How much dihedral does a model plane need (for RC)? I came across this post on RC Groups from Pat Tritle explaining how much he uses in his designs:
FWIW, Over the years in dealing with 3 ch (Rudder, Elevator & Throttle) airplanes, I have discovered a pretty general rule of thumb. On a typical high wing cabin or parasol type airplane airplane, 4 1/2 deg. dihedral works very well. Entering the turn with as little as 3 1/2 is do-able, but getting out of the turn is another story. On a shoulder wing, you can get away with 6 or 7 degrees, while low wings need upwards of 8 -10 deg.
Now, “dihedral effect” is also a factor. A high wing without dihedral will offer the efect of 2 – 3 degrees, where a shoulder wing will act like 0 degrees. Low wings, on the other hand, at 0 degrees will actually give the efect of “anhedral” and become somewhat unstable, requiring 2 – 3 degrees of dihedral to achieve a 0 dihedral efect. Wing sweep also plays a part, but that’s another story altogether.
With that, it’s easier to understand why low wing models need more dihedral to turn using only the rudder. Biplanes, for reasons unknown to me, tend to make their own rules. All 3 of my 42″ span Wright flyers, the ’03, ’09, and 1910 Model “B”, turn just fine on the rudder alone with only 3/8″ of dihedral per tip — now that’s something to think about!