petri

I'm planning on building a WWII profile twin (B26 maybe, haven't decided for sure) for 3d flying from depron this winter. Picked up a couple of GWS D drives and I'd like to run one "backwards" to cancel torque, make plane easier to hover etc. I can't find much for pusher props for electrics, any ideas? I'm thinking this could be pretty awesome to fly, seperate speed controls mixed to rudder maybe? Should rotate pretty quickly in a flatspin! Any ideas/help on any of this would be appreciated..... Thanks

Matt Kirsch

My Feedback: (21)

Electrics, with their easily-reversible motors, have made pusher props obsolete. That's why you don't see pushers for electrics. All you do is flip the prop over so it's facing forward, and reverse any two wires to the motor. Makes it difficult for those who want to make a scale P-38...

With the props out on the wings, torque won't be as big of a factor. Torque is worst when the thrust line lines up with the central axis of the plane. You can add a little left thrust to the left motor and a little more right thrust to the right motor to completely cancel it out. Then you'll have a scale B26, as most multi-engined planes had engines running in the "conventional" direction.

Flypaper 2

Petri: If you can find a top view of a PBY Catalina You will see that both engines are pointed outwards about 5 or 6 degrees. They fly quite happily on one engine.

petri

Thanks guys....feel stupid......I knew about running the motor backwards. It all made sense after grabbing a prop and looking at it, spinning it, flipping it around I think I'm going to go with an A26, more fuse side area for knife edge. Probably going to still do counter-rotating props to keep forces all evened out and not use any right or left thrust on either motor. I'm no aircraft design expert, but I'm thinking it would be more efficient in flight with everything straight and not having motors trying to pull the plane slightly sideways with side thrust and the other side cancelling it out, seems like a waste of thrust? I don't think I'll have to consider "engine out" performance, using the electrics, like I would worry about with gas or a full scale plane. Boats have used this system with twins for years, must be some advantage? I'm open to any ideas, comments.....

Matt Kirsch

My Feedback: (21)

petri,

You can't just run the motor backwards and get counter-rotating props. To get counter-rotating tractor props, you need to run the motor backwards AND have a pusher prop.

Unless, of course, all you want to do is perform flat spins. With one motor blowing forward, and one blowing backward, the plane will spin around its CG like a helicopter rotor.

I was talking about actual PUSHER applications. Because you can reverse the motor, you don't need a pusher prop. That's why you don't see any pusher props on the market for electrics.

I'm afraid the counter-rotating prop design is out of the question. Sorry.

Wright Flyer

I know that for some of the Wright Flyer kits, to counteract prop torque, some people ran the two motors in opposite directions but to do this they ended up having to carve their own (symmetrically mirrored) props out of a block of Balsa because, like Matt says, you can't buy electric "pusher" props (or perhaps more correctly "reverse rotation" props) because, in the electric world, as Matt says, normally if you want to reverse a prop it's because its pushing rather than pulling and in that case you simply mount the prop the other way round (generally so that the writing is ALWAYS facing forwards on most brands of prop). But for your scale application I fear you'd have to make your own props to have counter-rotating tractor props.

Cliff