1. Home
  2. Home Repair
  3. Fans : How many blades?

Fans : How many blades?

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

Reply to
charlie
Loading thread data ...

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.

Reply to
George

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

Dave

Reply to
XR650L_Dave

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

Reply to
HeyBub

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

Reply to
Bob-tx

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

Reply to
charlie

_________________________________________________________

Wrong!

See the below URL.

formatting link

Reply to
Freckles

Multi blade is definitely not the most efficient. The overriding design criteria in a sub is stealth.

Reply to
George

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 question was what was the most efficient.

Reply to
George

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.

Reply to
E Z Peaces

On Thu, 23 Jul 2009 16:19:52 -0500, "Freckles" wrote Re Re: Fans : How many blades?:

Interesting article. Thanks.

Reply to
Caesar Romano

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

Reply to
Andy

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.

Reply to
PatM

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.

Reply to
Ed Pawlowski

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.

Reply to
Walter R.

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.
Reply to
windcrest
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.

************************************************************************************ So much wrong information you have.

Many planes do have two blade props, except the ones that have three or four blades. Like the four blade Piper Meridian or the three blade Mirage. Want to check out some of the WWII fighter craft?

formatting link
Now, for industrial fans, just take a look at the offerings McMaster Carr has and you see many different number of blades.

formatting link

Reply to
Ed Pawlowski

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.

Reply to
mm

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

Reply to
mm

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

Reply to
Freckles

HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.