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The effect of dynamic stall limits the helicopter performance in several ways such as: The maximum forward flight velocity and thrust; High blade structural loads, which may result in excessive vibrations and blade structural damage; Control system loads, manoeuvre capability, and handling qualities; Helicopter dynamic performance.
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]
Phase lag may vary depending on rotor tilt rate, ratio of aerodynamic damping to blade inertial forces (Lock number), offset of flapping hinge from axis of rotation (e/R ratio), and coupling of blade flap, drag, and feather motions, and often results in cross-coupling between the aircraft control axes. Phase lag is a property of all rotating ...
In a stationary hover, each rotor blade will experience the same airspeed at a constant RPM. In forward flight conditions, one rotor blade will be moving into the oncoming air stream while the other moves away from it. At certain airspeeds, this can create a dangerous condition in which the receding rotor blade stalls, causing unstable flight. [5]
Typical rotorcraft blades have a Lock number between 3 and 12, [4] usually approximately 8. [5] The Lock number is typically 8 to 10 for articulated rotors and 5 to 7 for hingeless rotors. [3]: 186 High-stiffness blades may have a Lock number up to 14. [4] Larger blades have a higher mass and more inertia, so tend to have a lower Lock number.
The helicopter experienced failure of the blade rotor system, where one blade struck the fuselage, leading to a loss of balance and failure of all five rotor blades and subsequent separation of the rear fuselage and tail. May 22, 1968 23 0 0 Los Angeles Airways Flight 841: Paramount: California: Sikorsky S-61L
At the top of the mast is the attachment point (colloquially called a Jesus nut) for the rotor blades called the hub. The rotor blades are then attached to the hub, and the hub can have 10-20 times the drag of the blade. [1] Main rotor systems are classified according to how the main rotor blades are attached and move relative to the main rotor ...
De la Cierva had fitted the rotor of the C.4 with flapping hinges to attach each rotor blade to the hub. The flapping hinges allowed each rotor blade to flap, or move up and down, to compensate for dissymmetry of lift, the difference in lift produced between the right and left sides of the rotor as the autogyro moves forward.