Spoiler (aeronautics)

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A close look at the inner workings of spoilers in lift dump deployment during the landing of an Airbus A320.
A close look at the spoiler (the parts of the wing that are raised up) during the landing of an Airbus A321.
A view of the right wing of a Boeing 767-300ER during descent with spoilers partially deployed.
Spoilers deployed to slow down for descent on a Qantas Boeing 737-800.

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 that can be extended upward into the airflow to spoil it. By so doing, the spoiler creates a 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 without regard to affecting the lift, while spoilers reduce lift as well as increase drag.

Spoilers fall into two categories: those that are deployed at controlled angles during flight to increase descent rate or control roll, and those that are fully deployed immediately on landing to greatly reduce lift ("lift dumpers") and increase drag. In modern fly-by-wire aircraft, the same set of spoilers serve in both functions.

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 can 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 the turbulent airflow that develops behind them causes noise and vibration, which may cause discomfort to passengers. Spoilers may also be differentially operated for roll control instead of ailerons; Martin Aircraft was the first company to develop such spoilers in 1948.[1] On landing, however, the spoilers are nearly always used at full effect to help slow 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 less tendency to skid. (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 for turbocharged piston engines, which generate higher temperatures than normally aspirated engines.)

Spoiler controls[edit]

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.

Lift dumpers[edit]

Lift dumpers are a special type of spoiler extending along most of the wing's length and designed to dump as much lift as possible on landing. Lift dumpers have only two positions, deployed and retracted. Lift dumpers have one main function: putting the weight of the aircraft on the wheels for maximum braking efficiency.

Lift dumpers are almost always deployed automatically on touch down. The flight deck control has three positions: off, automatic ('armed'), and manual (rarely used). On landing approach 'automatic' is selected and at the moment of touchdown lift dumpers are deployed in a fraction of a second (flight spoilers will also be raised automatically).

Virtually all modern aircraft are fitted with lift dumpers.

A number of accidents have been caused either by inadvertently deploying lift dumpers on landing approach, or forgetting to set them to "automatic".

Incidents and accidents[edit]

  • American Airlines Flight 965 – Forgetting to deactivate the spoilers while climbing to avoid a mountain contributed to this crash on 20 December 1995.
  • TAM Brazilian Airlines Flight 3054 – This Airbus 320's pilots were aware of their deactivated starboard engine #2 thrust reverser,[3] 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; under one theory of the cause, they used an old procedure, which reduced the required runway length for landing but was superseded because it invited pilot error, which required them to leave the engine in idle rather than reverse thrust, and mistakenly left the engine at full power.[4] 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.[5]

See also[edit]

References[edit]

  1. ^ "Spoilers Aid Aileron Control." Popular Science, August 1948, p. 91.
  2. ^ "Accident report AAR-73-20". NTSB. 5 December 1973. Retrieved 2012-11-21. 
  3. ^ "Full cockpit-voice transcript of TAM A320 reveals clues to crash". flightglobal.com. Retrieved 2008-03-19. 
  4. ^ Final Report (PDF), Aeronautical Accidents Investigation and Prevention Center, October 27, 2009.
  5. ^ "Brazil pilots' last words aired". BBC. 1 August 2007. Retrieved 2008-03-19.