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> A good analogy is to look at biology - endoskeleton vs. exoskeleton. > Can't argue with the analogy. It is a good one. > > Our little VWs are stressed-skin vehicles. That's one reason why they're > simple, light, and cheap. This is debatable, however. I would argue that the T3 is less of a stressed skin design than 99% of modern production cars. Why? Several reasons. First, there is the very structural tunnel that runs down the center of our cars. This tunnel is a very heavy walled (compared to the rest of the sheet metal around it) tube that carries a significant portion of the loads on the car. Second, the body of our car is bolted to the floor pan. This is a significantly less structural joint than the 1" to 2" spaced spot welds holding modern uni-body cars together. I believe this is a large contributor to the somewhat lower bending stiffness of our cars. (see below). Third, our rear fenders are bolt-on, non-structural panels. Typical modern, uni-body cars include the rear fender (quarter panel) as part of the bodyside stamping making it a much more structural skin. Hoods, front fenders, doors and decklids are all considered non-structural, at least from a global stiffness standp! oint. We have all four fenders non structural, modern, uni-body cars only have two. Thus my argument that the T3 is less of a stressed skin design then the modern uni-body car. > However, they are (admittingly) also quite limited... they aren't that stiff This just isn't true.. Even by modern standards, the T3 is quite stiff, especially in torsion. The Type 3 has a torsion stiffness of a bit over 15,000 ft-lbs/deg and a bending stiffness of between 20,000 and 30,000 lbs/in. The best modern production cars have torsional stiffness of between 16,000 and 18,000 ft-lbs/deg. 10,000 ft-lbs/deg is more typical. Bending stiffnesses of modern cars can be higher with a range of values between 20,000 and 80,000 lbs/in. See the List archives for more details at http://vwtype3.org/listsearch/?post=/archives/2000/january/msg00540.html > Most modern production cars have an unstressed skin, which is one reason why the bodies crumple up so much > easier in collisions yet the passengers have a greater chance of living. Again, not true. Modern uni-body cars (likely to account for 90% plus of the new car population. Note, I said car not truck and SUV) are stressed skin designs. They have no frame type structures to carry loads. The loads are carried directly in the body panels. They do have non structural front fenders and closures. They crumple because we design the stressed skins to do just that with specific features in the panel designs to trigger and control where and when the panels buckle, fold, and crush. There are examples of modern cars with spaceframe construction (Audi A8) and with plastic, non structural skins (Saturns) out there, but they are a small percentage of the population. > Many race cars also have an unstressed skin. This is true, at least for NASCAR and your Saturday night local racers. Later, John Jaranson (that pesky Ford engineer) '71 FI Auto Fasty (Jane) '66 Square (Sophy) About Half a Late Square (Organ Donor) http://mywebpages.comcast.net/jaransonT3/jaransonT3/ ------------------------------------------------------------------- List info at http://www.vwtype3.org/list | mailto:gregm@vwtype3.org