Anyone deviate with their engine choice?

Discussion in '2-Stroke Aircaft Engines' started by Jeff Higgins, Dec 9, 2019.

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  1. Dec 10, 2019 #21

    Jeff Higgins

    Jeff Higgins

    Jeff Higgins

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    Slippage and breakage
     
  2. Dec 10, 2019 #22

    pictsidhe

    pictsidhe

    pictsidhe

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    Because of?
     
  3. Dec 10, 2019 #23

    Jeff Higgins

    Jeff Higgins

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    Dude, I’m beyond qualified to machine and make my own redrive and prop hub. I don’t overlook steps and I know what’s needed for it to safely function and last. Prime example: people often try to use pillow block bearings and a collar with set screw but neglect to realize the amount of thrust force on the bearings, shaft and collar. I’m no dummy. I’ll be fine.
     
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  4. Dec 10, 2019 #24

    pictsidhe

    pictsidhe

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    No offence, but you've not mentioned the issue that kills more beautifully and badly machined redrives than everything else put together...
    Google 'torsional vibration'. It's not a simple task to design around. But it is possible. Machining a good design is the easy part.
     
  5. Dec 10, 2019 #25

    Jeff Higgins

    Jeff Higgins

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    I was an ASE certified master tech for 17 years so I am aware of it. It’s the reason that front crank pulleys have a large amount of rubber cast between the inner and outer pulley, to absorb “harmonics”.
     
  6. Dec 10, 2019 #26

    Jeff Higgins

    Jeff Higgins

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    Car engines, that is.
     
  7. Dec 11, 2019 #27

    BBerson

    BBerson

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    I measured 90 pounds static thrust with a 20hp 250cc Fuji Polaris engine. 30" diameter and wide chord prop, direct drive.
    I think it weighs 30 or 40 pounds.
     
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  8. Dec 11, 2019 #28

    proppastie

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    I guess I do not understand it.....all those PPG engines do they have more than just a couple of pulleys and a belt drive?
     
  9. Dec 11, 2019 #29

    Jeff Higgins

    Jeff Higgins

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    That’s typically all they have because they use such a short, robust stub of a shaft and everything is well balanced.
     
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  10. Jan 16, 2020 at 6:31 AM #30

    Armilite

    Armilite

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    =================================
    The Arctic Cat JAG 2000 275 Twin Free Air is 20hp@6000rpm with a Muffler, JAG 3000 340 is 30hp@6000rpm with a Muffler, and 440 was 40hp with a Muffler. A Twin is going to be Heavier than a Single. 20hp x 7cc = 140cc with a Tuned Pipe Designed for 6500rpm. Hirth makes a Direct Drive Hub for there Engines but I have never seen anyone using it, or a photo of it. A Kawasaki 292 Single was rated 20hp@5500rpm with a Muffler, and 22hp@6000rpm with a Muffler. Every Brand Name (25+) Snowmobile Engines made a 292 Single. Kawasaki, JLO, Sachs, others, had threaded holes on PTO Case to run a Belt Drive. Since your only using it for Takeoff of your Motor Glider. You could turn it 7000rpm for 2 Minutes for takeoff, then throttle back to gain your desired Altitude.

    At 77F, using Calc: http://godolloairport.hu/calc/strc_eng/index.htm

    A 32" x 8 (2) Blade can be turned 7000rpm and make 137.76 lbs Static Thrust! Needs 19.547 hp. 2 min Takeoff only!

    A 32" x 8 (2) Blade can be turned 6000rpm and make 101.21 lbs Static Thrust! Needs 12.309 hp.

    A 32" x 8 (2) Blade can be turned 5500rpm and make 85.04 lbs Static Thrust! Needs 9.481 hp.
    ------------------------->
    A 32" x 13 (2) Blade can be turned 6000rpm and make 101.21 lbs Static Thrust! Needs 20.003 hp.
     
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  11. Jan 16, 2020 at 3:42 PM #31

    proppastie

    proppastie

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    Do centrifugal clutches adsorb harmonics? (slippage?)
     

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