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Date:         Mon, 18 Oct 2004 09:44:44 -0700
Reply-To:     Alistair Bell <albell@UVIC.CA>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         Alistair Bell <albell@UVIC.CA>
Subject:      Re: aerodynamics, was: 101 MPH Vanagon!
Comments: To: jimt <wetwesty@TACTICAL-BUS.INFO>
In-Reply-To:  <BD99135B.4307%wetwesty@tactical-bus.info>
Content-Type: text/plain; charset=MACINTOSH; format=flowed

sheesh!

I posted info about this a couple of months ago, wasn't anyone listening?

:)

Alistair

'82 westy, diesel converted to gas in '94

http://www.members.shaw.ca/albell/

On 18-Oct-04, at 5:29 AM, jimt wrote:

> 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. > > ðððððððððððððððððððððððððððððððððððððððð > 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 donÕt 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. >>> >>> > > ðððððððððððððððððððððððððððððððððððððððð > 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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