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Counter-rotating propellers

Discussion in 'The Okie Corral' started by gwalchmai, Jun 15, 2017.

  1. gwalchmai

    gwalchmai Lucky Member

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    Why don't all multi-engine airplanes use counter-rotating propellers?

    Did pushme-pullyou designs such as the Do-335 and the Skymaster use counter-rotating propellers?

    Do multi-engine jets use counter-rotating turbines?
     
  2. AK_Stick

    AK_Stick AAAMAD

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    Not sure about the DO, but the skymaster is contra-rotating, as they're in the same axis.

    Engines on the same wing, but turning the opposite way would be counter rotating
     

  3. itisbruno

    itisbruno Devious Member CLM

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    Science is hard.
     
  4. gwalchmai

    gwalchmai Lucky Member

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    Or technology, anyway.
     
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  5. gwalchmai

    gwalchmai Lucky Member

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    OK, good point. But if there's an advantage to counter-rotating on, say the P-38 or F-82, (torque balance, maybe) why aren't all multis designed to do it? Not enough benefit to justify the cost?
     
  6. Steel Head

    Steel Head Tactical Cat

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    IMG_9885.GIF
     
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  7. tous

    tous GET A ROPE!

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    You may be using an unclear definition.
    Counter-rotating propellers are on multi-engine aircraft and they are alone on one axis.
    The are counter rotating because the prop on one side tuns clockwise, the prop on the other side turns counter clockwise.
    The biggest problem is that you essentially have two different engines, one left, one right and the associated complexity of maintenance thereupon.

    You may be thinking of contra-rotating propellers such as we see in the Russian TU-95.

    For contra-rotating propellers, the opposite spinning propellers basically cancels the engine torque, but the require some magic engineering to get them to work.
    :wavey:
     
  8. Nucflash

    Nucflash

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    The Do-335 used counter-rotating propellers but not in the way that the Russian Bear bomber does (contra-rotating I believe has been stated here). It had a forward engine to pull and an aft engine to push the aircraft. Neither of the engines had counter/contra-rotating propellers although the two engines rotated opposite each other because one faced forward and the other faced aft..
     
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  9. AK_Stick

    AK_Stick AAAMAD

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    Cost.
     
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  10. itisbruno

    itisbruno Devious Member CLM

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    See, I tolt ya, science is hard.
     
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  11. AK_Stick

    AK_Stick AAAMAD

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    Those are kind of contra rotating, as they turn about the same plane. Though the engines actually turn the same direction, they're just mounted facing in different directions.

    Two engines on the same wing that turn the opposite direction, would be counter rotating. I.E. the Airbus A400M
     
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  12. aircarver

    aircarver Descent Terminated Silver Member

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    With the exception of the Russian 'Bear', the industry didn't adopt counter-rotating turbines because of ever tightening requirements for fuel economy. (The Russians don't care how much fuel the circa 1954 'Bear' burns.)
    American industry tried turbo-props in the same era (Viscount, Electra) and those lost out to jets in speed and economy. (The Navy kept the Electra (P-3 Orion) for patrol, 'cuz speed wasn't needed )
    Counter-rotating props allow a lot of power to be put through a disk size fixed by prop tip speeds hitting supersonic & wasting mucho energy, but the turbulence at the prop interface is itself wasteful of energy.
    Cargo planes (C-130) are a niche where turboprops are more efficient than jets, at the cost of speed .... but speed can be sacrificed for cost with cargo.

    No 'cuz the parts tail for a left and a right turning engine would be too expensive. They can all turn the same way and the torque can be compensated aerodynamically.
     
    Last edited: Jun 15, 2017
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  13. AK_Stick

    AK_Stick AAAMAD

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    Contra
     
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  14. aircarver

    aircarver Descent Terminated Silver Member

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    Some Piper twin trainers (PA-34 Seneca) had counter-rotating piston engines to minimize the P-factor when training for single engine operation. Piper doesn't make enough of these any more for me to say if it is still available if you ordered one, but maintenance was a PITA 'cuz you needed to stock parts for a left hand or a right hand engine ...:frown:
     
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  15. AK_Stick

    AK_Stick AAAMAD

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    I believe they atleast in the Lycoming brand were O and LO engines.

    O-360 conventional rotation
    LO-360 counter rotating (Left hand rotation)
     
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  16. aircarver

    aircarver Descent Terminated Silver Member

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    Yeah sorry was typing & conversing with two active toddlers ... :alex:
     
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  17. AK_Stick

    AK_Stick AAAMAD

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    All good my friend, all good.
     
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  18. tous

    tous GET A ROPE!

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    Bear = contra-rotating.

    Other than that, right on.
     
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  19. gwalchmai

    gwalchmai Lucky Member

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    Yes, that's more clearer. I meant counter, as in the P-38. IIRC, the P-82 (maybe the 38 as well) used mirror-image crankshafts (?).
     
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  20. Bruce M

    Bruce M

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    Isn't the better question why don't all twin engine planes look like this?
    [​IMG]
     
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