I'm scratch building a 60" wingspan profile model that will have a 25cc gas engine. The wings will be foam core. I'm using a 1.25" diameter aluminum tube to join the wings. How long would you make it? I have a 20" long tube, but I'm not sure if that's long enough.
I agree with Bob. I think that most manufacturers are running the tube into the wing too far. I have 2 airplanes that I scratch built with wing tubes. The first one is a 2M pattern airplane ( 11 lbs ) that uses a 7/8" CF tube that goes 8" into the wing. The second airplane is a 33% Laser that used a 1 1/2" CF tube that goes 11" into the wing. Whatever sleeve you use in the wing should be anchored at the root rib and a peice of ply at the other end that extends vertically to tie into the sheeting. For spar caps I use some 3K CF tow that extends at least 8" past the wing tube. This helps to avoid a stress riser.
The way we make our plug in wings is with a false rib at the end of the tube sleeve in the wing and then at the root of the foam we have a lite ply rib.... then we run a .75 inch wide by .007 thick carbon fiber tape from root to tip over the tube area.