For the record, I never called the fuselage tank "stupid." And, not on this thread - I commented on the pluses and minuses of the body tank on a thread going on on the General Forum.
Actually, I defended the body tank on that post - but questioned its virtues going forward.
The body tank is driven by the removable wings. It was an attractive feature - actually, it was the feature I was most interested in when I began my LSA search. My very first post on VAF concerned finding a suitable trailer, since I was unable to find hangar space. Trailering home looked like my only solution. Comments at the time, and since, have indicated trailering is not as viable as initially envisioned. Certainly, Vans has done little to promote this scheme. Occasionally, people post about home-brewed trailers, either contemplated or under construction.
The negative comments on trailering turned out to be correct - at least in my case - as I would no longer consider that in my current circumstances. Actually, I do not envision removing the wings ever again - altho, of course - I might. Likewise, I do not plan to remove the fuel tank ever again - altho that too seems to be an elusive goal.
When Boeig designs an airplane, they create a DR&O -Document - Design Requirements and Objectives. I was raised with that thinking, and apply it to everything I do. For the RV-12, the DR&O called out the ability to trailer - others used folding wings, Vans decided to remove them. From what I've read, Van, who is a sailplane fan, envisioned something along the lines of those sailplae trailers you can see at fields where soaring is common. Unfortunately, that vision never came to fruition, so the DR&O took a big shift - but the airplane design was already in concrete. It drove the single big main wing spar design, established the layout, and determined the CG. Definitely, moving the fuel out to the wings would back-drive a lot of changes into the airframe - probably more changes than would be considered practical, without a new clean-sheet-of-paper design.
The body tank was one fallout of the design goals, as it was probably decided early that wing fuel presented many more challenges, including connecting and disconnecting fuel lines repeatedly, and the serious problems of removing , transporting, and re-installing wings that had fuel in them.
So, the body tank was born. Problem is, with folks not removing the wings, that accomodation has become a problem. IMHO the body tank has definitely become a liability for the airplane - especially for the store bought crowd with A&Ps needing to pull the tank annually (unless Vans finally releases a split bulkhead change.) It would definitely work against the airplane becoming a standard FBO trainer.
The body tank has become a prime area of Plans changes and Service Bulletins. A veritable hotbed - in itself indicating the difficulties with the feature. So far, the tank has generated:
An early filler neck relocation
Sight glass material and installation change
A structural beef-up and support bolt change
An anti-rotation plate mod
A fuel gage installation
Sight glass elimination
A rear cabin window sealing addition
Added Installation of nutplates on the filler neck flange
A revised venting scheme
A second structural beef-up and second support bolt change.
As Scott has pointed out, many of these redsigns have involved a lot of test articles, analysis, and destructive testing. Expensive for the mothership.
Most of these changes open the door to creating problems where there were none - like accidentally shearing the frangible bolts, creating new tank fuel leaks, creating unremoved tank debris, feed and return line connection leaks. And draining the tank is downright dangerous. The new vent tubing presents opportunities for damage by baggage moving around. And more disconnections when removing the tank.
I'm an engineer, and don't expect every design to be perfect right off the board. Development is the word for honing and improving your initial design. The above list shows that there has been quite a lot of honing going on. And, as many posters have noted, Vans has stepped up to the plate and made the changes and improvements. The question is, how close are we to the end of the improvement process? And, at what point do you start to question your original goals and assumptions?
Scott discussed the two force vectors - horizontal and vertical (in a down direction), or a combination of those, that affected the loads imposed on the body tank during a crash sequence. . To my knowledge, no RV-12s have flipped, but lots of other RVs have. I wonder what the force vectors would be on a body tank full of fuel that has a vertical force in a vertical UP direction - which would be down when the airplane is upside down -even a slow flip - like the one that broke the necks of those two people discussed on the Main forum. This will create yet another fault path load vector, and the result of a failure in this scenario, could be ugly. Maybe the design team has already worked this situation. Maybe not. Info from the mothership is sometimes sparse. If not, will another accident - one involving a flip, result in yet another SB and another round of beef-ups. Time will tell - I hope I'm not the one to find out!
The body tank definitely needs to go. I've only come to that opinion in the recent past. This latest SB was sort of the straw for this old camel. I discussed this recently on the general Forum, if you missed it. It has too many defects from a maintenance and operational standpoint, and potentially unaddressed remaining safety issues.
My airplane has about 80-100 lbs of wasted Useful Load - that's as bad as a Skycatcher, which has too little Useful Load. Put a 15 gal tank in each wing, make the wings removable for maintenance only, get rid of the maintenance problems, the venting problems, the windshield crazing problems, the baggage space problems, the tail access problems, the crash-safety problems, add range and regain the lost Useful Load.
Will this ever happen? Probably not. And, if it does, likely not retrofittable, so it's all academic for the current crowd. But, if I were a big flight school, and wanted to buy 100 Trainers from Vans, I'd certainly have my list of Requirements. Getting rid of the body tank might be right up there. It was a good idea at the outset, but its Time has come. I don't think it's "stupid." I do think its original goal has disappeared and it has become a burden on both the manufacturer and the operators.
Bob Bogash
N737G
