Originally posted by ovfi
Michael you are correct, I over-exaggerated the drawing... but McGuire (post
#581) set the correct understanding for this case, whenever he countersteered
or not it has not affected the vehicle's heading in any meaningful way. The
others conclusions McGuire made in post #581 are perfect too, in my point of
I've been following this thread since its beginning, contributing when
possible but, since I read post #181 of R.W.Mackenzie (he suspected of the
underside contour of the side "pods" could cause severe lift forces), I'm
mostly reading, posting eventually, appreciating the Kafkian style of the
thread (T54 copyright), waiting for something new... but there's nothing new,
and I think it is the moment to open to the forum what I've researched and
found during this time.
Because of the point raised by Mackenzie in post #181, I contacted a friend
who is Phd on aerodynamics (difficult mission, because he's retired and
prefers to talk about fishing), and after I exposed the case to him he made
the following comments, which I have written to avoid memory failure:
1-Aero is a tricky matter and there's no substitute for wind tunnel tests.
Although we can raise points and made conclusions from our experience on the
theme, all these conclusions must be tested in a wind tunnel at least with
scale models, but using the correct Reynolds number. For example, using a
scale model of 1/4 we must multiply by 4 the wind speed to maintain the
correct Reynolds number.
2-Probably the '64 car had its aerodynamic lift forces increased relatively
to the '63 car mostly due to riding height increase than to the underside
contours of the side pods.
3-The most probable flow pattern under these side pods is that they act as
exhaust, the air flowing outwards on high speed riding.
4-When a racing car enters a low air-pressure region behind another car, its
drag and lift forces are reduced; for a cigar-shaped car the lift force has
little reduction compared to the great reduction in drag, but for the wide
flat bottom car usually the reduction in lift is as big as on drag. Possibly
this can be the reason why MacDonald was doing so good in traffic, with more
grip when behind others cars.
5-These side pods can become dangerous air "lockers" if the car makes a fast
move from a low air-pressure to a high air-pressure region, because when this
occurs the outflow from the underside of the side pods can be suddenly
blocked, inducing a strong rear lift pulse because of the shape and position
of the side pods behind front wheels. This strong rear lift pulse may have
sufficient magnitude to cause rear wheel spin at high speed. If this indeed
occurred to MacDonald, his engine over revved at the same time he lost rear
wheel grip, making him confuse on what was happening because the car had a
lot of grip until a tenth of a second before.
6-It is strongly recommended wind tunnel tests, at least with 1/4 scale
models and 600 mph wind, of the Thompson and Huffaker cars (this one to
measure the low-pressure area) to confirm that. Some Universities have the
facility and it would be a beautiful thesis for an American student...
Well guys, I'm having insomnia with this story for two weeks... now I feel
some relief...I'm ready to be crucified.
This just might be the key to the whole puzzle...if MacDonald got into the slipstream of Hansgen's car, and that rush of air coming off Hansgen's car trapped the air exiting the sidepods of the Allstate car under the pod, lifting the rear end of the car, causing wheelspin...THAT could very well be the reason the rear end of the car stepped out on MacDonald. It could have been a recurring phenomenon through the first and second lap of the race...if he was behind another car, in their wake, that might explain the over-revving that Rutherford commented on as they travelled down the backstretch shortly before the crash.
I realize that this is a hypothesis, and that it hasn't been tested in a wind tunnel, but the source lends a great deal of credence to this theory. It might not have been driver error at all...