Abstract: The expressions of the minimum and maximum pressure angles of a nose landing gear return cam of a certain airplane were deduced in this paper. The cam pressure angle of this airplane was compared with the angles of other airplanes of the same type. The contact surfaces of the top and bottom cams were found to be smoother and the friction coefficient was smaller at the initial stage, and the actual pressure angle was larger than the minimum pressure angle so that cams could return smoothly. But the contact surfaces of cams experienced wear during the application process, and surface roughness increased; with it the friction coefficient also increased. The minimum pressure angle increased correspondingly when the friction coefficient reached a certain numerical value. The minimum pressure angle for return then became larger than the actual pressure angle, so that cams couldn’t return. The pressure angle of the cam was not the larger the better. When the pressure angle of the cam increased, the friction coefficient also increased, which would make cams wear seriously. Manipulating the turning of the nose landing gear would be difficult as the driving load of the turn actuating cylinder would not be able to overcome the friction force or the gravity of the lower parts. The fault of this airplane return cam was corrected by an appropriate enlargement of the pressure angle of the cam without changing the nose landing gear buffer function, and the nose landing gear could manipulate turning easily as a result.

Key words: nose landing gear, cams, minimum pressure angle, maximum pressure angle, manipulating turning