Overview
Because aircraft fly at high speeds and have large mass, braking requires substantial deceleration force. On wet, snowy, or iced runways, control surfaces and landing-gear brakes alone are often insufficient, so thrust reversers are used. A thrust reverser redirects the engine exhaust from rearward to forward, producing thrust opposite the aircraft's motion and significantly improving deceleration on landing; it can even enable reverse taxi. Since the adoption of thrust reversers, typical landing rollout distances have decreased from about 3,000 m to under 450 m, increasing landing braking reliability.
Common Types of Thrust Reversers
01 Clamshell (bucket) type
The clamshell type uses two bucket-shaped doors that open to deflect the exhaust flow forward and generate reverse thrust. These reversers are mounted at the engine rear, have a relatively simple and reliable structure, but tend to be heavy and offer lower braking efficiency. Clamshell reversers are mainly used on turbojet engines or engines with low bypass ratios.
02 Cascade type
The cascade reverser consists of cascade vanes, blocker doors, and a movable outer cowling. When the reverser is actuated, the outer cowling moves rearward to expose the cascade vanes while blocker doors close to block the engine's forward flow; the flow is then directed through the cascade vanes and discharged forward, producing reverse thrust. Cascade reversers are mechanically more complex but are more compact and provide good flow guidance and higher braking efficiency. The Boeing 747 passenger variant uses cascade reversers.
03 Deflector-door type
The deflector-door type combines features of the clamshell and cascade designs. It has a ring of deflector doors around the engine periphery; when the reverser is deployed, the deflector doors open to block forward flow and redirect the exhaust, producing reverse thrust. Its structural complexity and braking efficiency lie between the cascade and clamshell types, and it has relatively high sealing requirements for the deflector doors. Wide-body airliners such as the Airbus A330 and A340 use this type of reverser.
