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Old 02-10-2013, 03:02 PM   #1
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Underside Aerodynamics

When I look under my BMW the whole thing is covered and aerodynamic, including fins for cooling on the differential. Vans aren't sports cars but it got me thinking about just how much drag there is underneath the van on the highway.

I started thinking about a series of panels or moldings out fiberglass or felt to smooth out the van. Seems to me there's some opportunity there. From the running board to the frame rail. Frame rail to frame rail. And keeping cooling in mind.

Any body ever done this kind of thing?

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Old 02-10-2013, 03:49 PM   #2
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Re: Underside Aerodynamics

Underside Aerodynamics

As far as our vans go, that is an oxymoron, especially a 4wd van.

I wouldn't be surprised to up 2+ mpg if I could clean up the underside to match my Jetta.

But, what would it do to off-road capabilities?

And what would you do with the axles?

A good front airdam and splitter would be a good start.


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Old 02-10-2013, 03:59 PM   #3
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Re: Underside Aerodynamics

You can't do much with the axles. From the front axle to the rear axle/side to side, and the rear section. The spare tire and the side sections act more like a drag shoot.
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Old 02-10-2013, 04:20 PM   #4
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Re: Underside Aerodynamics

I was thinking something similar. It will make a difference. It certainly does on big rigs, and that's why they get full aero treatments. And the undercarriage is a big factor in overall drag.

I was thinking about doing something similar to semi-trailes; basically a barge boards between the body and roadway. I would make them semi-flexible to prevent damage, but also retractable. Instead of rigid mounts, they would be hinge-mounted with pneumatic cylinders providing the vertical support. Then I can retract them under the van on command, and with air cylinders they can be pushed up anyways by a curb, etc if I forget. I'd do something similar under the front bumper. This will also have the benefit of better cooling, since the under-side will be a low pressure area with the air-dam and barge-boards.

I don't think an undertray will work well with the vans because the the solid axles aren't flush with everything else down there.

My whole reasoning isn't necessarily better gas mileage. Its because of the new trailer. When its all done it'll be about 42' long and 13' tall and 12,000 pounds empty. That'll require more power. But instead of adding more power to the van, I could reduce power needs by improving the aerodynamics of both, and should still be able to pull 6% grades at 65+.

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