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Old Jun 04, 2010, 12:52 PM
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techspy's Avatar
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Whats with the new alloy fan units?

First, I am not passing judgment, just trying to get some data.

Whats the advantage of the alloy fan units that seem to be coming out lately? The only thing I can think of is that it acts as a heatsink. I have an RC Lander alloy 90mm in my FlyFly Mirage and it flies ok. This is my 3rd Mirage and the first 2 used an HET 600-32 and a Midifan pro. Personally I liked the Midi setup better, and ended up putting it in a Sapac JAS-39 and it is as fast or faster than the Mirage, is supposed to be "draggier" and is heavier.

So, other than the heaksink aspect, what is the advantage of an alloy unit and is the advantage enough to overcome the extra weight?
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Old Jun 04, 2010, 01:00 PM
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Alloy is heavy. Can't beat carbon sandwich material then CRP.
Talking about the fan shroud here, not the core.
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Old Jun 04, 2010, 01:03 PM
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Yeah I should have specified that I am strictly talking about the shroud here and not trying to get into rotor/motor performance etc.
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Old Jun 04, 2010, 02:53 PM
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I'm about to test fly my Tam F-16 with midi and 10S. Medusa 3660-1300kv w/heatsink. Carl Rich setup and pretty cheap. Test running tonight.
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Old Jun 04, 2010, 03:42 PM
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Erik v. Schaik's Avatar
Uden Volkel, Netherlands
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To me the only advantage seems in LV/HA setups where the plastic fans melt the motor flange due to exessive heat which eventually may cause a crash of the rotor to the shroud with a big bang. The better dissipation of heat seems to be an excuse to stick with cheaper LV/HA systems. When going to Hv systems I think an Alu shroud isn't mandatory. A big disatvantage of alu housings are the straight stators used where the other fans seem to be more efficient and may be more acoustic friendly.
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Old Jun 04, 2010, 03:52 PM
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I can definitely relate to the heat issues as my first 90mm build with the midifan pro on 6s with a 600-32 eventually melted my plastic shroud mounting points, however since then I added a heat sink to the motor, and made carbon fiber "washers" and placed them between the motor and shroud and have not had an issue since. So, it seems the heat issue can be addressed cheaper and more efficiently than an alloy shroud. Now maybe my scenario isn't applicable being on the "smaller" side IE: 80 amps, 1500 watts. and my experience won't translate to a "high end" setup that these alloy shrouds are designed for.

I am curious to hear what the manufacturers/suppliers of these alloy units say justifies the extra cost and weight.
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Old Jun 04, 2010, 04:29 PM
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6s for 90mm is definately a LV/HA setup
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Old Jun 04, 2010, 05:41 PM
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Quote:
Originally Posted by Erik v. Schaik View Post
To me the only advantage seems in LV/HA setups where the plastic fans melt the motor flange due to exessive heat which eventually may cause a crash of the rotor to the shroud with a big bang. The better dissipation of heat seems to be an excuse to stick with cheaper LV/HA systems. When going to Hv systems I think an Alu shroud isn't mandatory. A big disatvantage of alu housings are the straight stators used where the other fans seem to be more efficient and may be more acoustic friendly.
This exactly what happened in my Sapac L-39 a couple weeks ago. Luckily it melted right as I was lifting off so I was able to keep the damage minimal. I thought I spit a magnet but when i took it apart the motor was full of melted plastic from the fan unit.
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Old Jun 04, 2010, 06:05 PM
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Quote:
Originally Posted by Doug Bateman View Post
Alloy is heavy. Can't beat carbon sandwich material then CRP.
Talking about the fan shroud here, not the core.
Alloy Aluminum is way cheaper than carbon, but yes carbon is the best for quality.
Aluminum conducts heat the best (vs. plastic, nylon, carbon, etc) so it should help with cooling quite a bit.
And especially when the shroud is fully exposed to the air.
Weight is good too.
The Skyworld JP-1000 (100mm) unit only weighs 140grams (4.93 oz)according to the spec sheet.
http://www.skyworld-rc.com/SkyWorld%...m%20manual.jpg
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Old Jun 04, 2010, 07:22 PM
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Aluminum doesen't handel drops well not that you shouls drop them, but it happens, and a dented intake isn't easy to fix or adapt. The heat sink value is good though.



Morris

Ductedfans-RC
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Old Jun 04, 2010, 10:54 PM
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Aluminum schrods

For what its worth, I was the first to make use of the aluminum schroud. How about 25 years ago. I offered it as a replacement for the PVC schroud, used in the AEROJET 46. ( The AEROJET 46 was ICDF using a .46 size glow engine. Made with a Dynamax rotor cut down to 4 inches.) When I got in to the EDF market the first fan I developed was a 4" fan using the Dynamax rotor parts. One reason was I had about 100 or so rotors. I also found it easier to machine aluminum thin wall tubing, instead of 4" PVC pipe. I also found that the aluminum schroud could machined thin, thus its ligher and stronger. As for a heat sink, it doesn't do anything, unless you have aluminum stator vanes to transfer the heat. I machine heat sink fins in the aft portion of the center body. Another reason, its easier to machine different sizes. Plastic requires molds, as do the epoxy layup schrouds.

My 2 cents worth

Larry E.
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Old Jun 05, 2010, 03:32 AM
My project: FAIREY DELTA 1
Erik v. Schaik's Avatar
Uden Volkel, Netherlands
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Quote:
Originally Posted by Matt Howard View Post
This exactly what happened in my Sapac L-39 a couple weeks ago. Luckily it melted right as I was lifting off so I was able to keep the damage minimal. I thought I spit a magnet but when i took it apart the motor was full of melted plastic from the fan unit.
WOW! That must be a very Amp hungry setup you used if the you had a meltdown right after take off! Or you did fastcharge your cells and did not take the time for the motor to cool down for the next flight

HV setups don't show this issue. I can recharge and fly within 8 minutes (that's 25A/1200W charger).
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Old Jun 05, 2010, 03:43 AM
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Quote:
Originally Posted by Erik v. Schaik View Post
WOW! That must be a very Amp hungry setup you used if the you had a meltdown right after take off! Or you did fastcharge your cells and did not take the time for the motor to cool down for the next flight

HV setups don't show this issue. I can recharge and fly within 8 minutes (that's 25A/1200W charger).
I flew a couple times on 4 cells and I don't remember how long between flights I waited but when I tried my 5 cell pack it melted lesson learned
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Old Jun 05, 2010, 06:26 AM
My project: FAIREY DELTA 1
Erik v. Schaik's Avatar
Uden Volkel, Netherlands
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Seems correct. It would be very unlikely the motor would get this hot within 5-10 seconds so it had to be "very warm" already which resulted in pre warmed plastic shroud.

Having good 4s setup upgrade to 5s would stress a motor very hard as well. A 5s motor will handle 4s or less for sure, but this is not often reverseable .The 16/15/2 or 2w20 can be used for 3s(250w) or 4s(550-600w) and are the only combinations I worked with like this (3s for maiden flight of my Uriah series and when CG and throws are correct I upgrade to 4s which resulted in 262kmh top).

I bet you'll never melt a shroud again

greets!
Erik
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Old Jun 05, 2010, 07:38 AM
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Australia
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A midi housing complete is 75g, my Alloy one is 91g. Mini housing is 48g, Alloy 57g. Not a huge difference and certainly not an issue when the applications are taken into consideration, the main one being high power, the alloy housings are very good for high power setups, this is where they are aimed at.

Techspy the lander fan suffers from the rotor being their local design, the Midi definitely outperforms it. The lander 90mm housing is also 15g heavier than the skyworld one.

You certainly dont need an alloy fan for a 1500-2000 watt Midi setup, but it has benefits when the power really starts to creep up. Another plus is the deformability or lack there of, many people have issues with deforming plastic shrouds when closing up foam airframes, it can also happen if your mounting blocks are not perfectly in line too. The alloy housing wont suffer from this problem.
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