Adverse yaw and aileron differential

[Art Horne]

Greetings,

I recently built a Great Planes "Old Timer 40" kit and modified it to use ailerons. It turned out beautiful but it flew horrible. It was almost impossible to turn. It had extreme adverse yaw. I've never had a plane do that before. I have the bad habit of only using the rudder on takeoff. Once it is airborne I only use ailerons and I'm sure that was a big part of my problem. I've since added coupling from the ailerons to the rudder and added differential into the ailerons in the transmitter. I haven't flown it since doing that but I'm hoping that will make a big difference.

This is a model with 74" wingspan and strip ailerons. I only put in half the dihedral that was specified on the plans. My question is, what part of a planes design causes it to have adverse yaw? I flew it twice and barely got it back in one piece both times. I understand what adverse yaw is and that co-ordinated rudder should take care of it and differential ailerons should reduce the magnitude but what caused the problem in the first place?

Thanks for any input.

Regards,

Art

[BMatthews]

Another part of the issue is flying speed. The closer to the stall you get the worse the model will show off its adverse yawing. And since this is intended to be a slow flying plane you've found out the hard way that it's an issue.

So build in some differential. You can do it easily by altering the servo's output arm angles and making new connecting rods to the aileron horns. If you can post up a picture of your servo setup we can direct you more clearly in how to do this.

But there's no doubt that as you want to fly slower and closer to the stall point that you'll want to learn to use some rudder coordinated in with the ailerons even if you do have it mixed in already.

[JetPlaneFlyer]

I've noticed adverse yaw is much worse on models with flat bottom or undercambered airfoils... This makes sense since these airfoils effectively already have the TE cambered down. Any further 'droop' of the TE caused by downgoing aileron travel significantly increases drag. On the other wing however the upgoing aileron reduces drag because the cambered down TE is lifted out of the airflow. These effects yaw the aircraft in the opposite direction to the desired turn. Narrow chord ailerons compound the problem.

Symmetrical or near symmetrical airfoils generally suffer less from the effect though on any aircraft adverse yaw is greatest as low speed and high AoA.

As noted above; the cure is lots of aileron differential, about 2:1 is a good place to start. Frise type ailerons or some form of ‘spade’ would also sort it out.

Steve

[vintage1]

Another trick is to rig both ailerons somewhat 'up' in the neutral position..

[Art Horne]

Success!!!

The mixing with rudder and adding differential to the ailerons made it fly like a trainer. It flys great.

Thanks for all your inputs. I've attached a couple pictures of it.

Regards,

Art