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When a hovering rotor is near the ground the downward flow of air through the rotor is reduced to zero at the ground. This condition is transferred up to the disc through pressure changes in the wake which decreases the inflow to the rotor for a given disc loading, which is rotor thrust for each square foot of its area.
The critical rollover angle is 5°-8°. Once exceeded, main rotor thrust continues the roll, and recovery via cyclic control is impossible. [1] A helicopter is susceptible to a rolling tendency, called dynamic rollover, when close to the ground, especially when taking off or landing. For dynamic rollover to occur, some factor has to first cause ...
The tail rotor's position and distance from the center of gravity allow it to develop thrust in a direction opposite that of the main rotor's rotation, thereby countering the torque effect created by the main rotor. Tail rotors are simpler than main rotors since they require only collective changes in pitch to vary thrust.
Rotor map of dynamic stall locations for all conditions. Stage 4: full separation of the flow on the upper surface of the airfoil can be observed, accompanied by the peak of nose-down pitch moment. Stage 5: the full flow reattachment is achieved as the AoA gradually decreases until it is fairly smaller than the static stall angle. [10]
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.
Above, the rotor is powered and pushing air downward, generating lift and thrust. Below, the helicopter rotor has lost power, and the craft is making an emergency landing. Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with ...
The tail rotor system rotates airfoils, small wings called blades, that vary in pitch in order to vary the amount of thrust they produce.The blades most often utilize a composite material construction, such as a core made of aluminum honeycomb or plasticized paper honeycomb, covered in a skin made of aluminum or carbon fiber composite.
Conservation of energy considers these parameters as well as the induced velocity at the rotor disk. Conservation of mass relates the mass flow to the induced velocity. The momentum theory applied to a helicopter gives the relationship between induced power loss and rotor thrust, which can be used to analyze the performance of the aircraft.