Thrust Reversal – Definition and Types

As soon as the planes land on the runway, they start to brake in order to stop as soon as possible and in the safest way. Airplanes are large and heavy vehicles. Therefore they use many methods in combination to slow down and stop on the runway. In this article we are going to explain thrust reversal system.

Jet-powered passenger aircraft basically slow down using three different methods simultaneously.

1- Brake mechanism in landing gear

2- Spoilers located in the rear of the wings

3- “Thrust reversal” system

Apart from these methods, especially by military jets, drogue parachute and wire arrestors (Runway Arrestor Gear Systems) are used to slowdown of the aircraft after landing.

What is Thrust Reversal?

Thrust reversal, as you can understand from the name, reverses the direction of the thrust provided by the engines. The high pressure air coming out behind the engines starts to be sprayed towards the direction of the aircraft as much as possible. In this way, both the aircraft can stop in a much shorter time and the load on the brake mechanism on the landing gear is reduced.

Basically, three different thrust reversal systems are used in jet-powered passenger aircraft:

1- Bucket/Target Type Reverser:

A Bucket type reverser is a hydraulically actuated system that uses bucket type doors to reverse the flow of the engine hot gas stream. Whilst in forward thrust, the bucket doors form the final tail pipe nozzle of the engine. When reverse thrust is selected by the pilot, actuators close the buckets over the hot gas stream deflecting it forward. A mechanical lock holds the buckets in their extended position. Aim is to allow thrust to be increased without the associated risk of an uncommanded, asymmetric retraction of the buckets. It is also possible for the aircraft to move backwards with this system (keep in mind that this type of backward move is not an efficient way).

2- Clamshell Door Reverser:

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 forward thrust.

3- Cold Stream Reverser:

There are two different versions of this type of thrust reversal system:

A) Cold Stream Cascade Reverser

While the engine cover is opened as a backward slide, the engine outlet is also closed.

B) Cold Stream Pivoting Doors Reverser

When the four small covers on the engine are opened, the engine outlet is also closed.