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Retreating blade stall is a hazardous flight condition in helicopters and other rotary wing aircraft, where the retreating rotor blade has a lower relative blade speed, combined with an increased angle of attack, causing a stall and loss of lift. Retreating blade stall is the primary limiting factor of a helicopter's never exceed speed, V NE. [1]
That is, the advancing blades operate at high Mach numbers so low values of AOA is needed but shock-induced flow separation may happen, while the retreating blade operates at much lower Mach numbers but the high values of AoA result in the stall (also see advancing blade compressibility and retreating blade stall).
[1]: 2–14 Rotor blades are designed to flap: the advancing blade flaps up and develops a smaller angle of attack due to a change in relative wind vectors, thus producing less lift than a rigid blade would. Conversely, the retreating blade flaps down, develops a higher angle of attack due to a change in relative wind vectors, and generates ...
This includes but its not limited to: Dynamic rollover, Ground resonance, Loss of tail-rotor effectiveness, Retreating blade stall,Dynamic stall, Vortex ring state, Servo transparency, Mast bumping, and Tailstrike. Because the main rotor is vital to keeping a helicopter in the air, any damage to can have disastrous consequences.
Single rotor helicopters are limited in forward speed by a combination of sonic tip speed and retreating blade stall.As the advance ratio increases, the relative velocity experienced by the retreating blade decreases so that the tip of the blade experiences zero velocity at an advance ratio of one.
When the helicopter rotor stalls, it does not do so symmetrically, because forward airspeed causes higher airspeed on the advancing blade than on the retreating blade. The retreating blade stalls first and its weight makes it descend as it moves aft, while the advancing blade raises as it goes forward. The resulting low aft blade and high ...
The coworker of a newly married woman says she used their recent company holiday party to swindle wedding gifts. After sharing a "sob story" about how she wasn't given enough money from her guests ...
A rotor blade produces more lift in the advancing half. As a blade moves toward the direction of flight, the forward motion of the aircraft increases the speed of the air flowing around the blade until it reaches a maximum when the blade is perpendicular to the relative wind. At the same time, a rotor blade in the retreating half produces less ...