here's a tidbit from 1922 which might help.
*The Aerodynamic Streamlining Template along with it's mirror-image as a streamline body of revolution,in free flight away from ground effect has Cd 0.04.
*When the AST is lowered into ground reflection its drag doubles to Cd 0.08.
*Lifting it and adding wheels raises the drag to the neighborhood of Cd 0.13.
*If lowered back down to zero ground clearance,rolling on an ultra-smooth roadway,its drag would be Cd 0.08.This has been proven empirically in wind tunnel tests.
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*We've never altered the body,but it's drag can be reduced by 38% just by lowering.
