decreasing lift and increasing drag, causing roll and yaw.

poilers, general description

Spoilers increase drag and reduce lift on the wing. If raised on only one wing, they aid roll control, causing that wing to drop. If the spoilers raise symmetrically in flight, the aircraft can either be slowed in level flight or can descend rapidly without an increase in airspeed. When the spoilers rise on the ground at high speeds, they destroy the wing's lift, which puts more of the aircraft's weight on the wheels.

The flight spoilers are available both in flight and on the ground. However, the ground spoilers can only be raised when the weight of the aircraft is on the landing gear. When the spoilers deploy on the ground, they decrease lift and make the brakes more effective. In flight, a ground-sensing switch on the landing gear prevents deployment of the ground spoilers.

Incidents and accidents

* Air Canada Flight 621 - Premature deployment of the spoilers at low altitude contributed to this crash in Toronto on 5 July 1970.

*United Airlines Flight 553 - Forgetting to deactivate the spoilers contributed to this crash at Chicago Midway International Airport on 8 December 1972.

*American Airlines Flight 965 - Forgetting to deactivate the spoilers while climbing to avoid a mountain contributed to this crash on 20 December 1995.

*American Airlines Flight 1420 - Forgetting to deploy the spoilers contributed to this crash at Little Rock National Airport on 1 June 1999.

*TAM Brazilian Airlines Flight 3054 - This Airbus 320's pilots were aware of their deactivated starboard engine #2 thrust reverser, [citeweb|title=Full cockpit-voice transcript of TAM A320 reveals clues to crash|url=http://www.flightglobal.com/articles/2007/08/02/215869/full-cockpit-voice-transcript-of-tam-a320-reveals-clues-to-crash.html|publisher=flightglobal.com|accessdate=2008-03-19] and so apparently did not attempt to use it to brake when attempting to land at São Paulo's Congonhas Airport on 17 July 2007. The plane's spoilers may have been their only method of braking at speed. The plane slid off the runway, over a major highway, and ploughed into a warehouse, killing all 186 on board as well as several on the ground. It was Brazil's worst aviation disaster. [citeweb|title=Brazil pilots' last words aired|url=http://news.bbc.co.uk/2/hi/americas/6926679.stm|publisher=BBC|accessdate=2008-03-19]

References