Date:         Sun, 29 Jul 2007 23:02:40 -0700
Reply-To:     Alistair Bell <albell@UVIC.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Alistair Bell <albell@UVIC.CA>
Subject:      Re: Some aerodynamic ideas..
Comments: To: Don Hanson <dhanson@GORGE.NET>
In-Reply-To:  <000401c7d257$6063f620$30b2d8d1@dhanson>
Content-Type: multipart/mixed;

lets not get too technical Don:)

  un-attached flow can be less drag in certain situations. initiating
separation of laminar flow has been used to reduce drag. but that's
on pretty smooth bodies. the lumpy van is not in the same league.

boundary layers are pretty darn thin, I think with the van(and its
speed)  we're talking more gross aero effects. See attached image for
some simple flows around various vanagons.

Alistair



On 29-Jul-07, at 8:11 PM, Don Hanson wrote:

Well the rear certainly does drag along a lot of turbulent air.  But the
front end starts all the turbulence, and once it becomes un-attached
from
the object, it hardly ever goes back into a smooth, linear flow,
which has
the least drag..  So the air probably is pretty disturbed all along the
sides and roof.
Under, you have the boundary layer to consider, probably beyond our
discussion here, though a belly  pan would do wonders, and it
wouldn't make
the Vanagon into a Frankenstein with visible add-on body work.
   For the rear, perhaps you could fabricate some kinda "Space Case"
type
luggage compartment that might fill the vacuum behind the rear...Or a
slick
receiver hitch cargo/aero compartment AND another mounted right
behind the
rear glass..The  least that would give you would be some "free" (no
negative
aero consequences) carrying capacity for bulky items..
   You might get some small improvements with flaps and spoilers..but
that
would take real science to see if indeed it actually worked...The
wing on
the 928 rear hatch was just such a beastie...not a wing for
downforce, but a
spoiler to help release the air and reduce drag..The 928 also came
with full
belly pans...but like everything on that particular car, they were
over-engineered and total pain...it took an hour to change the oil
because
of those belly pans..
   Don Hanson

----- Original Message -----
From: "Alistair Bell" <albell@uvic.ca>
To: "Don Hanson" <dhanson@GORGE.NET>
Cc: <vanagon@GERRY.VANAGON.COM>
Sent: Saturday, July 28, 2007 11:00 PM
Subject: Re: Some aerodynamic ideas..


> Don,
>
> good points but what about the rear end? In my opinion its the
> draggiest part of the beast.
>
> Alistair