Quote:
Originally Posted by aerohead
I've got a small book published by SAE entitled:Aerodynamics:Recent Developments,published maybe late 1980s/early 90s.
In the book,another marque,maybe Fiat ( I'll look) had a 2/3rd scale composite car model which could be assembled to create a myriad of car configurations.
What I remember off the top of my head ( and my memory is dubious ),is that they found no hard and fast rules,and air directed up or down or around could play havoc with the Cd,say lowering upper body drag while increasing under body drag.
I'll dig that out for tomorrow.
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The paper I have is SAE 860212,'Car Underside,Upperbody and Engine Cooling Systems Interactions-and Their Contributions to Aerodynamic Drag,by A.Garrone and M.Masoero,Fiat Auto Wind Tunnel Dept.,1986.
The paper runs to 8 pages.
It was a full-scale model,not a scale model.
* Underbody drag of bellypan,suspension,wheels and wheelhouse was found to be nearly same as upperbody drag.
* Cooling system drag was measured at Cd cs 0.017.
* Base drag of upperbody was 50% of upperbody drag ( the car looks like a Scion xA).
* Sealing the cooling sys. lowered underbody drag but increased upperbody drag.It should be 'optimized' as Korff/Morelli have done.
* these folks also came up with the 2.5-degree diffuser for bellypan.
* For a low-drag car,a front airdam increases drag.
* In a low-drag car,the underbody can constitute 50% of the drag.
From their diagrams you get the idea that moving the stagnation point around could conceivably degrade performance if you weren't careful.
From Hucho's book,which cites the 'ideal' nose,if you ascertain the stagnation point there,and then place the grille opening there,then maybe that's a good bet for general purposes.
If you have the 'length',then GM's 'bottom-breather' appears to be a great way to go.
Historically,moving the cooling system to the rear,as with Probe-IV,V,GM Ultralite,GM Precept,appears to offer even better savings with zero opening at the front at all.