Monocoque help, what alloy to use

[Darren]

I am making a Monocouque from scratch, it is an alloy, riveted, bonded arrangement for a single seater, and so to my problem.

I started by using 5052 - T32, all was going along ok until i started to rivet the tub together, the rivits bunched up the alloy and squashed the alloy out from beneath them, resulting in a very much less than profesional finish.

After a bit of searching on the net a solution was found, 2024 T3. A sample riveting proved my therory the 5052 was soft, but the next problem was I couldn't bent the 2024 tight enough and it will crack along the bend without warning, once again not a happy situation.

I spoke to a bloke who builds cars and he sugested 5251, the local aircraft factory sugested 6061, the local fabricator said 5083 there is a new(ish) product 6013 and I am confused

Are any of you wonderful people from the racing industry in the 70's and what would the material of choice have been. The style of chassis is along the line of the Lola T332.
Thanks for you anticipated help

 

[Clayton]

Hi Dazza
Can’t really help regarding the 70’s, but 2024-T3 is commonly used in the aircraft industry. You just need to increase your bend radius to stop it cracking. Get yourself a copy of AC 43.13-1A (Acceptable methods, techniques and practices for aircraft alterations ) You will find you’ll need to add a few bent sheets to the folder to increase the radius. It’s also not recommended to weld.
If you want to weld as well, 6061-T6 seems popular.
Hope this helps.

Clayton

 

[Phil]

Dazza:
The 50 and 30 series alloys are non hardening, good for bending projects but not having the tensile strength you woud want.
20, 60, and 70 series alloys all have various alloying elements like silicon, titanium, manganese and even iron to provide ability to heat treat.
I would say 6061 alloy is probably a good compromise between strength and workability, and although you may have some problems bending it, you can overcome that with some heat.
Most metal supply houses don't stock 6061 T-0 as it age hardens. You may buy a sheet of T-0 and find it cracks mostly because it has hardened over time, and your bend radius is too tight.
If you need to bend 6061 sheet the spec is bend radius = 3 times thickness which may not give you the crisp bends you want. If you apply some heat you can bend to a minimum radius close to sheet thickness. This means the outside is stretching, the exact place where your cracks are appearing now.
You didn't mention what type of rivet you are using, and I would assume a structural rivet that is expanding in the hole, and tearing that soft alloy.
If you search the forum there are a bunch of posts further discussing this topic.
Hope som of this helps.
Cheers
Phil

 

[Marcus]

See also

http://www.gt40s.com/forum/lola-t70-lounge/22490-lola-t70-scratch-build-4.html

 

[Randy V]

Not sure this will be of much help - but the last few times I've tried working with 2024-T3 have resulted in extreme disappointment. Particularly disappointing since I had apparently pulled from the wrong bin when I thought I was pulling 6061-T6..
In my opinion - the 2024-T3 is probably just fine for flat or nearly flat panels that require no welding.. Even trying to bend a 24" long panel with a 1" radius took all the mite I could muster and even then, it resisted holding it's shape far more than anything else I've even encountered.

 

[Lynn Erickson]

I am making a Monocouque from scratch, it is an alloy, riveted, bonded arrangement for a single seater, and so to my problem.

I started by using 5052 - T32, all was going along ok until i started to rivet the tub together, the rivits bunched up the alloy and squashed the alloy out from beneath them, resulting in a very much less than profesional finish.

After a bit of searching on the net a solution was found, 2024 T3. A sample riveting proved my therory the 5052 was soft, but the next problem was I couldn't bent the 2024 tight enough and it will crack along the bend without warning, once again not a happy situation.

I spoke to a bloke who builds cars and he sugested 5251, the local aircraft factory sugested 6061, the local fabricator said 5083 there is a new(ish) product 6013 and I am confused

Are any of you wonderful people from the racing industry in the 70's and what would the material of choice have been. The style of chassis is along the line of the Lola T332.
Thanks for you anticipated help

Check this out
GENERAL ALUMINUM INFORMATION from Aircraft Spruce
Aircraftspruce is an aircraft/ racecar supplier and ships all over the world. I am a licensed aircraft mechanic and have built several aircraft and racecars both aluminum and Carbon/epoxy.
Basically if you are going to weld it use 60 series
rivet it use 60 or 20 series
most aircraft are made of 2024 and riveted
For bending it is the heat treatment not the alloy that makes it hard to bend. the harder alloy treatments make it hard to bend with a small radius, so increase the radius or use a softer alloy treatment.
Rivets are also a science, many need to be heated and quenched before use. there are rivets that are ready to use without quenching again it depends on the heat treatment of the rivet not the alloy. these rivets you should find will work very well for an aluminum frame
SOLID ALUMINUM RIVETS from Aircraft Spruce
Very good info from Vans aircraft http://www.vansaircraft.com/pdf/section_5r9a.pdf
http://www.vansaircraft.com/pdf/section_5r9b.pdf
As you see I am listed as just a Rookie on this forum
hope this helps

 

[Darren]

Thanks for the responses.
Rivets that I am using are AN470-6, still learning this little art, but I think this is just an issue of practice.

The major problem I am having is the 2024 bend radius wont fit the bulk heads and other brackets I have, the radius is to large which is why I believe the material used was something else. I think the 2024 that has been used in race cars in the late 60's when the cigar shape was common, the large radius' posed little problem.

It looks to me that 6061 might be the best bet, I will get small sections of the others for an experiment.
Looks like I will have some reading to do with the AC 43.13-1A and Otto69, thanks for the tip on adding the extra sheets, i have been flat out trying to work out where to get a radius bar made, great solution.
Well to continue reading all the links you guys have given, thanks again

 

[Clayton]

No worries Dazza
The sheeties showed me how you can add small bent sheets to increase the bend radius for different thicknesses. You’ll be surprised at what you can do with 2024-T3. Admittedly they do use “0” condition for complex bulkheads and heat treat afterwards.
Those are big rivets you’re using, could you reduce the size and add more of them ?

Clayton

 

[Darren]

They were the rivets that was used, 1 every 1.5", this is to attach the sills and bulkheads. the service channels etc are 1/8 and 426 in other places.
Next I will want to build a mono 40 if I could just get some dimensions:2thumbsup: