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Old cars tested in modern wind tunnels
I have a copy of the German magazine Motor Klassik that features a bunch of old cars tested in the Volkswagen wind tunnel. The data shows very clearly how optimistic pretty well all the Cd figures are that were quoted at the time of the cars' release. (Cw = Cd.)
https://i.postimg.cc/MTFcNyX7/IMG-0905.jpg https://i.postimg.cc/y62jSRn3/IMG-0906.jpg Kamm K3 low drag research vehicle (Cd = 0.37): https://i.postimg.cc/7LBMPJf6/IMG-0909.jpg BMW Wendler (Cd = 0.44): https://i.postimg.cc/15x0zQ5p/IMG-0907.jpg Tatra 87 (Cd = 0.36): https://i.postimg.cc/VkmjjWtv/IMG-0908.jpg All wonderful cars for their time, but obviously all with pretty bad Cd values in any modern context. I simply don't believe any old drag figures - instead, I look at the rated engine power and the top speed. For example, the Panhard Dynavia did 81 mph on 28hp, and if we accept these figures, it certainly had low drag. https://i.postimg.cc/jdLVRy2W/Figure-2-F.jpg |
don't believe
It would be informational to retest all the vehicles under contemporary conditions and examine the difference.
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I happened to come across this Volkswagen press release from 2015 this afternoon. It mentions the testing of the Sagitta in 2013 after it was discovered still intact at a car show:
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Further, they tested it in various configurations: Quote:
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But Vman455, I don't understand!
How can the V2 Sagitta possibly be low in drag? It doesn't match The Template in any way at all! How could they have made such a major error? (Gorgeous car by the way - and a brilliant drag figure.) |
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It has never actually existed... or didn't you realise that? |
Well that's a mentally ill/deliberate misinterpretation of what I said.
What I was trying to say is, that they would have done a lot better if they had used the template as a sort of... well template, the steepness of that rear is utter malarkey. |
Is there any indication as to why they were wrong? Were they lying? Or was it measurement error or calculation error? I remember reading that the Lotus europa with its claimed 0.29 drag coefficient was with aerodynamic tweaks not offered on the car. Is there any difference in how the calculations were done then? Other than lack of digital systems.
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Modern wind tunnels don't agree today. Zeppelin tunnels didn't require a rolling roadway.
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T'would be interesting to see what further he has to say. ;) |
But why don't they agree? Barometric pressure? Or are the other variables not able to be controlled well enough?
I don't know how wind tunnel calculations work. But it seems to me that the same car should produce the same results given the same conditions, given the same car either the conditions are different or the measurements are off. Presumably positioning the car fractions of a degree off head on might make a difference. Am I overthinking this or is it just random variation? |
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