Date: Wed, 24 Mar 2004 14:29:55 -0600
Reply-To: Stan Wilder <wilden1-1@SBCGLOBAL.NET>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Stan Wilder <wilden1-1@SBCGLOBAL.NET>
Subject: Re: Vanagon Drag Coefficient?
In-Reply-To: <410-2200433242065215@earthlink.net>
Content-Type: text/plain; charset="US-ASCII"
Airflow calculations become ridiculous.
I just have to quote from Porsche maximum speed testing.
911 Porsche with the wedge bumpers (Prior to 1970 that had the big shock
absorber bumpers) had less drag and ran six miles an hour faster at top
speed.
Again on the 911, top speed increased by one mph for each outside mirror
that was removed.
We're talking about 144 mph reduced down by these slight drag effects.
Lay your torpedo silhouette alongside the silhouette of a 911 Porsche to see
the 30% reduction.
Other than wind drag, the 912e 1976 Porsche with 89 HP would run 115 mph and
it cost $11,000.00 new. The 911 of the same year with 190 HP would run 144
mph, but cost $27,000.00 ....... that is the price of an extra 29 mph top
end that nobody has ever been able to find a use for other than professional
race teams.
If you go back and relate the year of manufacture of your VW Bus, Van,
Vanagon you'll see they were all designed to run in 55 to 65 mph speed
limits.
Stan Wilder
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com]On Behalf
Of Randy Bergum
Sent: Wednesday, March 24, 2004 2:07 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: Vanagon Drag Coefficient?
If you could round off the front a little more, that would save a bit. VW
found that rounding the nose of the original bus, 30% drag reduction was
realized! (This from a professor at engineering school)
Bruce Carmichael has done research on torpedo design for the navy, and
found that by using a laminar flow shaped body, they could use a much
larger frontal area and volume than the standard cigar shape for the same
drag. This shape was roughly like an egg up to around 40% or so from the
front, then necked in to cause favorable pressure gradients and keep things
flowing as best they could. I can't remember the numbers, but the drag was
reduced to something around 20% of original. I recall that they made a
body of revolution from a good laminar airfoil curve raised to the 3/2
power to account for the 3rd dimension.
Unfortunately the navy nixed the idea, because it didn't fit into their
idea of how a torpedo should fit and work inside the launching tubes.
Look at new cars and see how windshield seams and bumps are being reduced
way down, and airflow is smoothed more. For an extreme example, see the
one liter car that VW made recently.
But what the heck do I know?
Randy Bergum
> [Original Message]
> From: Frank Grunthaner <FrankGRUN@AOL.COM>
> To: <vanagon@GERRY.VANAGON.COM>
> Date: 3/23/2004 4:58:17 PM
> Subject: Re: Re: Vanagon Drag Coefficient?
>
> In a message dated 3/23/04 4:18:24 PM, wilden1-1@SBCGLOBAL.NET writes:
>
>
> > Before the golf ball dimple technology works you need a full belly pan
and
> > enough horsepower to make the project worthwhile.
> > For a good working example just lay down and look under a Porsche of any
> > year.
> >
> > Stan Wilder
> >
>
> Stan,
>
> This is a good point and I have considered 0.0625 inch thick Al sheet for
> such a purpose, but never quite had the time to do it.
>
> More effective, though, would be a pressure deformable inflatable
truncated
> hemispherical surface mounted to the rear of the Vanagon. By controlling
the
> inflation pressure, at a constant velocity, while optimizing manifold
vacuum,
> one should be able to reduce drag by 20% or more. If you then fixed the
shape
> and made a mold, one could market a baggage extension which also reduce
drag.
> Does require moving outside the original vehicle envelope!
>
> Frank Grunthaner
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