Adverse yaw is a fact of life caused by rolling. It is not caused by the aileron drag. If it were then it would be very easy to avoid on all full size planes by using differential and saving the pilot having to operate the rudder. But it isn't designed that way full size, because differential can't work! It has been tried though a long time ago when people didn't know much. Someone gave the example of the Tiger Moth which has a clever bellcrank so that the downgoing aileron starts going down then comes back up again. Yet as Pilot magazine remarked in an article about flying the Tiger Moth about 2 years ago, the phrase "adverse yaw could have been invented for this plane". But it has enormous differential so how can it have such appalling adverse yaw?

Adverse yaw comes from the rolling motion. Lift force acts at right angles to the direction of travel of the wing. When the plane is rolling the upgoing wing is travelling along an up slope so its lift force is angled backwards by the same amount and pulls it backwards. The downgoing wing's path is angled downwards so its lift force is angled forwards, pulling it forward. That is adverse yaw. It is not caused by ailerons in the air stream and aileron differential can't cure it. If you fly slowly but try to roll at the same rate the path of the wings is steepened so the change in angle of the lift force is also changed that much more. Long spans mean that for the same roll rate, the tips travel a steeper slope than for a short span and once again the change in angle of the lift force is greater. That is why long spans and slow speeds cause greatest adverse yaw.

The cure is to use rudder to counter the advesre yaw. Use your tx to mix in enough to do the job. Some full-size planes even jet fighters have aileron to rudder mix and if its good enough for hot-shot F-4 Phantom fighter pilots it's good enough for us!

Many model fliers confuse an offset rolling axis with adverse yaw. They see the roll looks odd, they have heard the phrase "adverse yaw" so they put the 2 together quite wrongly. Differential can cure an offset rolling axis, so these modellers put in differential, the offset axis is cured and they proclaim that differential cured their adverse yaw!

What about Frise ailerons that have downgoing bit of the upgoing aileron to counter adverse yaw? Firstly, that is not aileron differential. Secondly, the downgoing snub is a pure drag creator, like a mini-airbrake. It has been shown that the increase in drag from using the rudder is less than the increase in drag from Frise ailerons which is why they are mostly not used, as overall aircraft/glider performance is therefore slightly better when rudder is used.