Quote:
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Originally Posted by basjoos
I thought the lowest Cd for a ground vehicle was 0.11, which is what they claim is the Cd for the Aptera.
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All the texts I've read (Hoerner, Hucho, an SAE symposium, and another) claim that 0.15
appears to be the lowest cD for a
blunt body,
w/ wheels,
in ground effect. In the symposium, one professor argued that cD could be lowered further by removing vehicle lift, but the issue was contentious.
This was all before CFD, though (1970's).
The lowest theoretical drag shape near ground effect (w/ out wheels) was a shape very similar to the Aptera (~0.09-0.11 mark). The Aptera's wheels are far from aerodynamically clean (two control arms in the breeze). Solar cars supposedly have a cD of 0.09, but they don't seem like blunt bodies to me.
I should add that these might have been 2d shapes (i.e. infinite span). 3d shapes can have lower drag. If that is the case, sorry for being misleading.
I believe a slippery slope some might be falling into is claiming cD*A as cD, which is often done and easily confused.
- LostCause