Drag penalty for having a shallow rear window angle, and using spoiler to re-attach ?

[aerohead]

Originally Posted by freebeard

When the target is 22 degrees, in plan that's 44 degrees --close enough to 45.

In my experiment with Zeppelin-izing a Beetle I established a 45 degree bulkhead and found where the gentlest curve to reach it was.



The solid bulkhead is where a boat tail without the reflex curve would terminate. The open bulkhead is at the original bumper location. I think terminating in a vertical line instead of a low point would impart directional stability.

I guess I've never posted the picture, but I established that a Studebaker Starlight-style V-shaped window would not impair rear vision. Cooling would be through the front of the rear fenders. Oversize like Tatra to allow either side to work in a crosswind.

The 1981 VW-'Drop' Shape wind tunnel model had 100% boat-tailing in plan-view. At Cd 0.16, it made it to' candidate' status as a low drag basic body. The bummer was, just as with the Klemperer 'van' of 1922, which VW used for the VW 2000 concept; the driver couldn't see out of either the front or rear of the car.
As a NISSAN gravity-racer, with a supine driver, yes.

[tomi_k]

Free to download:

https://www.researchgate.net/publica...00000/download

[aerohead]

Originally Posted by tomi_k

Free to download:

https://www.researchgate.net/publica...00000/download

From: SAE Paper 840300, by Ahmed et al. :
* The model exhibited it's highest drag at 30-degree downslope, Cd 0.378
* researchgate shows Cd 0.351- 0.365 for the same 30-degees.
* they might have kept testing until they 'proved' critical Reynolds number.
* at 30-degrees, they're in the 'forbidden zone' of bistable flow.
* the lowest drag was achieved with a 9-degree slope, at Cd 0.2298.
* with 10-degree plan-taper, and a 10-degree diffuser, the drag minimum of Cd 0.214, compared to Cd 0.25 for the initial model condition, according to Bearman et al.'s research.
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I don't know why they would intentionally choose the worst-case scenario to begin with. And the initial drag disparity is discomforting.