Welcome to the party Airborne
. Based on your description I was envisioning something like what @Al_delaIglesia
pictured in post #3. Estes sells a similar widget:
View attachment 537771
Build your own custom fin jigs with the template makers available here:
that definitely helps you get the line straight.
for NON-Thru-The-Wall fins the next trick is making sure you fin aligns with the line. I have been using 1/16” “balsa fillets”, basically 1/16” balsa sheet to start, measure a piece 1/16” wide by the root chord length of your fin. Definitions here courtesy @RandyT0001
see post 3
I am sorta new at the rocket thing and am confused by the fin surface nomenclatue. Leading edge, Trailing edge, semi-span, root length equal or greater than half the diameter of the tube it is mounted to. Tip Chord length, Root Chord, Sweep length, and sweep angle??? A drawing would help...
align one side of the fillet with the line, use single or double glue joint technique (I like double, gives a fast tack). Make sure all your fillets are the SAME side (clockwise or counterclockwise) to the lines. Allow to dry. Because these are so light, the go in place easy and don‘t have a tendency to drift while drying. I may put a rubber band around the ends if the moisture of the glue causes it to curl.
once dry, attach your fins to the OPPOSITE side of the line (counterclockwise or clockwis, depending on how you attached the fillet) so your fin root edge is aligned with the LINE you drew (so if your balsa fillets May range from 1/14” to 1/18”, doesn’t matter, you aren’t using the “far” side anyway.)
you still need a means to prevent lateral tilt, although for the most part lateral tilt of a few degrees shouldn’t affect flight.
advantage of the balsa fillet is not just alignment, because it provides for surface area the fin “tacks” faster with wood glue (although @kuririn
cheats and uses a touch of CA for initial tack.). perhaps more importantly, it provides a stronger fin-tube attachment again due to larger surface area. Usually the balsa 1/16” balsa fillet can be hidden by an overlying fillet Once dry. If symmetry is a big thing for you, after the fin is adequately tacked you can add another balsa fillet on the other side for symmetry and even more strength.
this is a nice trick especially for minimum diameter birds where Thru-The-Wall fins aren’t an option.
also something to think about for Cub Scout or other youth group builds, since it is so easy to do you can “prep” the rocket tubes with the balsa fillets prior to the group build (doing 12 or 24 tubes should take you less than an hour) since I think fin attachment is probably the toughest part of a group build.