Air frame or metal shaping gurus - flat curves in aluminum

Yes...thats the idea. and the pipe tool will come in handy for something else. What have you got to lose?

Craig

 

Scooter I did one from steel exactly like yours. I just muscled it around the buck and put a few very small screw holes in it so I could screw it to the wood ribs as I went. Used washers on the screw to keep them from damaging the skin. Wrapped it up, cut to size, welded the seam, took out all of the screws, pushed the buck out and welded up the screw holes. Voila. the outer shell was done. Unfortunately and as per usual I took no pictures of the process.

 

I wonder if you get the aluminum loosely wrapped around the buck if you could use some nylon straps with turnbuckles to pull the aluminum skin up tight against the bucks all the way around. It would probably spring back a lot though when you released the straps.

When I made a steel gas tank once that was sort of a long trapezoid shape, I made the long tube shape first with one long welded seam, then I made wood bucks to make the end caps to match with rolled over edges on the end caps, and butt-welded them on. It was a big pain making the long tube shape. I used lots of big hunks of bar stock and lots of C-clamps and a lot of brute strength and big dead blow hammers. I think it would have been impossible to make the tube shape to fit the end caps perfectly, so it was easier to make the tube shape and then make the end caps to fit the tube.

I welded the baffles in before I welded the end caps on.

 

AF! I was just about to say "where's the pictures" and then I read your last sentance. Bugger!

Sounds like you did what I was thinking of doing from the very beginning.

 

Sorry I get so involved in what I am doing that I almost always forget to take progess pics.

 

This is something that has crossed my mind as well. I think maybe attaching the skin to the caps and baffles before buttoning up the seam would be help for this case for exactly what you just mentioned.

 

HAHA! I do it to. D'OH!

 

How bout some thin wall aluminum pipe, then just squash it to fit your inner panels? Then it would be seamless except for the end caps?

 

Yes, but $$$$! I would have to start with something about 12" in diameter. Not sure I've ever seen anything that size and thickness. Does it exist?

 

Here is anouther spin on the tubing if you have a flat steel table. Just clamp the tube to the table with a shim under each endand pull up.

Remember when you work with aluminum to protect the finish when you slide it through. You could lay a blanket down to avoid scratches.

I think what you really need to find is a buddy with a slip roll.

Jeff

 

How are you planning on handling the long seam ?

Besides rivets.

 

I've been offered some help with the slip roll. So I have that option still. Just wondering if it really gets me much further than just annealing it and pulling it over the buck and fastening it down.

Here's a good question. Let's say I do anneal it and pull it over the buck. It will want to return to it's flat state and to keep it from doing that it will need to be fastened to the baffles. Will it eventually lose tension and relax or will it technically always remain in tension? Again, never worked with aluminum. I'm just thinking that if it remains in tension it may not be the best thing for the seam. Would think there would always be that tendancy for it to pull at the seams and rivets. The for SURE wouldn't happen if I useda slip roller and got the initial shape to begin with.

Am I off here? Will annealing do the trick and allow it to relax enough not to pull at the joints after it's completely assembled? Am I over thinking this like everything else?

 

First the joint will be riveted. I have a friend who is a bitchin' TIG welder and he's going to run the seam for me, then I will apply the sealer for the rives and for extra measure of protection (assuming this sealer will be compatible at ALL with regular unleaded fuel).

 

3003 is annealed. bends soft like butter

 

Oh... okay.

 

I was hasty, should have said 3003-0 is dead soft annealed. When you buy it be specific. Tempered can be harder to bend. As with 3003-T( )

 

Right, right... okay. That's what I was thinking, but then I remembered we're talking about H34. However. Maybe I should be looking at -0 to save me a step.

 

If it's annealed it won't try to flatten back out as badly.

If you have access to a slip roll and a tig welder you could always just roll it into a tube, weld the seam then flatten the tube into the shape you like and cut your baffles and ends to fit the squashed tube.

I think unkl ians suggestion in post #16 would be the way I would go at it. Use that technique to fit it as close as possible to your buck use the ratchets straps to pull it tight against the buck and check the fit. That will save you having to drill a bunch of holes in the aluminum and screwing it to the buck. Remember every time you drill a hole you are creating a potential leak so the fewer holes you cut or drill the better off you will be.

I would weld the baffles from the inside and put the seam at the top.

Not really a right way to do it, just depends on the tools you have at your disposal and which way you are most comfortable with.

 

One more thing to think about with aluminum is mounting. Aluminum cracks easyer and you need to make sure you have wide contact on the lower mount to take the weight of the fuel. I would concider looking into a bladder, for safty. Hate to see all that work go up in flames. I would build it in steel if it was my car for this reason alone.

 

Like Ian said, you'll probably not have to anneal any of the other pieces. It should be a easy tank to form. You could use straps to hold it in shape, on the buck, while it is tacked together. Just make sure you can get the baffles and end plates in.

 

I have always understood that you are supposed to use 5052 for fuel tanks. I am not sure why, but I think it has to do with its corrosion qualitites. When we build tanks it is always 5052.
Jimmy White

 

That was going to be my VERY NEXT question.... corrosion! And if I went 5052 I would definitely have to anneal it to work it, right? Much harder than 3003 series.

 

Wrong.

B2 is the base, A-2 is a topcoat.


FYI, the B is the consisentcy and the 2 is the work time i.e. 2 hours. B 1/2 is 30 minutes etc.

A is thinner and runny.

1422 B-2 is what you need. Make sure if you use it to mix it up good. Nothing worse than sealant that never kicks.......messy.

BTW, I worked fuel cells for 6 years.

 

I was wondering about that statement. I was also under the impression that's what the letter codes stood for. The sealer we use (as mentioned) is a B series. It's of a sticky peanut butter consistancy. It's not difficult to spread and as long as the prep work has been done, it will never ever pull away from the material. We actually did some tests on surface treatments and we actually glued two pieces of aluminum together with the sealer and were able to pick a very substantial amount of weight and not have them pull apart. Very impressive! I have faith in the sealer, but am wondering about its compatibility with regular unleaded gasoline now. It says "all fuels", but seems there is some differences in opinions about that here.

 

Well 25 years of fuel cell repair is what I base my statement on. We only used B when working overhead and you didnt want it to drip off. A will run into holes and seal better. B works well with jet fuel not so well with gasoline.

 

It sounds as though the cradle design will be significant, in not causing a crack issue to propagate.(sp?) She's gonna be a beautiful tank when done.

 

Who did you work for Roothawg? Didn't you guys top coat with "Monkeyblood" ? All my experince was with Fairchild Metroliners and they built there tanks dry so they were leakers. When I first started out I remember launching aircraft in the morning with a bar of soap in my pocket, instant fuel leak repair.

 

Monkeyblood......yeah we used that on the Westwinds. Now they tell us it is a big time carcinogen...go figure.

I worked B-52's for 6 years, worked on Westwinds and Jet Commanders 1121, 1123 and 1124 for a few years,Hawker 800's, <-----(controlled leak)Boeing 727's and most other commercial airliners, no widebodys though. I have worked some of the San Antonio sewerpipes though. I have been in aviation since 1988. So, 20 years I suppose.

Now, I am with the FAA. No more fuel cells for me. I prolly whacked about 15 years of life off already.

 

An H-series temper like 5052-H32 is strain-hardened, which means that the material will have stresses introduced into its structure when the sheet is formed. These residual stresses will tend to make the sheet remain flat. They also contribute to the strength and hardness.

Annealing the sheet to full-soft or 0 temper will remove these residual stresses, so it will be as if the "memory" of the material were erased. Forming the bend radii over the buck should strain harden the material somewhat (though likely not as much as forming it on the slip roll would) and thereby help it hold its new shape. I would expect some springback but I don't think it would try to flatten right out. I don't think the springback would be a problem in terms of structural integrity (i.e. rivet failure or cracking of the shell), but I wonder if it might produce some unsightly dimpling or creasing at the seams.

For that reason, I think Unkl Ian's earlier suggestion of forming the small radii first and overbending them is a good one. I'm really looking forward to seeing what you come up with!

 

You are absolutely right to be concerned about compatability...

The fuel here in the 5 counties surrounding Milwaukee, WI was "reformulated" several years ago and they added MTBE. Nasty shit that I think causes more problems than it solves. I have had several times where it ate the fuel lines from the inside out. Fuel lines look OK on the outside, but if you slice them lengthwise, the inside was attacked and reduced to powdered rubber! Black powder in the fuel filters is the giveaway. Many of the small engines on our construction equipment have suffered as well - carb diaphragms hardening, the aforementioned fuel lines, and even the gas tanks themselves! Many Briggs & Stratton engines use a two-piece steel tank that has a crimped seam and sealed with what looks like (but may or may not be) Loctite 518 anaerobic sealer. The MTBE eats that sealer too and then the fuel tanks leak!

I would at least double-check with the manufacturer about your sealer's compatability with gasoline, gasohol, and of course MTBE before making that really cool tank. Who knows where you will need to fill up with fuel at... My $.02