FUEL TANK

[Murray Randall]

 I'm getting my act together for wing bay fuel tanks.  My thinking is 1/4" Divinycell,  7781 weave glass cloth, Dow 411-350 Vinylester resin.   I would appreciate recommendations and advice on the subject.   Many thanks   Murray

[mmorrison123]

That's how I made the tank for my Pietenpol and it was the worst building experience I had. My first attempt was to put 2 layers of cloth plus resin between 2 sheets of polyurethane and squeegy out the resin, then peel off one piece of plastic, lay the cloth on the foam, and remove the other piece of plastic. This did not leave enough resin in contact with the foam and when hard the fiberglass easily peeled off. Next I brushed resin on to the foam and tried to lay fiberglass cloth on to the wet foam. It went on crooked ant there was no way to reposition the wet, sticky cloth correctly. I had wet cloth strands on every part of my body as a result of trying to get the cloth on straight. Finally a friend gave me the solution. You cut your cloth pieces to size, position them on the foam, then roll them up and just off the edge of the foam piece. Now paint the resin on the foam and unroll the cloth into the correct position. Add more resin to saturate the cloth. Just that easy! I hung in and finished the tank, but I think I would opt for a riveted tank next time. 

Malcolm Morrison
wienerdogaero.com

[Murray Randall]

Jeeze     thanks   oh dear    I had doubts before but now I'm damn near terrified.    Trouble I see in the alumin tank is that the Pro Seal is no more fun than the resin.     I TIG welded a tank just once and the most beautiful of welds showed blue 100 LL stains every six inches or so on P testing.        Took hours of grinding, rewelding.     No matter which way I turn I get into personal skill set limits.   Have to face it, one of the stated purposes of experimental aircraft rules is built for education.

[Sam Buchanan]

I consider a riveted, prosealed tank to be the easiest route to a leak-free tank.

[Murray Randall]

That's exactly what Steve said

[PropMan]

Proseal isn't that bad,  it's the way I'm going.  Get everything set up before you start.

[Murray Randall]

.030?   

[Sam Buchanan]

.030?    

0.025" and a box of gloves. Have a coffee can with MEK in it to drop your clecoes in as you pull them. Lots more info on sealing tanks here:

my RV tanks

[Murray Randall]

What great batch of advice Sam. Many thanks. I hope the other Eagle builders that also have minimal tank building experience get to see that material!!!   

[Alan Waters]

I have had the thought of manufacturing an alum. pressure tested,TIG welded tank. I contacted Sam Buchanan to inquire about a pattern for his XL which he no longer has. If anyone is interested, create a poster board paper pattern for your individual aircraft and send it to me for an estimate. I would guess about $300.00 material and labor.
Contact me at alanelizabeth@gmail.com    Send your phone number or I'll send you mine. 


 About me. Certified welder employed by General Dynamics Corp. Have a shop at home. Have LE, LEXL and DE plans. Leaning toward the DE.

Regards to all, Alan Waters

[stevejahr]

Composites do not have to be hard... but like any material you need to understand their tradeoffs and techniques.

The strength comes from the fibers not the resin nor the foam.  The primary function of the foam is to serve as a form to hold the flexible composite in shape until it cures and hardens.  The secondary function of the foam is to provide separation between structural layers to improve strength with less composite material.

The normal function of the resin is merely to hold the fibers from sliding against each other and it does not take much to accomplish this.  And from a minimum weight perspective you want the least resin with the most fiber.  But for a fuel tank... here holes matter so you want extra resin compared to most applications.  The fabric has some spring to it so what I would recommend here is resin up the glass (or carbon...) cloth being a bit liberal with the resin.  You can do this right on the foam actually and an old credit card makes a decent squeegee for spreading resin.  Placement on the foam which should not be critical because you *did* cut the fabric over-size ;-)  And follow up with a 6 mil plastic sheet on top.  What you are doing is almost like vacuum bagging.  You work the resin under the plastic and the plastic will compress the fabric fibers and keep them from popping back allowing air into the composite.  Oh and do not wait until full cure to remove the plastic... remove it while the resin is still just a bit green and it will come off much easier.  When removing the plastic do not pull up, peel pulling across.

The technique I have seen most often involves making flat panels separately and then gluing them together with a glass reinforcement of the corners.  Note that the glass does not like to bend sharply so put a fillet in all corners... or the glass may make its own fillet with air entering the composite.

Adding the last panel... and having it sealed... tricky no matter what the material is.

[Murray Randall]

Attached is a sloppy sketch I drew up to see if anyone would quote a bladder.  I put the inlets on the front in the sketch by mistake.  They certainly should be on the inside!    $300 sounds like a good fair price, that I can't afford for two tanks or maybe I'm just stubborn and want to grunt thru it.  But email me at aeroads@comcast.net if you'd like. I can sharpen up the dimensions on the sketch it would help you. I only put one rib inboard and did not run a compression piece thru the fuel bays. So my dim's are different than the plans.  But that's a lot of work and expensive alum for $300 and I'm not talking cheaper.  That's fair as it is!!!

[CHARLES DEBOER]

Does anyone have a weight on the fuel tank as built for the LE or XL.  I have found a weight for the minimax tank (6 lbs. 9 oz.) that will fit into our wing.  Trying to find out if it will be a weight increase.

[Murray Randall]

If you made one tank of .025 6061 the tank, less seams caps flanges outlets would be on the order of 1.5 lbs by napkin calculation.  What mtl are those MiniMax tanks?   

[CHARLES DEBOER]

Does anyone have a weight on the fuel tank as built for the LE or XL.  I have found a weight for the minimax tank (6 lbs. 9 oz.) that will fit into our wing.  Trying to find out if it will be a weight increase.

I can only guess the material is a Poly.... .. something.  Whatever they use in one of those rotomolding machines.  It looks like a fogy yellowish white.  (think really bad yellow teeth)  About .125 thick.
ANYBODY KNOW WHAT THE LE XL FIBER GLASS TANK WEIGHS?