Counteracting torque - Need help!

[zbrubaker]

Here's the scenario...I'm designing a parkflyer size Cessna 337 Skymaster. Powerplants will be two GWS IPS. Ideally it would be great to have the props counter rotating so that the torque would nullify itself, but there just aren't may options in this regard. So...what would be the best way to minimize prop torque with two inline motors?

[Ollie]

Reversing rotation of a motor isn't necessary on a tandem motor arrangement because the torque will cancel. The only thing that has to be done is to pull the rear prop off, turn it over and remount it so that it provides forward thrust with the normal motor polarity and rotation when the shaft points to the rear.

What could be easier?

[zbrubaker]

Originally posted by Ollie
Reversing rotation of a motor isn't necessary on a tandem motor arrangement because the torque will cancel. The only thing that has to be done is to pull the rear prop off, turn it over and remount it so that it provides forward thrust with the normal motor polarity and rotation when the shaft points to the rear.

Not quite...basically what you just said is 'turn the motor around and it will work fine'. If the rear motor/prop rotation is the same as the front motor/prop, they will end up blowing towards each other. Reversing the prop doesn't change the direction of thrust.

In order for the torque to cancel, the props need to be turning in opposite directions. If they are turning in the same direction, the torque will basically double.

I understand what your saying, but it will only work if the prop has reverse pitch.

[HarryC]

You need a pusher prop, they are made in the more common larger sizes for ic motors, but I don't know if anyone makes them at the very small size.

[zbrubaker]

Originally posted by HarryC
You need a pusher prop, they are made in the more common larger sizes for ic motors, but I don't know if anyone makes them at the very small size.

I know...like I said, unfortunatly there aren't many options for pusher props for this size of plane.

[Ollie]

Oops!

[Sparky Paul]

Wire the motor to use a normal prop. Forget the torque situation.

[zbrubaker]

Originally posted by Sparky Paul
Wire the motor to use a normal prop. Forget the torque situation.

Why do you say that Paul? I would have thought that two props spinning in the same direction along the centerline (sort of) of the plane would make for very poor right turns and very dicey left turns.

[rorywquin]

Originally posted by Ollie
Oops!

not like you to slip up ;)

[rorywquin]

Originally posted by zbrubaker
Why do you say that Paul? I would have thought that two props spinning in the same direction along the centerline (sort of) of the plane would make for very poor right turns and very dicey left turns.

What direction do the props turn on the real one ??

[Sparky Paul]

Originally posted by zbrubaker
Why do you say that Paul? I would have thought that two props spinning in the same direction along the centerline (sort of) of the plane would make for very poor right turns and very dicey left turns.
.
The plane won't be that responsive.

[zbrubaker]

Could you please explain that a bit Paul? I'm just trying to understand the 'why' behind what your saying.

[zbrubaker]

Originally posted by rorywquin
What direction do the props turn on the real one ??

I'm not sure...I've tried to look on the internet about it, but I cant find anything. I pretty sure they are counter rotating. Otherwise the rear prop would be less effiecient

[Sparky Paul]

Torque effects can be overstated.
With a rotary motored Camel, which has a large heavy motor, the torque effect was what killed most of the people that flew it.
With a small park-flier, the inertia of the plane will damp out any torque effects.
My push-pull Kadet 337 uses a pusher prop on the back motor, which runs "normally" so any torque effect from both motors is cancelled. However it will perform adequately on both or either with nothing alarming occuring when either motor quits.
Another version of it made closer to scale flies equally well, with both running or only one.. makes little difference.
The most noticeable difference in flying between the two is the more scale-like is more sensitive in pitch, due to a much smaller horizontal, than the more Kadet based version.

[vintage1]

Lord. You guys started drinking for Xmas already?

The camel suffered from gyroscopic effects due to the heavy spinning motor. Not the same as torque.

Torque isn't generally a problem until the model airspeed drops, and then it usually rolls the model into a left wing and nose dropping stall and recovery.

In flight, the wings resist the rolling motion and a little right trim on ailerons keeps it all level.

You can reduce torque by using smaller prop and less gear reduction. Id go for the 3.75 gearing and the 7x6 props on this one.

Mix a little right stick in with the throttle.