Thrust reversal - INTRODUCTION

INTRODUCTION

Fig. 15-1 Comparative landing runs with and without thrust reversal.

1. Modern aircraft brakes are very efficient but on wet, icy or snow covered runways this efficiency may  be reduced by the loss of adhesion between the aircraft tyre and the runway thus creating a need for an additional method of bringing the aircraft to rest within the required distance.
2. A simple and effective way to reduce the aircraft landing run on both dry and slippery runways is to reverse the direction of the exhaust gas stream, thus using engine power as a deceleration force. Thrust reversal has been used to reduce airspeed in flight but it is not commonly used on modern aircraft. The difference in landing distances between an aircraft without reverse thrust and one using reverse thrust is illustrated in fig. 15-1.
3. On high by-pass ratio (fan) engines, reverse thrust action is achieved by reversing the fan (cold stream) airflow. It is not necessary to reverse the exhaust gas flow (hot stream) as the majority of the engine thrust is derived from the fan.