Aerodynamics

[Joe Yakubik <75363.2524@CompuServe.COM>]

As a trained electrical engineer with more than a few aerodynamics courses under
my belt, who also flies high performance airplanes for a living; I know enough
about aerodynamics to know that I don't know squat. 

I do know, however, that it is not as simple as Eric F. makes it when he quotes
someone else and says:

"The Cd is measured in force/area.  It is not the drag, but the drag
coefficient.  To do a true comparison between vehicles you'd have to multiply
the Cd x the frontal area."

Followed by his original statement:

"The 5KCSTQ has a larger frontal area than the base 5K so it will have more drag
(Measured in pounds) than the 5K."

Both of these statements are wrong.

Cd is not measured in force/area.  It is a coefficient, it has no units.  This
was pointed out by someone else earlier.

Simply because the 5KCSTQ, or any other object for that matter, is bigger, does
not automatically give it a higher Cd, or mean it has more drag (two related,
but separate topics).

If you were to start taking parts off the front end of your car to reduce your
car's frontal area, I'd think you'd find that you have actually increased your
car's Cd.  Turbulence, eddys. pressure build up, etc.

It's not even as easy as saying the smoother (more laminar) the airflow, the
better. 

Here's a fun example:  Two golf balls, each exactly the same size, one dimpled,
one not.  The dimpled one flies further due to the way the dimples cause
turbulence on the ball.  By being physically "dirtier" it is aerodynamically
"cleaner".

Due to the complex shapes of cars, this analogy does not translate directly --
don't leave your car out in the hail storms.

I stand by the Scharff's previous position:  Cd's:  a nice number, but by itself
it doesn't mean much.

Joe Yakubik