David Carter wrote:

Paul,

Unless I'm "reading too fast" and "thinking too slow", I believe you have
been writing your equations for speed squared" as "mph squared" instead of
what I am used to seeing, "ft/sec squared".  If only  doing proportional
comparisons, not actual pounds of drag, then no problem.

Sea level air density is .00238 on my std atm chart (.0023769).  That is
close to the value of .00260 you are using, which is somewhat below sea
level - or in a higher pressure area in a duct.

I first noticed this in your e-mail of 6 Mar 99 4:06pm re "What I know so
far about rad ducting", then again later that day at 10:46pm, same subject.

Multiply mph X 1.466666666666 to get ft/sec.

David Carter

The constant .00238 is slugs per cubic foot.
A slug is equal to 32.17405 pounds.

The constant I use (0.0026) gives an answer in pounds per square foot
when velocity is expressed in MPH.

100 MPH ^ 2 times .0026 is  26 pounds per square foot which I know to be
dynamic pressure at 100 MPH at sea level.  

Von Mises states on page 34 dynamic pressure is 108.9 pounds per square
foot at 300 FPS at sea level.

300 FPS is about 204.6 MPH

Using my constant and MPH:
204.6 MPH ^ 2 times 0.0026 is 108.8 pounds per square foot at sea level. 
Close enough.

Paul Lamar
 
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