Civil Aircraft Thrust Reverser Application

TRs are not required by the regulatory authorities (i. e., FAA and CAA). The com­ponents are expensive, heavy, and only applied on the ground, yet their impact on an aircraft’s operation is significant due to additional safety through better control and reduced time for stopping, especially during aborted takeoffs and other related emergencies. Most airlines want their aircraft to have TRs even with the increased DOC.

Aircraft designers must ensure that TR efflux is well controlled – there should be no adverse impingement of on aircraft surface or reingestion in the engine. Fig­ure 10.26 shows a typical satisfactory TR efflux pattern.

In general, there are two types of TRs: (1) operating on both the fan and core flow, and (2) operating on the fan flow only. The choice depends on the BPR, nacelle location, and customer specifications.

The first type, which operates on the total flow (i. e., both fan and core), is shown at the top of Figure 10.27. There are two types: (1) the sliding-port aft-door type, in

Figure 10.27. Types of thrust reversers

which the doors slide to the aft end as they open up to deflect the exhaust flow; and (2) the fixed-pivot type, in which the doors rotate to a position that deflects the exhaust flow.

The second type of TR operates on the fan flow only. There are two types: (1) the petal-cowl type, shown in the middle of Figure 10.27; and (2) the cascade-cowl type, shown at the bottom of Figure 10.27. There are two cascade types: the con­ventional type and the natural-blockage type. The Bombardier CRJ700/900 aircraft uses a petal cowl TR of the natural-blockage type. The external cowls translate back, blocking the fan flow when it escapes through the fixed cascades that reverse the flow. This design is attractive with a low parts count, scalability, easier maintenance, and a relatively higher retarding energy. The petal-cowl type operating on the fan flow is suitable for short-duct nacelles, as shown in the figure. The petal doors open on a hinge to block the secondary flow of the fan when it deflects to develop reverse thrust.

TRs are applied below 150 kts and are retracted at around 50 kts (to avoid re­ingestion of engine efflux), when the wheel brakes become effective. The choice of the TR type depends on a designer’s compromise with the available technology.