Aircraft powered by piston and turboprop engines feature propeller blades that pull or push on the air around the aircraft to provide propulsion. As piston engines have become more powerful, they require more and more propeller blades.
To understand why, we need to understand the working principle of a propeller. The purpose of a propeller is to “absorb” the power produced by the engine and transmit that power to the air passing through the propeller, which generates the thrust force that propels the aircraft through the air. Therefore, if the propeller and engine are not properly matched based on the power of the engine, the system is inefficient.
As engine power increases, the designer has several different options to design an aircraft propeller that can efficiently absorb that power. However, most of these options have severe drawbacks.
Therefore, there are two viable options for increasing a propeller’s output. Either you can increase the blade’s width, or chord, or increase the number of blades on the propeller. Increasing the blade chord is easier, but once again, changing the chord affects the aircraft’s aerodynamic efficiency. Thus, this leaves us with the last option, increasing the number of aircraft propeller blades. By doing so, you increase the solidity of the propeller disk, the space that the propeller rotates in. By increasing the solidity, the propeller can transfer more power to the air, thus increasing thrust.