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Old 05-20-2020, 01:16 PM   #1 (permalink)
aerohead
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'Ideal' shape for low drag

The 'ideal' shape for 2-D flow of struts/symmetrical wing sections was obtained by S. Goldstein,in 1938, and is presented in Fig. 2.28, page 244, of 'AERO-HYDRODYNAMICS OF SAILING, INTERNATIONAL MARINE PUBLISHING,Camden,Maine, copyright 1979, 1988, by C.A. Marchaj.
The drag is governed by surface friction and pressure drag. There exists a single iteration of the struts which embodies the least drag.If it is lengthened,the surface drag increases,along with an overall drag increase.
If the strut is shortened,pressure drag increases,increasing the overall drag.
This one geometry of struts is in the bottom of the drag 'bucket.'
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The same holds true for 3-D flow streamline bodies of revolution. Both surface friction and pressure drag bottom out with a body of Length-divided by Diameter = 2.5. Yielding Cd 0.04. As a half-body,in ground reflection,this body produces Cd 0.08. Adding wheels increases drag to Cd 0.13.
According to Hucho,this drag can be reduced by integrating the wheels into the body. According to Goro Tamai of M.I.T.,a proper set of wheel fairings can reduce the wheel drag approximately 70%, allowing in the neighborhood of Cd 0.095. Honda achieved Cd 0.10 in 1994 with their 'Dream' solar racer.
The 2013 Cambridge University Eco Racer CUER solar car was measured at Cd 0.11.
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The 'template' is intentionally fashioned after the Cd 0.04,2.5 L/D, streamline body of revolution.
Hucho says aerodynamics is about pressure drag.
Hucho says pressure drag is about separation.
The 'template' is incapable of producing separation,by default.
Without separation it achieves the drag minimum recognizable,as Hucho puts it.With tighter wheel fairings it's quite likely that she would have mimic'd CUER's Cd 0.11.
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If you want to believe that aerodynamics is a 'black art',I can't stop any of you. The evidence suggests that it's quite easy to construct really low drag automobiles with out any further research or expenditure. Off - the -shelf technology if you will.
And this argument would date to 1922.

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Last edited by aerohead; 05-20-2020 at 01:19 PM.. Reason: add data
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