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A lower number of inflection points relates to a smoother shape function curve, translating to a more aerodynamically efficient shape. So an aerodynamically efficient shape would have a shape function curve with low number of inflection points and gradual rate of change in area.
How to create a Shape Function Graph of a Car Design
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The smaller the Cd the lesser the power loss. The power loss induced by aerodynamic drag increases at a cubic rate of the velocity variable:
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References:
https://www.ijert.org/research/aerodynamic-development-of-a-solar-car-IJERTV4IS060435.pdf
Design report/ Analysis study of Solar Cars:
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Sunswift eVe - https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=1146&context=aero_fac
Honda '96 Dream - http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.461.3467&rep=rep1&type=pdf