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Old Dec 08, 2009, 08:24 PM
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tom bacsanyi's Avatar
farmington hills mi.
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20 lb thrust 12 blade 125mm fan F-7U Cutlass

I've been running three scratchbuilt 90mm fans at about 3kw and now that there is attention given to the sound of high blade count fans, I decided to try a 12 blade 90mm fan. The base blade angle for both fans was 42 degrees (midi is higher at 48 degrees) and though the 12 had narrower blades, the total area was somewhat greater. This was strictly a sound thing and I hoped efficiency would not be adversely affected. The fuselage of my Fly Fly 86 is screwed nose down to a crutch which is standing on a digital scale. The 6 blade ran 2800 watts and gave 7 lb 7 oz thrust. The 12 blade ran a little over 2900 watts and gave 7 lb. 9 oz. This was not spliting hairs so I would say the efficiency was about the same as close as I could tell. That was good news. The sound seemed similar at full throttle but much quieter at part throttle and has me wondering? The video is here:

http://www.rcgroups.com/forums/showthread.php?t=1155719

Here is stuff on the 6 blade fans:

http://www.rcgroups.com/forums/showthread.php?t=993159
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Last edited by tom bacsanyi; Mar 25, 2010 at 04:39 PM. Reason: This will become a build thread on the Cutlass
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Old Dec 10, 2009, 12:06 PM
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DForbes's Avatar
Michigan
Joined Jun 2005
620 Posts
Quote:
Originally Posted by tom bacsanyi View Post
I've been running three scratchbuilt 90mm fans at about 3kw and now that there is attention given to the sound of high blade count fans, I decided to try a 12 blade 90mm fan. The base blade angle for both fans was 42 degrees (midi is higher at 48 degrees) and though the 12 had narrower blades, the total area was somewhat greater. This was strictly a sound thing and I hoped efficiency would not be adversely affected. The fuselage of my Fly Fly 86 is screwed nose down to a crutch which is standing on a digital scale. The 6 blade ran 2800 watts and gave 7 lb 7 oz thrust. The 12 blade ran a little over 2900 watts and gave 7 lb. 9 oz. This was not spliting hairs so I would say the efficiency was about the same as close as I could tell. That was good news. The sound seemed similar at full throttle but much quieter at part throttle and has me wondering? The video is here:

http://www.rcgroups.com/forums/showthread.php?t=1155719

Here is stuff on the 6 blade fans:

http://www.rcgroups.com/forums/showthread.php?t=993159

Tom, you are the man. Nice work!

When you say quieter at part throttle, do you mean the 12 blade at part throttle?

Dennis
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Old Dec 10, 2009, 05:50 PM
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tom bacsanyi's Avatar
farmington hills mi.
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Updated video

Dennis,
The 12 blade fan was much quieter at part throttle but seemed to be just as loud at full throttle.

The earlier 6 blade fans had light weight balsa fairings. The more recent tests used a Midi aluminum spinner and I suspected that the increased mass lowered the critical speed to the region of the full throttle. All tests were done with well balanced fans and critical speed vibration can not be eliminated by balancing. I consequently ran the 12 blade without the spinner and the full throttle sound was greatly reduced! Running without a spinner costs about 4% in thrust so I added balsa fairings as in the earlier 6 blade fans. I added a third run to the video with the 12 blade fan and balsa fairing. Now if it would stop snowing.....

The earlier video with the added third run is is still located here:
http://www.rcgroups.com/forums/showthread.php?t=1155719
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Old Dec 10, 2009, 06:32 PM
Dave Appleton
Liverpool, Great Britain (UK)
Joined May 2004
466 Posts
Great work Tom, whats the next step? Lets have a look at the stator assembly...or is it the same as the 6 blade version?

cheers

Dave
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Old Dec 10, 2009, 07:32 PM
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farmington hills mi.
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Quote:
Originally Posted by Fire42 View Post
Great work Tom, whats the next step? Lets have a look at the stator assembly...or is it the same as the 6 blade version?

cheers

Dave
This is a Midi housing with some reinforcements. These fans are all running 36-80-1100kv Medusa motors on 12 cells and Turnigy 100A hv esc's. My next fan will be 120mm and will use the new 200A Turnigy. I was thinking 15 blades and the success of the 12 blade makes it a go.
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Old Dec 10, 2009, 07:48 PM
EDF rules... :)
AirX's Avatar
Joined Nov 1999
13,535 Posts
Hi Tom,

Good work. I think the 12 blade with your balsa spinner works pretty good and sounds great.

Eric B.
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Old Dec 20, 2009, 05:41 PM
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tom bacsanyi's Avatar
farmington hills mi.
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Well it didn't stop snowing so...........

I have a ski set up for my flyfly F-86 (not a very bright idea) so I flew it a couple flights today off the snow. The drag on an already draggy plane was way more than just noticeable The short video was all full throttle, ~ 2800 watts, and the fan sound is way less and not as irritating. You can clearly hear the turbulent roar coming off the skis. Camera ran out of batteries and my videographer ran out of airplane but it was the sound I was after. The plane weighs 10+ lbs and is pushed around quite well. This fan has almost identical measured performance over the 6 blade so the sound factor made it all worthwhile
Video link here again with added flight video :

http://www.rcgroups.com/forums/showthread.php?t=1155719
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Old Dec 20, 2009, 10:30 PM
efflux RC's Avatar
United States, CA, Santa Clarita
Joined Aug 2009
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Very interesting thread Tom.
I hope to learn a few things here.
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Old Dec 21, 2009, 06:48 AM
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USA, TX, Grapevine
Joined Dec 2008
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Wow, this is fantastic. I have to say you are the man. Making your own EDF fan rigs is amazing. Way to go.
I find it interesting in that a 12 blade fan isn't really all that much more powerful than the 6 blade fan. But then I got to thinking that it may be some cavitation effects happening in a static thrust environment like you depicted. The 12 blade isn't getting enough air flow to keep the blades loaded up good. The extra blades are being starved by their adjacent neighbors. Maybe when flying it might help or something.
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Old Dec 24, 2009, 08:41 PM
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farmington hills mi.
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125mm 12 blade.

A while back I started a 40% scale up of my old RBC F7U Cutlass (see my avitar). It had a 90 mm midi and flew great till pilot error took it's toll. The new one was to have 2 ea. 90 mm midi's. I am modifying the plans to take one 125 mm fan. I stated previously that I was thinking 15 blades but the hub just got too busy so it is 12 blades. The fan is assembled and just needs shaping of the blades and od. reduced to fit. The 125 mm housing is laid up with a layer of Kevlar roving, two layers of bidirectional cloth, and another layer of roving. It is 2mm thick and very rigid. Each blade has anodized base to enhance the epoxy bond and a carbon fiber pin thru the base. There is a Kevlar wrap at each end of the hub. The stators and motor housing will have to wait because I want a close fit to the motor od. The Neu 15-27 with 8mm shaft is on order and may take 8 weeks. Meanwhile, I can work on the plane.
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Old Dec 25, 2009, 12:43 AM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
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ever thought about adding some twist to the blades at the base ?
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Old Dec 25, 2009, 07:45 AM
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farmington hills mi.
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Air Sally,
The pitch at the base is 50 degrees and 27 degrees at the tip.
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Old Dec 26, 2009, 06:11 PM
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Joined Dec 2009
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Very impressive stuff. My U-2 has a similar scratch built 4" fan (5 blade). I'm struggling with where/ how to find motors in the 95-110mm range. If you care to waste a few seconds, here's my thread on trying to convert old nitro fans to electric, but not having much luck.

Thanks,
Matt
http://www.rcgroups.com/forums/showthread.php?t=1160822
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Old Dec 27, 2009, 02:03 PM
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Tom

How did you form the twist? Can you provide some details on how you fabbed the blades?
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Old Dec 27, 2009, 06:23 PM
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farmington hills mi.
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Twist

Quote:
Originally Posted by efflux RC View Post
How did you form the twist? Can you provide some details on how you fabbed the blades?
The 90mm .025 thick 2024 aluminum blades were formed over a 1.5 in. dia. Delrin bar with a hose clamp. The 125mm .040 thick 6061 aluminum blades were formed over a 2 inch aluminum bar with a wood form block. Dowel pins were used to locate the blade on the magic angle to get the right twist.
The blade shape is a cylindrical surface so there is only a simple large radius bend.
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