Aerodynamic Suburban or GM SUV (92-99)

[aardvarcus]

Big Dave/Freebeard,
The tail is another good idea, but the rear overhang would get long in a hurry for a decent tail length on a Suburban. The Blazer/Tahoe/Yukon wouldn’t be so bad.

[aerohead]

Originally Posted by aardvarcus

Aerohead,
I was planning on following the AST-II top profile and the AST plan taper profile (4:1 aspect ratio?) you had previously shared, unless you think there is a reason to use a different profile on this vehicle.

Thanks for sharing the VW picture, that is very helpful for designing the tire fairings. I am a bit surprised by the size of the leading faring for the rear wheels. I am also surprised by how much wider the fairings are than the wheels/tires. This may be way too complicated, but I had considered using a “U” shaped aft tire fairing with an open back and ducting some engine bay air into the aft tire fairings to “fill the wake” once the fairing ended.

The Buchheim et al contour for roof and sides is a known quantity,so if it will save weight it would be good.
The AST-II is 1-degree more conservative with the roofline.I've not compared the plan-view.
4:1 would be safe for the sides.Some of the lowest drag vehicles have used it.
FYI: the 1981,Randal L. Peterson,NASA boattail was good for a 32% drag reduction.Torbj'o'rn Gustavsson,KTH,Department of Aeronautical and Vehicle Engineering,Royal Institute of Technology,Stockholm,Sweden,mentioned that
"A less curved (NASA) boattail would (sic) probably given larger differences between a full boat-tail with fully attached flow and a truncated boat-tail."
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The Mair tail architecture would better satisfy the attached flow condition

[elhigh]

Originally Posted by aardvarcus

Big Dave/Freebeard,
The tail is another good idea, but the rear overhang would get long in a hurry for a decent tail length on a Suburban. The Blazer/Tahoe/Yukon wouldn’t be so bad.

The 'Burban has a pretty big booty to start with. That's a lot of tail to wag.

[acparker]

Would enough advantage be obtained by doing a Dodge Xplorer type conversion, a domed roof with tapered rear extension?

[aardvarcus]

Aerohead,

Conservative is fine, I would rather stay in the safe zone for semi-permanent bodywork versus an add on piece. I did some overlays of the diagrams you provided and of the top view of a Suburban.

[aerohead]

Originally Posted by acparker

Would enough advantage be obtained by doing a Dodge Xplorer type conversion, a domed roof with tapered rear extension?

*It looks like your roofline already has some down-sweeping camber,setting you up for some boat-tailing.I don't know if lofting the roof to get more would pay for itself.We have very limited data on this one.
*Any boat-tailing should help if you can tolerate the added length.




Here you can see some wind tunnel-derived values for a van-type vehicle,including boat-tailing

Member orbywan has seen mpg success with boat-tailing to his Ford Motorhome


Softening the edges will kill vorticity,lowering drag,as in this GM Optimum boat tail

The ideal,is probably the inflatable tail,which deploys automatically,and stows automatically

[aerohead]

Originally Posted by aardvarcus

Aerohead,

Conservative is fine, I would rather stay in the safe zone for semi-permanent bodywork versus an add on piece. I did some overlays of the diagrams you provided and of the top view of a Suburban.

The sides of the car have the slowest air,and least kinetic energy.Unless the sides converged exactly as the roof,as in a pure streamline half-body,they would not be able to tolerate as much contour as the roof flow.
The drag minimum 3.92:1 contour for 2D flow might be a safe place for us


The MG EX 181 used a plan-taper very much like it and recorded Cd 0.12.

[freebeard]

"basiswiderstand eines stumpfen Körpers durch massnahmen am Heck"="base resistance of a blunt body by measures at the stern"

I'm less impressed by the base plates. Their only half effective.

The Tailwind project reminds me of Redneck's Metro.

[botsapper]

'slammed and 'tailed Sub

[aerohead]

Originally Posted by freebeard

"basiswiderstand eines stumpfen Körpers durch massnahmen am Heck"="base resistance of a blunt body by measures at the stern"

I'm less impressed by the base plates. Their only half effective.

The Tailwind project reminds me of Redneck's Metro.

*yeah,the base plates held out the promise of easy manufacturing and a minimum of material,but in a crosswind (as we're likely to have most of the time) their performance falls off.
*Redneck's Metro tail is delicious! Morelli would love it.