A typical helicopter inlet containing output shaft was studied by three-dimensional turbulent numerical calculation code NAPA in this paper.The inlet was redesigned by modifying the curvature of upwind side of the inlet and adding an optimal spike on the backward of output shaft

and then simulated using NAPA program.The results show that

as output shaft blocks the flow path in the original inlet

there is a large separation zone behind the shaft and a turn loss in upwind of the shaft

thus inducing a serious distortion in the inlet.By modification

the separation zone behind the shaft and turn loss at upwind side are reduced.Modifying inlet maintains high pressure recovery

and the distortion index is reduced by 74% at most.