Date: Mon, 18 Oct 2004 13:52:10 -0400
Reply-To: Darren Lastfogel <dlastfogel@PLYFORMS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Darren Lastfogel <dlastfogel@PLYFORMS.COM>
Subject: Re: aerodynamics, was: 101 MPH Vanagon!
Content-Type: text/plain; charset="iso-8859-1"
Streamlining a vanagon. Wow who would have ever thought, surely not the VW
engineers. Cool stuff though.
-----Original Message-----
From: Alistair Bell [mailto:albell@UVIC.CA]
Sent: Monday, October 18, 2004 12:50 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Re: aerodynamics, was: 101 MPH Vanagon!
On 18-Oct-04, at 8:08 AM, Bruce Nadig wrote:
> O.K., I've seen all sorts of formulas and explanations for
> aerodynamics and
> drag. What I haven't seen is actual numbers for a Vanagon. Does anyone
> know
> the actual coefficient of drag for a Vanagon? Does anyone know what
> frontal
> area of a Vanagon is? Without this information, all the formulas in
> the
> world are pretty useless for us.
>
> Inquiring minds want to know.
>
> Cheers,
> Bruce
> motorbruce
> motorbruce@hotmail.com
yes, posted it a while back, her is a copy of original post:
From: albell@uvic.ca
Subject: vanagon top speed - more info
Date: September 4, 2004 11:48:56 AM PDT
To: vanagon@GERRY.VANAGON.COM
some list members have thougth that my extrapolation of Martin
Jagersand's drag measurements is in error. I did state that it was a
rough estimate, and was more of an illustration of increase power
required to move our big boxes at speeds near or over 100 mph (160
kph).
So I re-examined the approach...
first the "original" data:
Martin's data:
Converted into Imperial units:
Speed (mph) Total drag (hp)
33.67 -10.72
44.89 -26.41
56.11 -46.59
67.33 -71.25
78.55 -102.59
89.78 -138.00
101.00 -180.49
112.22 -225.29
And now the new approach:
The SA magazine "Car" tested the SA 5 cyl passenger Vanagon back in
'91. That van had an engine output of 100 kW (134 hp) and 200 Nm (147.5
lb ft).
Their tested top speed was 159 km/h (99 mph).
The "theoretical" top speed, in 5th at 6250 rpm was calculated to be
188 km/h (117 mph).
From an old Road and Track test of the 1980 Vanagon I found a Cd figure
of 0.44, and from the above article I found the frontal area of the SA
van measured as 3.59 m2 (38.6 ft2). Using a weight approximation of
1720 kg (3792 lbs) I used the calculator on this webpage:
http://www.davewin.com/tech/horsepower_calc.shtml
to arrive at these results:
speed (mph) power required (hp)
50 19.3
60 30.6
70 46.1
80 66.4
90 92.2
100 124.3
110 163.2
120 209.7
130 264.6
140 328.5
these results show a much lower power requirement than the
extrapolation of M. Jagersand's data and also his original data. It
does again show the massive increase of power required to move the van
above 100 mph. It also is in close agreement to the road test results
from SA.
I do wonder about the drag calculation, but for purpose of this
discussion I'll leave it alone.
The original claim of 112 mph then would be estimated to require 171.9
hp. To push the van to 115 mph would need 13.4 more hp.
Another's member's claim of 140 kph (87.23 mph) would require 84.5 hp.
To push it to the round imperial figure of 90 mph would require and
additional 7.7 hp.
I would opine that a stock wasserboxer Vanagon cannot exceed 100 mph on
level ground, and in still air. Safe assumption seeing as the SA 5cyl
couldn't break the 100 mph barrier.
So send those photos in showing speedometers pegged :)
But an interesting side note, if one could reduce the Cd from 0.44 to
0.40, then the power required at 100 mph drops from 124.3 to 114.1.
And if we could really streamline the box to give a Cd of 0.30 (without
increasing frontal area) then you would only need 88.6 hp to do 100
mph.
Fun eh?
Alistair
'82 westy, diesel converted to gas in '94
http://www.members.shaw.ca/albell/
