"Bob Engelhardt" wrote in message
...
Maybe OT, but not as much as many.

I have a fairly large centrifugal blower (squirrel cage) & I'd like to
know its CFM. It has a well defined opening, so knowing the velocity of
the air is what I need.

I can think of a couple of approaches. The first that comes to mind is
placing a surface in the air stream & measuring the force exerted on it. I
know that there is a relationship between the air velocity, the surface
area and the force (drag), and I could find a formula on the web, but I
worry that a little bit of knowledge could be a dangerous thing. I.e., I
suspect that this is a complicated subject and an understanding should
accompany formula use. But if someone here has the understanding & could
give me the right formula, that would be great G.

Another approach is to measure the pressure in the stream & derive
velocity from that. I think that this would be subject to even more
complications than using force, but maybe not. Anyone know? If it's a
reasonable approach, what about a formula?

Or, I could get/make a _really big_ poly bag & time how long it takes to
inflate. Much too crude for my taste.

Advice anyone?

Thanks,
Bob

Talk to a local sailor. Borrow his wind guage. They fairly cheap for the
plastic ball ones.