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Old 05-11-2020, 01:40 PM   #3 (permalink)
aerohead
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Just read this thread.I'm away from my library and do not have access to my materials.
While I don't disagree that there is evidence that there are discrepancies between early data compared to more contemporary data obtained for the same vehicle/model,there do exist modern data which compares favorably with early reporting.
I don't believe that broad stroke generalities best serve this argument,but rather, maintain that any specific vehicle should be treated on a case-specific basis.
The Tatra was incapable of 'low drag' due to its aftbody.
Of thefive 'K-cars' built by Fachsenfeld at FKFS,only the Mercedes-Benz'experimental-chassied,diesel-powered,overdrived,1941-42 K-5,personal personal car of Kamm's was rated as low as Cd 0.23.It's the only 'drop-nosed' K-car.It's the only K-car with full wheel skirts.K-5 maybe the only K-car with Kamm's patented cooling system (which is what he is actually famous for,as the
'Kamm' -back is actually the property of Fachsenfeld,and the reason Hitler wanted Fachsenfeld at FKFS).K-5 had the longest aftbody of all the K-cars,the secret to its low drag.
Airfoil shapes would be relegated to sub-critical Reynolds number solar racers,and NACA (NASA) quanta would be valid.
The really 'low-drag' shapes which could be applied to passenger cars would be based upon Paul Jaray's,1922, streamline half-body,which modern wind tunnels and CFD re-verify,with each generation of university investigation.
In his second edition of Aerodynamics of Road Vehicles,Hucho wrote that any difference in drag,associated with wheel rotation during testing indicated such an insignificant difference in results that it wasn't pursued.General Motors Research Labs had come to the same conclusion from it's testing at Cal Tech in 1953.It would have been considered an absurd proposition in truck and trailer testing,due to wheel environment turbulence.Only open-wheel race cars were deemed worthy of the extra trouble/cost.
Today's F-1,Indycar,and NASCAR' billion-dollar racing programs mandate that 'ALL' areas of aerodynamics be investigated.
One curiosity always hiding in the room is that,given rolling-road wind tunnels,and million-dollar public relations budgets,and the ability to develop 'porous' low-drag wheelcovers,when tasked with setting land speed records,all auto manufacturers choose the totally sealed,convex disc,MOON wheel covers,the lineal descendant of WW-I era aviation; and can be seen on all extant Boeing 727s.
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