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According to the laws of physics, any force (or action) produces an equal force (or reaction) in the opposite direction. This means the torque (rotating force) produced by a helicopter's blades tends to turn the fuselage (the main helicopter body) in the opposite direction. All helicopters have either a second propeller or another device to counteract the torque of the main blade. In most helicopters, a tail rotor balances the torque by pushing in the opposite direction to the main rotor. Some helicopters have two rotors mounted on the same shaft, which turn in opposite directions to cancel the torque. Others (notably the large military Chinook helicopters) have a rotor at the front and a rotor at the back and cancel the torque by turning in opposite directions. Tail rotors solve one problem but can cause others. Noisy and dangerous to passengers, the tail rotor of a helicopter is also highly susceptible to damage from passing birds or debris. This is a big problem, because a helicopter with a damaged tail rotor is dangerously uncontrollable. NOTAR helicopters have a giant fan inside the fuselage that sucks in air just behind the cockpit and blows it out again through a side hole near the tail. This produces the same sideways force as a tail rotor, but is quieter and safer. Among the many innovative designs to appear during this V/STOL era was Vertol's Model 76, the first aircraft in the world to make use of the tilt-wing concept. The single example produced (serial 56-6943) was funded jointly by the Army and the Office of Naval Research (ONR), and made its first hovering flight in the summer of 1957. The VZ-2 was powered by a single fuselage-mounted YT53-L-1 turbine engine driving, via extension shafts, two rotor/airscrews attached to the tilting wing. For vertical takeoff and landing the leading edge of the wing, and its attached propellers, would be rotated to point directly upwards. Once the machine had reached a safe height the wing would slowly be rotated downward into the normal flight position, and the craft would fly off in the conventional fashion. Unlike other contemporary tilt-wings the VZ-2 was also equipped with two small tail-mounted dueled fans meant to provide additional lateral control. The aircraft's most characteristic features were its high T-tail and helicopter-style bubble cockpit enclosure. helicopterThey can move up and down (flapping), back and forth in the horizontal plane, ... This system generally appears on helicopters with two rotor blades. ... The Piasecki helicopters also use tandem rotors – one toward the front of the ... www.daviddarling.info/encyclopedia/… Rotor ConfigurationsThe Piasecki helicopters also use tandem rotors—one toward the front of the helicopter and one at its rear. The Kaman HH-43 uses two intermeshing rotors. ... www.centennialofflight.gov/essay/..… - Increasing lift on helicopter rotor blades and aircraft propellers ...The same lift forces introduced into the helicopter rotor system would be ... Extending outward from the hub 9 are a plurality of blades in two sets 1 and 2. ... are four located to the front and back of the inner drive-shaft and left ... www.patentstorm.us/patents/5167384/…
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