Pusher Prop or Reverse Engine?  
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All Forums >> RC Airplanes >> Twin & Multi Engine RC Aircraft >> Pusher Prop or Reverse Engine?
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Pusher Prop or Reverse Engine? - 5/2/2008 5:57:30 PM   
Radical Departure



Posts: 115
Joined: 7/19/2003
From: Fayetteville, AR, USA
Status: offline 		Hi All..
Am planning my build of the KMP Adam A500, my first twin. Am setting it up w/ electric motors, and have a couple questions I can't seen to find answers for via forum search.

This is a push-pull configuration. I'm assuming that no thrust needs to be set, just use whatever is given on the firewall?
Now to the part that confuses me 2 motors out of the box, typically rotate clockwise, as seen from behind the prop, according to how the leads are plugged on a typical single setup. This is fine, since one in front and rear, that would seem to offset torque. A pusher prop would seem to push the air out in this case, as IF the motor was ran reversed? Is that correct? If you ran one motor reversed, that would put all the torque to one side, correct? It would seem easy to want to reverse the rear motor and run a standard prop, but am thinking that again, both motors would therefore turn the same direction hence too much torque?

If someone can set me straight on push-pull, it would be appreciated!

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Radical Departure..
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RE: Pusher Prop or Reverse Engine? - 5/2/2008 7:47:42 PM   
smedsky


 

Posts: 218
Joined: 1/14/2003
From: Kirkland, WA, USA
Status: offline 		I think props are very ineficient when turning in the backwards direction from which they were designed but if motors are mounted fore and aft I think the torque will cancel out

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RE: Pusher Prop or Reverse Engine? - 5/2/2008 7:58:02 PM   
evan-RCU



Posts: 2678
Joined: 2/4/2002
From: Charlotte, NC, USA
Status: offline 		Keep the motors turning the same way and put a pusher prop on the rear..

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RE: Pusher Prop or Reverse Engine? - 5/2/2008 8:38:52 PM   
Red B.


 

Posts: 1022
Joined: 8/29/2002
From: Jonkoping, SWEDEN
Status: offline 		I have flown a Cessna 337 twin that had two OS46 engines, the rear one modified to run in the reverse direction and using a tractor type propeller. Torque was not an issue at all. Tractor propellers are easier to find, available in more sizes and are usually less expensive than pusher-type propellers.

< Message edited by Red B. -- 5/2/2008 8:42:04 PM >

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/Red B.

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RE: Pusher Prop or Reverse Engine? - 5/2/2008 9:31:20 PM   
Villa



Posts: 875
Joined: 8/12/2003
From: Wilson, NC,
Status: offline 		Hi Radical Departure
I designed and built a SPAD pusher/puller using two standard .28 Magnum engines and 9 X 6 props. The rear was a pusher prop. My plane could not do a crisp snap roll. Since I do snap rolls with all of my planes, I decided that the reason was the props going in opposite directions. As I recall, it could also not do a good Hammerhead stall. What Red B is suggesting may be the way to go. Since it is electric you can experiment with both. Let us know.

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       Post #: 5

RE: Pusher Prop or Reverse Engine? - 5/10/2008 12:05:06 AM   
Boomerang1



Posts: 870
Joined: 6/24/2005
From: Sydney, AUSTRALIA
Status: offline 		I had a similar problem for pusher props for a scale model. I just run the motors in reverse & use tractor props fitted backwards on the shafts, that is the CURVED face of the prop MUST face forwards.

As for the torque of the two motors together in the same direction? , just the same as the torque of one bigger motor if you ask me. - John.

BTW, sharp looking plane!

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< Message edited by Boomerang1 -- 5/10/2008 12:08:53 AM >

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RE: Pusher Prop or Reverse Engine? - 5/10/2008 12:51:04 AM   
Wayne22



Posts: 4349
Joined: 4/10/2002
From: Edmonton, AB, CANADA
Status: online 		One of the primary reasons of having a pushme pullyou configuration is that the torque from each motor cancels out the torque from the other making for much better handling qualities. If the rear motor is reversed (and a tractor prop used) the torque will be additive resulting in an increased yaw tendancy to the left. Since you don't have a rudder in the slipstream, it may cause handling problems at low speeds. Pusher props are very much available from Zinger, Master airscrew, APC and Graupner. Pusher props for electrics, thought, are pretty rare..... but there is law saying that yoiu have to use electric props...FWIW.





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RE: Pusher Prop or Reverse Engine? - 5/12/2008 4:01:33 PM   
Radical Departure



Posts: 115
Joined: 7/19/2003
From: Fayetteville, AR, USA
Status: offline 		Hey Guys.. thanks for the info. From what I'm reading, since there are several pusher props available for electric, it shouldn't be too difficult to finish with a setup that cancels torque and pushes it throught the air as designed.
Boomerang1, the pic does very little justice to the kit. A far better representation can be seen in the June Model Airplane News. It would have been the cats meow to have been able to get one unpainted. Since its my first scale project, I'm in the process of taking it down to the primer, for a final pearl white paintjob that will reflect Adams N501AX, #C0002. Man.. you talk about some work.. it'll take me 3 months or better just to get that much done! But.. may as well take time and do it right... we'll see just how sturdy the Black and Decker Mouse sander is!

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Radical Departure..
..from controlled flight

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