Hi Stan, I did some work on a scale ship (5M), and I settled on a solid carbon rod from CSTSales(.com) around .75 inches (sleeved in alum to protect from dings). If you want to do some aerobatics, this is as small as I'd consider. I made my joiner tube from 3 pieces of brass tubing, 1 that went thru the body to the end of the root ribs, then 1 each in the wing to a depth of about 10 inches, past a subrib. I worked out the dihedral in the angle between the root and subribs.
A lot of this depends on the weight of your ship, and if you're going to aerotow it vs winching it. You've identified your ship as aerobatic, that's tougher than just thermal. Less than 25 lbs will be considered 'light', and that will simplify things. If you can get in touch with some of the other scale guys out there, they will be able to give you some more ideas / size suggestions - the joiner / spar are the heart of your ship, make them right. I found a VERY helpful group of scale builders out there, hope you do too. Good luck, Brent RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
