The World Of Aviation

Variable pitch propeller is a special type of propeller with blades that can be rotated around their long axis to change their pitch. If the pitch can be set to negative values, the reversible propeller can also create reverse thrust for braking or going backwards without the need of changing the direction of shaft revolutions.

Such propellers are used in propeller aircraft to adapt the propeller to different thrust levels and air speeds so that the propeller blades don't stall, hence deteriorating 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 keeps the same is called a constant speed propeller.

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