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What are the pros and cons of a pull push propeller in comparison to a counter rotating propeller?enter image description here

David Teahay
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  • By counter rotating do you mean both in pull configuration? – fooot May 17 '18 at 18:01
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    And by counterrotating, do you mean one propeller immediately behind the other as in some later P51 configurations? – BillDOe May 17 '18 at 18:36
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    On an ultralight? I would think biggest CON is the weight of a structure to hold all that mass, vs small engines just on the wing. Someone a while back, and I can't find a picture of it, had a small plane with small twin engines, that had a very open canopy, intended for nature shoots. Drawing a blank on the name of it. Was an interesting design. – CrossRoads May 17 '18 at 18:40
  • Take a look at some of the configurations here [1] [1]:https://www.google.com/search?q=ultralight+twin&tbm=isch&source=iu&ictx=1&fir=ZEBebWpSkIfB-M%253A%252CD5pyd5RCZYONLM%252C_&usg=__gp48hX2PiFstvq7ZxNFUl9iDHqc%3D&sa=X&ved=0ahUKEwjH-oqStY3bAhVDq1MKHY9BDMAQ9QEIpQEwBg#imgrc=ZEBebWpSkIfB-M: I think I might be thinking of the Red & Yellow pusher in the 4th row [Air-Cam][2], that's the one https://www.pilotmix.com/images/ac_images/crop/optimized/385_886eb87452a5cacaed28104680a83b63.jpg [2]: http://www.aircam.com – CrossRoads May 17 '18 at 18:52
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    center of gravity is a serious concern, too. – user3528438 May 17 '18 at 19:52
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    Is nobody going to comment on that registration...? – Sanchises May 17 '18 at 20:21
  • don't know about the general concept, but looking at the photo, I wouldn't want to fly something with center of thrust and center of mass so high. – SF. May 18 '18 at 13:04

2 Answers2

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Pusher-puller multi engine vs single or multi engine contra rotating propellers:

Pros:

  • Ideal configuration for a multi engine aircraft as it eliminates thrust asymmetry in the event of an engine failure.
  • As a consequence, improves safety during takeoff, landing and low speed, low altitude flight.
  • Can be a useful arrangement for multi engine flying boats.
  • Does not require oppositely geared engines nor heavy gearboxes.

Cons:

  • Engine crankshaft on the A/C centerline requires a more unorthodox airframe to accommodate which can present additional design challenges.
  • Does not fully eliminate propeller slipstream yaw depending on the aircraft layout.
  • Does not eliminate or reduce yaw from P-Factor.
  • Can be noisier inside the cabin than a twin with wing mounted engines.
  • Aft mounted Engine can be more difficult to cool due to indirect ram airflow.
  • Disrupted airflow from fwd propeller reduces the efficiency of the aft propeller.
Romeo_4808N
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  • You might want to add the lower efficiency of the rear propeller in a tandem configuration (when both are running), because it works in flow accelerated already by the forward propeller. This is especially noticeable at low speed. – Peter Kämpf May 18 '18 at 19:10
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A push-pull arrangement with a "puller" propellor in front of a "pusher" can give rise to problems of aerodynamic interference with the rear propellor at higher power levels, this was a problem with the Dornier 335 fighter.

J. Southworth
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  • "can give rise to problems of aerodynamic interference with the rear propeller at higher power levels"......the engine to be used is 6.5hp...will there still be aerodynamic interference? – David Teahay May 18 '18 at 13:52
  • Assuming that you're talking about a microlight aircraft or something similar, I would not expect serious problems. The Dornier 335 had two Daimler Benz DB603 engines with 1800 to 2000 hp each. – J. Southworth May 18 '18 at 14:33
  • "aerodynamic interference with the rear propellor" - could you please be more precise? Any sources? – Peter Kämpf May 18 '18 at 18:59
  • Offhand, I can't be too precise but if you think about it, a tractor propellor creates spiral pressure waves behind it and this will affect the functioning of the pusher propellor when it's blades intercept these pressure waves. If nothing else, the efficiency of the pusher propellor may be reduced. In the Dornier 335, the situation was complicated by the fact that the pusher propellor was mounted slightly higher than the front tractor propellor. – J. Southworth May 19 '18 at 09:49
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    The book Hitler's Luftwaffe by Tony Wood and Bill Gunston mentions the interference problem without going into more detail. I expect this would have taken the form of vibration and possibly fatigue induced failure if this was severe enough. – J. Southworth May 19 '18 at 16:56