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Why the number of fan blade are mostly odd numbers?

A

ayabrea

Member
I never bother to count the number of blade a CPU or casing fan has.... but recently the post abt broken fan blade made me curious....

My cpu fan has odd number, my psu fan has old number of blade too even the fan blowing me has odd blade too...

There are even numbers one but less and not that preferred...

Any explanation for this?

🙂
 


<<

<<

<< It is part of my evil plan. >>



bleh >>

Don't bleh at me foolish mortal. >>




I now have my new quote of the week. Thanks, Yakko. For some reason, I just blurted out a "Bwuahahahah!" When I read this. You are feeling "Kingly" today, huh?
 


<< Because fans with even numbers of blades encourage the use of articles and plural nouns. >>



Best reponse evar.
 


<< MichaelD,

No uppercase. >>




Ah, I can see your Kingly Attitude extends even unto those who attempt to worship your royalness. OK, yakko, I'll fix it. 🙂
 


<< I never bother to count the number of blade a CPU or casing fan has.... but recently the post abt broken fan blade made me curious....

My cpu fan has odd number, my psu fan has old number of blade too even the fan blowing me has odd blade too...

There are even numbers one but less and not that preferred...

Any explanation for this?

🙂 >>




Fans, propellers, turbines well, just about everything has a odd number of blades. The most important reason is the stability of the turbine. A rotor with an odd number of rotor blades (and at least three blades) can be considered to be similar to a disc when calculating the dynamic properties of the machine.

 

The number of blades depends on the required flowrate, pressure differential, power limit, and safety (so that it would not chop your finger if you are dumb enough to ...). In short, it's e = mc^2. There you go😀.
 


<<
Fans, propellers, turbines well, just about everything has a odd number of blades. The most important reason is the stability of the turbine. A rotor with an odd number of rotor blades (and at least three blades) can be considered to be similar to a disc when calculating the dynamic properties of the machine. >>



THANK YOU Carbonyl!!!

i knew there had to be at least one intelligent engineer type person in this forum! 😀
 


<< Fans, propellers, turbines well, just about everything has a odd number of blades. The most important reason is the stability of the turbine. A rotor with an odd number of rotor blades (and at least three blades) can be considered to be similar to a disc when calculating the dynamic properties of the machine. >>



Can you explain how a 5 bladed propeller would be superior to a 6 bladed propeller then?

Also, if they're so unstable, why does almsot every small airplane have a 2 bladed prop on it, and almost every old WWII warbird have a 4 bladed prop on it?

Please explainyour science.
 


<< Can you explain how a 5 bladed propeller would be superior to a 6 bladed propeller then? >>


You need something to hold up the arm/propeller at the axis, and if a turbine had an even number of blades, at the moment the X blade is getting bent backwards from the force of the wind, the opposite would be in the windshade of the arm or support and have the minimum force and become unbalanced.




<< Also, if they're so unstable, why does almsot every small airplane have a 2 bladed prop on it, and almost every old WWII warbird have a 4 bladed prop on it? >>



2 is much cheaper and not a huge deal becasue the aeroplane is relativly symetric at the prop but require higher rotational speed to yield the same energy output. As you noted though 4 is not used much anymore.

I'm not a pro just recalling from physics classes about 7 years ago...There is also somthing to do with harmonics between odd and evens.
 
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