Date: Fri, 27 Nov 1998 00:33:57 -0600
Reply-To: Blue Eyes <lvlearn@MCI2000.COM>
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Blue Eyes <lvlearn@MCI2000.COM>
Organization: Vexation Computer
Subject: Heroes needed to collect data points
Content-type: text/plain; charset=us-ascii
In view of all the thousands of hours Vanagon nuts think about powering their
vans along highways, why don't we have a chart showing the total load and road
horsepower consumed for every speed from 40 to 80 mph? Even if you know your
engine's torque curves, BSFC curves, and horsepower curves, you can't figure
out your appropriate gearing without knowing your vehicle's speed/load curve.
If we know speed and load, we can compute required horsepower for each speed.
I want to know the exact power required to move a well defined Westy or
Vanagon for each one mph increment from 40 to 80 mph. I don't know of any
reasonably easy non-speculative way to be CERTAIN of (not guestimate) these
figures without actually measuring the load for each speed.
Here is what I propose. The following wonderfully informative procedure would
be illegal to perform on the public roads. So only brave souls who would like
to be illuminated by the glowing admiration of their fellow Vanagon List
members of today and for years yet to be experienced, should consider serving
their fellow Bus nuts in this special service. (Sly fox attempts to seduce)
This would provide all the data points needed to create an accurate chart of
our vehicles' speed/load and speed/horsepower curve.
First we need a sufficiently powerful, cruise control equipped tow vehicle
with an openable rear access to the passenger area. An accurate measured
speed versus speedometer reading conversion chart must be generated for the
tow vehicle. Actual speeds from 40 to 80 mph must be accurately known. this
conversion chart would show the target indicated speedometer mph for each
actual speed. This calibration can be done by timing measured mile increments
between Interstate highway survey marker signs with a stop watch and
calculator. This calibration procedure takes MUCH more time than actual cable
towing tension tests. But calibration must not be skipped because few auto
speedometers are accurate within 3 mph over this range. Why bother of doing
the test without even knowing what speed you're actually going? Digital pulse
speedometers calibrated at 60 mph are spot on at all other speeds, so a tow
vehicle with one would be preferred. Any Lincolns with a roll down back
window? I didn't think so.
Next we need a free rolling Westy or Vanagon test vehicle with its tires
pressurized to their suggested Westy values. If a 100 pound kid can't keep
the test vehicle rolling on level pavement once it's moving, its rolling
resistance defect should be corrected before testing.
Both the tow vehicle and the test vehicle should have communication radios.
CBs or hand held radios would do.
We need an accurate, easily read tension scale attached to a fixture inside
the tow vehicle in a way that allows accurate tension readings to be read for
each speed increment. A second person in the tow vehicle could record
readings, or the driver could voice record them with a cassette recorder.
We need a tow link between the vehicles. I like strong springy water ski rope
since it's elastic enough too average variations rather then make the scale
dance unnecessarily. I need help in estimating how long the link should be to
allow drafting effects to become trivial before the test vehicle enters air
disturbed by the tow vehicle. The distance depends on the tow vehicle. A .27
coefficient of drag Passat and a Mack truck make different wind effects.
I'd really like to hear from anyone who has a line on how others have gathered
this kind of information. I don't want more Gestimates. It's time to do it
well instead of backward guessing on the basis of a string of assumptions as
long as your arm.
This isn't beyond our capabilities. Set speed to actual 40 mph, stabilize and
record tow cable tension. Increase by 1 actual mph, record observation.
Repeat 39 more times and it's done. I expect the actual test would go off
fairly quickly, probably taking no more than 30 seconds per observation, and
perhaps less. But during this 20 minute run, the testers would be violating
man made laws to sample the effects of nature's laws.
I believe Vanagon lovers would reference this wonderfully instructive data
set thousands of times over the years to come. It is the logical basis for
making lots decisions about our Vanagons and Westys. I know I'm asking a
lot. But I'm asking all the same.
Plenty of us could convert this data to "road horsepower." Then we can plot
it to a beautiful, intuitively understandable information chart that
describes what you are doing every minute you drive down the highway. A
printout of this belongs in your glove box. You like wall posters? I'll
print up a stack of them on my C sized plotter in colors, maybe 30' by 30" if
you like. It can live on VW I-net sites for all to see and print out as they
may please. Let's make this happen. It's time to correct our basic
information gap. Who will collect the data? We need team of heroes.
John
