Overview
Because aircraft operate at very high speeds and have large mass, braking requires substantial deceleration force. On wet, snowy, or iced runways, lift spoilers and wheel brakes alone may not provide sufficient deceleration. Engine thrust reversers redirect the engine's exhaust flow forward to produce thrust opposite the aircraft's motion, significantly improving deceleration during landing and, in some cases, enabling backward taxiing. Since the adoption of thrust reversers, landing rollout distances have been reduced from about 3000 m to under 450 m, improving landing reliability.
Types of Thrust Reversers
1. Bucket-type (clamshell) thrust reverser
The bucket-type reverser uses two bucket-shaped doors that deploy to deflect the exhaust flow forward, generating reverse thrust. This reverser is mounted at the rear of the engine. Its structure is relatively simple and reliable, but it is heavy and less efficient at braking. Bucket-type reversers are mainly used on turbojet engines or engines with low bypass ratios.
2. Cascade thrust reverser
The cascade-type reverser consists of cascades, blocker doors, and a translating outer cowl. When deployed, the outer cowl moves aft to expose the cascades and the blocker doors close to block the engine's normal forward flow. The flow is then redirected through the cascades and expelled forward, producing reverse thrust. Cascade reversers are more complex but more compact and aerodynamically efficient than bucket-type units. They offer higher braking efficiency and are used on large transport aircraft such as the Boeing 747.
3. Diverter-door (translating-door) thrust reverser
The diverter-door reverser combines features of bucket-type and cascade-type systems. It uses a ring of diverter doors around the engine. When the reverser is activated, the diverter doors open to block the engine's forward flow and redirect the exhaust to produce reverse thrust. This design has complexity and sealing requirements between those of cascade and bucket types, and its braking efficiency is intermediate. Wide-body aircraft such as the Airbus A330 and A340 commonly use diverter-door reversers.
