Constant Speed Props

Discussion in 'Technical' started by bob44, Jan 1, 2013.

  1. bob44

    bob44 Member

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    On radial engines during the 1930 and 1940's, how common was a failure of the constant speed prop?
    Esp. P and W's common engines.
     
  2. Jack_Hill

    Jack_Hill Member

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    Difficult to say.
    Wich country, wich constructor ?
    Accidents occured, of course, with, sometimes aircrafts and pilots losses, but seemed to generaly work well with
    Inline or radials engines.
     
  3. nuuumannn

    nuuumannn Well-Known Member

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    In what context? failure of the CS governor itself or the blade actuation mechanism inside the prop hub? The Hamilton Standard C/S 'Hydromatic' prop commonly used on P&W engines in the time specified worked on differential oil pressure acting against a piston, which drove a moving cam inside the hub, all governed by the governor. This was done with oil pressure. If there was no oil pressure, i.e. failure of the oil pump, the whole thing will go south, engine and all.
     
  4. bob44

    bob44 Member

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    Both, governor and/or the blade mechanisms.
    Assuming there was no oil pressure problems.
     
  5. nuuumannn

    nuuumannn Well-Known Member

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    To be honest, I've never heard of such a thing - that doesn't mean it didn't happen, of course (someone might be able to provide examples?). The hydromatic prop was quite hardy and the cam mechanism a chunky piece of metal. The governors used on these were pretty simple and robust; both prop and governor undergoing regular overhaul.
     
  6. nincomp

    nincomp Member

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    I do not know about the props for radial engines. For Allison engines however... In the following P-38 training film, the pilots are told to rev the engines prior to take off to make sure that the propeller governors work. If one fails the engine "runs wild".
    That advice is at about 7 minutes into the film.


    View: https://www.youtube.com/watch?v=PHSH1ZGSWe0
     
  7. stona

    stona Well-Known Member

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    The DeHavilland propeller/CSU (DH/5/39) proved so unreliable that it was not fitted to aircraft ear marked for Fighter Command. They were fitted to tropicalised aircraft and caused much trouble,particularly for the RAAF. There were problems with the blades "sticking" due to the cold and oil bubbling with consequent over revving of the Merlin engines. Engine oil seals failed due to overheating and pressure with subsequently disastrous consequences for the engine.
    Cheers
    Steve
     
  8. bob44

    bob44 Member

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    [QUOTEI do not know about the props for radial engines. For Allison engines however... In the following P-38 training film, the pilots are told to rev the engines prior to take off to make sure that the propeller governors work. If one fails the engine "runs wild".
    That advice is at about 7 minutes into the film.

    ][/QUOTE]

    As far as I know, this was SOP for all constant prop engines. When doing the run up to check mags, the pilot would "exercise" the props, pulling the prop lever through its range, to "loosen up" the mechanism, making sure the oil is flowing and everything is working.
    The P38's had Curtass electric props, no oil, but still mechanical/electric parts to fail. I have read many P38's sent to England had a problem with runaway props, traced back to corrosion in the prop control switches?
     
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