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Old 05-11-2020, 05:54 PM   #9 (permalink)
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Originally Posted by aerohead View Post
*The Cayenne's aft-body is mutilated,allowing a moment arm extending rearwards,beyond the greenhouse,of which the low pressure of the turbulence can act to produce lift.The Jaguar I-pace has the same flaw,as well as others.
*If the roof-line and greenhouse are extended,separation-free,along with the lower body,to the end of the vehicle,the entire wake is of uniform low pressure,and cannot act vertically to produce lift,as you've eliminated the moment arm.
I am sorry, but that completely ignores the major reason that lift occurs on cars. The lift - especially rear lift - in most cars doesn't come from the wake (ie separated flow). It comes from the accelerating flows over the curved upper surfaces.

Originally Posted by aerohead View Post
*A streamline body,by definition,is separation free.As a drag-minimum body,they are in the 'bucket',as Abbott and Von Doenhoff would describe it,at an angle-of-attack which is incapable of generating lift.Yes,the growing longitudinal cross-section does produce accelerated flow and lower pressure as per the Bournoulli Theorem,however,any' lift' generated by the differential there is cancelled by the high pressure attacking the forebody,and pressure recovery over the tail.They are a zero-lift shape.
I am sorry, but that is wrong. An aerofoil has attached flow and can develop lift. You may choose to orientate a streamlined body (like an aerofoil) so it doesn't generate lift, but that is not the same as saying "streamline bodies are incapable of generating lift", as you previously wrote. In fact - of course - the best lifting bodies are streamlined.

Originally Posted by aerohead View Post
I know that you are prejudiced about data from non-moving floor wind tunnels,but I'll mention that Spirit of Ecomodder measured essentially zero lift at DARKO,at 135-miles per hour,Cd 0.218 as a BEV, 128-mph speed potential according to one of the racing teams at Bonneville,and with a nearly 50-50 weight distribution,was rock solid cruising at 108-mph on the interstate highway in Arizona,in a crosswind.Everything done to the truck was inspired by Jaray's research of 1922.
I am sorry, but you are confusing cause and effect. You can be certain the upper surfaces of your car were developing lift. However, if the car in fact didn't develop overall lift, it would have been because of the low pressures developed under the car by its bellypan.

Note: all of this can be directly measured on real cars using a surface pressure disc (easy to make yourself), a Magnehelic gauge and a sealed reservoir.
Modifying the Aerodynamics of Your Road Car

A really good book that should be added to the library of everyone working in automotive aerodynamics, as well as those making car aero modifications at home. - Rob Palin, former Tesla aerodynamicist
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