Starting this section, I need to state up front that I am not sold on the idea of using aileron differential. I
have tried it, but never found it to help. It was first used on slow moving full scale planes that were not aerobatic,
to correct adverse yaw. In pattern we spend half our time inverted, and aileron dif works totally opposite what you
need when you are inverted. But, a lot of guys swear by it. So I will give you the details of setting it up, and
let you decide if you want it or not.
Aileron differential is simply a mix that deflects the up aileron more than the down aileron deflects. The reasoning
is that the wing that is being raised will develop more drag than the wing being lowered. This causes the plane to yaw
away from the direction of turn. To counter this drag, we put more of the upward deflected aileron into the airstream
to balance the drag on the opposite wing.
To check if you need aileron dif, fly perfectly vertical up-lines. On the line, roll the plane and watch it.
If it rolls on a string and stops still going vertically, you're good. Don't worry about using aileron dif. If
the plane appears to wallow, or barrel role, with heading deviation as it rolls - then some dif may be helpful.
(Be advised that certain designs, like the CAP232, tend to barrel no matter what you do. You will just have to fly around
it.) Before adding the dif, double check to make sure the plane will fly a hands-off, full power up-line. I have
found that a lot of barrelling planes were simply in need of a vertical thrust line adjustment. If everything checks
out, then try adding the dif.
Most radios have a built in Aileron dif mix ready to go. Just activate it and make sure the top aileron moves more
than the down aileron. Start with 5 to 10%, and re-check to see if it helps. If you fly a lot of 3D, you may choose
to use an ailevon function on the radio instead. This option will allow you to set the aileron up and down as a
percentage of full travel in each direction. The additional advantage is it allows you to mix aileron into the elevator
halves - giving you some roll control, even while hovering. The military has been using this technique on fighters for
decades, so there is something to it.