Custom Astro van aero high top

[Stacygifford]

Hey guys, it has been a LONG time since my last post.

I am currently building a 4x4 Astro camper van, but my inner ecomodder keeps showing through. the van now has a 6.0 LS with a 6l90 for double overdrive as well as a partial camper conversion.

I have been wanting to buy a high top (from a junk yard) but I'm not sure i can stomach the fuel economy hit with how awful most high tops are. I really want to keep the thing getting over 20mph hwy. (goal of 25mpg @60mph)

So, the logical idea is to build a high top in the Foamy style following the aerodynamic template.

Which of theses 3 do you think will work best? all 3 have been set to the exact same height (13" higher than the factory roofline) Assuming frontal area is the same between all 3.

[Stacygifford]

small photo of the van for those interested

[freebeard]

Which of theses 3 do you think will work best?

None of them. They are a misapplication of the template as a tool. You'd have to drop the ground plane to your ground. It presumes a half-circular crosss section.

But you are probably looking only at the loft line. The critical part is the rise above the windshield. Are you looking for maximum interior height or volume? If you look at the low pressure area just abaft the windshield header (easier said than done, right?) just filling that void then rising to the height requirement would be optimal. Here an example for comparison.



Fineness ratio is your friend. This suggest a cab-over. Colani was a genius.


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I've seen a box van that had a cab fairing shaped like this over a conventional windshield and doors. Then you can go straight back rather than rising.

Plus.... free sun visor!

[Stacygifford]

I am aware that it is not the intended use of the template. Going off the intention of the template would suggest the use of the longest as it is the closest to the intended use of the template.

I need an increase of interior height of approximately 12-15" with as little impact to fuel economy as possible.

Originally Posted by freebeard

Fineness ratio is your friend. This suggest a cab-over. Colani was a genius.

Being that the height and length are being held constant, I'm not certain how the fitness ratio is coming into play (it is staying the same)

[freebeard]

Being that the height and length are being held constant

There is that whole box ahead of the A-pillar. The depth of the windshield is appromimately equal to the diameter of the tire, so ~24" of opportunity there. A prism for sightlines to traffic lights and overheads.

I think the VW woody is a good example for the six simple curves it's fabricated from.

[Stacygifford]

interior volume isn't the concern here, there is zero reason for me to extend the roof in front of the A pillar.

maybe I am completely misunderstanding what you are trying to communicate.

[Hersbird]

I would keep it simple. If you need 12 inches, go up 12 inches. Then just taper it back at a flat 20 degree slope. Make a center keel with those basics and add ribs arched to the front and sides like an upside down flat backed boat.

[freebeard]

maybe I am completely misunderstanding what you are trying to communicate.

I get that a lot.

Zero interest is not zero reason.

[Stacygifford]

Originally Posted by freebeard

Zero interest is not zero reason.

From a fabrication and practicality standpoint, there seems to be no aerodynamic advantage. Given that below the high top the rest of the van will not be changed. if the windshield to a pillar radius was less harsh, there could be some benefit to steering more air around, as apposed to over (such is the purpose of the overhang) all of this is beyond the scope of the project, it is also ugly as sin.


The basic design of the VW above is more of what I am going for. I can build any roof profile that I want in cad and C&C cut the foam supports to match. I'm just wanting to know which profile will be best for drag reduction within the constraints that I have defined.

[freebeard]

Fair enough.

Do you think the simple curves on the VW example would perform similar to the Cybertruck, as I do? Here's a picture I produced for another thread. ecomodder.com/forum/showthread.php/new-seeking-aero-advice-my-brick



Pilasters on the front corners copied from Hersbirds's Hi-Lo camper, mirror moved away from the A-pillars, Turnpike Cruiser skirts, and a Coanda nozzle external duct to reduce the wake to an aerospike.