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Re: air drag



At 10:05 AM 2/6/01 -0500, Bob Muir wrote:
Has anyone determined drag coefficient interms of cross sectional
area for coffee filters

I'm not 1000% sure what shape of coffee filters you are using, but people
certainly know the coefficient of drag for various standard shapes. I like
table 7.3 on page 89 of Wegener, _What Makes Airplanes Fly_.
http://www.amazon.com/exec/obidos/ASIN/0387947841

Among other things it lists:
sphere or ball: 0.47
open half-sphere, streamlined orientation: 0.38
solid half-ball, streamlined orientation: 0.42
open half-sphere, parachute orientation: 1.42
shallower bowl, parachute orientation: 1.38
flat plate 1.17

, i.e., c1 and/or c2 in the expressions:
Fdrag = -c1*v and Fdrag = -c2*v*v?

Fowles says that for spheres c1 = 1.55e-1 times diameter and
c2 = 0.22 diameter squared.

What kind of expressions are those? They don't pass the dimensional
analysis test.

I expect these to be incorrect for something shaped like a coffee
filter.

Certainly a cup or bowl shape is different from a sphere. And certainly it
matters what orientation you choose.