Just a point to consider, locking the tube end to the spar is not a perfect solution. The spar is strong enough for the job intended. With the tube end locked to the spar the tube end will act like a pivot point for all of the wing load. All wing load will be transferred to the root connection of the tube not the root of the spar. Hopefully this goofy setup will be strong enough for what we use it for. Just think, a little good engineering and this wing would weigh less, be easier and cheaper to make and stronger... unforgivable!