Engine Installation Losses

The engine as installed in the helicopter will usually not deliver the same power as it does in the engine manufacturer’s test cell for a variety of reasons. Some of these reasons and their possible effects are as follows:

Inlet pressure losses due to duct friction

Inlet pressure losses due to a particle separator

Exhaust back pressure due to friction

Exhaust back pressure due to an infrared suppressor

Rise in inlet temperature due to exhaust reingestion

Compressor bleed

Engine-mounted accessories

Since it is not practical, or even possible, to give methods here for evaluating the magnitude of these various losses, the aerodynamicist must enlist the aid of a specialist to make a study of the specific engine installation. For the example helicopter, it will be assumed that inlet friction decreases the engine power by 2% and that no other losses exist. Thus 98% of the ratings shown in Figures 4.1 and 4.2 will be used for illustrative calculations.