It seems to be generally assumed that the Contra drive will eliminate engine torque effects on a model. In arguing the point with a twin engine enthusiast I'm afraid I lost.

Upon reconsidering the matter it now seems to me that with a single motor shaft drivng some mechanism (no matter how complicated) will produce torque when it accelerates, decelerates or encounters external resistance, per Newton's laws. So I don't see how elimination of torqe can be added to the many advantages of the Contra drive.

What are the counter arguments ?

Is not eliminated, just almost canceled between the two props, but as both props are not identical and the motor itself is turning is not 100% cancelled

Just my opinion

I agree with Tuny. I flew first time the contra this week and clearly there is not torque effect during the takeoff as we usually feel when using single prop drives. Also I could not feel any torque effect when going from level fly to vertical up that are usual in a single prop drive. It was very windy but noticed that rudder is a lot more effective as many have been reporting and corrections to this issue has been explained in other threads. I also noticed that ailerons are more effective but I could be wrong since this could be because of the wing design. I got only 10 flights so I need to fly more to digest more information on trimming when using the contra. However, for sure trimming is a lot easier base on my first observations.

Torque is only one of the effects either cancelled or greatly reduced by the Contra. And I honestly believe torque is relatively minor in most models. Gyro precession is probably the largest one greatly reduced with the contra. P-Factor is another one practically eliminated. And then the greatly reduced spiral slipstream is the last.

The Contra won't make a poorly designed or set-up model in to the perfect plane. And it does have it's own aerodynamic needs from an airframe. But it is the closest to getting "pure" thrust as we have right now. That's an opinion based on over 1,200 flights with a Contra equipped pattern model.

If I were discussing the Contra with a twin-engine enthusiast, I would probably mention two examples from general aviation: The Cessna 337 Skymaster twin with the push-pull engines; and the Piper with the counter-rotating props (Seneca perhaps, I forgot which model).  While not identical to the Contra set-up that we have for models, these twin engine configurations demonstrate that there are ways to manage the untoward effects of having two props that involve sharing the same thrust line and contra-rotation.  The twin enthusiast would then have to disprove the engineering know-how that made these two very successful GA configurations work for many years of safe operation in the hands of satisfied customers.  Not sure I could make a cogent argument out of it, but then again, it would be difficult for the other guy to argue against these terrific twin engine aircraft!

PA39 contra rotating Twin Commanche

Uhoh Tony said Spiral slip stream! Iam picturing the flyinCajun bustin in like the KoolAid man any moment! haha

I thought Brenner would jump in and answer this one, but since he didn't here goes. Yes, the motor does produce a torque that reacts against the airframe, and it produces rpm, in order to transmit power to the props. Power is a function of torque x rpm. The props absorb this power and if we assume 100% efficiency for a second, the product of torque and rpm would be the same at the prop as it is at the motor. Then given a 10 to 1 gear ratio, the props are turning at 1/10 the rpm of the motor and have 10 times the torque. Conclusion, the airframe sees 1/10 the torque it would if it were a direct drive setup like an outrunner with the same prop load at the same rpm . So it isn't eliminated, but is greatly reduced and as Tony said, it is probably not as significant a factor as the spiral slipstream .

Jim O

I am copying and pasting what Brenner wrote in his contra thread. It is clear like water:

1/.. P-factor from prop blades having unequal angles of attack is cancelled out.
2/.. Motor torque into the airframe is divided by the gearbox gear ratio.
3/.. Gyroscopic moment is cancelled out
4/.. Spiral airflow over the wings, stab, & rudder is straightened.
5/.. Propeller efficiency is increased by 10%
6/.. It makes a funny noise when the plane flies. (not loud, just funny...)
7/.. It's much harder to stop the props from digging into the grass when you drag your plane back to the pits.

In the first page of the contra manual there is more detail. I could scan tomorrow is someone is interested.