[aerohead]

Background: For a "streamlined car",we can turn to the man who first used the term in 1922,Paul Jaray.Jaray was an aeronautical engineer with the Zeppelin Werke,involved in airship design which includes "Los Angeles" built for the U.S.under the Versailles Treaty.--------------------------------------------- ( from Hucho ) It was Jaray who recognized that the flow around a body of revolution ( spheres,cones,ellipsoids,cylinders,etc.) of very low drag in free air,is not axially symmetrical close to the ground.As a result,the drag increases.--------------- Where ground clearance approaches zero,the optimum shape for a low drag is a half-body,which forms a complete body of revolution together with it's mirror-image produced through reflection from the roadway.THIS IS EXTREMELY IMPORTANT!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!! Refer to Figure 4.118------------------------------------------------------------------------ Also from Hucho,is a table which shows one of the lowest Cd belonging to a "streamline body" of Length/Diameter ratio of 2.5:1,@ Cd0.04.This image is from Hoerner's book of 1965,which is also in his 1951 book,and comes from : Goethert,Drag Measurements on Streamline Bodies in the High-Speed Tunnel of the Deutsche Versuchsanstalt fur Luftfahrt,Berlin,Zentrale fur Technisch-Wissenschaftliches Berichts 1944,p.377.------------------------------- I've taken this profile as the "minimum" for use in the template as it is drag-free(profile) and has the minimum wetted area to also minimize friction drag.-------------------------- The linear progression combines mirror-image of the 2.5:1 streamline body to create the "pumpkin-seed" Jarayesque form above the ground,with curves just "slow" enough to guarantee arrached flow.------------------------------------ You will see Fig.4.119 from Hucho which illustrates a 1966 VW Beetle in "mirror" and will notice that from the graph,at super-critical flow,the ellipsoid of lowest drag also occurs at a fineness-ratio of 2.5:1.------------------------- From Marchaj' book I've included a table of "sections" which includes a drag table showing form-drag and friction drag combining for "Total drag". You will see that a drag minimum occurs for wing-loke structures at a fineness ration(aspect-ratio/thickness-ratio) of 3.92:1.----------------------------- I've included some tables from Fluids texts which shows some forms and their respective drag coefficients in both 2-and 3-dimensional flow,at varying Reynolds Number.---------------------------------------------- I placed Sunraycer under the template,it was a perfect match.Bill Watson's airship "White-Dwarf" of 1984 is about 2.57:1 ratio.Watson worked with Burt Hibbs,aerodynamacist for Sunraycer.Both of AeroVironment.-------------------------------------------------- This shape seems to end up on some of the most efficient vehicles known in the world,I believe it to be a shoe -in for aero-modding.-------------------------------------- Those with more advanced aerodynamic toolbags will will no doubt venture out into some of the more exotic shapes,but for amateurs,I believe this form can serve us well.------------------------------------------ Good design and engineering calls for the bare minimum to get the job done.Using the minimum will guarantee lowest weight,most efficient use of material and energy and lowest economic and environmental impact.