Torsional Vibration on a long shaft?

Discussion in 'Mazda Rotary' started by RSD, Jun 1, 2019.

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  1. Jun 7, 2019 #61

    RSD

    RSD

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    For me it is going to be a fun aircraft to fly, I haven't specifically looked for potential weight savings but I haven't noticed anything that looked over engineered or probably not needed. Being a trainer it is built reasonably solidly knowing that it would probably suffer the odd hard landing etc.
     
  2. Jun 7, 2019 #62

    BBerson

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    I am wonduring how these rotors or engines are coupled? (I don't know anything about rotaries)
    But I am trying to couple two small industrial engines.
    I think a custom engine is much lighter than coupling multiple engines.
     
  3. Jun 7, 2019 #63

    RSD

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    I don't know the specifics but they were mounted one above the other according to a drawing that I saw on the www.
     
  4. Jun 7, 2019 #64

    TFF

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    Slapping two engines together in drag racing was big in the early 60s. I think some of the side by sides were driving a wheel each. Streamliners at Bonneville are using multiple engines on the really fast cars.
     
  5. Jun 7, 2019 #65

    BJC

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    TFF, that hot rod reminds me of several cars in a local museum.

    To those of you who are gear heads and will be vacationing in Florida:

    Bring lots of money; you make it possible for us not to have a state income tax.

    Schedule half a day at the Don Garlits Museum of Drag Racing, just south of Ocala, on I-75. See https://garlits.com/

    The museum has other drivers’ cars, and you don’t need to be a big fan of drag racing to enjoy it. When you finish seeing the drag racing museum, go to the other building and check out Don’s collection of old cars. Or check out the A-7 on a pole.


    BJC
     
  6. Jun 7, 2019 #66

    rv7charlie

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    The thermal limit is in removing waste heat from the rotor assembly. Turbo for more power per rotor would just make the problem worse.
     
  7. Jun 7, 2019 #67

    pictsidhe

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    Not for more power per rotor, but to raise the BMEP and lower the rpm that the thermally limited power is produced at.
     
  8. Jun 7, 2019 #68

    rv7charlie

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    Maybe, but unlikely. The rotary (at least the Mazda based version) is an inherently low torque, high rpm engine. As a loose analog, consider a 'low rpm turbine'.

    Remember, the E-ehaft (crank) is turning at 3X rotor rpm, so 1/3 the torque. There have been a few 'pie in the sky' ideas of taking power directly off a rotor, but I've never seen anyone build a functional, working model from the drawings.
     
  9. Jun 7, 2019 #69

    wsimpso1

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    These engines are kind of neat this way. For a single, you have a rotor and periphery housing, a front cover, a back cover, and an eccentric shaft with one eccentric that goes through the whole stack. Two rotor has front cover, rotor and housing, intermediate cover, rotor and housing, back cover, and eccentric shaft with two eccentrics. You can stack up as many as you want with intermediate covers, rotors and housings, one front cover, one back cover, the custom parts are just the manifolds and the eccentric shaft. I suppose you would run into shaft strength/stiffness at some point...
     
  10. Jun 7, 2019 #70

    rv7charlie

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    Don't know about that particular case, but it's been done lots of ways. Aviation applications typically would use some type of overrun clutch on both engines, so loss of one won't take out the other.
     
  11. Jun 7, 2019 #71

    BBerson

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    That stack ability is neat. Looks like the center output shaft is spline coupled. Is that considered rigid or some lash?

    Looking at this animation:https://en.m.wikipedia.org/wiki/Wankel_engine
     
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  12. Jun 7, 2019 #72

    BBerson

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    I am looking more to simplify and make one rigid engine from two.
     
  13. Jun 8, 2019 #73

    rv7charlie

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    The 13B has a 1 piece E-shaft. The 20B 3 rotor has a 2 piece shaft, that is a press (interference) fit; the joint is in the wider intermediate housing. Can't say for sure, but I'd bet that the 4 and higher count engines use rigid couplings, as well.
     
  14. Jun 8, 2019 #74

    RSD

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    Generally yes a one piece e-shaft. I haven't seen any rotaries with more than six rotors in a line but whether that is because of lack of need, lack of space in an engine bay, or whether six is the limit on the length of the shaft I don't know.

    But anyway...


     
    Last edited: Jun 8, 2019
  15. Jun 8, 2019 #75

    wsimpso1

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    Oh, it has to be rigid, which would drive some sort of press fit.
     
  16. Jun 8, 2019 #76

    RSD

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    Was confirmed to me today that six rotors on one shaft is the limit currently due to twisting shafts beyond that.
     
  17. Jun 8, 2019 #77

    wsimpso1

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    Looking for animation, all that I saw was of the rotor running. There is a fixed gear and a gear in the rotor, and that keeps the rotor in time. The eccentric shaft runs down the middle with a big journal for each rotor. The rotor transmits power to the eccentric... Is that what you were talking about?

    looks pretty good. The flywheel attachment to the eccentric shaft is rigid. The key is to align a counterweight to the correct position, that huge nut with 360 ft-lb of torque on it locks flywheel and hub to the eccentric shaft.

    For three and four rotors, folks have talked about how they are more than one piece. I am unfamiliar...

    Billski
     
  18. Jun 8, 2019 #78

    pictsidhe

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    I'm wondering if you could make split bearing holders for centre bearings. As rotors are fitted, assemble a bearing holder over the next 'main bearing' and slide on the intermediate.
     
  19. Jun 8, 2019 #79

    wsimpso1

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    Oh so there is a limit...

    On two rotor engines the eccentrics are at 180 degree from each other and they just alternate. On more than two, is there any logic to the firing order, and what is customarily used in each of three, four, five, and six rotors?

    Next, I am curious what the max continuous hp (cooling limited) are for aluminum housing engines. And is it different between side ported and peripheral ported systems?

    Billski
     
  20. Jun 8, 2019 #80

    Hot Wings

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    Split the shaft in half and take the power off the middle like a Porsche 917? A reverse rotation peripheral port should be simple enough?
     

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