Theory of Rotary Wing Flight Practice Test

Retreating blade stall happens in forward flight when the rotor disk experiences a big difference in lift between the advancing and retreating halves. As forward speed climbs, the advancing blade encounters higher relative wind and supplies more lift, while the retreating blade has to take on most of the remaining load. To keep the rotor balanced, the retreating blade must increase its angle of attack. But the retreating blade is already working in a lower-speed flow, so pushing its angle of attack higher brings it closer to, or into, stall. When the retreating blade stalls, lift on that side drops abruptly, causing a rapid roll or loss of control.

That’s why high forward speed, or excessive airspeed, is the speed condition most associated with retreating blade stall. Very slow or moderate forward speeds don’t push the retreating blade toward stall in the same way, and altitude doesn’t directly set this stall tendency by itself.