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Dissymmetry of lift [1]: 2–20 [2] (also known as asymmetry of lift [3]: 342 [4] or asymmetric lift [5] [6]) in rotorcraft aerodynamics refers to an unequal amount of lift on opposite sides of the rotor disc. It is a phenomenon that affects single-rotor helicopters and autogyros in forward flight.
Flapback [1]: 3:28 or blowback [2]: 2–14, 2–20, 2–21 [3] is the tilting of a helicopter rotor disc, usually aft (backwards), which occurs in several circumstances. In normal operating circumstances, forward flight results in flapback caused by dissymmetry of lift and the transverse flow effect.
Overhead view of helicopter rotors. The rotor tips travel much faster than the inner sections, so produce more lift. (For the purposes of this article, the demarcated circular regions are irrelevant and should be ignored.) A helicopter rotor blade is an airfoil, which is driven through the air to create lift. The lift generated is proportional ...
Dissymmetry of lift is an aerodynamic phenomenon caused by the rotation of a helicopter's rotors in forward flight. Rotor blades provide lift proportional to the amount of air flowing over them. When viewed from above, the rotor blades move in the direction of flight for half of the rotation (advancing half), and then move in the opposite ...
The advantage of the coaxial rotor is that, in forward flight, the lift provided by the advancing halves of each rotor compensates for the retreating half of the other, eliminating one of the key effects of dissymmetry of lift: retreating blade stall. However, other design considerations plague coaxial rotors.
Witnesses have revealed what they saw take place at the moment of impact during the horrifying collision between an American Airlines jet and an Army helicopter over the Potomac River. On ...
A man whose wife was on the American Airlines plane that collided with a U.S. Army Black Hawk helicopter in Washington, D.C. has revealed the final text he received from her before the crash. On ...
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]