The role of a thrust reverser when landing an airplane is to improve the braking capacity of an airplane by redirecting forward at least a portion of the thrust generated by the turbojet engine. In this phase, the reverser obstructs the gas exhaust nozzle and directs the exhaust flow from the engine toward the front of the nacelle, thus generating a counter-thrust that is added to the braking of the wheels of the airplane.
The means implemented to produce this reorientation of the flow vary according to the type of reverser. However, in all cases, the structure of a reverser comprises moving cowlings that can be moved between, on the one hand, a deployed position in which they open within the nacelle a passage intended for the deflected flow, and on the other hand, a retracted position in which they close this passage. These moving cowlings can also provide a deflection function or simply activate other deflection means.
In grid-type reversers, for example, the moving cowlings slide along rails so that when retracted in the opening phase, they uncover grids of deflection veins arranged in the thickness of the nacelle. A system of connecting rods links this moving cowling to locking doors that are deployed inside the exhaust duct and block the outlet in direct flow mode. In door-type reversers, on the other hand, each moving cowling pivots so as to block the flow and deflect it and is therefore active in this reorientation.
Generally, these moving cowlings are actuated by hydraulic or pneumatic actuating cylinders that require a network for transporting a fluid under pressure. This fluid under pressure is conventionally obtained either by tapping air from the turbojet engine in the case of a pneumatic system, or by sampling from the hydraulic circuit of the airplane. Such systems require significant maintenance because the slightest leak in the hydraulic or pneumatic network may be difficult to detect and risks having damaging consequences both on reversing and on other parts of the nacelle. Moreover, because of the reduced space available in the front frame of the reverser, the installation and protection of such a circuit are particularly difficult and bulky.
To overcome the various drawbacks associated with pneumatic and hydraulic systems, the manufacturers of thrust reversers have sought to replace them and equip their reversers as much as possible with electromechanical actuators that are lighter and more reliable. Such a reverser is described in the document EP 0 843 089.
By using such actuators, it is possible to produce a servocontrol of the deployment and closure movements of a reverser cowling on the basis of the position of the cowling in its travel between its open position and its closed position.
To this end, it is known to use absolute position sensors arranged on the cowlings and/or the actuators, but also speed sensors mounted on the axis of the electric motor of the actuator, as is the case in the document WO 2006/134253.
In such conditions, in case of failure of these sensors, the movement of the cowling can no longer be controlled.
It is also known, notably from the document WO 03/010430, that when an interruption occurs in the retraction or deployment, for example in the event of a temporary outage of the electrical power supply followed by a restart, the cowling of the thrust reverser automatically returns to its reference position corresponding to its retracted position. It is therefore not possible to know exactly the position of the cowling until it has reached its retracted position.