Over the course of aviation history, many different types of airplane propellers have been used in piston engine-driven aircraft, as advances in materials and engineering opened up greater and greater possibilities in the aircraft propeller's design and engine performance. In this blog, we will explore some of the different types of propellers used over the years.
The first propellers were fixed-pitch, meaning they could not be adjusted in their mountings on the propeller hub, and were made of wood. They were not carved from a single piece, but built layer by layer with specially prepared wood, with black walnut, sugar maple, yellow birch, and black cherry being the most commonly used. Today however, they have been all but supplanted and are typically only seen on historical examples.
Metal fixed-pitch propellers were first invented in the 1940s. Made from aluminum alloy, they were specially treated to be less prone to warping in extreme heat or cold. Today, almost all propellers, including the types on this list, are made from metal so that the propeller lifespan is increased.
Ground-adjustable propellers can have their pitch (the angle the blades are facing) changed, but only when the propeller is not turning. A clamping mechanism holds the propeller blades in place, and the blade’s angle can be changed by loosening this mechanism. There is no way to change the blade’s pitch mid-flight however, so ground-adjustable propellers are not used in modern aircraft.
Controllable pitch propellers can alter the blade’s pitch during flight, while the propeller is still running. This means that the blade angle can be altered to adapt to changing flight conditions. The number of pitch positions is limited and can be adjusted between minimum and maximum pitch settings.
Constant speed propellers accelerate when the airplane dives and slow down when the aircraft climbs due to the changing load on the engine. This is accomplished by the propeller governor, which senses the aircraft’s speed and changes the blade angle to maintain a specific RPM regardless of the aircraft’s operational conditions. This lets the pilot keep the engine speed constant, which lets the pilot focus on other flight conditions.
Feathering propellers are used with multi-engine aircraft. If one or more aircraft engine parts fail, these propellers reduce propeller drag to a minimum. Feathering propellers can change the blade angle of a propeller to 90 degrees and are usually feathered when the engine of the aircraft fails to generate the power needed to turn the propeller. By rotating to an angle parallel to the line of flight, drag is greatly reduced on the aircraft, allowing it to function as a glider.
Lastly, reverse-pitch propellers are controllable aircraft propellers whose blade angles may be changed to a negative value in-flight. The purpose of a reversible pitch is to create a negative blade angle to produce thrust in the opposite direction, which is done to reduce airspeed during landings and take pressure off the brakes.