Based on the principle of direct and indirect testing methods of transmission efficiency

the transmission efficiency experiment of the helicopter main gearbox was carried out for the first time in China. The results showed that transmission efficiency was positively related to input torque and oil temperature

and negatively related to the input speed. The transmission efficiency changed obviously under low torque. The rate of change of transmission efficiency with rotating speed was obviously smaller than that with torque. The indirect testing method results of transmission efficiency were greater than direct testing method. With the increase of input torque

the relative difference between indirect and direct testing methods of transmission efficiency decreased gradually

while it was not obvious with the rotating speed. The results of error analysis showed that the limit error of indirect testing method was less than that of direct testing method

and the maximum error of direct and indirect testing method was 1.28% and 0.72%

respectively.