Aluminium monocoupes and kit cars

[singlecoil]

Sam_68 said:

singlecoil said:

How about using steel, and seam or stich welding it (or even spot welding it)? Steel is heavier than aluminium, but it is also stronger, so thinner stuff can be used.

:cough: GTM :cough:

It works, but it's not outstandingly light, and it rusts.

or, indeed...

:cough: Robin Hood :cough:

Stainless steel, so it doesn't rust, but it's heavier and more difficult to work.

Both prove that its certainly possible, but both also suggest that there's no overwhelming technical advantage to be gained?

Unless the design of the car calls for the type of chassis that requires it, such as an open car with doors, or maybe a front wheel drive car, both of which are problematic with space-frame construction.

[Stubby Pete]

The Quantum Xtreme has a stainless steel monocoque and is very stiff. A fully built road trim car with fuel, screen etc weighs in at around 650kgs which is marginally heavier than a spaceframe "7" but it is also a bit bigger than most.

[EFA]

singlecoil said:

How about using steel, and seam or stich welding it (or even spot welding it)? Steel is heavier than aluminium, but it is also stronger, so thinner stuff can be used.

Thats why a Robin Hood is such a great car eh???

Moving on....

Lots of criticism of the CAV stainless monocoque - sure it addresses the core issue with the real GT40 from a corrosion perspective, but it has been suggested (maybe by their competition) that the material would render the mono prone to cracking.

The RCR chassis is made of very thick aluminium sheet. What's also worrying is that on an early RCR40 car I saw. key parts of the bulkhead had to be cut away to fit the A/C.

Lots of steel in Tornados apparently carbon monocoque. Mr Sheldon talks the talk. Reminds me a lot of Mike Brewer.

[singlecoil]

EFA said:

singlecoil said:

How about using steel, and seam or stich welding it (or even spot welding it)? Steel is heavier than aluminium, but it is also stronger, so thinner stuff can be used.

Thats why a Robin Hood is such a great car eh???

Plenty of other cars use steel monocoques. Robin Hoods are not a very good example of any of the types of construction they have used over the years.

[slomax]

Anyone remember the Robin hood Bullet from a few years ago?



IIRC that was built using a riveted and glued aluminium monocoque that was self jigging. Nice idea- but i can't help but think that MEV with the eco-exo has done a better job of getting practically the same vehicle.

[mickrick]

A box is a box.
If you make a box out of square tubular steel, you can add diagonals.
Or, you can panel the sides with sheet. It'll do the same job.
You can do the same with a bulkhead. Panel it, or add a diagonal.

I can't see any reason why a tub folded out of aluminium, provided it's designed well, can't be as stiff as a tubular chassis.
A lot of tubular chassis are paneled for stiffness anyway.
I don't agree a spaceframe chassis would be easier to make than a folded, laser cut monocoque.

I think the issue, is how a monocoque is fixed together. What if an aluminium monocoque where to be seam welded?
You can also cut and flare a lot of holes in an aluminium monocoque, without losing any structural integrity. It would be bloody light!

Just my oppinion. I'm not a scientist, or structural engineer.

[Ferg]

Perhaps it would be an idea to machine an aluminium monocoque from solid.

[slomax]

Ferg said:

Perhaps it would be an idea to machine an aluminium monocoque from solid.

You're kidding right?

This simply cannot be done- the size of the block needed would be rediculous, considering you will be machining 99% of it away.

If you look at something like a Pembleton, the Box frame welded chassis is skinned in aluminium, which, from what i understand gives at most of its strength. These can then be made a LOT stronger by simple, but time consuming finishing touches, like rolling the edges instead of just bunging on some edging and bonding it as well as riveting it.





(I am aware that this is the case for a lot of kits and older cars, but the pembleton is a good example and i am familiar with it)

pictures borrowed from http://www.pembleton.co.uk/

[egomeister]

slomax said:

Ferg said:

Perhaps it would be an idea to machine an aluminium monocoque from solid.

You're kidding right?

This simply cannot be done- the size of the block needed would be rediculous, considering you will be machining 99% of it away.

This simply cannot be done economically

[slomax]

egomeister said:

slomax said:

Ferg said:

Perhaps it would be an idea to machine an aluminium monocoque from solid.

You're kidding right?

This simply cannot be done- the size of the block needed would be rediculous, considering you will be machining 99% of it away.

This simply cannot be done economically

Fair point. You would have to be a complete nutjob to attempt it. Imagine the CAD file

[Ferg]

LOL!!!

[Sam_68]

mickrick said:

I can't see any reason why a tub folded out of aluminium, provided it's designed well, can't be as stiff as a tubular chassis.

Yes indeed; it can. In fact it can be significantly stiffer, for a given weight - that's why serious racing cars went over to this method of construction in the late '60's and early '70's, before it was superseded by composites.

The problems are around (a) keeping it stiff, so that the joints don't relax as the tub flexes in regular use and; (b) the economics of manufacturing it.

mickrick said:

I don't agree a spaceframe chassis would be easier to make than a folded, laser cut monocoque.

If you have the machinery to lazer cut and accurately fold the panels kicking about at the back of your garage, the that's probably a fair comment. Sadly, I don't.

I (or anyone else), can nip down to Machine Mart on a Sunday morning and buy the necessary tools to cut and weld the steel tubes that form a spaceframe. We can then trundle off down to the local steel stockholders and buy the tube we need for relatively little cost.

Remember that to achieve decent stiffness:weight on an ali monocoque, you need to use honeycomb panels. These are bloody expensive to start off with, and then you either need to invest in the technology to cut, fold and jig them yourself, or to pay someone else to do it for you.

...and the end result is a tub that is only a little lighter than the cheap and easy spaceframe that you could have knocked up in your garden shed. It may or may not be stiffer (depending on how good your design was), but that's almost academic, because any reasonably competent spaceframe will be stiff enough.

mickrick said:

What if an aluminium monocoque where to be seam welded?

You end up with a structure that is both expensive and not especially light. Ask the guys who built the Renault Spider.

The problem there is welding aluminimum: it's a slow, skilled job, and for practical purposes you have to use fairly thick aluminium sheet or sections. Lightweight aluminimum monocoques tend to use honeycomb panels with very thin (18 or 20 gauge) skins over a very delicate core. Seam-welding a whole tub out of the stuff would be an absolute nightmare. The Renault Spider used much heavier sections, to form a 'tub' similar to the Elise's bonded tub, but the Renault was heavier, more expensive to manufacture and (allegedly) less stiff.

Edited by Sam_68 on Saturday 6th November 16:44

[Sam_68]

slomax said:

egomeister said:

slomax said:

Ferg said:

Perhaps it would be an idea to machine an aluminium monocoque from solid.

You're kidding right?

This simply cannot be done- the size of the block needed would be rediculous, considering you will be machining 99% of it away.

This simply cannot be done economically

Fair point. You would have to be a complete nutjob to attempt it. Imagine the CAD file

Perhaps not as ridiculous as all that: Google the chassis construction of the Alfa Romeo Tipo 33, which originally used cast magnesium frames front and rear, joining a pair of large diameter longitudinal 'pontoon' tubes.

Lots of Formula cars used bulkheads machined out of solid alloy, too.

Neither technique is particularly cheap or friendly for the low-volume special builder or kit car manufacturer, though, and you've still got to figure out a way of joining the bulkheads to each other.

Of course, the idea of building a monocoque out of a single, homogenous shell rather than lots of little bits that then need to be rivetted together is appealing. If only you could find a light, stiff material that could be moulded instead of being machined into shape.

Edited by Sam_68 on Saturday 6th November 17:25

[Ferg]

Sam_68 said:

If only you could find a light, stiff material that could be moulded instead of being machined into shape. :scatchchin:

[GTRene]

the design of the Beck 904 mono from stainles steel does not look so complex, how strong/rigid would such be...its all welded I believe.







love such car.



http://forums.pelicanparts.com/porsche-911-technic...

[mickrick]

"If you have the machinery to lazer cut and accurately fold the panels kicking about at the back of your garage, the that's probably a fair comment. Sadly, I don't."

Ah,if we're talking about Jo Bloggs building a one off in his shed, fair comment.
I was under the impression we where talking kit car manufacture.

Although you could cut accurately enough with a jigsaw if you're building a one off, and a hand sheet metal folder isn't megabucks. I bet you could pick a nice heavy one up off ebay.
For honeycombe sheet you don't need a bender. Just a router.

Of course Carbon is better, but unfourtunately I don't have an autoclave kicking about behind my shed!

[Ferg]

mickrick said:

Of course Carbon is better, but unfourtunately I don't have an autoclave kicking about behind my shed!

Perhaps GRP then...

[mickrick]

Aaaaarggggh! The dreaded frozen snot!
I work on boats all week. I hate the stuff!

[Ferg]

Makes nice light monocoques.

[Sam_68]

mickrick said:

Ah,if we're talking about Jo Bloggs building a one off in his shed, fair comment.
I was under the impression we where talking kit car manufacture.

We are. How many kit car manufacturers have you visited, and how much money do you think there is to be made in this industry, even when we aren't in a major recession.

I've been interested in and involved with the kit car industry for over a quarter of a century, and I've simply lost count of the number of wannabees who have appeared, built a car or two, then disappeared. Most kit car manufacturers have facilities and equipment that are not far removed from one man in a shed, and finding funding for more ambitious projects is the quick way to the bancruptcy courts.

mickrick said:

For honeycomb sheet you don't need a bender. Just a router.

Could you give me a link for self-bending honeycomb sheet, please?

You need some sort of bending brake, at least, to make sure that it folds cleanly along the correct line. Admittedly not a major problem, but you're then only one step away from using composite skinned honeycomb sheet, which are a major advance on ali honeycomb.

We obviously have different standards of accuracy and quality if you think you can build an acceptable tub with a hacksaw and hand-folding.

You don't need an autoclave for fibre composites - ask GTM (or Murtaya? I haven't visited their facilities, but certainly the Minari that their tub was based on was wet lay-up) - though admittedly you get a lighter, stronger product if you do.