Hi KW Counter,

The joint should ideally be four times the diameter of the spar, obviously the length remaining on each wing that is undamaged will determin the length and may vary from the ideal but anything less compromises strength. Overlap the spars as much as possible to arrive at the same wing span of the original wing, cut at an acute angle and glue together, this is much stronger than a butt joint. Then splint either side with birch or similar extending at least 1/2" either side of each end of the joint. When you re sheet the now joined and splinted wing add 4" of fiberglass cloth for a little mental reassurance

Cheers,

Colin