Fuel Tanks: Aluminum or Carbon Fiber?

[emerjer]

I'm considering on making a carbon fiber fuel tank for this coming up year and was wondering as to what everyone's opinions are on this matter. In the past few years, I've been using the common aluminum, but this year I would like to make it more complex and hopefully lighter as well.

I know that there are a few teams that use carbon on all sorts of parts on their car (i.e. RMIT, and others). Would we be sacrificing the cost portion of the comp. if I choose this route?

Mainly what I would like to know is what people think about the:

Advantages and Disadvantages of using Aluminum vs. Carbon (vice versa) as far as the design goes?

The time it takes to make the tank of Aluminum vs. Carbon (I have a little over a week)?

The cost report aspect of the competition with regards to the Aluminum vs. Carbon?

The weight comparison of of the Aluminum vs. Carbon (assuming you have the same design, same carbon thickness as aluminum; except with the additional internal epoxy is added for sealant)?

Also, would anyone recommend a sealant epoxy?

Thanks to all who contribute,

Jeremy Smith
Fuel System Manager
Cal Poly Pomona FSAE
www.csupomona.edu/fsae (http://www.csupomona.edu/fsae)

[emerjer]

I'm considering on making a carbon fiber fuel tank for this coming up year and was wondering as to what everyone's opinions are on this matter. In the past few years, I've been using the common aluminum, but this year I would like to make it more complex and hopefully lighter as well.

I know that there are a few teams that use carbon on all sorts of parts on their car (i.e. RMIT, and others). Would we be sacrificing the cost portion of the comp. if I choose this route?

Mainly what I would like to know is what people think about the:

Advantages and Disadvantages of using Aluminum vs. Carbon (vice versa) as far as the design goes?

The time it takes to make the tank of Aluminum vs. Carbon (I have a little over a week)?

The cost report aspect of the competition with regards to the Aluminum vs. Carbon?

The weight comparison of of the Aluminum vs. Carbon (assuming you have the same design, same carbon thickness as aluminum; except with the additional internal epoxy is added for sealant)?

Also, would anyone recommend a sealant epoxy?

Thanks to all who contribute,

Jeremy Smith
Fuel System Manager
Cal Poly Pomona FSAE
www.csupomona.edu/fsae (http://www.csupomona.edu/fsae)

[Dr Claw]

what about a vacuum formed plastic gas tank? you can get the complexity that you're looking for and it'd take less time to make than carbon fibre anything since you can make the form out of wood (just cut out cross sections and screw them together) and minor surfacing with bondo.

[VFR750R]

With Carbon I would consider some sort of bladder for it. With E85 I would recommend an alternative to aluminum, not required but know that aluminum will disolve in E85 over long periods of time. Nascar tanks have bladders, I would talk to ATI or some other bladder makers and see what they would do without rules on tank material.

[NetKev92]

Ditto on the bladder for a CF tank if you go that way, but I'd personally lean toward aluminum having played with composite for a variety of things. It would be just nigh impossible to get a fuel-tight tank with a wet layup without a lot of excess layers or a layer of sealant added to the inside to seal it. Long-EZ aircraft homebuilders often have leaks when they first finish their wet layup tanks. You could do an RTM part to avoid pinholes, but you'd need molds and a lost foam mandrel for the interior.

[Wizard]

We have run ATL custom bladders for several years now (which is the safest and only permanent solution in my opinion) but we have made a "temp" tank out of aluminum to confirm our design before spending big bucks on a bladder and also to get the car running since bladders can sometime take several weeks to construct.

I know Penn State also had a carbon tank but I think they found a sealer or epoxy that was fuel safe. Maybe someone that has done a carbon tank can comment on any safety issues.

Since you have "a little over a week" I would recommend the aluminum route since you can output a useable tank in a short amount of time.

For sealing an aluminum tank I would recommend POR-15 US Standard Tank Sealer. Works great. A trick is to scuff with scotch brite the interior surfaces before welding the tank together and then rinsing the tank after welding with acetone until it comes out clean before starting the sealing processes. This will give the sealer a great surface to bond to. The weight of aluminum tank is really driven the thickness of material you can weld.

[Wesley]

POR-15 is incredible stuff. I think if you left a car coated in POR-15 out in a field it'd last until the sun novas.

[emerjer]

Cool, thanks everyone for your input in such a timely manner....After much deliberation, I think that I'm gonna make an aluminum one first and then make a carbon one.

Thanks again everyone and Merry Christmas!!!

[Mike Cook]

Wizard,

This POR-15 stuff. Is there any other reason to use it other than sealing the tank? We have built aluminum tanks for 4 years and never had a problem with them leaking, so long as we checked them and re welded anything that initaly leaked. Thanks.

[Wizard]

The main reason we sealed it was we had a flange hole with studs that the pump bolted onto. At first we didn't POR-15 and it leaked around the bolts even though we used a fuel resistant sealer. Cleaned the tank out, sealed it with POR-15, no leaks. Our second attempt we sealed it right off the bat and never a single leak. Chasing leaks is never fun and many times very time consuming. My experience is to just seal it right from the start and not chase your tail.

From a safety standpoint I don't know if it helps but the coating is rather thick and tough so if a crack in a weld would occur (i.e. from an accident) I would rather have a sealed tank next to me than an unsealed tank.

[Krister]

Stupid question, do you seal inside or outside (or both) of the tank with POR-15?

Krister

[Mike Cook]

Thanks

[Wizard]

Krister,

You only seal the inside. Also I would recommend only getting the 8 oz. can. And they recommend not to reuse so if you are testing multiple tank designs just get several 8oz cans and not a larger qty (unless you are sealing all the tanks at once).

[repeatoffender]

<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by Wizard:
The main reason we sealed it was we had a flange hole with studs that the pump bolted onto. At first we didn't POR-15 and it leaked around the bolts even though we used a fuel resistant sealer. Cleaned the tank out, sealed it with POR-15, no leaks. Our second attempt we sealed it right off the bat and never a single leak. Chasing leaks is never fun and many times very time consuming. My experience is to just seal it right from the start and not chase your tail.

From a safety standpoint I don't know if it helps but the coating is rather thick and tough so if a crack in a weld would occur (i.e. from an accident) I would rather have a sealed tank next to me than an unsealed tank. </div></BLOCKQUOTE>

why dont you use an o-ring to seal it? saves using sealant