Teardrop roof for boxy SUV?

[Bicycle Bob]

In the VW pic, the smoke was introduced at the back, so you would not see any roof-top turbulence. Wondering where to start on a Jeep, I'd be inclined to just keep it under 30 MPH, and get a car for highway use.

[winkosmosis]

Originally Posted by Bicycle Bob

In the VW pic, the smoke was introduced at the back, so you would not see any roof-top turbulence. Wondering where to start on a Jeep, I'd be inclined to just keep it under 30 MPH, and get a car for highway use.

I do have a car, a Miata.

I'm not actually going to do this mod, unless I someday become a fiberglass pro like bondo, but I'm curious whether it would decrease drag.

Edit: Maybe it wouldn't be that difficult actually. The sides could be made of plastic and bolt to the roof rack rails, with a lot of slats going across. With a thin load floor, it could carry light stuff like clothes, food, etc, for expeditions

[shovel]

My zr2 blazer weighs about as much as an XJ (~3900lb empty), and it starts getting "floaty" around 85mph, less (as in, within highway speed limits) when I'm driving against a good head wind. I remember this feeling from my old TR7 that would go nose up and scare the crap outta me at 120 (back then I was actually just stupid and did my high speed playing on public highways)

So.. I'd be a little afraid to make my vehicle look TOO much like an airplane wing. I bet your ugliest frontal spots aero-wise are the corners of the hood and the corners of the windshield, maybe you can shave-and-french those down into a slipperier shape and then add the little tail spat thing to your hatch?

[winkosmosis]

The 4WD XJ weighs only 3100lbs or 3200lbs. But I don't think a curved top is enough to create dangerous lift-- even on an actual wing, only a tiny fraction of lift comes from the bernoulli effect. I could see the shape causing lift in the back and downforce in the front though.

[winkosmosis]

I wonder if a curved fairing like I drew on the front could both reduce drag AND improve cooling. The way I picture it, at highway speed most of the air that hits the radiator bounces back out and goes over the hood. A fairing like that would act as a scoop, preventing flow from bouncing back out and up. At the same time the flow that hits the fairing from the front is smoothly guided up and onto the top of the hood.

[Cd]

I had wondered the very same thing, especially after seeing the roofline of the Honda Element

[winkosmosis]

I wonder if they made the roof like that for aerodynamic reasons.

I do remember reading that more and more cars are getting arched roofs for aerodynamics, but I guess the question is whether you reduce total drag by adding an arch to an already flat roof and increasing frontal area

[Cd]

I have no idea what I'm talking about, but I would guess that it all depends on if the airflow is attached at the start of the roof. I have seen some amazingly sharp corners retain flow, such as on this video.

http://www.youtube.com/watch?v=z7TrxIDWDz4

[winkosmosis]

That is interesting. I guess the only way to know would be to tuft test, but that would require mounting a camera on a stalk to see the roof

[winkosmosis]