PSRU Gear Ratio vs. Prop Tip Speed

Discussion in 'Chevy' started by TXFlyGuy, Jan 18, 2017.

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  1. Jan 20, 2017 #21

    BBerson

    BBerson

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    I think the C-185 seaplane is around 1100 fps at takeoff. Not much choice with direct drive.
    But with a gear drive the designer has the option to choose lower tip speed.
    Did the aircraft or prop designer recommend an optimal prop rpm so the builder could then choose a proper gear ratio?
    I think the gear ratio should be calculated after optimal prop rpm is determined.
     
  2. Jan 20, 2017 #22

    Swampyankee

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    The engine and prop makers always talked to each other, so set the ratio based on prop makers' estimates.
     
  3. Jan 20, 2017 #23

    N8053H

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  4. Jan 20, 2017 #24

    TXFlyGuy

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    And the people at Titan Aircraft are working in concert with Whirlwind on the development of this propeller. Providing the performance criteria and engine operating specs.
     
  5. Jan 28, 2017 #25

    skypuppy

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    Don't forget to add forward speed to the prop rotational speed in calculating prop tip speed. IIRC, the torque curves on the LS engines are pretty flat (relatively) so you may be spending lots of money for diminishing returns.
     
  6. Jan 28, 2017 #26

    TXFlyGuy

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    The gear reduction ratio is 2.21-1. That will allow for slow tip speeds, and let the engine run at a good rpm. PSRU not ready for shipment until June, this year. The propeller might be ready by April.
     
  7. Feb 3, 2017 #27

    TXFlyGuy

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    The LS3 is undergoing Dyno break in right now, plus the programming of the ECU for max torque between 2500 and 4500 rpm. The 2.21-1 ratio will work just fine.
     
  8. Apr 6, 2017 #28

    TXFlyGuy

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    I have been advised that a 94" propeller will be the goal, as it will work better than the 96" version. Here is a photo of an MT 94" prop, on a 3/4 scale plans built Jurca P-51:
    IMG_1490.jpg
     
  9. Apr 6, 2017 #29

    Swampyankee

    Swampyankee

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    As long as the blades aren't heavily stalled.
     

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