An actual question my five year old asked me and I couldn’t answer, please help!
In: Physics
Its a balance between a lot of factors
Each additional blade adds more weight and cost which requires stronger($$$) engine components to overcome the increased drag from additional blades trying to move through the air. They also disturb the air they pass through so having 8 blades instead of 4 won’t give you twice the power because the extra blades are now passing through disturbed air and not working as efficiently. Generally you get better results from increasing the length of the propeller but this requires a stronger propeller($$$)
Generally the better option is to have a second cheap engine/propeller set (think twin engine propeller planes or the Chinook), or to use more elaborate propeller setups like [Contra-Rotating propellers](https://en.wikipedia.org/wiki/Contra-rotating_propellers) which boosts propeller efficiency giving you more thrust with the same horsepower despite driving two different sets of blades. This was used on the later Spitfires to get the most power possible out of their limited propeller diameter.
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