Windmilling characteristics are one of the important performance indices to engine design and assessment.It is very difficult to accurately determine engine windmilling characteristics

in particular windmilling drag

for the windmilling state seriously deviates from the engine design point.This paper described the mechanism of the aero-engine windmilling drag

and theoretically deduced the formula for determining it in the simulated altitude test

and finally the experimental method for determining the engine windmilling drag was introduced.The method was satisfactorily applied to the windmilling characteristics test of a turbofan engine.