Originally posted by Jim Schwagle
Drill a hole through them and secure with nut and bolt. If you can put them inside the nose, such as next to the tank or in the compartment under the tank you can secure them with epoxy. Don't rely on the stickum. In my experience, it won't hold.
There’s usually some vibration involved that could loosen the adhesive you use and why risk it. You can use epoxy, but why bother. Use Jim’s method, or make a cavity from a balsa block and put the weight inside, then glue it to the fire wall or inside next to the tank. Remember to make the cavity as snug as possible.
Remember, whatever method you use, test balance the bird first before you glue or screw. Both of these methods will add some minor weight to the overall balance and will require some (if any) placement adjustments.