Adding An Extra 3 Gallon Fuel Tank Bay?
 

Wondering if anyone has done this. My project came with quick build wings and fuel tanks. I read WAY to many write-ups of these tanks developing weeping rivets and tiny leaks that require tank removal & surgery to seal back up. My fuel sender cover's are not yet installed. I peered in there with flashlight and mirrors and don't like what I see. I feel that they were way too stingy with the tank sealant. Building my RV-10 tanks, I used probably more sealant than necessary, but I KNEW they would never leak from the beginning, and would not develop one in the future. Sure I added several ounces of sealant to each tank, but worth the weight penalty IMHO. Since nothing is yet painted, my plan is to remove each tank and open up each bay from the baffle, inspect and re-seal each rib on both sides with a fillet of sealant, and place a larger dab of sealant on each rivet shop head and seal the baffles with Van's tank repair covers (wheel covers). I am also strongly considering splicing an additional 3 gallon bay on the inboard end of the tanks and shifting the tanks outboard accordingly. Only a 6 gallon increase total but gives a 45 minute or so cruise range increase without the complexity of auxiliary fuel tanks, transfer pumps, or plumbing. Anyone do this? I find a lot of threads and builder logs on installing aux tanks, and even building larger tanks during the original tank build, but I am not interested in this option.

Not to rain on your parade, but if those tanks are already built, you're likely fixing something that ain't broke. ;-)

If you cut into every bay for access, you create that many more opportunities for leaks.

More is no guarantee of better with tank sealant. Just read through all the accounts on the intewebs of fixing leaks after massive sealant use. It's all about proper prep and proper application. I sealed 2 standard RV-7 tanks, *and* 2 leading edge aux tanks, with *one* standard kit of Van's Flamemaster sealant.

I can testify that converting the leading edge into a fuel tank is a lot of work. My personal opinion, FWIW, is that splicing a bay onto an existing tank, moving the filler outboard, plugging the original fill hole, etc, would be a *lot* more difficult, and would require a lot of extra work to deal with the cosmetic issues once done.

YMMV, worth what you paid, etc...

Charlie

Builer?s method
 

I wouldnt fix a problem until it is a problem.
Add capacity is not easy and doesnt buy much unless you also add bladder to the pilot and passenger.

Lastly, if the original builder used normal dies, and not tank dies, ther is a good chance there wont be any leaks.

If you have to go in there, I would cut a hole in the back baffle, fix the problem, and then consider using the hub caps as the patch. This will give an extra pint or so per hubcap with no other impact. I havent done this, but is in the back of my mind if I ever find a leak.JMHO YMMV

You could probably get more range by adding oxygen and flying higher.

A couple of issues to think about in adding to the fuel tank on the inboard end:

1) if you shift the whole tank outboard, all of the match-drilled attachment screws, and the z-brackets, may not line up as you shift outboard. On the other hand, with all the modern CNC punching, maybe the hole spacing is uniform enough that you could shift the tank outboard and the screws might still line up. Of course there will be new screws to add at the outboard end where you shift into what would usually be just riveted leading edge.

2) splicing wing skin to the inboard end of the tank and not having it leak is going to be very tricky. Its one thing to make a bigger tank from scratch, using all one sheet for the skin. But to add onto a built tank by butt-splicing another skin section, and get that sealed up, that is going to be a lot of work.

I also contemplated additional fuel capacity. I have often thought of additional fuel as a safety buffer for long flights. However, from my almost 8 years of flight experience now with the 9 I will tell you up front -- you don't need the extra 6 gallons reserve. With standard tanks I have an average flight time of 4.5 hours with a 30 minute reserve. In reality the longest leg I have ever flown was just under 4 hours. That is a long time for your butt to be sitting in that seat. I do understand there may be specific missions that require longer legs but for the average RV9 flight, not necessary.

Steve,

While I'd disagree with the OP's proposed methods, flying longer legs is rarely the motivation for tankering fuel. Those of us who fly out of places where fuel is cheaper, or where we can have our own supply (cheaper, auto fuel, etc), or intend to fly to locations without fuel (with the intent to return), can think of many other reasons.

Charlie

Then there are those of us who live in a country where there are a LOT of miles between airports. All it takes is for your destination to have a breakdown in their fuel pumping equipment and you're stuck. Tankering fuel is a necessity in more sparsely-populated locales.

Also, if you are considering flying IFR, one must be aware of the need to get to an alternate. That alternate may not be nearby. That extra six gallons of fuel might be the make-or-break feature in bad weather conditions.

I'm very satisfied with the workmanship of my QB tanks. 220 hours TT, flying since February 2016, no sign of any leaks.

Take the tanks off the wings and put twenty gallons of fuel in them. Roll the around every few days to check for leaks.