I'm working on an Own design 3D/Freestyle. I have a shape and wing section and planform.

My question is simply how is dihedral calculated? or is it purely trial and error.

Any help much appreciated.

For a 3D/Freestyle model, you want the less dihedral you can get so you minimize roll coupling when you apply rudder. 0 degress is the ideal. But if it's low wing you have to compensate for the pendulum instability, then 1 degree dihedral or no dihedral at all and 3 to 5 degree sweepback is the most recommended.

Heed EagleOne's advice.

Basically, it is not a calculation... it's a design decision.

....and if your decision proves to be incorrect, either find a buddy with a tablesaw to whack the wing apart and reglue it at the correct angle, or have a prepared statement ready to recite all the reasons why your design's incorrect dihedral was purposely done to enhance it's amazing flying characteristics in other areas that those of lesser knowlege can only fantasize about!

The wing palnform I'm using is a flattop layout with a swept leading edge and slightly swept trailing edge.

The Pattern plane in my avatar is my own design that uses this wing and is totally pure in KE.

Will thickening the root section improve stall characterisitcs for freestyle?