Date: Mon, 29 Apr 1996 14:26:00 -0400 (EDT)
Sender: Vanagon Mailing List <vanagon@vanagon.com>
From: Porter_Fred%PAX9@mr.nawcad.navy.mil
Subject: Re: aerodynamics (Seriously...)
This post will provide lotsa opportunity for well deserved ribbing.......
While driving around the salty/muddy roads this winter, I noticed that the
air tended to separate from the surface of the van near the area of the aft
body panel seam, or the seam just infront of the cooling air intakes at the
back of my vanagon. This was indicated by the wet body panels infront of
the seam and behind the seam the surface of the van was dry. Why is this
important? If my observations and hypothesis are correct, then the cross
sectional area contributing to separated pressure drag is the cross
sectional area outlined by the transition between wet to dry body panels.
If the separation point could be moved rearward on the van, the cross
sectional area for pressure drag would be reduced. By putting vortex
generators near the transition line (experimentation would be required) the
spearation point could be moved rearward, the cross sectional area reduced
and drag decreased.
If you are unfamliar with vortex generators, look at the wing of an airplane
next time you travel somewhere without driving your van. The little metal
tabs sticking up on the wing at (usually) regularly spaced intervals at an
angle to the airflow on the outboard leading edge or upstream of the flaps
or ailerons are vortex generators.
This is similar to why golf balls are dimpled. If hit the same, a smooth
golf ball will not travel as far as a dimpled golf ball. If this worked,
the drag would be reduced (somewhat) and mpg increased.
Experimentally, the placement of the vortex generators (vg's) could be
optimized for a driving speed by getting a bunch of the adhesive backed
magnets and gluing the metal tabs to them. Before placing the vg's on the
van surface, tape a grid of yarn tufts on the van surface and drive at your
normal cruising speed with somebody in a vehicle beside you video taping the
behavior of the tufts in the airflow. This will provide baseline data to
judge the effect of the vg's when placed at different locations on the van.
Then place the tabs in a line parallel to separation line. Do the
driving/video taping thing again. By using the magnetic tabs, the location
of the tabs will be easily changed without using paint damaging adhesives.
Start the tests with the line of vg's in front of the separation line and
repeat the test several times. Each time, incrementally move the line of
vg's rearward. Additional experiments could/should be done with size, angle
and spacing of the vg's (i'm not an aerodynamacist, so I can't provide
guidance here, infact my whole theory may be flawed, but thot experiments
are fun).
have fun poking fun,
porter_fred%pax9@mr.nawcad.navy.mil
relax and spin
87 syncro
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