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I want to make a car consisting of a tubular frame with a skin draped over it.
Carbon fiber materials are expensive to make if you want to give them a shape. You have to weave and ply and set this material. There's no real efficient mechanised system to do this.
But you can easily make carbon fiber
tubes, all the same shape. You can produce them en masse.
So you simply take many carbon tubes, attach them to each other via an aluminium piece (I don't know the English word. Is it "joint"?)
Ok, so now you have a very light-weight and strong structure which will protect the passengers.
You put the electric motor, batteries, seats, etc... inside this structure.
Now you can put a skin over this car. A strong, flexible but very thin polymer. (BMW has already such a concept - see link).
This skin is "draped" over lightweight, much thinner tubes, which don't have to be strong because they serve no protection function. They can be made of polyester or another cheap material. These tubes are just needed to give the car an aerodynamic shape, which is obtained by draping the skin over the tubes.
You don't need metal for this skin, as is the case in ordinary heavy cars.
That's it.
Now you have a much better car than all the other cars. At last we can use carbon fiber in a car, as the main structural element.
I made a rough sketch of it.
As you can see from my exposé, I am an experienced car designer. The idea is not plagiarism from BMW, because I do carbon fiber tubes in an electric car which is not so hot so that the polymer skin can be used in earnest.
Sketch of the car
http://i3.photobuck...briddiesel/skin.jpg
This is a sketch of the car. [django, Aug 28 2008]
BMW "Gina"
http://www.ted.com/pages/view/id/203
A video about the skin. [django, Aug 28 2008]
Types of bodies and chassis
http://www.autozine...s/tech_chassis2.htm
[mylodon, Aug 28 2008]
Slipcover autobody
Slipcover_20autobody
Not quite the same idea. [phoenix, Aug 28 2008]
[link]
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[+] but why not make the joints out of carbon-fibre also? like plumbing supplies. Note that a skinned car is a return to a frame-based vehicle from the modern "unibody" construction and you may have issues with aerodynamics at high-speed and unattended vandalism. |
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/Ok, so now you have a very light-weight and strong structure which will protect the passengers. / |
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Two thirds correct. You need some ductility (energy absorption) if you want to protect the passengers. |
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Yep, vandalism, didn't think of that. Big problem. But then, the skin would be a rather inexpensive polymer that can be replaced easily (in contrast with a rigid piece of bodywork). |
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Carbon fiber joints would be expensive because their form is complex. That's why I thought aluminium. |
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// at last we can use carbon fiber in a car // -- see link. |
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Use tubes! Of course, why didn't we think of that? |
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The problem is the joints, they usually create stress concentrations that make the tubes weak. I'm not saying you can't, as modern CF bike frames have proven, but you seem to be glossing over the tough bit. The interface between the CF and the aluminum can be handled several different ways but since it is nearly impossible to attach to each fiber of a CF tube, the system is a weak point. It's greatest weakness is usually in torsion on the joints, your drawing shows many small tubes which is not the way to go. Gear the design to a few large tubes or pairs of small tubes connected by flat sheets to handle the torsion especially if you are getting rid of the structural skin. I'd also suggest even if you get rid of the classic metal skin, you include other similarly stressed flat skins. |
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Also aluminum is also an issue as it stress hardens and becomes brittle. Many racing leagues have banned the use of Al in roll cages for this reason, as they sometimes snap and spear instead of flex and protect. |
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FlyingToaster-- It's not really a return to the traditional ladder frame construction, it's more like a spaceframe construction, like the Pontiac Fierro, BMW Z1, or Catterham 7. it's often considered to be better than the more commonly unibody structure. I don't think there would be any high speed aerodyanmics issues if it was properly aerodynamiclly designed, in fact it might be easier to make a very aerodynamic design with this construction. I do see the issues with vandalism, and think the skin might be just not very durable, however it wouldn't be essential to the cars opperation, so it would be totally possible to drive around even if huge holes were ripped in the skin. |
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