A controllable pitch propeller allows a pilot to adjust the angle of the propeller blades to suit different situations. It can increase power to combat headwinds or increase speed. It also allows feathering of blades in case of engine failure and can aid takeoff and cruising.
A controllable pitch propeller can vary the pitch of the aircraft propeller blades from inside the cockpit. By adjusting a switch on the instrument panel, a pilot can change the pitch of the propeller blades to best suit any given situation. At startup, the controllable pitch propeller blades are feathered or trimmed so that they do not push or push the aircraft. This allows the engine to warm up without stressing either the engine or the braking system. Also, when encountering a strong headwind, the controllable pitch propeller can be changed to a pitch that produces more power to combat the extra force the plane is fighting.
As the pitch or angle of the propeller is altered, the power output effects of the propeller are altered. The propeller’s design allows it to attack the air and grab it, just like the threads on a screw. That is why a ship’s propeller is often referred to as a screw. Just like the threads on a screw grip the wood and pull the screw into the wood, propeller blades grab the air and pull or push the plane forward. Changing the pitch of the propeller blades is similar to changing the threads on a screw from extremely coarse threads to very fine threads.
Just like a finely threaded screw, changing the controllable pitch prop to a certain pitch allows the prop to spin many more revolutions to cover the same amount of air space. This gives the plane more power, but less speed. Conversely, changing the controllable pitch propeller to a pitch more like a coarse thread screw allows the engine to rev less while covering the same amount of air space. This gives the plane more speed, but less power. By manipulating the controllable pitch propeller, the pilot can adjust the pitch to best suit the aircraft and weather conditions.
On multi-engine aircraft, the controllable pitch propeller allows the pilot to feather the propeller blades if one engine fails. This reduces the drag on the inoperative motor and prevents the disabled motor from being rotated by wind hitting the propeller blades. This also allows a cargo plane pilot to change the controllable pitch propeller to aid takeoff when the plane is heavily loaded. When the plane reaches cruising altitude, the propellers adjust to assist in cruising and save fuel.
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