On Jul 23, 10:04*pm, "Walter R." wrote:
I once bought a 24" box fan at he HD. It had about 5 narrow blades and it
looked like it would throw a lot of air.

I returned it after 20 minutes. It just made a lot of noise and did nothing
but churn air. Too much turbulence and not enough air movement.

After many years of experimentation I have settled for 3 blades, low speed,
high angle of attack, like shoveling snow with a biiig shovel.

Ceiling fans are also low speed because you want to keep the noise and
vibration down. They, too, benefit from the same principle: Wide blades (3
or 5), low speed, high angle of attack (slope).

Air plane propellers are faced with different dynamics: Small planes
universally have a two bladed propeller. Makes a lot of noise and shoves a
lot of air because there is no churning. But, you don't want your ceiling
fan to rotate at 4000 rpm.

--
Walterwww.rationality.net
-"Bob-tx" wrote in message

...



I was shopping for a ceiling fan at a light store (not a big box no nothing
store), and was told by the salesman that a three bladed fan pushed more
air than a four or five bladed fan. *Didn't make sense to me so I asked why
that was and was told he didn't know why, but that is the way it is. *I
asked if a two bladed fan pushed even more air, but he didn't know and of
course didn't have any. *I bit my tongue and didn't ask about a one bladed
fan.

I didn't buy anything yet.

Is it true that a three bladed fan pushed more air than a four or five
bladed fan, and if so, WHY???

I sure would appreciate any info you guys in the know can offer.

Bob-tx- Hide quoted text -

- Show quoted text -

we did a project on window type fans undergrad. turned out that
diameter was the big determinant of flow, higher speed on the same fan
didn't increase the flow much; but it did increase the turbulence,
which might be just as useful if you're not sitting in the direct
blast of the fan. of course, that increased noise also, which makes it
sound like there's more flow.
also, of course, ducting/shrouding the fan gave big increase in flow
vs turbulence, but everybody probably knows that already.