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