twin engine question

[81zapper]

Thinking of building an electric foam board twin motor plane and maybe quad one day
How do you determine when to have motors spinning in the same direction or opposite direction?
Is it just a general rule to have twins rotate opposite?

 

[pressalltheknobs]

Thinking of building an electric foam board twin motor plane and maybe quad one day
How do you determine when to have motors spinning in the same direction or opposite direction?
Is it just a general rule to have twins rotate opposite?

A inertia of a rotating motor tends to twist the vehicle in the direction of the rotation which will cause it to steer in that direction.

Unless you have good reason not to, it is always better to have the motors on a twin, counter rotate because they will cancel out the torque steer. You can compensate with thrust angles and control surfaces but that will only minimize the effect.

On a quad its very important because while it may be possible to stabilize a set of props that all rotate in the same direction the stabilization will start off biased to one side and limit the overall range of control. Since there is nothing to be gained, it is not done. The one exception is tri-copters and related set ups where there is explicit yaw control that can be mechanically positioned to balance out sideways drift.

 

[81zapper]

Thanks

makes sense Thanks for the input appreciate it


pb

 

[quorneng]

The other thing to remember is that compared to full size most model planes are considerably over powered so the effects of motor torque are more pronounced.
This was why only the most powerful and light full size prop planes have counter rotating props for example the Lockheed Lightning, DH Hornet. Even the four engined Airbus A400M Atlas has counter rotating prop pairs on each wing.

 

[Capt_Beavis]

The need for counter rotation is overstated in my opinion. The axis of rotation of of each motor is different and the torque on the center of the plane is actually in counter directions. I have a delta ray I put brushless motors on. I did both CCW for each motor and CCW/CW and I noticed no difference in flight. I now have counter rotating props just because it is kind of cool on a plane and there are plenty of props available. But the FT Mini Cruiser with a twin power pack comes with two CCW props.