reversers and a/c speed

[Old Fella]

Using Reverse Thrust.

Whether it is the "hot stream" or the "cold stream" mass air flow being diverted to provide reverse thrust the effective speed retardation is achieved by redirecting the gas or mass air flow foward, ideally fully opposite to the forward flow direction, but generally at around 45 degrees forward. It has been mentioned that it is inlet drag which is the primary contributor to speed reduction. This is not supported by either Rolls Royce (The Jet Engine) or General Electric (The Aircraft Gas Turbine Engine and its operation), each of whom stress the reversal of gas or cold stream flow as being the means by which speed is reduced with no mention of the effects of inlet drag. Reverse thrust is very effective in "washing off" speed to a value where less brake energy is required and is usually fully cancelled by 60 Kts to preclude re-ingestion of gas flow or ingestion of FOD.