Thrust reversing

In the aeronautical field, the reverse or thrust reversing is a device making it possible to direct towards before the push exerted by an engine with Hélice or reaction with an aim of slowing down the plane and of reducing the distances at the time of the Atterrissage.

The thrust reversing is especially used on the civil aircrafts, or the military aircrafts which of it are derived (transport aircraft, supply craft, etc…), but it also equips some fighters like the Tornado or SAAB 37 Viggen.

Although it is assembled on the majority of the civil aircrafts equipped with engines, this equipment is however not obligatory on this type of plane. Moreover, the certification of an apparatus is done without the use of the reversers.

Principle

On a propeller engine, one reverses the Pas Pale S so as to direct forwards the breath created by their rotation.

On a reaction engine, variable components are moved in order to seal the conduit more or less completely, which deviates forwards the flow of hot gases of the turbine and cold gases of the blower on the engines with double flow.

Use

The commercial aircraft equipped with engines often have, because of their aerodynamic configuration optimized for their cruising speed (800 with 900 km/h), a rather high speed of landing (about 250 km/h). With other devices like the air-brakes, the additional braking brought by the thrust reverser makes it possible not too much not to request the brakes of the wheels and to shorten the distance from rolling.

The procedure of braking then consists in, once the plane is on the ground, deploying the reversers, then to increase the mode of the engine after the touch of the wheels to recreate push (the idling engine being practically at the time of the phase of landing) which will be then directed forwards with an angle of 45° (to avoid the re-injection of combustion gases in the Turboréacteur) and will slow down the plane.

Safety devices prohibit the deployment of the reversers during the flight (the thrust reversers are spread only when the landing gear left and touches the ground). In spite of that, some accidents took place following an inopportune release of the reverse during takeoff or the flight, such as for example the crash landing of the flight 402 TAM which has occurred on October 31st, 1996. Other accidents were caused by a bad release of the reverse at the time of the landing. The investigation will say if the dysfunction of the one of the two thrust reversers played a part in the catastrophe of the Vol 3054 TAM which has occurred in July 2007.

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