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Old Feb 16, 2014, 09:24 PM
Wonderfully Wicked
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Old Apr 06, 2014, 12:54 PM
chuck
santa barbara, CA
Joined May 2009
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don , is there a formula for figuring what the rpm increase would be if i removed half the blades from a rotor and came up w/ the correct kv to equal the wattage of the rotor w/ all the blades? in other words does the load drop in half? i doubt it as rpm vs load is not linear. u always seem to know the math .

thanks , chuck
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Old Apr 08, 2014, 06:09 PM
Wonderfully Wicked
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From what I could find on multi-blades, reducing the blades from say 12 to 6 would half the power requirement, assuming each blade is loaded equally. So if you want equal watts on the new rotor, then the rpm will have to increase until the watts are equal. Watts are based on rpm cubed, so 2^(1/3)= 1.26 times the RPM is needed, so for example the 64mm CS 12 blade fan and 2700 KV, if you drop to 6 blades you need a KV of 1.26*2700= 3402 KV to get the same watts on the 6 blade version of the rotor. It would be interesting to see if it holds true to this calculation.
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Old Apr 08, 2014, 11:02 PM
chuck
santa barbara, CA
Joined May 2009
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thanks don , sounds like u figured me out. always looking for that free lunch performance wise and wondered what the c/s would be like at 6 blades . i have always felt the lower ir in the hi kv motors was a plus for power vs weight . the specs on the 64 say 38k max and just thought it may still sound good as the 70mm does at the higher revs . just need to find a rotor only and start cutting .

btw , u might want to list the 2w25 along w/ the 2w27 as higher power option for the 10blade 70. we have been using that combo and it may be near the limit but seems to work well . fwiw.

chuck.
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Old Apr 08, 2014, 11:32 PM
Wonderfully Wicked
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The sound is suppose to be a factor of number of blades and number of stators, so it may still be relatively quieter than a a low blade count fan with only a few stators.
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