Ideas for blowers--new fan design, and blower for 15-30Ah backpack battery

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I had an EGO blower mysteriously quit on me four days ago and I took it apart. I think I have a fan design that would be more efficient. When you look at the design of the jet fan in EGO blowers, you'll notice that the angle of the blades as they extend out decreases and is steepest at the bases of the blades. Also, the breadth ("broadness") of the blades decreases as you go farther away from the bases of the blades, the blades taper out in a way.  If you multiply the broadness by some coefficient, maybe 1.5 or 2, will that make the fan blade move more air while spinning slightly more slowly? I know that I want to test this by designing it and using the Dremel idea maker and then creating a clay mold for the finished piece so I can cast it in ABS plastic (if possible), if not, aluminum... something light but durable.

I also would like to see if you go for a 15 to 30Ah backpack battery a blower that uses more input power and perhaps a fan that has blades that are broader but angled and curved the same way and that taper by the same factor.  This blower would blow 1000+ CFM at some speed... maybe 125mph... It would use a much higher input power.  Something for the professional, something that could replace a backpack blower.
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TheAtomTwister

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Posted 4 years ago

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Blue Angel, Champion

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The blades of the impeller have a variable pitch because the velocity of the blade varies from base to tip relative to the air moving past it, i.e. the speed is higher as the radius increases.

As far as casting the impeller goes, make sure whatever you do it ends up extremely robust as it will be spinning extremely fast! 20,000 RPM is no joke!

Agreed, a large multiple battery pack backpack would be a fantastic idea for somebody using the blower in a larger or commercial application. This idea has been kicked around here before and get a lot of support.
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TheAtomTwister

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That is correct. My Toro Ultra Blower Vac has a metal impeller that goes 13000RPM or something like that. I calculated that using sound frequency. 

Yes, the idea is to keep the blade pitch based on distance exactly the same while simply making the blades more broad and making them taper by exactly the same factor. The tip appears to be only very slightly narrower than the base if it is at all. If I use broader blades, I would expect the fan to be slowed a bit. I do wonder if it will move more air, however. There is also a slightly simpler fan design that I could use. Its blades are pitched at 45 degrees from the base to the tip. This fan might need to be made of aluminum or something. I'd have to calculate the forces on it. I can test it on a system that would make it go 30,000 RPM, really pushing it. I can then try different blade breadths for the 45 degree blades and get a look at their efficiency as I manipulate fan speed, fan torque, among other things.  The broader the blades are, the more torque the fan will need to spin at the same speed. With several 45 degree based designs, I would imagine that pressure changes would allow the fan to blow at very high velocity due to changes in momentum and pressure of air.

At 24000 RPM, which translates to 400 revolutions per second, the tips of the blades of this 45mm radius fan should be going at 400 times 2 pi times .045 meters.That would be about 2500 times 0.05, or about 125 meters per second. They are accelerating fast enough to shift direction of velocity by 800 pi radians per second, which will yield a very high centripetal acceleration, and when mass is accounted for, it would be duly noted that the fan will need to be pretty sturdy to stay in one piece. There is also of course to note the force of air on the fan blades. I sort of want to just make some fans and test them out on this system that I'm going to build.
 
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So I just bought the Kobalt 80V blower, and its motor actually maxes at 24000RPM, hence the 400Hz sound it emits.  Its fan is smaller in diameter, yet it does move more air at 22000RPM than does the EGO, according to a test in which I mounted an EGO tube onto the front of the Kobalt and blew a ball into the air much like Kite Army did, except I was in the house. I did the same with the EGO and confirmed higher CFM of the Kobalt with EGO's tube.  It therefore moves over 480CFM when its motor is going 22000RPM, and of course even more when its motor goes the full 24000, and its front without any tube is smaller in diameter than the front of the EGO blower tube, so that air is moving at a bit more than 92mph. It uses broader fan blades, exactly as I suggested that EGO use, but not as broad as I'd like to see.

I say, for the next generation EGO fan if there will be one, let it have 2x blade breadth, 2x number of blades, 1/2x blade thickness, change material to aluminum for sufficient structural integrity at high rotational speed.  This should move more CFM while being more quiet. The rotational speed of the motor with the new fan will not need to be as great to get the same amount of CFM as it does at its current speed with its current fan. Still, I get concerned about a 6600Hz sound that would come from it were it spinning at 300 revolutions per second with the new fan (18000RPM).  This fan would need to be well balanced, of course. I find that the price might go up with an aluminum fan like this, but I know that this would much more like an actual jet turbine fan with its overlapping blades, and it would do much better when air needs to be pressurized.
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I like your comments Atom.  Sometimes above my knowledge, but that is what makes it rather fascinating.  Thank you.