The air that goes through the grille and through the radiator has to go
somewhere. Mostly, it goes out under the car. When this is combined with
the airflow going under the bumper, the result is high pressure under
the front of the car, resulting in that floating feeling. An air dam
diverts some of the air that would normally go under the car around to
the side, which lowers the pressure.
Some of the studies done in the '60s on American cars showed that there
was a negative pressure area near the front of the hood, which turned
positive about halfway back and peaked at the base of the windshield.
That's why Chevy built the cowl-induction system for the Camaros and
Chevelles.
So the roadster hood sees pressure from underneath and on top,which
makes it balance out pretty nicely even when the hood latch fails -
until a truck goes by and disrupts the flow. I'd guess the "bow wave"
from the truck deflects the over-hood airflow, and the pressure under
the hood causes it to lift.
--
Gordon Glasgow
http://www.gordon-glasgow.org
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