helicopter

The helicopter is controlled by varying the rotor pitch (the angle of the rotor blade as it moves through the air). For backwards flight, the blades in front of the machine have greater pitch than those behind the craft. This means that the front blades produce more lift and a backwards thrust. For forwards flight, the situation is reversed. In level flight, the blades have unchanging pitch.

For more than thirty years the Sea King, manufactured in the UK by GKN Westland, has been one of the most versatile helicopters in the world. It is a twin-engined, all-weather helicopter, which is able to detect and destroy submarines, as well as performing search-and-rescue functions, and providing logistical support.

Initially developed as an anti-submarine helicopter, the Royal Air Force also use Sea Kings for air-sea rescue. Search-and-rescue helicopters, like this one at RNAS Culdrose, Cornwall, are equipped with hydraulic hoists capable of lifting up to 272 kg/600 lb. The cabin can carry up to 22 survivors, or 9 stretchers and 2 medical officers.

Powered aircraft that achieves both lift and propulsion by means of a rotary wing, or rotor, on top of the fuselage. It can take off and land vertically, move in any direction, or remain stationary in the air. It can be powered by piston or jet engine. The autogiro was a precursor.

The rotor of a helicopter has two or more blades of aerofoil cross-section like an aeroplane's wings. Lift and propulsion are achieved by angling the blades as they rotate. Experiments using the concept of helicopter flight date from the early 1900s, with the first successful lift-off and short flight in 1907. Ukrainian–US engineer Igor Sikorsky built the first practical single-rotor craft in the USA in 1939.

A single-rotor helicopter must also have a small tail rotor to counter the torque, or tendency of the body to spin in the opposite direction to the main rotor. Twin-rotor helicopters, like the Boeing Chinook, have their rotors turning in opposite directions to prevent the body from spinning. Helicopters are now widely used in passenger service, rescue missions on land and sea, police pursuits and traffic control, fire-fighting, and agriculture. In war they carry troops and equipment into difficult terrain, make aerial reconnaissance and attacks, and carry the wounded to aid stations. A fire-fighting helicopter was tested in Japan in 1996, designed to reach skyscrapers beyond the reach of fire-engine ladders.