Hi hamed-khorrami ,

The Nexstar was my first plane that I did most of my beginning learning on. The Sr, Falcon was my second plane. After flying both of them with the factory set dihedral, I modified the wings on both and flew them with 0 dihedral. I loved it! They both flew beautifully, each like a more advanced plane, especially the Sr. Falcon! To take the dihedral out of the already assembled wing on the Sr. Falcon, I used a sliding radial arm saw to exactly cut the wing joint in the center. I then matched the exact angle of the dihedral degrees on the saw and skimmed each wing joint with the saw blade to give a flat, 0 degree joint between the two wing halves. I drilled some holes in each wing half, eppoxied in some dowels to connect the wings and put a thick coating of epoxy on the entire wing joint surface. The new wing joint was very strong and the plane flew like a dream!
For me it was easier and much more excting to fly then flying a regular trainer.
Hope this helps.

tkeeg