If you have not got the wings covered yet, you might want to consider as a retro fit using a uni directional; Carbon, Kevlar, or S-glass spar cap on the main spars. The idea is to have the bending stress in the out most part of the spar cross section see the high strength reinforcing fibers rather then balsa.

Again for people just starting Kadet Senior construction I would highly consider using spruce, poplar exc for the main spar and taper the doublers.

I have painfully learned that balsa has no place for main spars or main longerons in this type of construction.

SGG B.S.A.E