Like all powered aircraft, helicopters operate on the principles of lift and thrust. Lift is the force that pushes the aircraft up into the sky, and thrust is the force that propels the aircraft forward. In a fixed wing aircraft, like a conventional passenger jet, lift is provided by the wings, and thrust is provided by the engines. In a helicopter however, both lift and thrust are generated by the helicopter’s main rotor.
The main rotor, mounted horizontally above the aircraft’s fuselage, is arguably the most important part of the helicopter. The main rotor provides the lift and thrust that allows the helicopter to fly, as well as move laterally, make turns, and change altitude. The main rotor is powered by a crankshaft connected to the engine. Key to controlling the main rotor is the swash plate assembly, which consists of two parts, the upper and lower swash plate. The upper swash plate connects to the mast, or rotor shaft, through linkages, and the blade grips, which connect the blades to a hub at the center of the rotor. A nut called the Jesus nut mounts the hub on the helicopter’s mast, and control rods from the upper swash plate connect to the blades. These control rods transfer movements in the upper swash plate to the blades.
Meanwhile, the lower swash plate is fixed, and doesn’t rotate. Between the upper and lower swash plates is a set of ball bearings, and allows the upper plate to spin freely on top of the lower plate. Control rods attach to the lower swash plate, and are connected to the pilot’s controls in the cockpit. Therefore, when the pilot operates the controls, their inputs are transmitted via the control rods to the lower swash plate, to the upper swash plate, then to the control rods that connect to the blades, thus affecting the blades, changing their airfoil, and steering the helicopter.
However, the main rotor spinning generates an enormous amount of torque that, if left unchecked, would cause the helicopter to spin uncontrollably and make it impossible to fly. Russian-born engineer Igor Sikorsky overcame this problem by adding a tail rotor to his design, which would be emulated by the vast majority of over helicopter designs. A tail rotor is a vertically-mounted rotor in the tail of the aircraft, which spins in opposition of the torque generated by the main rotor. This effectively negates the main rotor’s torque, balances the helicopter, and allows it to fly in a controllable manner.
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