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A controllable-pitch propeller (CPP) or variable-pitch propeller is a type of propeller with blades that can be rotated around their long axis to change the blade pitch. Reversible propellers—those where the pitch can be set to negative values—can also create reverse thrust for braking or going backwards without the need to change the direction of shaft revolution. ==Aircraft== Propellers whose blade pitch could be adjusted while the aircraft was on the ground were used by a number of early aviation pioneers,〔(Aeroplane propellers )Flight International 9 January 1909〕 including A. V. Roe and Louis Breguet. In 1919 L. E. Baynes AFRAeS patented the first automatic variable pitch airscrew. 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 a 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 Aircraft Company — as the Gloster Hele-Shaw Beacham Variable Pitch Propellor — 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 blade 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. A 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 Smith Engineering Co. in the United States also developed controllable-pitch propellers. Smith propellers were used by Wiley Post on some of his flights. Another common type was originally developed by Wallace R. Turnbull and refined by the Curtiss-Wright Corporation. This electrically-operated mechanism was first tested in on June 6, 1927 at Camp Borden, Ontario, Canada and patented in 1929 (). It was favoured by some pilots in World War II, because even when the engine was no longer running the propeller could be feathered. On hydraulically-operated propellers the feathering had to happen before the loss of hydraulic pressure in the engine. 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. The Silence Twister prototype kitplane was fitted with the V-Prop, an automatic self-energising and electronically self-adjusting VP propeller.〔(【引用サイトリンク】 Silence Twister )〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Variable-pitch propeller」の詳細全文を読む スポンサード リンク
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