Controllable Pitch Propeller - Aircraft

Aircraft

Propellers whose blade pitch could be adjusted while the aircraft was on the ground were used by a number of early aviation pioneers, including A.V. Roe and Louis Breguet.

The French aircraft firm Levasseur displayed a variable pitch propeller at the 1921 Paris Airshow which it claimed had been tested by the French government in a ten-hour run and could change pitch at any engine rpm.

Dr Henry Selby Hele-Shaw and T E Beacham patented an hydraulically-operated variable-pitch propeller (based on a variable stroke pump) in 1924 and presented a paper on the subject before the Royal Aeronautical Society in 1928, though it was received with scepticism as to its utility. The propeller had been developed with Gloster - as the "Gloster Hele-Shaw Beachem" - and was demonstrated on a Gloster Grebe where it was used to maintain a near-constant rpm.

The first practical controllable pitch propeller for aircraft was introduced in 1932.

Such propellers are used in propeller-driven aircraft to adapt the propeller to different thrust levels and air speeds so that the propeller blades don't stall, hence degrading the propulsion system's efficiency. Especially for cruising, the engine can operate in its most economical range of rotational speeds. With the exception of going into reverse for braking after touch-down, the pitch is usually controlled automatically without the pilot's intervention. A propeller with a controller that adjusts the blades' pitch so that the rotational speed always stays the same is called a constant speed propeller. A propeller with controllable pitch can have a nearly constant efficiency over a range of airspeeds.

The most common type of controllable pitch propeller is hydraulically actuated; it was originally developed by Frank W. Caldwell of the Hamilton Standard Division of the United Aircraft Company. This design led to the award of the Collier Trophy of 1933. de Havilland subsequently bought up the rights to produce Hamilton propellers in the UK, while the British company Rotol was formed to produce its own designs. The French company of Pierre Levasseur and the US Smith Engineering Co. also developed controllable pitch propellors. Smith propellers were used by Wiley Post on some of his flights.

As experimental aircraft and microlights have become more sophisticated, it has become more common for such light aeroplanes to fit variable-pitch propellers, both ground-adjustable propellers and in-flight-variable propellers. Hydraulic operation is too expensive and bulky, and instead light aircraft use propellers that are activated mechanically or electrically. Some are manually operated, some are controlled by electronics; and one, the "Silence V-Prop", is fully self-powering and self-adjusting.