• Welcome aboard HomebuiltAirplanes.com, your destination for connecting with a thriving community of more than 10,000 active members, all passionate about home-built aviation. Dive into our comprehensive repository of knowledge, exchange technical insights, arrange get-togethers, and trade aircrafts/parts with like-minded enthusiasts. Unearth a wide-ranging collection of general and kit plane aviation subjects, enriched with engaging imagery, in-depth technical manuals, and rare archives.

    For a nominal fee of $99.99/year or $12.99/month, you can immerse yourself in this dynamic community and unparalleled treasure-trove of aviation knowledge.

    Embark on your journey now!

    Click Here to Become a Premium Member and Experience Homebuilt Airplanes to the Fullest!

Fuel Tank Sealing Tips

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.

GESchwarz

Well-Known Member
Joined
Oct 23, 2007
Messages
1,250
Location
Ventura County, California, USofA.
I would like to know how to close up an aluminum wet-wing fuel tank so that it will never, ever leak in a thousand years.

I have never done this before, but I think I have some pretty good ideas about how to do it. I want to run them past you veterans to see if you have any better ideas.

I have formed aluminum ribs that exhibit crimped flanges which mate to the inside of the skins. So this is an uneven surface. I think it might be a good idea to apply a coat of polysulfide sealant to the mating surface of the flange so as to fill the low spots of the crimps so that the resulting mating surface is more flat to the the skin to which it will be mated. This first coat would be allowed to cure before the actual mating. Before mating, a second coat of polysulfide would be applied.

Preping of the bare metal mating surfaces should be done with the same discipline to achieve a good bond as you would for a structural epoxy joint...Detergent clean, mechanical abraid, acid etch, DI water wash, rinse, and dry immediately prior to application of the sealant.

Every rivet hole that penetrates through the walls of the tank should receive a small bevel on both sides of the sheet. This bevel would provide a small volume of space for polysulfide be applied, that will not be wiped clean by the rivet as it passes through the hole. Upon bucking or pulling of the rivet, the rivet shank will expand into that space, the polysulfide will extrude out filling any leak in the immediate area of the rivet shank.

Before the final assembly of skins to the underlying ribs and spars which define the walls of the wet-wing fuel tank, the polysulfide is liberally applied to all mating surfaces. When the skin is put in place, it must be done so that it is not allowed to come back off. If this happens, the proseal will have been pushed out to the edges on either side of the joint, leaving very little polysulfide to fill any voids when it is layed down the second time, thus creating leak paths.

The skin should be well clecoed in place and rivited entirely before the polysulfide cures.

Mixing of the two parts of the polysulfide compound in the corect proportions must be done very accurately to ensure that it cures. It should be done at a temperature that is low enough so that it will not cure before all the riveting is completed. But as far as I know, polysulfide takes many hours or even days to cure. I am not sure if that is normal.

I have some gaps in the neighborhood of 1/4" at the corners of some ribs that I must filled. Can I fill those gaps with pieces of foam and seal them up with polysulfide? What kinds of foam can withstand exposure to automotive gasoline and avgas? Polyether Polyurethane, aka last-a-foam; Divinycell foam; Polyurethane foam?

That is all I can think of. I am soliciting your suggestions and criticism.
 
Back
Top