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The effect of airfoil geometry on dynamic stall is quite intricate. As is shown in the figure, for a cambered airfoil, the lift stall is delayed and the maximum nose-down pitch moment is significantly reduced. On the other hand, the inception of stall is more abrupt for a sharp leading-edge airfoil. [8] More information is available here. [13]
In aviation, and in particular in helicopters, servo transparency (also called servo reversibility or jack stall), [1] is a phenomenon affecting the servomechanisms (or servos) that assist a helicopter's flight controls, which, in certain flight conditions, can result in a significant stiffening of the controls handled by the pilot.
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]
Dissymmetry of lift in an American-style helicopter. Consider a single-rotor helicopter in still air. For a stationary (hovering) helicopter, whose blades of length of r metres are rotating at ω radians per second, the blade tip is moving at a speed rω meters per second. As the blades rotate, the speed of the blade-tips relative to the air ...
The angle of attack can be increased to compensate, however beyond a certain point the rotor blades stall and lift rapidly decreases. Rotor stalls are not recoverable because the descending helicopter has airflow moving upwards through the rotor disc, so even full down collective will not restore normal airflow. When the helicopter rotor stalls ...
Nasa’s Mars helicopter Ingenuity will never fly again, the space agency gas said.. The pioneering robot vehicle was the first ever to achieve powered and controlled flight on another world. It ...
The signs of VRS are a vibration in the main rotor system [8] followed by an increasing sink rate and possibly a decrease of cyclic authority. [9]In single rotor helicopters, the vortex ring state is traditionally corrected by slightly lowering the collective to regain cyclic authority and using the cyclic control to apply lateral motion, often pitching the nose down to establish forward flight.
In a helicopter the maximum forward speed is defined by the turn speed of the rotor; at some point the helicopter will be moving forward at the same speed as the spinning of the backwards-moving side of the rotor, so that side of the rotor sees zero or negative airspeed, and begins to stall. This limits modern helicopters to cruise speeds of ...