--Original Message----- From: Bob Peck [mailto:[EMAIL PROTECTED]
>If you wanted to incorporate a little dihedral in the center panel of >a 3 piece wing, what would be your procedure? In my experience I have been able to bag wings with a maximum of about 5 degrees of dihedral as one piece. The only limiting factor is the mylar being forced to make compound curves in the area of the dihedral joint. I know I used to bag one piece WACO two meter wings with single top and bottom mylars. I can't remember what the dihedral angle was but it was between 3 and 5 degrees, I think. At some maximum dihedral angle you will need to start using separate mylars on each side of the dihedral joint or at least make relief cuts along the chord line of the mylar for some distance. The only down side of using separate mylars or relief cuts is a slight cosmetic issue since you will be left with an unsightly line where the mylars are not continuous. The separate left and right mylars can be joined with a flexible plastic tape on the back side. This tape will hold the mylars together but allow the seam to open sligthly as needed when the mylars are forced to conform to the dihedral angle at the same time that they also must follow the wing curvature. You will need some sort of dihedral bed to bag the wing panel on top of. With low dihedral angles, you can just make the outer foam cutting templates taller than the center templates and the foam beds themselves will give the needed dihedral angle. If your dihedral angle is too large and/or your foam board too thin, you will need to construct some sort of thing to bag the center panel over that has the correct angle. This could be constructed of plywood or you could cut foam wedges with a hot wire that would sit on the bench under the foam beds while bagging. The final issue has to do with the spar system in the center panel. There is no problem with the wing skins making the dihedral angle and no changes would need to be made to the skin layup even if you have a stressed skin wing. Any spar system used would, of course, no longer just be a straight spar but would need to have the dihedral bend. The tube spar system that I use would appear to be a problem. Perhaps not though. Most theorists will tell you that the tube "spar" doesn't really carry much bending load. If so, then I would (and perhaps soon will) try the following; Build two separate foam cores, a left and a right, each piece has a root rib on each end made of 3/16" ply. Each piece is about 30" span (the semi-span of the center section)and has installed in it a 30" X 1/2" carbon tube. Sand the required dihedral angle into each center rib with a bench top 10" or 12" disk sander. Join the left and right panel with epoxy and a 6" dihedral joiner. I would just use the aluminum tube joiners that I now use for joining the tip panels to the center panels of my three piece wings. If the theory is correct and the tube spar doesn't really carry much load then the small, light joiner should be enough. Only testing will tell. If it weren't strong enough then a stronger, heavier joiner would be required or a small top skin doubler would have to be added. If you are contemplating a real full depth spar system that carries almost all bending loads then I don't have much to offer other than a link to Mark Drela's Supra plan in the Allegro-Lite files section; http://groups.yahoo.com/group/Allegro-Lite/files/Supra/ The Supra has a center section with dihedral and a "real" spar. Detailed plans of the entire model and spar system are included in the above link. Phil 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.
