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Old 09-04-2020, 11:02 AM   #10 (permalink)
aerohead
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Cadillac

Quote:
Originally Posted by JulianEdgar View Post
And re the Cadillac. It's not a car I am familiar with, but I see a Cd listed of 0.29. From that, you can be pretty confident of attached flow right down to the trailing edge of the boot lid, and from that, you can be pretty confident of a fair amount of rear lift as the air travels around the curve from the roof to the rear window. (I'd be happy to see some smoke stream pics, if anyone can find them.)

If the car develops at 100mph 30.6-pounds of rear lift, and 40.8-pounds front lift, I'll let someone else find the frontal area and do the calculations for the coefficients of front and rear lift. My guess, and it is only that, is that the figures would be quite different in free air (and not a tiny wind tunnel), but even as they are, you can start getting a feel for how car shapes produce lift.

As to Aerohead's calculations, he is either deliberately muddying the water or is confused. No one is expecting the car to fly - yet another strawman argument of the type that Aerohead is so fond of adopting.
1) the published drag coefficient is Cd 0.32.
2) the published frontal area is Af 24.5-sq-ft ( 85.078% of gross area )
3) a scaled comparison to the template suggests perfectly attached flow at the decklid spoiler.
4) at 100-mph, the car generates 30.6-pounds of rear lift, retaining 98.3 % of it's static wheel loading.
5) EPA test weight of the car is 4298-pounds.
6) 48 % of weight is borne by the rear axles ( 2063-pounds )
7) at 172-mph, rear lift is 90.52-pounds, compared to 207-pounds for a 1969 Volkswagen 1600 Squareback.
8) Hucho stated, in his 2nd-Edition, that if the car's aft-body trailing edge was simply raised to the elevation of the production spoiler, both lift and drag characteristics would be improved. One can infer what they wish.
9) the fastest posted speed limit in the United States is 85-mph.
10) rear lift on the Cadillac at this velocity is statistically meaningless.
11) it would be less with the template. By default.
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Last edited by aerohead; 09-04-2020 at 11:04 AM.. Reason: typo
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