The helicopter's name means spiral wing, not heli plus copter
The Frenchman Gustave Ponton d'Amécourt coined hélicoptère in 1861 from the Greek helix, meaning spiral, and pteron, meaning wing. English speakers split it the wrong way, which is how we ended up with helipads and quadcopters. The machine itself had to wait decades for engines light enough to lift a person.
Early models ran on rubber bands or spindles and stayed toy-sized. Steam engines helped researchers study rotor aerodynamics for half a century before the airplane, but never had the power for a crewed craft. Internal combustion changed that at the end of the 1800s, yet for decades the core problem remained that an engine's output could barely beat its own weight in vertical flight, so designers used the smallest engines they could find.
The Focke-Wulf Fw 61 of 1936 was the first practical, fully controllable helicopter. Between 1939 and 1943 Igor Sikorsky refined his VS-300 through four versions, settling on one main rotor plus a small tail rotor, and his R-4 became the first to enter full-scale production in 1942. In December 1951 the Kaman K-225 pioneered the turboshaft, a turbine that delivered lots of power for little weight, and today nearly every helicopter but the lightest uses one.
That tail rotor exists because a spinning main rotor tries to twist the fuselage the opposite way. Alternatives include a fan hidden inside the tail and the NOTAR system, which uses the Coandă effect along the boom. Some designs avoid the problem with pairs of rotors turning in opposite directions, mounted one behind the other, side by side, stacked on one axis, or angled to intermesh overhead. Tip jets, which spin the rotor from its blade ends, generate no torque at all.
A gearbox sits between engine and rotor. Engine shafts turn at 3,000 to 50,000 revolutions per minute, while main rotors spin at just 300 to 600 and tail rotors at 1,000 to 5,000, so reduction gears step the speed down and bevel gears turn the drive through right angles. A freewheel clutch lets the rotors keep turning if the engine quits, allowing an unpowered descent called autorotation. Pilots fly with four controls: cyclic, collective, pedals and throttle.
Source: Helicopter
