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I read that a three blade can improve climb performance and decrease noise. How does that work?

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At the absolute simplest, compared to a two-bladed propeller, a slightly smaller three-bladed propeller can produce more thrust at a given RPM, improving climb performance. Because of the smaller diameter, the propeller tips actually travel slower than the equivalent two-bladed design, reducing noise inside and outside the airplane.

Hartzell Propeller has a great set of technical answers about propellers. Their explanation of why more blades produces less noise is pretty good:

A 2-blade propeller produces two pressure pulses per revolution, where a 3-blade propeller will produce three smaller pulses per revolution (for the same amount of total thrust) which is inherently smoother and therefore quieter. The 3-blade propeller will generally have a smaller diameter than the 2-blade propeller that it replaces, which also reduces the tip speed and noise.

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  • $\begingroup$ Thanks for the answer! if it produces more thrust at a given rpm, does the engine use more gas, or the same? $\endgroup$ Dec 23, 2013 at 15:38
  • $\begingroup$ I imagine it would use more fuel as it's doing more work (producing more thrust). The Hartzell FAQ I linked mentions that two-bladed designs are the most efficient, but that more blades can produce more thrust and therefore can be advantageous. $\endgroup$
    – egid
    Dec 24, 2013 at 3:47
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    $\begingroup$ A practical aspect using more blades is larger ground clearance. $\endgroup$
    – yankeekilo
    Dec 24, 2013 at 11:12
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    $\begingroup$ @Garrison Neely: a simplification, but for a given engine fuel usage is more or less proportional to power output, as example HP or KW. At a given speed, power output is proportional to thrust. $\endgroup$
    – ghellquist
    Dec 20, 2018 at 21:27

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