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  1. #1

    Electric Power Plants

    I was reading about the electrical prototypes in EAA SportAviation, July issue. The articles mention various power plants that deliver 27 hp with 20 KW and 54 hp with 40 KW and various voltages---no amps discussed. Is there a basic article or forum that explains the electrical parameters of motors/generators used in this airplanes? Thanks

  2. #2
    Dana's Avatar
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    HP and kW are both measures of power. 1HP = 0.746kW so 27HP = 20kW, etc.

    The current (amps) depends on the voltage. Volts X amps = watts so your 20kW motor would draw 833A at 24V, 416A at 48V, 200A at 100V, etc.

  3. #3
    Got that--and helpful---so, how do you calculate how long the battery will operate the prop ? Obviously depends upon work load but is there a typical formula for prop/gross wt of plane calc?
    Thanks

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    Matt Gonitzke's Avatar
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    The battery's capacity will help you determine how long you can operate the electric motor. For example, a 500 A-hr battery would deliver 50 amps for 10 hours, or some other product of current and time that multiples to 500 A-hr. So the 20kW motor being operated at 100V draws 200A and would have a battery life of 2.5 hours with the fictional battery I made up as an example.

    I guess I'm not completely sure what you mean when you refer to 'prop/gross weight of plane' calculations. If I may assume you are trying to size a powerplant and propeller for a particular aircraft, a good aircraft design or aircraft performance book will contain the numerous equations necessary to size the powerplant and propeller.

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    Dana's Avatar
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    Quote Originally Posted by Matt Gonitzke View Post
    The battery's capacity will help you determine how long you can operate the electric motor. For example, a 500 A-hr battery would deliver 50 amps for 10 hours, or some other product of current and time that multiples to 500 A-hr. So the 20kW motor being operated at 100V draws 200A and would have a battery life of 2.5 hours with the fictional battery I made up as an example...
    ...and before anybody gets excited, that's a 20 kW-hour battery. That's a big battery. With current Li-po battery technology, that's 220 lbs of batteries. For only 27HP.

  6. #6
    Matt Gonitzke's Avatar
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    Indeed. That was made up to make the numbers easy, and highly unrealistic with today's battery technology.

  7. #7
    steveinindy's Avatar
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    Quote Originally Posted by Dana View Post
    ...and before anybody gets excited, that's a 20 kW-hour battery. That's a big battery. With current Li-po battery technology, that's 220 lbs of batteries. For only 27HP.
    Yeah, welcome to why most of us (over the age of 30) will never see anything bigger than a small LSA powered by electric motors in our lifetimes. All of this effort and money are being spent on the aviation equivalent of a sideshow attraction.

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