Build hours: 168
Final Thoughts on Long Range Tanks
Early on in the build process, Sandi and I decided that we wanted to do some oversea's flying to Europe to visit some students of ours and as a vacation. That meant I needed to increase the capacity of the fuel system in our RV-9A. The stock fuel tanks hold 18 gal each. Depending on how what your fuel burn rate is, that is 4-5 hours of time minus an hour for reserve.
I did some hunting online to see how other builders expanded capacity. Of the few I found, they elected to add outboard tanks and/or tip tanks. One company was starting to make these little tube tanks that fit in the lightning holes in the outboard portion of the wing. I didn't want multiple tanks to manage, so outboard tanks were out. The tube tanks really didn't add a lot of extra fuel. Van's was selling tip tanks for $2,000, which was way over-priced.
So I came up with the bright idea of expanding fuel capacity by creating a single fuel tank in each wing but just making it larger. I did this by creating a leading edge fuel tank skin that runs the entire length of the wing. The standard RV-9 configuration is a 6-bay fuel tank on the inboard portion of the wing and a 6-bay leading edge portion on the outboard. There is a seam in the middle where the two meet. I expanded the fuel tank to 9-bays in each each, adding 3 additional tank ribs. Since I was going to the trouble of bending a new skin I might as well make it long enough to run the lenght of the wing, giving it a smooth look.
Assembly of the tank was no different than the standard tank. I bought a long piece of aluminum sheet, drilled and bent it the shape of the standard tank skin. From there I continued as if it were a normal tank.
With that all being said.... was it worth it?
Tips for those who try this:
1) Don't drill any of the screw holes in the spar until after the tank is done, then back drill them. The guarantee's proper alignment.
2) One flange of the baffle is bent past 90 degree's. This is important as it allows the skin to sit better on the spar flange.
3) Given the length of the tank, make sure that we you go to install the baffle that there is no twist! I cleco'd the baffle in place, then used a level at various points down the length of the tank to check.
4) The root and outboard ribs of the tank have one rivet hole that is slightly different than the interior ribs. Remember this when match drilling the skins.
5) The spacing I chose for the addtional nutplates wasn't close enough. I have slight puckering between screws. I'd figure out a way to get them closer next time. I used the existing rivet holes for one leg of the nutplate. Make sure the spacing is at least the same as the inboard ones.
6) Do not underestimate the amount of force it takes to bend aluminum. I used a contraption made of wood and it was not adequate. If you can find someone to bend it for you great... I used a 1" pipe for the bend. If not, devise a metal contraption. I have an idea for one if you want to make one.
7) Get help when it comes time to proseal, particularly the baffle.
8) You'll notice that the top side of the stock fuel tank skin has a slight curve to it. If you can do this on the new skin, do. I have a couple of spots on mine where the skin buckled when trying to put it in the cradle. This small curve prevents that from happening. I'm sure Van's uses a roller system to put this curve in, I just didn't think about it or have the setup to do it.
