wing tanks vs. fuselage tank
If it's within your budget, you could build and retrofit new -3B wings to an older -3 kit. I hear that Van's gives a good discount for new wings for older -3 owners (kit or flying).
Project or flying, if you decide to modify the original wing for spars and tanks, you've got quite a job ahead. Main thing?: get hot on drilling out rivets. Assuming the spars/wings are mostly assembled, to put the spar mod on, you'll be drilling a hundred or more 1/8" rivets out of the spar caps - most from the 1/2" - 1" buildup near the root. You'll be taking dozens more out of the angle bars on the fwd side of the spar, and all over the spar web, to clear away the inboard ribs & skin for the new tanks. You can't make (m)any mistakes in there either, and still call it an airworthy spar.
Now, all that said, think about that fuselage tank (coming from a guy with a fuselage-fuel RV3): it is located in the strongest part of the structure, with thick angle bars and stringers all around ... i.e., in an overturn accident, and given a properly reinforced tank, the tank won't breach (read the NTSB reports on overturned RV's - a number of them breach and catch fire). You've got a single mechanical fuel guage, so you'll always know to the gallon your fuel state (read those NTSB reports again: many RV accidents are fuel starvation, failure to switch tanks). Sure, having 24 gallons of gas in the cockpit can be unnerving, especially if the dang thing springs a leak ... which it did on me once - had a thin stream of fuel spraying on my legs for a few minutes until I got down. After that, I had a special tank built with an internal bladder, and reinforced welds all around - gas has to get through the bladder, the tank skin, the welds, and then another layer of sealant and reinforcing metal before it gets to me (ok, I went overboard on this ... but it's just amazing what being aloft with a puddle of gas in the cockpit will do to your mental state afterwards). The point being, you can do a lot of things to that fuselage tank to make it leak-proof, and largely unbreachable in a forced landing.
Ok, I'm off the soapbox now. Good luck with your ideas; the -3 is the best performance-for-cost out there, so have at it
- Steven
700+ RV3 hours
(note the photo: 16 gallons exactly ...)