Aerodynamic Brick Thread: 1990 Vanagon Carat

[dhehnke]

I recently became a Vanagon owner after discovering the world of Subaru engine conversions on these, and realizing that it was possible to own a reliable one!

I know this is not a great starting point for good mph or aerodynamics, but being an aeronautical engineer I could not help but try.

I came across this design for an aft wing/spoiler for square bodied vehicles, but couldn't find any specific examples of it being used. So it was time to prototype! The shape kind of resembles an inverted airfoil, and it seems likely to me that it could help draw air gently into the large low pressure zone behind a van like this, hopefully reducing drag and maybe improving wind handling.

I haven't tested it yet, it needs a coat of epoxy to weatherproof it, but I managed to get all the angles correct and it fits well by using the hatch to compress it against the body.

Thanks for any comments. I'll post some results when I get them, and I will likely continue modding it.

Dan

[dhehnke]

I forgot to mention, my other goal was to make it fairly unobtrusive, and easy to remove. As it is it only obscures maybe 25" (I meant to say 25%! Big difference, sorry) of the top of the view out the back window, which is not bad, and it swings up with the hatch.

I may add sides of some sort that start from the most aft point and taper down to nothing near the bottom of the back of that van. Maybe heavy duty sailcloth or something that can tension and still be easy to put on and remove.

I like the idea of the diffuser fins on the bottom, but that would be a later project...

[chefdave]

Looks bit like a mini kamm back. If set up right and sides filled should work very well.

[Ecky]

Originally Posted by chefdave

Looks bit like a mini kamm back. If set up right and sides filled should work very well.

The difference being that the leading each is up in the airstream, forcing high speed air down into the car's wake.

I'm far from an aeronautical engineer, but I'm generally under the impression that anything that creates turbulence is going to have an energy toll, and although you're directing air downward into a turbulent low pressure zone, you're using energy to do it. So, the extra energy your inverted airfoil is using may or may not have a positive effect.

[dhehnke]

My thinking is the the height above the back of the van will be pretty critical, sizing this gap. Right now I have it about 1.5" I think (will check later) above the back, which has it still sitting lower than the high point on the top of the van, so no additional frontal area. It's not too hard to adjust this gap though.

[dhehnke]

Ecky, I think the idea is not to create turbulence, but to energize the air in a way that reduces the wake, resulting in a much smaller "cloud" of turbulence being carried behind the car.

[westygo]

Lots of room for aero improvement on these things. Look underneath, a properly sized air dam and belly pan would do a lot.
Nice project, looks well done!

[gone-ot]

Have you considered adding some air-pressure tubes or transducers at the high and low-pressure locations to *SEE* exactly how well (or not) everything is working?

[cRiPpLe_rOoStEr]

IIRC there is only one Vanagon in my hometown, probably imported by the local consulate of Germany. Even though nowadays it might be easier to find parts for the Subaru engines, the Wasserboxer still amazes me somehow.

[freebeard]

Welcome. I noticed your name on the front page yesterday as newest cult member.

Have you lurked here much? Have you used the Search function?

Other members have talked about, and possibly implemented, this before. I'm skeptical — search for Koenig-Fachsenfeld tearing edges. Or box cavities. Or vortex generators.



This is known to work. It could be truncated to the length added by your wing. The motherload of work on the aft end is at:

http://ecomodder.com/forum/showthrea...rag-33568.html

Unfortunately it has been bit by the Photobucket bug. There is a browser extension to fix that but I don't have it. My own suggestion, since you're an aeronautical engineer (airframe or powerplant?), would be Coanda nozzles.



The reason I say this is that the rear engine configuration provides a ducted flow of heated, at least 1500cfm, air from the cooling system. I think exhaust is best just dumped, it's corrosive.