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4 Answers

Propeller Efficiency

Asked by: 4448 views Aerodynamics, Aircraft Systems

Which statement is true regarding propeller efficiency? Propeller efficiency is the A

OPCION A: ratio of thrust horsepower to brake horsepower.

OPCION B: actual distance a propeller advances in one revolution.

OPCION C: difference between the geometric pitch of the propeller and its effective pitch.

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4 Answers



  1. Nathan Parker on Sep 05, 2012

    Efficiency has no units of measure, so you know it can’t be B or C, which have dimensions of Length.

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  2. Eric Hawicz on Sep 05, 2012

    The answer can also be found in the PHAK, Chapter 4, on the section on basic propeller principles.

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  3. Steve Pomroy on Sep 05, 2012

    Hi Khoda.

    Efficiency is a measure of how well a device (such as a propeller) converts an input into an output. For a propeller, the input is brake horsepower, and the output is thrust horsepower. Divide the two and you get a number between 0 and 1. This is your prop efficiency, where 0 means that all of the input is lost to waste (inefficiencies), and 1 means that the conversion is perfect (not gonna happen in the real world). Efficiency can be converted to a percent if you multiply by 100. Nathan also raises a good point about units/dimensions.

    Cheers,
    Steve
    http://www.flightwriter.com
    http://www.skywriters.aero

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  4. superbird3000@yahoo.com on Oct 02, 2012

    The correct answer is option C.

    100% efficiency would indicate that the propeller moves forward the entire pitch of the prop in one revolution. Since nothing is 100% efficient, the prop will move somewhat less than the actual pitch, which results in a ratio. That is your efficiency (if the pitch is 42″ and the efficiency is 80%, then the actual forward movement in 1 revolution would be 33.6″). This is consistent with boat propellers as well.

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