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Default Fans : How many blades?


"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


the amount of air pushed is proportional to the surface area of the blades,
all other things being equal.


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Bob-tx wrote:
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


Single is the most efficient. The reason is additional blades disturb
the air which makes the trailing blade less efficient. The main reason
for multi blade is balance and aesthetics.
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On Jul 23, 4:56*pm, "Bob-tx" wrote:
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


3 blades is most efficient for wind turbines (electricity windmills),
same might be true for fans.

Dave
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XR650L_Dave wrote:
On Jul 23, 4:56 pm, "Bob-tx" wrote:
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


3 blades is most efficient for wind turbines (electricity windmills),
same might be true for fans.


And twenty blades is most efficient, or at least the most quiet, for nuclear
submarines. Go figure.


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Default Fans : How many blades?

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




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"George" wrote in message
...
Bob-tx wrote:
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

Single is the most efficient. The reason is additional blades disturb the
air which makes the trailing blade less efficient.


that's why we always see airplane propellors only having one blade.


The main reason for multi blade is balance and aesthetics.



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"charlie" wrote in message
...

"George" wrote in message
...
Bob-tx wrote:
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

Single is the most efficient. The reason is additional blades disturb the
air which makes the trailing blade less efficient.


that's why we always see airplane propellors only having one blade.

__________________________________________________ _______

Wrong!

See the below URL.

http://www.aerospaceweb.org/question...on/q0039.shtml







The main reason for multi blade is balance and aesthetics.





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HeyBub wrote:
XR650L_Dave wrote:
On Jul 23, 4:56 pm, "Bob-tx" wrote:
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

3 blades is most efficient for wind turbines (electricity windmills),
same might be true for fans.


And twenty blades is most efficient, or at least the most quiet, for nuclear
submarines. Go figure.


Multi blade is definitely not the most efficient. The overriding design
criteria in a sub is stealth.
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charlie wrote:
"George" wrote in message
...
Bob-tx wrote:
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

Single is the most efficient. The reason is additional blades disturb the
air which makes the trailing blade less efficient.


that's why we always see airplane propellors only having one blade.


The question was what was the most efficient. Many early propeller
implementations had single blade props with a counterweight. Sometimes
the most efficient isn't the most practical so you have design tradeoffs.



The main reason for multi blade is balance and aesthetics.



The question was what was the most efficient.
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For single-engine piston aircraft (that would be planes with top
speeds around 200-300 mph) a three-blade prop produces more force
which means a faster climb rate. But, at the expense of more
resistance and therefore a less efficient cruise.

But-- there is fast airflow against the prop. Which you don't have
with a ceiling fan. Nor is the ceiling fan producing anywhere near
the thrust of an aircraft prop.

The point being, not a good comparison between the two.

See which fans blow more air on you, then look at the electricity
consumption of each...


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On Thu, 23 Jul 2009 14:38:56 -0700 (PDT), against all advice,
something compelled Shaun Eli ,
to say:

See which fans blow more air on you, then look at the electricity
consumption of each...




Oh Jeeze.

It's a ceiling fan. It will blow plenty of air. Buy the
quietest one that looks the best to you, in your price range.

Blades. Sheesh.



--

Don't worry about people stealing an idea. If it's original, you will
have to ram it down their throats.
- Howard Aiken
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Bob-tx wrote:
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


I have 2 20" box fans. The one with 3 8" blades blows a lot more air
than the one with 5 2" blades. That's because the 3-blade fan has more
blade area.

However, the 3-blade fan is much noisier. That's because broad blades
have more turbulence at the tips than do narrow blades.

Depending on total blade area, a particular 5-blade fan may push more
air than a 3-blade. Anyway, the 5-blade fan is likely to have narrower
blades, which can make it quieter and more efficient.
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On Thu, 23 Jul 2009 16:19:52 -0500, "Freckles"
wrote Re Fans : How many blades?:

See the below URL.

http://www.aerospaceweb.org/question...on/q0039.shtml


Interesting article. Thanks.
--
I filter all messages from google groups.
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E Z Peaces wrote:
Bob-tx wrote: Depending on total blade area, a particular 5-blade fan may push more
air than a 3-blade. Anyway, the 5-blade fan is likely to have narrower
blades, which can make it quieter and more efficient.


Andy writes:

Anyway, a 5 blade fan looks better -- more elegant...

Little 3 blade ceiling fans are cheapies --- less blades is cheaper
to produce.....

Go with the five blade. You won't regret it.....

Andy in Eureka, Texas

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On Jul 23, 4:35*pm, "HeyBub" wrote:
XR650L_Dave wrote:
On Jul 23, 4:56 pm, "Bob-tx" wrote:
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


3 blades is most efficient for wind turbines (electricity windmills),
same might be true for fans.


And twenty blades is most efficient, or at least the most quiet, for nuclear
submarines. Go figure.


I was going to upgrade to the 20 blade prop, but the dealer wanted too
much for it and the after-market ones looked too flimsy.


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"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

The salesman is an idiot. The number of blades is only one of many factors
determining air flow. Diameter, pitch, blade with, and speed all come into
play. To make a statement that one number of blades is better than another
is pure lack of knowledge.

Buy the fan that looks best to you and it will move plenty of air. Be sure
to get one that is very quiet.


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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.

--
Walter
www.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



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On Jul 23, 3:56*pm, "Bob-tx" wrote:
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


He was right, especially at higher speeds. But at extremely low
speeds the 4 or 5 blade might be better because the tubulence has more
time to infill again. It all has to do with turbulence. Planes have
2 blade props, can blow you over, but need to run high speed. If you
look at the big industrial ceiling fans they install in gyms,
factories and big box stores, they are all 3 blades and have a large
diameter.
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Steve Daniels wrote in
:

On Thu, 23 Jul 2009 14:38:56 -0700 (PDT), against all advice,
something compelled Shaun Eli ,
to say:

See which fans blow more air on you, then look at the electricity
consumption of each...




Oh Jeeze.

It's a ceiling fan. It will blow plenty of air. Buy the
quietest one that looks the best to you, in your price range.

Blades. Sheesh.





Glad somebody said it straight-up!

I skipped the research, aerodynamics study and analysis on the last one I
bought. Instead I used this approach:

Walking through Borg for nails or some **** like that one day.
Stack O' boxes - 52", white, 5 blade, 3 speed, single light,
reversable, special purchase, 19.95 (-10% coupon I had).
18 bucks
Sold!
It runs
It blows a bunch of air fine
It's quiet
It don't wobble
Done deal
Move on
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On Thu, 23 Jul 2009 14:56:01 -0600, "Bob-tx"
wrote:

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???


Yes, with a three-bladed fan, the blades don't come by so often. This
gives the air time to relax and it's more compliant when the next
blade comes.

With a five-bladed fan, the air is always on the alert, it's not
surprised and it resists being pushed around. Like a militant teenager
being hassled by the police.

This is the same reason the guy told me when I was going to stay at
his apartment overnight, that I should sleep with him in his bed,
instead of on the sofa. On the sofa, i would relax and not resist
him. In his bed, next to him, I would always be on the alert and he
woudln't be able to do anything to me.

The bed was the five-bladed fan and the sofa the 3-bladed, according
to him.

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

Bob-tx




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On Thu, 23 Jul 2009 17:24:36 -0400, George
wrote:

charlie wrote:
"George" wrote in message
...
Bob-tx wrote:
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
Single is the most efficient. The reason is additional blades disturb the
air which makes the trailing blade less efficient.


that's why we always see airplane propellors only having one blade.


The question was what was the most efficient. Many early propeller
implementations had single blade props with a counterweight. Sometimes
the most efficient isn't the most practical so you have design tradeoffs.



The main reason for multi blade is balance and aesthetics.



The question was what was the most efficient.


It was which pushed more air. That might be one meaning of more
efficient, but ...
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"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


My house has 4 ceiling fans. 1 has 3 blades, 2 have 4 blades and 1 has 5
blades. They all have 3 speeds and all are reversible and very quiet.

As far as I can tell they all do the same excellent job of moving air about.
Without scientific instruments to take measurements, I don't think anyone
would be able to tell if one was more "efficient" than the others.

Freckles



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G. Morgan writes:

mm wrote:

This is the same reason the guy told me when I was going to stay at
his apartment overnight, that I should sleep with him in his bed,
instead of on the sofa. On the sofa, i would relax and not resist
him. In his bed, next to him, I would always be on the alert and he
woudln't be able to do anything to me.



WTF???


for the humor impaired - I thought it was LMAO funny...
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On Jul 23, 4:56*pm, "Bob-tx" wrote:
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


of course, the maximum air comes from a fan with no blades. the blades
only get in the way.
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On Jul 23, 5:19*pm, "Freckles" wrote:
"charlie" wrote in message

...







"George" wrote in message
...
Bob-tx wrote:
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
Single is the most efficient. The reason is additional blades disturb the
air which makes the trailing blade less efficient.


that's why we always see airplane propellors only having one blade.


__________________________________________________ _______

Wrong!

See the below URL.

http://www.aerospaceweb.org/question...on/q0039.shtml


interesting. how would that compare with keeping two blades,
increasing the surface area? the way propellors on ships do it?
as a side note, i note that submarine props, which i imagine rotate at
slow speeds to reduce cavitation/noise, are more in the multiple
narrow blade format.


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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.
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On Jul 23, 4:56*pm, "Bob-tx" wrote:
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


since nobody has mentioned it yet, odd-number of blades is less likely
to be out of balance too much compared to even number of blades. with
even number of blades, each blade has to balance the individual blade
directly across; but with odd number of blades, each blade has to
balance the average of the two blades across; less variation in the
average of two than in a single sample.
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z wrote:

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.


With an open fan, I imagine one limitation is turbulence on the sucking
side of the blade if the air can't change direction fast enough to fill
in the vacuum smoothly. If a fan had an intake duct to give the air a
couple of feet (maybe more) to accelerate toward the fan, maybe the
blades could grab more air at high speed. Increasing diameter would be
more efficient.
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On Fri, 24 Jul 2009 11:42:25 -0400, blueman wrote:

G. Morgan writes:

mm wrote:

This is the same reason the guy told me when I was going to stay at
his apartment overnight, that I should sleep with him in his bed,
instead of on the sofa. On the sofa, i would relax and not resist
him. In his bed, next to him, I would always be on the alert and he
woudln't be able to do anything to me.



WTF???


for the humor impaired - I thought it was LMAO funny...


But true. That's what he told me. I felt like I was a girl with a
guy lying to me about his intentions.

I thought we were just having dinner together at one of those very low
cost buffets in Las Vegas, until he started paying me compliments. I
felt like a girl then too.

Anyhow I slept on the sofa.
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On Thu, 23 Jul 2009 19:04:13 -0700, "Walter R."
wrote:


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.


No of course not. This is all nonsense. Keep the fan still and
rotate the house.


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So, a box fan is likely to deliver more air flow than a wire
cage fan?

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"z" wrote in message
...

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.


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Stormin Mormon wrote:
So, a box fan is likely to deliver more air flow than a wire
cage fan?


No, but hundreds of them stack more neatly.


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"Bob-tx" wrote in news:4a68c053$0$23774$bbae4d71
@news.suddenlink.net:

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



Ideal number of blades is, of course, 42.
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On Thu 23 Jul 2009 01:56:01p, Bob-tx told us...

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


Two, three, four, or five blades matters far less than the CFM (cubic feet
of air per minute) delivered at all speeds, usually three. The number of
blades is often more an issue of aeshtetic preference than performance.
Other factors such as the degrees pitch of the blades and the RPM determine
how much air is delivered.

We have seven ceiling fans in our house, ranging from a top price of around
$600 down to one that costs only $70. The high end fans have five blades
(54" blade span) and were chosen not ony for performance but also for
aesthetics and motor warranty. The least expensive fan is smaller (42"
blade span), has a smaller motor, shorter warranty, and delivers somewhat
less air, but it was ideal for the location it was selected.

Do you homework... You'll rarely get a good answer from store personnel
unless it's a fan specialty store with well-educated staff.



--
Wayne Boatwright
------------------------------------------------------------------------
Food is so primal, so essential a part of our lives, often the mere
sharing of recipes with strangers turns them into good friends.
That's why I love this community. Jasmine Heiler, about recipezaar.com



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XR650L_Dave wrote:
On Jul 23, 4:56 pm, "Bob-tx" wrote:
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


3 blades is most efficient for wind turbines (electricity windmills),
same might be true for fans.

Dave


No, the two-bladed fan is most efficient, but *only* when you
coat both blades with WD-40.


--
PB
"I suspect you're an arrogant little ****ant who grew up in the
Red Bull generation." - CJW
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