Contra-rotating propellers....

Discussion in 'Aviation' started by Lucky13, Apr 28, 2014.

  1. Lucky13

    Lucky13 Forum Mascot

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    Seeing that a contra-rotating propeller was patented by F. W. Lanchester in 1909, why wasn't it experimented more with, maybe not for WWI but for WWII?
    Was there anyone who fiddled with this more than others, US, GB etc., etc?
    What difference would it have made, in for instance the Spitfire or the Bf 109, would it have improved their performance enough to make it worth while?
    Maybe something for the Halifax/Lancaster or B-17/B-24?
     
  2. GregP

    GregP Well-Known Member

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    One of the big problems with contra-rotating propellers is that one has a thinner casing and one has a thicker one. The thinner one sets the g-limit, and the contra-prop planes are all seriously into g-limits with the props.

    The contra-prop Douglas Skyshark actually lost both props in flight and landed with the engines running but no props! It wasn't a good landing.

    At Chino, we built a Spitfire once with a Shackelton contra-prop unit and the g-limit was too low and we said so at the time. It has been converted back to single prop configuration.

    The contra props have good qualities almost balanced by the bad qualities. If they work, it's great. If they don't, you could have a very bad day.

    The Soviet Bear bomber doesn't seem to have issues with it, but they aren't throwing it around the sky at 6+ g's either. They DO have other issues and tend to melt their cowlings due to the 14,500 ESHP engine's heat signature.
     
  3. Shortround6

    Shortround6 Well-Known Member

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    It took quite a while for the contra-rotating propeller to equal the efficiency of the single prop. They are also heavier than a single prop. IF you transmit the power of the engine you are using effectively using a normal 3-4 blade prop why use the contra-rotating propeller? using a 6 bladed contra-rotating propeller on a 1000-1200hp engine is like sticking 9in wide drag slicks on a car with a 150hp engine. Looks koool but actually slows it down.

    If you have 2000hp and are limited in the prop diameter you can use, then by all means try the contra-rotating propeller but be aware of some of the problems like Greg mentioned.
     
  4. Clayton Magnet

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    I remember that Shackleton prop install on the Spitfire, it was cool. I seem to remember Steve Hinton suggesting that it should make an attempt on the time to climb record, whatever happened to that?
     
  5. GregP

    GregP Well-Known Member

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    The aircraft was taken to the UK where it flew for awhile and was converted back to stock engine and propeller configuration.

    Don't believe Steve ever attempted a record ROC in it. Might be interesting to do that in Voodoo or Strega today.
     
  6. Koopernic

    Koopernic Active Member

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    #6 Koopernic, Apr 28, 2014
    Last edited: Apr 28, 2014
    I don't believe there would be much improvement in performance, though there is an improvement in propeller efficiency for a given diameter.

    However contra rotating propellers can produce enormous improvements in handling and safety to the extent that an aircraft with poor handling can develop excellent handling.

    One problem is the effect of gyroscopic precession caused by the propeller. Hence when the aircraft is taking off and lifts its tail the pitch change causes a swing right or left depending on direction of rotation. This problem can be serious and if not handled by a well trained pilot has killed many pilots.

    The second problem is that the circulation caused by the prop wash can cause one wing to stall before the other which can cause the aircraft to flip, ground loop etc. This effected both the Me 109 and Vought Corsair and was partially cured, at least in the landing/take off configuration in latter models the same way by fitting of an extended tail yoke so that the vulnerable wing was above its stall angle when sitting on the tail in the three point attitude.

    The third problem is that the direction of flight is altered due to prop wash which forces the pilot to continuously adjust the trim of the rudder depending on power. Apparently some ww2 pilots used this to make their aircraft 'crab' sideways to throw of the deflection aiming of the enemy.]

    A fourth problem was directionality of turning, eg something to the effect that a Zero can out turn a Wildcat turning left but not right (something like that)

    During the first would war rotary (as opposed) radial engines would rotate the whole engine to achieve sufficient cooling. The effects of gyroscopic precession were very severe with very strange handling in the Sopwith Camel. Some Siemens Schukert fighters had a gear box to ensure the prop rotated at half speed in the opposit direction thereby cancelling the gyroscopic precession effect.

    To me its a dam fine idea and would have cut training time, pilot work load and improved handling significantly.
     
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