What Are the Types of Aircraft Propellers?
Many aircraft today rely on the use of propellers for motion. Although modern piston-powered aircraft have advanced propellers made with more powerful materials, they still feature a surprising resemblance to the earliest types of propellers. Fixed-pitch and ground-adjustable propellers are the simplest types, but there are multiple variations and classes beyond these examples. Here, you will learn about some of the characteristics of several types of propellers.
The fixed-pitch propeller is designed to be one individual part, often made of aluminum alloy or wood. It typically uses two blades and is called fixed-pitch because only one pitch setting is available. This propeller is designed to be most efficient when kept with a fixed rotational and forward speed. The speeds of both the airplane and the engine should be set, and any change in either of these speeds will result in a reduced efficiency of both the propeller and the engine. Many single-engine aircraft and airplanes of low speed, range, power, or altitude use the fixed-pitch propeller. Some advantages of this propeller are its low cost and simple operation, as it does not require the pilot to input controls during flight.
Variable Pitch Propellers
Variable pitched aircraft propellers allow for more flexibility of flight and movement as compared to a fixed pitch aircraft. In times of war, the variable pitch was changed during flight, though generally in the past, the variable pitch of the propeller was changed manually before each flight. Today, we have control panels which can automatically change the pitch of the propellers during flight. Not only do these control panels make it easier to control pitch, but they also avoid the risk of manually handling metal blades.
Test Club Propeller
The purpose of a test club propeller is to break in and test reciprocating engines. It is designed to place the correct load amount on the engine during the test break-in period and features a multi-blade design which provides extra cooling airflow during testing.
The ground-adjustable propeller essentially operates the same as the fixed-pitch propeller, except that it features the ability to adjust the blade angle, or pitch, when the propeller is not turning. The clamping mechanism which holds the blades in place can be loosened while grounded to allow for adjustment. However, once the clamping mechanism has been tightened, the pitch of the blades cannot be adjusted for variable flight requirements. It is not common for the ground-adjustable propeller to be used on present-day aircraft.
With the controllable-pitch propeller, you can change the blade pitch, or angle while the propeller is rotating, allowing the propeller to assume the ideal blade angle for specific flight conditions. The propeller can either have a fixed amount of pitch positions, as with the two-position controllable propeller, or it may allow for any angle between the minimum and maximum pitch settings of a given propeller. Another advantage of the controllable-pitch propeller is that it allows the possibility of attaining the desired engine RPM for a specific flight condition.
Constant-speed propellers use propeller governors to adjust the blade pitch, or angle, automatically without the need of interference by the pilot. A natural phenomenon causes propellers to slow down as an aircraft climbs and to speed up when the aircraft dives because of the resulting load on the engine. The propeller governors are designed to counter this effect and keep speed as constant as possible. When the aircraft begins a climb, the blade angle of the propeller is decreased so as to prevent the engine speed from decreasing. The blade angle of the propeller is also increased to prevent overspeeding when the aircraft begins a dive. In instances where the throttle setting is changed instead of a change in speed caused by diving or climbing, the blade angle is adjusted as required to maintain constant engine RPM.
Feathering propellers are constant-speed propellers designed with the ability to adjust the blade angles to approximately 90 degrees in the case of an engine failure. By setting the angle of the blades in a feathered propeller parallel to the airstream, drag is greatly reduced. The aerodynamic forces keep the propeller blades feathered, and the angle helps prevent windmilling.
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