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        Data Evaluating Relative Fan Efficiencies (Comparing an array of 90mm fans)

#1 Herb Oct 13, 2011 05:29 PM

Evaluating Relative Fan Efficiencies (Comparing an array of 90mm fans)
5 Attachment(s)
Once in a while an EDF fan comes along where there's plenty of measured data to evaluate how good it is :) ...

Here's some nice and complete systematic data for the new 90mm JetFan :


Of great relevance of the overall fan efficiency, defined as

efficiency = (mechanical work done per unit time) / (input power) , in e.g. (N.m/sec)/Watts

A good substitute for the above quantity is, based on simple formulas relating work to fan thrust and fan efflux:

efficiency = (const.) x thrust^(3/2) / (input power)

You would imagine that if somebody is really serious about designing an efficient fan they would take the time to actually do relative measurements of different designs, in order to figure out which rotor/stator design in the end is best.

Indeed that is how serious fan designers (eg WeMoTec, Daniel Schuebeler etc.) indeed do it ...

But then often a new design comes up (nowadays every other week, in some cases a copy of somebody else's rotor, with one blade added or subtracted so it don't look like a copy ;) ) - without any clear measurements of anything.

If it is a clear shameless copy of a DS-51 fan, then it has to be as good as the DS-51, right ?

Then the relentless overhype follows ("20% more efficient than anybody elses fan'" - to the point that now the overall efficieny adds up to 110% :D), and more adverts such as "best fan I ever tried in my xx" etc.

Now, the Jetfan 90 data is interesting and accurate enough to pull out :

1) the relative efficiencies of different motors in the JF

2) the very slow rise of efficiency with power/voltage

3) the large errors inherent in all these measurements

4) the wide spread in motor efficiencies (up to 31%).


#2 Herb Oct 13, 2011 05:38 PM

A couple of obvious things stand out from the above data:

1) The overall Jetfan 90mm efficiency seems comparable to the WeMoTec Midifan (=2.8 on above scale) in the 2000W range, when using similar motors.

The JF's efficiency seems lower by around 10% compared to the DS-51, which remains the crown jewel of efficiencies in the 90mm range.

2) There's quite a bit of fluctuation in the data points. Some of it is measurement errors in the thrust.

3) The five lowest efficiencies are associated with Tenshock inrunner motors (data at 1.43, 1.86,1.66 and 2.56 kW) and Skorpion outrunner (1.44kW).
Clearly the price savings with the TS china motors is offset by -31% runtime compared to the better motors due to their rather poor efficiencies.

4) The five highest efficiencies are associated, not surprisingly, with HET 700 (1.22, 1.97 and 4.27kW), ARC (1.48kW) and Neu (2.84 kW).


#3 Herb Oct 13, 2011 05:51 PM

Taken at face value the above data means that it does make a big difference which motor you put in your fan.

The difference in efficiency between the top and bottom points is ca. 31%.

Thus the worst motors (TS, SK) will therefore require 31% more battery power to do the same work as the most efficient motor ... Not a small difference.

Yes of course you can get your battery glowing hot and still get the same output power from a miserable motor.

But the message seems clear at least from the above data ... stay away from (those) Tenshock and (those) Skorpion and go for Het 700 or Arc; if you have the money go for the Neu ;)

Anything new ? Probably not, one knew all along that Steve Neu knows how to make superb motors.

The interesting aspect is that Arc and HET are also excellent motors at ca. half the price ...


#4 Herb Oct 13, 2011 06:05 PM

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In the end there's of course other considerations in picking a fan: price, quality of materials, durability etc.

If you like many thin blades make sure they stay on for a while ;)

This is what happens to a plastic jetfan rotor when you inadvertently drop it on the table :o:

Will those thin blades break by just looking at them, on the inevitable $20 china copy that will appear in a few weeks ?

For now, I will stick with proven performers that will not endanger bystanders when you run the power up ;)


#5 corsair nut Oct 14, 2011 09:50 AM

damn! that sucks. did you contact rainer and rico about that?

im waiting for my second unit to come in. going to deck out a fly fly F-86 after loosing my RCL T-33 to unknown cause.

#6 Eddie P Oct 14, 2011 06:16 PM

Sorry about the fan Herb, and I appreciate the thoughts on the fan comparisons. This isn't the first multibladed fan that has snapped off blades at the slightest provocation though. Some very expensive fans have had the same fate for less of an offense.

The DS-51 is a great fan, always was, still is. Same with some other "classics". Folks are so bitten by the sound issue though, as it is a trendy thing, that efficiency seems to have taken a back seat to other advances. I don't blame anyone for it, I like the "whoosh" sound too, more than a scream. It never really used to cross my mind about the sound but now I have to agree I do appreciate a slightly more quiet fan.

So while the DS-51 high blade count fan and other high blade count fans have moved forward in the total package of performance and "sound" it stands to reason that some offerings will come out to give the potential customer what they think they want. Today, that's a high blade count and a "whoosh", and all that at a low price too. Efficiencies? Most think that's in fashion too, but some want in on a trend, and now. (hence the place in the market for the exploding Chinese copy multiblade fan and others too). Like Levi's Jeans, "Quality never goes out of style". For EDF's, "High Performance never goes out of style". Having said that, Levis did make a lot of acid wash jeans in the late 80's, and huge bell bottoms at least two major time frames in history. :popcorn: They may have been quality but they were loud in their own way, as in screaming 3 bladed loud. Not sure how acid wash jeans and bell bottoms would hold up on an efficiency graph, but.. ;)

#7 Herb Oct 22, 2011 01:29 PM

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EDF Fan efficiency comparison as a function of Watts (actually kW) ,

Red dots : JetFan 90mm

Green dots : WeMoTec MidiFan 90mm

Purple dots : Stumax 90mm


Generally the WeMo data is based on Het 600 and Arc motors (all 36mm diam), the Stx data on the newer HET 700 motors.


#8 Kevin Greene Oct 26, 2011 09:56 PM

Where does the HET fan fit into this equation??...I bought an HET 90mm fan and it is powered by an 1865kv 700-60 Typhoon on 8S...

THANKS for all of your work!!!


#9 Herb Oct 27, 2011 07:20 PM

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Hi Kevin,

In the past HET has done a pretty good job in designing their fans ... they were very close to the WeMoTecs.


For the 90mm HET 9305 I include both new fan (700) and old fan data.

Red dots : JetFan 90mm

Green dots : WeMoTec MidiFan 90mm

Purple dots : Stumax 90mm

Orange dots: Het 90mm fan


#10 Eddie P Oct 31, 2011 02:51 PM

That's some interesting data. Thanks for posting that Herb.

#11 Herb Nov 05, 2011 12:53 PM

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Hi Eddie ... I am still looking for some good quality DS-51 data to add to the graph. Daniel measures his thrust in a different way, so a direct comparison with the way others measure thrust and efflux is not useful.


When I find it, I will add it.

#12 Herb Nov 18, 2011 12:57 PM

4 Attachment(s)
Data for Vasafan 90mm carbon [ http://www.ready2fly.ch/shop/USER_AR...e2b30ffbed14c2 ] added, relevant formulas included in pdf file.


Even though it's made out of carbon (lightweight) and therefore quite expensive, the VasaFan does not to seem to give any real advantage over say the WeMo or Het fans ... Possibly due to the very basic & somewhat crude blade design.

Red dots : JetFan 90mm

Green dots : WeMoTec MidiFan 90mm

Purple dots : Stumax 90mm

Orange dots: Het 90mm fan

Yellow dots : VasaFan 90mm


#13 Herb Nov 20, 2011 12:40 PM

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Just ordered this new 12-blade 90mm fan for testing :)



Those blades look quite delicate :eek: ...


#14 Herb Nov 26, 2011 04:44 PM

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Weight comparison between the WeMoTec Midifan and the CS 12-blade fan, both with same HK 1900kv 36mm edf motor:

339g vs 428 g (+89g).

The motor is the same in both cases and weighs 249g.

Thus WeMoTec Midi fan by itself weighs 90g, and CS 12-bl fan weighs 180g (+100% ).


#15 Herb Dec 03, 2011 12:01 PM

11 Attachment(s)
CS 90mm 12-blade data from Dave and others added :

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

Note the comparatively low efficiency of the CS-12bl fan esp. at higher watts.

A ton of turbulence = cool sound ;)


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