Abstract: An experimental study of the flow in a helicopter inlet with front output shaft was completed in low speed wind tunnel.The flow characteristics of the inlet in the flight envelope,in particular at yaw angles from 0° to 135°were investigated.The static pressure distributions along the duct,distortions of the flow field at the inlet exit section and total pressure recovery coefficients had been measured and analyzed.The results show that total pressure recovery coefficient of this type inlet is increased in every yawed flight,and are less related to the yaw angle.But the regions of local flow separation and distortion factor of the flow at the exit section are relevant closely to the yaw angle.Moreover,the characteristics of the flow at the exit section is the best at yaw angle equal to 90 degree,but these characteristics will deteriorate abruptly as the yaw angle is more than 90 degree.