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Date:         Mon, 18 Oct 2004 06:29:47 -0600
Reply-To:     jimt <wetwesty@TACTICAL-BUS.INFO>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         jimt <wetwesty@TACTICAL-BUS.INFO>
Subject:      Re: aerodynamics, was: 101 MPH Vanagon!
Comments: To: vw4x4@FYI.NET
In-Reply-To:  <4173AB76.7010500@fyi.net>
Content-type: text/plain; charset="ISO-8859-1"

The formula for drag through a medium is:

Drag = 1/2 D x Cd x A x Vsquared

D = density of medium (in this case air) Cd= drag coefficient (slipperiness) (need to know this value or get a wind tunnel) A = the frontal area V = velocity

Note where the coefficient and area are in the equation. Then comes the kicker. Note that velocity gets squared. With squaring there is always a point where the squared item goes from insignificant to very significant. In this case the velocity we are traveling at.

This number is then added to the rolling drag. Computed from weight volume and resistance items. Then you get your total drag or resistance to movement.

0.00255754 1 16 1 0.04 0.00255754 0.5 30 1 0.04

Above shows that a flat box surface presented in direct resistance comes up with the same value as the lower slippery vehicle that has about twice the area presented.

•••••••••••••••••••••••••••••••••••••••• jimt Planned insanity is best. Remember that sanity is optional. http://www.tactical-bus.info (tech info) http://www.westydriver.com

On 10/18/04 5:39 AM, "Eric Zeno" <vw4x4@FYI.NET> wrote:

> Aerodynamically everybody seems to be missing one thing. > If I have a very unslippery vehicle with a coefficient of 1 (flat surface) > and a slippery vehicle of .5 and the surface area in question on the .5 > vehicle is 3 times the area of the vehicle with a rating of 1, the .5 > vehicle is much higher in resistance than the vehicle with a rating of 1. > > > Interesting! By what critera is the surface area measured? > I've never seen spec's > on this. Eric > > > jimt wrote: > >> On 10/17/04 8:53 PM, "Stan Wilder" <wilden1-1@SBCGLOBAL.NET> wrote: >> >> >> >>> With less than 100 hp the dream of 100 in a Vanagon is just a dream unless >>> you drive off cliff and read your airspeed indicator on the way down. >>> I think Bruce just dropped the hammer on his hybrid toy to see how >>> everything behaved and reached that 101 as part of the test but that brings >>> up the speedometer error that is about 10% and that means he was only doing >>> 92 mph. Well within reasonable speeds for Texas Highways for all Pickup >>> trucks, SUVs, MPVs, 18 wheelers, and Rice Rockets of both the two and four >>> wheel varieties. >>> >>> Stan Wilder >>> High Performance Ceramic Coatings >>> www.engineceramics.com >>> >>> >> Last year after a proper breakin on my subie mod I took it out on the flats >> on i70 towards kansas. Took it up to just under 6k on the tach. At that >> speed my speedo is definitely off by very close to 15 percent. (only goes >> to 85). However 5.8 x 18 is comfortably (uncomfortably) over 100mph. Havent >> done it since and donΉt plan on it. Even at a moderate 80mph a crosswind is >> not nice in a vanagon or any slabsided vehicle. For a regular vanagon to >> hit those speeds is right at the cutoff. The subie electronic cutout is at >> about 6.2k the vanagon electronics cuts out at about 5.8k plus or minus a >> little. I am told that the last couple years of the vanagon the ecu cutout >> at 6k but no change was made to part numbers. >> >> Aerodynamically everybody seems to be missing one thing. >> If I have a very unslippery vehicle with a coefficient of 1 (flat surface) >> and a slippery vehicle of .5 and the surface area in question on the .5 >> vehicle is 3 times the area of the vehicle with a rating of 1, the .5 >> vehicle is much higher in resistance than the vehicle with a rating of 1. >> >>

•••••••••••••••••••••••••••••••••••••••• jimt Planned insanity is best. Remember that sanity is optional. http://www.tactical-bus.info (tech info) http://www.westydriver.com


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