couple of things,

Chris- yup, the underside is a mess. height ride shouldn't make that
much diff. Lowered race cars with damns and skirt etc aside. Thinking
about it, maybe higher vans would suffer less drag underneath,
(perhaps less ground effect drag).

Dave - hard to explain all in short form. But what you are looking
for in an aerodynamically slicker shape are gentle transitions in air
pressure. In the vanagon, if one could colour the air around the van
as it moves, red for high pressure, blue for low, then you'd see red
at front, blue at rear, and the various hues between. having the pop
top the way the bunny van had it would be, IMHO, in a region of lower
air pressure than the front of the van . maybe think of it as
"filling in a space". I'd even make a beer bet it contributes less
drag than the standard pop top

the biggest drag in the van is the low pressure at the rear. I'd
guess it dwarfs any other factor.

Its all best guesses, but as others have said, common sense seems to
fail in fluid dynamics.

alistair

On 20-Jan-10, at 10:08 AM, Chris S wrote:

People tend to pay attention to what they see and ignore what they
don't. If the top of our Vanagons looked like the underside we'd do
something about it. There's quite a bit of airflow and consequently
drag generated there, especially in the taller vans, and that presents
a big opportunity for improvement.

2010/1/20, Alistair Bell <albell@shaw.ca>:
> Not so fast there DM, we've hashed  this before :)
>
> Leaving aside the big low pressure area behind the van, its seems
> from the limited info out there, that the luggage rack on a standard
> westy is a bit of a drag.
>
> See the pics here:
> http://shufti.wordpress.com/2009/11/10/vanagon-bustle/e349/
>
> alistair
>
>
>
> On 20-Jan-10, at 7:22 AM, Dave Mcneely wrote:
>
> Though our vehicles are far from aerodynamic, I would think this would
> be much less so.  David
>
>
> On Wed, Jan 20, 2010 at 9:18 AM, Alistair Bell wrote:
>
>> yes, makes you wonder about possibility of water/wind ingress when
>> driving.
>>
>> alistair
>>
>>
>>
>> On 20-Jan-10, at 6:13 AM, Dave Mcneely wrote:
>>
>> Has  a poptop, but no luggage rack.  I've never seen one like that.
>> That's a lot more interesting than the playboy bunnies on the side.
>>
>> David
>

--
Chris S.
Disclaimer: "Death and serious injury may occur"