ORIGINAL: bigal126

I have some experience here.
Rule of thumb for neutral flight characteristics: Wing below the thrust line should have some dihedral. Wing on the thrust line should have no dihedral (flat wing). Wing above the thrust line should have anhedral.

When I built a 30cc goldberg sukhoi, I used a 3/4 diameter carbon tube. I purchased a 36'' long tube and a phenolic tube from TNT landing gear. I went through 4 ribs including the root rib. If I remember correctly, I cut a total of about 4 inches off the 36''. It is holding strong with no issues. You can see some pictures here. Hope it helps.

http://www.rcuniverse.com/forum/m_10...m.htm#10635342