- Howard TangLv 61 decade agoFavorite Answer
KLM Fokker 70 with reverse thrust applied. The two surfaces behind the engine can be seen in the deployed position, diverting the engine exhaust gases forward
Thrust reverser on a Turbo-Union RB199 jet engine
Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's output so that the thrust produced is directed forward, rather than aft. This acts against the forward travel of the aircraft, providing deceleration. Thrust reversers are used by many jet aircraft to help slow down just after touch-down, reducing wear on the brakes and enabling shorter landing distances. It is also available on many propeller aircraft through reversing the controllable pitch propellers to a negative angle.
Reverse thrust is typically applied immediately after touchdown, often along with spoilers, to improve deceleration early in the landing roll when residual aerodynamic lift and high speed limit the effectiveness of the friction brakes located on the landing gear. Reverse thrust is always selected manually, either using levers attached to the thrust levers, or by moving the thrust levers into a reverse thrust 'gate'. When thrust is reversed, passengers will hear a sudden increase in engine noise, particularly those seated just forward of the engines.
The early deceleration reverse thrust provides, can reduce landing roll by a third or more. Regulations dictate, however, that a plane must be able to land on a runway without the use of thrust reversers in order to be certified to land there as part of scheduled airline service.
Once the aircraft's speed has slowed, thrust reverse is deselected to prevent the reversed airflow from raising debris in front of the engine intakes where it can be ingested, causing foreign object damage. Thrust reverse is effective at any speed, and, in unusual circumstances, can be used all the way to a stop, or even to provide thrust to push the aircraft backward, though aircraft tugs or towbars are more commonly used for that purpose.
If the full power of reverse thrust is not desirable, thrust reverse can be operated with the throttles set at less than full power, even down to idle power, which reduces stress and wear on engine components. Reverse thrust is sometimes selected on idling engines to eliminate residual thrust, particularly in icy or slippery conditions, or where the engines' blast could do damage.
- 1 decade ago