Date: Sat, 28 Jul 2007 14:37:59 -0700
Reply-To: Alistair Bell <albell@UVIC.CA>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Alistair Bell <albell@UVIC.CA>
Subject: Re: Power output of actual vans? (long)
In-Reply-To: <cad.1637ae1d.33dcfa85@aol.com>
Content-Type: text/plain; charset=US-ASCII; delsp=yes; format=flowed
Finally a worthwhile discussion :)
Frank, hats off on your undercarriage work. Definitely a do-able
solution. The rear low press problem is harder. Instead of trying to
fair that area how about an attempt to "curve the flow" in there?
While not nearly as effective it may be more practicable. I'm
thinking of wings/winglets on top and sides. We've seen some full
width top wings and the smaller deflectors (linked posted on list a
few years ago, NZ? firm making small deflectors).
A splitter also may be effective. Flat panel perpendicular to rear
hatch, length to be determined.
I have a spare small water tunnel that my revell Vanagon model would
fit in. Would be useful for flow visualisation and perhaps some
scaled drag values.
Alistair
On 28-Jul-07, at 1:01 PM, Frank Grunthaner wrote:
In a message dated 7/28/07 11:05:21 AM, syncrolist@bostig.com writes:
> Ha I liked your reply Frank. Excellent. We have multiple dyno
> charts all
> taken from the same chassis dyno for a vanaru 2.2, tiico HO, 2
> wbxers, 4
> different zetecs, 1 supercharged zetec, and coming soon e85
> naturally aspirated
> zetec, and e85 supercharged zetec.. as well as the upcoming turbo
> kit(the entire
> exhaust tract is now complete) Having all this info from the same
> dyno is
> quite nice, and really the only way to do it. As Mark points out,
> it is the
> "complete" inforamtion that is really required. BTW Frank, Clint(a
> listmemeber
> and solidworks guru) is helping us model the vanagon so we can put
> it into a
> CFD virtual wind tunnel... my intention is to build a collaspable
> colluder
> cone (see through on top) to see how much fuel efficiency we can
> gain at cruise
> with a simple strap on cone of reasonable size that is easy to
> produce and
> inexpensive. I think given the low pressure area we always drag
> around behind
> us, it may be a substantial improvement.
>
> Jim Akiba
>
>
> Jim,
Egad a reply to one of my rants! Exciting! I fully agree that results
from
the same dyno with the same operator seriously increase the quality
of the data
but more importantly the reality factor inherent in its comparative
interpretation. For some time my son and I were developing a
Solidworks based model of
the Westfalia to tighten up the drag issues. Our power numbers come
to second
difference velocity curves taken at the Pomona International Dragway
(when
unoccupied by paying nutsos). We were also looking at FemLab for a
far more
detailed treatment.
In the course of these experiments, two areas showed enough promise to
warrant some measurements. We looked at the rear drag profile and
undercarriage
sealing. For the rear drag issue, we modeled pressure zone profiles
and put
together three plastic hemi-balloons and taped then to the rear. I
have to go back
to my notes at the time but we reduced drag by 12 to 18%. In one
test, the
number was 33% but it couldn't be duplicated. (In the spirit of some
tuners, I
should have used this for an SAE paper). The upshot of this was that
I got pulled
over (we were testing at night on the Palmdale highway) by the CHP
and got
ticketed for occluded rear vision. Went to the court to fight the
ticket. Had a
full sheaf of papers. The judge listened attentively (!). He remarked
that
when younger he had had a bay window bus that just blew all over the
road and
asked if such mods would have any effect on stability. I offered that
it was in
the relm of possibility. I them looked around the courtroom to see
blank stares
for a mass of humanity that that must have thought I came from area 51.
Finally the judge stopped the discussion, announced that this was the
singularly
most unusual anti-ticket response he ever heard, congratulated me for
originality and dismissed the ticket with a warning about frightening
other drivers at
night.
The point here relates to the fundamental flaw. The rear balloon
worked, we
had an idea for speed related inflation, etc, etc, but no answer for
rear
vision. Practicality --- zip, but fun.
The second idea worked well and is a real solution. The open
underside of the
vanagon is a real drag component. We got a set of thin 0.0625 inch Al
sheet
stock and enclosed (frame rail to frame rail) and basically covered the
underside from the front to the transmission. We added louvered slots
for the
radiator air flow, left the spare tire cover operable and stayed away
from suspension
components. Big decrease in drag - minimum 8% max 15%. 15% came when
we added
the Diesel sound box cover. Serviceability was a problem. The system
has been
removed as I complete the front to back dual muffler system for the
TDi and
the diesel fired heater. No temperature measurements, but we provide
for air
inlets at front by gas tank and at egress at the rear. Work in progress.
Frank Grunthaner
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