1.) For use of Braking in aircraft, while landing:- Normally, a commercial aircraft lands at a speed of 240–260 km/h. At this high speed, if we apply mechanical braking, it will cause more wear and tear in the brakes. To avoid this, reverse thrust is used which direct the thrust forward, resulting in braking.
2.) While reversing on the taxiway or on the runway:- In some airports, where the pushback tractor in unavailable, the aircraft can reverse itself from the gate, by use of Reverse Thrust. This system is known as Powerback.
But it is banned at some of the airports, because, opening the reverse thrusters at the gate can damage the airport terminals, or can harm the ground equipments and personnel, due to the high speed JET BLAST.
The types of reverse thrust systems are—
Use of variable pitch propeller in Propeller driven aircrafts:-
Propeller-driven aircraft generate reverse thrust by changing the angle of their controllable-pitch propellers so that the propellers direct their thrust forward. This reverse thrust feature became available with the development of controllable-pitch propellers, which change the angle of the propeller blades to make efficient use of engine power over a wide range of conditions. Single-engine aircraft tend not to have reverse thrust.
Target type thrust reversal:-The target thrust reverser uses a pair of hydraulically-operated "bucket" type doors to reverse the hot gas stream. For forward thrust, these doors form the propelling nozzle of the engine. In the original implementation of this system on the Boeing 707, and still common today, two reverser buckets were hinged so when deployed they block the rearward flow of the exhaust and redirect it with a forward component. This type of reverser is visible at the rear of the engine during deployment.
Clam Shell type thrust reversal:- The clam-shell door, or cascade, system is pneumatically operated. When activated, the doors rotate to open the ducts and close the normal exit, causing the thrust to be directed forward. The cascade thrust reverser is commonly used on turbofan engines. On turbojet engines, this system would be less effective than the target system, as the cascade system only makes use of the fan airflow and does not affect the main engine core, which continues to produce thrust.
Cold stream type thrust reversers:-
Doors in the bypass duct are used to redirect the air that is accelerated by the engine"s fan section but does not pass through thecombustion chamber(called bypass air) such that it provides reverse thrust.The cold stream reverser system is activated by an air motor. During normal operation, the reverse thrust vanes are blocked. On selection, the system folds the doors to block off the cold stream final nozzle and redirect this airflow to the cascade vanes.
The cold stream system is known for structural integrity, reliability, and versatility. During thrust reverser activation, a sleeve mounted around the perimeter of the aircraft engine nacellemoves aft to expose cascade vanes which act to redirect the engine fan flow. This thrust reverser system can be heavy and difficult to integrate into nacelles housing large engines.
基本都有，有些民航機甚至還能倒車（倒機），不需要牽引車就能從停機坪倒退到滑行道。
介紹一些有反推裝置的民航機和發動機吧：
1.) For use of Braking in aircraft, while landing:- Normally, a commercial aircraft lands at a speed of 240–260 km/h. At this high speed, if we apply mechanical braking, it will cause more wear and tear in the brakes. To avoid this, reverse thrust is used which direct the thrust forward, resulting in braking.
2.) While reversing on the taxiway or on the runway:- In some airports, where the pushback tractor in unavailable, the aircraft can reverse itself from the gate, by use of Reverse Thrust. This system is known as Powerback.
But it is banned at some of the airports, because, opening the reverse thrusters at the gate can damage the airport terminals, or can harm the ground equipments and personnel, due to the high speed JET BLAST.
The types of reverse thrust systems are—
Use of variable pitch propeller in Propeller driven aircrafts:-
Propeller-driven aircraft generate reverse thrust by changing the angle of their controllable-pitch propellers so that the propellers direct their thrust forward. This reverse thrust feature became available with the development of controllable-pitch propellers, which change the angle of the propeller blades to make efficient use of engine power over a wide range of conditions. Single-engine aircraft tend not to have reverse thrust.
Target type thrust reversal:-The target thrust reverser uses a pair of hydraulically-operated "bucket" type doors to reverse the hot gas stream. For forward thrust, these doors form the propelling nozzle of the engine. In the original implementation of this system on the Boeing 707, and still common today, two reverser buckets were hinged so when deployed they block the rearward flow of the exhaust and redirect it with a forward component. This type of reverser is visible at the rear of the engine during deployment.
Clam Shell type thrust reversal:- The clam-shell door, or cascade, system is pneumatically operated. When activated, the doors rotate to open the ducts and close the normal exit, causing the thrust to be directed forward. The cascade thrust reverser is commonly used on turbofan engines. On turbojet engines, this system would be less effective than the target system, as the cascade system only makes use of the fan airflow and does not affect the main engine core, which continues to produce thrust.
Cold stream type thrust reversers:-
Doors in the bypass duct are used to redirect the air that is accelerated by the engine"s fan section but does not pass through thecombustion chamber(called bypass air) such that it provides reverse thrust.The cold stream reverser system is activated by an air motor. During normal operation, the reverse thrust vanes are blocked. On selection, the system folds the doors to block off the cold stream final nozzle and redirect this airflow to the cascade vanes.
The cold stream system is known for structural integrity, reliability, and versatility. During thrust reverser activation, a sleeve mounted around the perimeter of the aircraft engine nacellemoves aft to expose cascade vanes which act to redirect the engine fan flow. This thrust reverser system can be heavy and difficult to integrate into nacelles housing large engines.