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Old Dec 07, 2011, 11:54 AM
jean-claude Terrettaz
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Fantastic Herb, very informative. I know why I like my Stumax fan
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Old Dec 08, 2011, 12:04 PM
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Hey JC, yes the SM fan seems like a good design
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Old Dec 15, 2011, 03:17 PM
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There's still a lot of spread (plain measurement errors, and different measuring setups) in the CS-12bl data.

So that data seems so far inconclusive as to whether that fan is worth the money or not

Seriously, I don't think anybody has the courage to go above 2000W for fear the CS-12bl fan might just disintegrate (see post no. 1).
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Old Dec 25, 2011, 03:46 PM
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I don't like the out-of-the-box design of the 12bl CS fan a whole lot ...

The blades don't sit rigidly in the hub no matter how tight the bolt is. That means a potential fan explosion as soon as you have the tiniest vibration or resonance ... An improperly mounted and/or out of balance motor will only make matters worse.

I measured a bit of unevenness in the blade weights due to the manufacturing process, they are around 2.91 g each plus or minus a percent or so. Making the blade weights even (or evenly distributed, whatever that means) is not practical, and a waste of time (see below).

The only way to improve things is to first make the whole assembly more rigid by gluing the blades to each other. The blades are thoroughly cleaned with alcohol, then a thin coat of epoxy is applied where they touch each other.

One thing one needs to keep an eye on is that the blade assembly (the 12 blades + 2 aluminum ring-shaped retainers) don't get accidentally glued to the aluminum hub and nosecone. Otherwise it would get a lot more complicated later to fit the fan to the motor shaft .

Later the fan will have to be painstakingly balanced on a good static magnetic balancer, like most other fans I owned before.

There is clearly no point in balancing the fan (or individual blades) before they are glued in, as the added epoxy will throw off any previous balance

So, the balancing has to be done after the glues has set...

.
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Old Dec 25, 2011, 03:49 PM
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Too bad there's not to many measurements left on the JePe 90mm carbon fan, it is very light !

www.jepe.org

I have to see if I can find some useful thrust/watt data somewhere ...

.
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Old Dec 29, 2011, 01:31 PM
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I did find some old JePe data on his carbon fan, which I added. I am still a bit unsure about his measurements though .

www.jepe.org

Red dots : JetFan 90mm

Green dots : WeMoTec MidiFan 90mm

Purple dots : Stumax 90mm

Orange dots: Het 90mm fan

Yellow dots : VasaFan 90mm

Cyan (light blue) dots : CS 90mm 12-blade 90mm

Magenta (purple red) dots : JePe 4-bl carbon fan


.
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Old Jan 03, 2012, 12:38 PM
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Some older Schuebeler DS-51 data added ...

http://www.schuebeler-jets.com/index...=13&Itemid=116

Red dots : JetFan 90mm

Green dots : WeMoTec MidiFan 90mm

Purple dots : Stumax 90mm

Orange dots: Het 90mm fan

Yellow dots : VasaFan 90mm

Cyan (light blue) dots : CS 90mm 12-blade 90mm

Magenta (purple red) dots : Schuebeler DS-51 carbon fan

Black dots : JePe 4-bl carbon fan (Spiderfan)

.
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Old Jan 04, 2012, 05:29 PM
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I got this new balancer from HK and was quite eager to test it to see if it's any good

http://www.hobbyking.com/hobbyking/s...idProduct=7702

For $16 it's pretty well made but the key issue is if the thicker shaft is true.

Extreme accuracy ?? We shall see

There's an easy way to test it with a fan, namely use a fan that is known to be perfectly balanced - like the WeMoTec Midi Pro rotor.

WeMoTec uses German electronic balancing equipment made by Schenck, accurate to 1/1000 of a gram and very expensive !





http://translate.google.com/translat...n&hl=&ie=UTF-8
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Old Jan 04, 2012, 05:45 PM
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This is what the HK $16 balancer looks like,

My 8-yr old custom made $3 magnetic balancer (it uses a $3 Prather finger balancer shaft, and two WD HD magnets) is shown for comparison.

The CS 12-bl fan was previously balanced in the usual way by using thin small strips of red electrical tape, applied to the inside of the hub.

Slow cure thickened epoxy works just as well. Or hvac adhesive-backed aluminum tape.

The balancing process requires some patience ... First check which side is heavier, apply small bits of electrical tape to the other side, usually on the inside of the hub. Then check the balance again, add more tape bits etc.

After a while one will see that the fan does not stop its rotation on a specific spot, which means it's very close to balanced.

Some fans are very close to balanced, and will require a minimal amount of tape. Some others are quite unbalanced or wildly off center, and will therefore require a bit more weight.

.
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Old Jan 04, 2012, 05:46 PM
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After some testing, the HK balancer seems to work ok, but is not more accurate than my old $3 one ...

.

Balancing a 90mm EDF Fan (WeMoTec vs. ChangeSun 12 blade) (4 min 14 sec)
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Old Jan 06, 2012, 12:34 PM
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... given the spread in the efficiency data it is hard to come yet to a definitive conclusion.

Nevertheless it seems that for the Change Sun 12-bladed fan the improvement in the noise comes at the hefty price of :

a) heavy weight (180g, twice the weight of the MidiFan), due to a heavy rotor that puts stress on the motor bearings ;

b) a possible danger of blade resonance & explosion unless the blades are glued in properly and the fan is re-balanced ;

c) a fairly miserable performance compared to most decent EDF fans.

Specifically, as an example:

the CS fan requires 2100W to generate ca. 2.4 kg of thrust, while the WeMoTec Midifan only requires ca. 1400W to generate approximately the same amount of thrust. On 6S that is ca. 105A vs. just 65A for the Midi.
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Old Jan 06, 2012, 10:06 PM
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Herb, can you add a legend your efficiency charts? It's really hard to keep opening and closing ti because i forgot which color is which fan, lol.
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Old Jan 08, 2012, 09:47 PM
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Quote:
Originally Posted by Herb View Post
......Specifically, as an example:

the CS fan requires 2100W to generate ca. 2.4 kg of thrust, while the WeMoTec Midifan only requires ca. 1400W to generate approximately the same amount of thrust. On 6S that is ca. 105A vs. just 65A for the Midi.
That is a good "laymen" definition of efficiency, for most people! Show them the watts (thus the weight and cost to achieve fan motion) and then show them the thrust. But, I'd be really interested at the efflux velocity for the thrust measurements as well. For example if the CS90 were to be 30 percent higher, I assume we would have a very interesting dynamic play out of the efficiencies in an installation in flight? Of course, "ass"uming can be a dangerous game.

Also Herb, can you explain again your exact metric of efficient on the left vertical axis of the graphs? It's numbered from 0 to 5. Thank you for the data, it's interesting to see it all play out on paper. I'm curious as to the wide array of data plots in the CS and the JF however. Cheers!
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Old Jan 09, 2012, 11:03 AM
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Quote:
Originally Posted by Eddie P View Post
... Herb, can you explain again your exact metric of efficient on the left vertical axis of the graphs? It's numbered from 0 to 5. Thank you for the data, it's interesting to see it all play out on paper. I'm curious as to the wide array of data plots in the CS and the JF however. Cheers!
Hi Eddie, what is plotted is explained in the first post ... You can take the highest valued points as being roughly in the (overall) 65% efficiency range.

So what are plotted are relative, not absolute, efficiencies. Which was good enough for me.

As I said above, the wide spread in the data indicates a) different setups (specifically, motors with varying degree of efficiency, a surprisingly big spread), b) poor measurements (eg Watts are not measured simultaneously with thrust), c) air blows on scale etc.

Btw Eddie, efflux can be computed from thrust, so it's not an independent variable. Note that this aspect has been folded into the (correct) static efficiency measurement, which does not, here, just divide thrusts by watts. The latter would be an incorrect efficiency measure.

Here is a simple example of a formula that allows one to compute efflux from thrust.

In general efflux can be measured, but interpreting the rsults is not trivial if the velocity distribution coming
out of the fan is not constant (some fans have a slight velocity increase in the radial direction).

The formula says

v (efflux) , in meter/second = Square root [ Thrust / (1,225 * A_eff ) ] * 100

where:

Thrust = thrust in Newtons ( kg x 9.81 )

1,225 = a constant which depends weakly on air temperature, density, pressure etc.

A_eff the relevant fan area in dm^2 ( total area of fan - area of motor shroud).

In the case of the WeMoTec Midifan this quantity is 49.4 dm^2 = 4940 cm^2 . For the DS-51 fan, it is 51 dm^2.

Note that if a thrust tube is used, then the relevant area is the exit one.

It is important that the efflux is computed for a given thrust, under the *same* conditions (with or without thrust tube in both cases).
For some fans, thrust increases or decreases quite an bit when a thrust tube is added.

As an example of the practical usefulness of the formula, consider again the Midifan at 3515 Watts
which generates (with a HET motor) about 49.05 N of thrust.

Then the above formula gives the estimate

v = Square root [ 49.05 N / ( 1.225 * 49.4 dm^2 ) ] *100 = 90.03 meter / second = 202 mph

.
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Old Jan 09, 2012, 10:51 PM
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Yeah, I went back and looked at the first post

How would you measure efflux velocity from the thrust measurements? A simple mass flow equation? (again, ) I think I'll run some numbers, the graphs are a great source of info.
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