Counter Rotating Props

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Counter Rotating Props

Postby jerrac » Sun Nov 15, 2009 9:24 am

Is there a model airplane engine that has counter rotating propellers? As in two propellers, one that rotates clockwise, one counterclockwise. If there is, where can I find one?

Thanks!
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Counter-rotating props

Postby przybylski » Sun Nov 15, 2009 4:23 pm

I have never heard of a commercially made model engine which was fitted with the gearbox necessary for counter-rotating props. This would add a lot of weight, and in a small engine, there would be no advantage.
OS of course, did at one time offer a factory fitted gear reduction unit on their 61, but this still only involved one propeller. The advantage there, lay in the fact that the engine was able to turn a larger, higher pitched prop. DuBro and Byron also made these reduction units, although these were belt drive, not gears. In the early 1960's, a modeller in England made a scale C/L Fairy Gannet (won the Scale event at the British Nats with it) and it DID have counter-rotating props, although from memory he used 2 engines to drive them. I think he had an OS Max 35 driving the front prop, and a Max 15 on the rear. The model and the gearbox were descibed in AeroModeller magazine around 1962. BOB
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Postby Frank Klenk » Mon Nov 23, 2009 6:43 pm

Jerrac

At the Toledo Hobby show in 2007 one of the booths that was selling electric motors had one with counter rotating props. Sorry but I can't remember the name. Maybe you can do some searches and come up with it?
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running backwards

Postby pdb » Tue Nov 24, 2009 6:43 pm

Some of the old Cox reed valve 049s would run backwards. If you could carve a suitable pair of props you would be in business. How large an engine do you need?
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Counter rotating props

Postby przybylski » Fri Dec 04, 2009 4:19 pm

See eBay item #280433656700 BOB
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Postby raglafart » Fri Dec 04, 2009 10:33 pm

I remember seeing in an Aeromodeller some years ago, maybe the 60's or 70's and there was a Super Tigre Team race or Speed engine that was pictured with counter rotating props. I recall the caption on the picture said that the power required to drive the gearbox outweighed any performance increase from the theoretical superior propeller arrangement.
Anyone else remember seeing that one?
Cheers John
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Postby blacksea7 » Sun Jan 03, 2010 7:02 pm

They're right... on small engines by the time the gear box is made it outweighs any possible gain... weight, friction, etc. I manufacture over driven coaxial drives for my 5' boats.. weight hardly matters with 75CC plus of supercharged engine in front of it however finding props to absorb the energy is ... challenging... as is the outdrive, prop mounting, etc... but when it works, does it work!!!
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