Here is an part of one of my columns from R/C Report on dihedral and stability. Also some photos of my high wing planes.

Roll Stability:

Let’s talk about dihedral. In the first place, there is dihedral and there is dihedral effect. Dihedral is the upward bend in the wing. If the wing is bent downward, this is called negative dihedral or anhedral. Dihedral effect is the result of having dihedral or other things that make your plane react just like the bent wing does. Dihedral effect gives your plane roll stability. It also results in roll coupling.

Let me make my position clear from the git-go. In RC terms, I do not want any roll stability. In engineering terms, I want neutral roll stability. In English, I want the plane to go where I point it and stay in the attitude I place it in. I think this is a pretty common desire for all acro fliers.

Dihedral generates positive roll stability and it will cause roll in the direction of the rudder. Anhedral generates negative roll stability and roll opposite to the rudder.

Two other things give dihedral effect, wing sweep and wing location on the fuselage. Sweep back generates positive roll stability and roll with the rudder. Sweep forward will cause the opposite.

Wing vertical location on the fuselage causes dihedral effect. A high wing location is equivalent to about 3 degrees dihedral on each side. I surmise this because it normally takes me 3 degrees of anhedral (angling the wings downward) to cancel out the dihedral effect. A low wing location will cause the opposite. If you have a low wing plane, you’ll need a little dihedral or sweep back to cancel the effect of the low wing location.

Most of you have flown a plane that was really unstable in roll, but you didn’t know it. When it’s inverted a Big Stick is unstable in roll. A Big Stick has a high wing and a small amount of dihedral. Turn it over and what do you have? A low wing plane with anhedral. Disaster, right? No, just a pain in the neck to fly. Even worst is a high wing trainer with more dihedral. Even fly a trainer inverted. Wasn’t it a pain to keep the wings level and to make a turn? Sure it was. The plane was roll unstable. It wanted to roll back over and get stable. It wasn’t a disaster, but it was work compared to a sport plane that has a low wing and dihedral. The low wing location and the dihedral cancel each other out, giving you a neutrally stable plane. Flip the low wing sport plane over and what do you have? A high wing plane with anhedral. That’s why I put anhedral in most of my high wing planes. A high wing plane with anhedral will do knife edge, point rolls and outside maneuvers much better than one with a flat wing and a great deal better than one with dihedral.

You can see from the photos that I have a lot of experience with high wing planes with anhedral. My present Stick is the red & white Ultra Stick with an OS .55AX. Great combo. No roll in knife edge and does knife edge loops. I did mix out the pitch with down elevator when I put rudder in.

Look at the nose on photo of the yellow Joss Stick that is inverted in the cradle. It could easily be a low wing plane with a little dihedral.