Fuel tank installation

[jrbirdman47]

Anybody got pics of the structure for their wing fuel tank installation. No real guidance on that and I just did what looked like would work and be light, so just curious what y'all came up with.

[Steve]

Anybody got pics of the structure for their wing fuel tank installation. No real guidance on that and I just did what looked like would work and be light, so just curious what y'all came up with.

Take a look here:
http://www.angoraaffaire.com/leu/gastank.htm

[jrbirdman47]

Wish the pics showed more detail of how/ where the tank actually mounted. Looks like it has attach bolt holes along the front, but what do the bolts go through? I must assume there is a flange mated to the spar somehow that the bolts go through and not the spar cap itself. Don't know about the rear. Maybe it sits on the diagonal gusset? I figure the tank itself is rigid enough not to need any external support in the middle.

I used the Team Mini-Max 5 gallon aluminum tanks and my structure is finished so I was mostly looking for reinforcement that what I did was OK based on what others have done. I think if anything I probably erred on the overbuilt side, but the tank mount structure added about a pound or so more total weight than the non- fuel tank wing. The tank itself weighs 4.5 lbs, so I wonder what kind of weight savings the glass tank afforded as well. (I never was all that great at glass work, so mine would have weighed in the neighborhood of 56 pounds..... )

Anybody else use the aluminum tanks and have installation pics?

[Tom H]

Jrbird, I built the original tank for LE Treehugger using fiberglass and vinyl-ester resin.  I put a flange along the bottom/front to sit on the lower cap of the main spar, and put a flange on the rear/diagonal part of the tank to sit on the diagonal brace.  I believe we used #10 screws to hold the tank to the spar cap and diagonal brace.  I have attached pics which should illustrate this.

After some use of the tank in the airplane, we were getting some scum in the carburetor, which we think was from the tank.
We originally thought that the scum was degradation of the resin.  But, after some thought, I now think that the scum was silicone caulk residue that I used as a coating over the foam core to make removing the foam easier from the cured tank (see the pic of the tank build to help understand). 

Anyway, we removed the fiberglass tank and replaced it with a similarly shaped/sized tank that I welded up from aluminum, and that is in the airplane now, and working well.

It sounds like you did something similar from your description.

[jrbirdman47]

I used the Team Mini Max 5 gallon aluminum tank and decided to place it on rails. the outboard rail rests on the lower spar caps and the inboard rests similar to what you did, on the diagonal gusset at rear. The forward end of it rests on a cleat the same size as the lower spar cap which is fastened to that cap.

The rails had to taper in the middle to clear the diagonal, but that would be done anyway to save a little weight. I used 1/8" plywood to reinforce the rails notch where it fits at the ends, figured if they were going to fail it would be by cracking with the grain at that notch and the plywood should prevent that.

I then glued cleats on top of the rails in front of and behind the tank to hold it in place, leaving 1/16" all around for a strip of rubber to dampen vibration. I plan to band the tank to the rails with the fiberglass banding you see wrapped around boxes for shipping so I added two small spreaders between the rails at the point where the band goes around to keep it from bowing the rails inward when tightened.

First pic shows rails being glued in place
Second pic shows the tank laying on the rails, viewed from behind
Third shows tank on rails viewed from outboard

(Rubber isolation strip not installed yet)

[jrbirdman47]

Also wondering how folks dealt with the area where the filler neck protrudes through the fabric. If you have pics it would be helpful.

I'm not there yet, but had in mind to construct a ring that would fasten to the tank and allow fabric to be glued to it. It would form a sort of scupper and be large enough to get fingers into for removing the filler cap and maybe even have a small drain tube to allow any spill to drain overboard.

[Tom H]

JR, the wooden ring around the filler neck in one of the pics I attached earlier was used to glue fabric to.  It supported the fabric, and allowed a secure seal of the fabric to filler neck to prevent fuel from getting inside the wing.  Fuel could be spilled during filling, but the angle of the top surface of the wing caused the fuel to quickly run off - no scupper required.
Also, the plans show a forward facing ram-air tube on the top of the filler cap.  This ensures positive pressure in the tank, allowing fuel to flow to the engine.

[jrbirdman47]

OK, that makes more sense. Just seal it so that no fuel gets in the wing at all. Thanks!