To overcome the problems of low drag on large aircraft with high momentum, the designers have introduced a variety of drag inducing devices such as:

• Spoilers

• Lift dumpers

• Speed brakes

• Thrust reversers

When landing the aircraft, for the different landing distances required are based on variables such as;

“ Thrust Reversers” are used as the braking system of the aircraft. In modern aircraft, the braking system in the wheel are sufficient during normal conditions. Thrust reversers change the direction of the aircraft’ s exhaust gases so that they are directed forwards, rather than backwards. The method of redirecting the flow varies with the size, configuration and the manufacturer of the engine. When the runway becomes icy or snow covered, stopping the aircraft requires an additional procedure. This is where“ Thrust reversers” are used. In this way, the pilot is able to reduce the landing distance of an aircraft. In high by-pass ratio engines the majority of the thrust is derived from the fan airflow( bypass air from the fan), the core air from the engine will exit normally. So changing the direction of the fan airflow would create a net reverse thrust. Thrust reversers are used to change the direction of the fan airflow. In Turboprop aircraft reverse thrust action is used by changing the pitch of the propeller blades. The pitch in which the blade provides reverse thrust is called the“ beta range”. Usually, a hydro-mechanical system is used to change the blade angle, giving a braking response when activated. Ideally, the airflow should be directed in a completely forward direction to gain the complete drag to stop the aircraft; however, this is not possible, mainly due to aerodynamic reasons. A discharge angle near 45 degrees is usually chosen, resulting in a proportionally effective reverse thrust than the thrust of the same engine in its normal direction.

There are several methods of obtaining reverse thrust on“ turbo-jet engines”: 1. CLAMSHELL TYPE deflector doors to reverse the exhaust gas stream.

2. BUCKET TARGET SYSTEM with external type doors( Bucket doors) to reverse the exhaust. 3. Fan engines utilize BLOCKER DOORS to reverse the COLD STREAM AIRFLOW SYSTEM.