Description

Retreating blade stall is a hazardous and damaging flight condition in helicopters and other rotary wing aircraft, where the rotor blade on the retreating side of the rotor disc in forward flight and therefore with the smaller resultant relative wind exceeds the critical angle of attack. Retreating blade stall is one of the primary limiting factors in a helicopter's airspeed, and the reason even the fastest helicopters can only fly slightly faster than 200 knots (about 370 km/h) though various changes can be made to conventional helicopters to try to overcome this limit such as streamlining, lifting surfaces and secondary forward propulsion.