Slightly OT, but does anyone know the efficiency of the thrust
reversers?
I mean, lets say an engine outputs 20.000 lbf of thrust at e.g N1 80% in "normal forward" setting.
At N1 80% REVERSE, will it have a 20.000 lbf opposite thrust??
On the order of 40% or less.
First, the fan on a high-bypass turbofan produces about 75% of the thrust.
Second, only the fan exhaust is diverted by the reversers.
Third, there will be some efficiency losses.
Fourth, max RPM or thrust will be less in reverse than in normal operation.
So, the basic equation is Reverse thrust = [Fan thrust (reversed) - HP thrust (residual)] x Efficiency factor
or
Trev = [75% Tfwd - 25% Tfwd] x Fe
Trev = 50% Tfwd x Fe
Given the RPM restrictions and efficiency losses, a 20% efficiency loss is reasonable, so
Trev ~~ 50% Tfwd x .8 ~~ 40% Tfwd