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Some trees (for example maple trees) have seeds that have wing-like structures that enable the seed to spin to the ground in autorotation, which helps the seeds to disseminate over a wider area. The most common use of autorotation in helicopters is to safely land the aircraft in the event of an engine failure or tail-rotor failure.
A semi-rigid rotorhead does not have individual flapping or drag hinges but provides for flapping and lag motion through gimbal mounting. [3] A common example of a semi-rigid rotor is a teetering rotorhead found on the Robinson family of helicopters.
The charts show the added lift benefit produced by ground effect. [ 3 ] For fan and jet-powered vertical take-off and landing (VTOL) aircraft, ground effect when hovering can cause suckdown and fountain lift on the airframe and loss in hovering thrust if the engine sucks in its own exhaust gas, which is known as hot gas ingestion (HGI).
Helicopters with fly-by-wire systems allow a cyclic-style controller to be mounted to the side of the pilot seat. The cyclic is used to control the main rotor in order to change the helicopter's direction of movement. In a hover, the cyclic controls the movement of the helicopter forward, back, and laterally.
Tandem-rotor helicopters, however, use counter-rotating rotors, with each cancelling out the other's torque. Therefore, all of the power from the engines can be used for lift, whereas a single-rotor helicopter uses some of the engine power to counter the torque. [1] An alternative is to mount two rotors in a coaxial configuration.
A helicopter's main rotor hub. The vertical rods are at the end of the control chain that starts with the pilot controls. Helicopter flight controls are connected to the main and tail rotors, and include a cyclic stick, broadly to control forward-aft and left-right movements, a collective lever, broadly to control vertical movements, and anti-torque pedals, to control left and right yaw.
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The FAA states "The height–velocity diagram or H/V curve is a graph charting the safe/unsafe flight profiles relevant to a specific helicopter. As operation outside the safe area of the chart can be fatal in the event of a power or transmission failure it is sometimes referred to as the dead man's curve."