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Jan 21, 2009, 03:13 PM
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Dr Kiwi's Avatar

EMP-Neodym Electric Scimitar (ES) propellers

Steven Chao at Cermark generously sent me a range of his new electric props to try out on my thrust stand - this, dated November, 2008, is what is posted on their website.

CERMARK introduces a new line of electric scimitar propellers designed specifically to meet the rigors of our high performance electric flyers.

First, the wicked scimitar shape of these blades reduces wave drag at high radial velocity. Second, the specially designed upturned “tiplet” minimizes prop tip turbulence. Third, the disc or hub is lightened using multiple designed cavities. Fourth, a complete set of shaft adapters or inserts are provided with every electric scimitar blade. Finally, these aerodynamic blades use improved composite for superior rigidity.

The unusual blade shape gives more power than your conventional electric prop blades. Because they are more efficient, they will provide you with longer flights.

1. Efficient aerodynamics
2. Reduced noise
3. High rigidity
4. Greater power
5. Larger selection (4.1” to 30” - 50 sizes)
6. Improved efficiency (input to thrust)

My thrust stand is limited in the prop size/amount of power it can handle so what I asked for were sizes which matched as well as possible with APC E props within that same range.

The 5x5 is unavailable at this time, but what I have are: 4.1x4.1, 6x4, 7x4.5, 7x6, 8x4, 9x4.5, 10x5, 10x6, 11x5.5, 12x6, 13x8. Herein these are referred to as, for example, 6x4 EMP (matched by 6x4 APC E).

These props are stamped with the makers name - XYH, China. ShenZhen Xingyaohua Industrial Co., Ltd. This company produces numerous inrunner and outrunner brushless motors which appear under a whole collection of brand names - including EMP (ElectricModelPower), OK (these I've tested for Gemini Power Systems); I think perhaps Hextronic may be the same thing, and even the Aeronuts motors too. Many of the props sold by Hobby City (particularly the folders) are XYH products.

I found a reference to maximum rpm which I should include here for completeness - 205,000rpm/diameter (I somehow doubt that I have a motor capable of getting the 4.1x4.1 up to 50,000rpm!)

It will take me a long time to work my way through these (especially since it is the start of a new Semester at Chattanooga State and my teaching load leaves me little free time right now)... however, as they say, "have patience, my son" and all will be eventually revealed.

The shape of these props is distinctive, with the curved tiplets reminiscent of some Graupner props, and the hubs are large compared with those of, especially, GWS HD props. I'm not sure what they are made from, but these all dull-black props, look and feel (and sand) as though they have carbon fiber reinforcing. They are very nicely molded, though some of them needed a fair amount of attention before they were correctly balanced [it was 2hrs work to balance the complete selection!]. A very good selection of adapter rings is provided for each prop.

Most of those in my "selection" proved to be heavier than comparably sized APC E props, and a LOT heavier than comparably sized GWS HD.

4.1x4.1 EMP = 4g, 4.1x4.1 APC E = 3g

6x4 EMP = 5g, 6x4 APC E = 5g, 6x4 APC Sport = 5g, 6x4 HZ = 4g

7x4.5 EMP = 13g, 7x6 EMP = 14g, 7x6 APC E = 8g, 7x6 APC Sport = 12g, 7x6 APC SF = 5g

8x4 EMP = 14g, 8x4 APC E = 11g, 8x4 MAS Electric Only = 11g, 8x4 MAS G/F 3 = 11g, 8x4 GWS HD = 5g

9x4.5 EMP = 18g, 9x4.5 APC E = 17g, 9x5 GWS HD = 7g

10x6 EMP = 20g, 10x5 EMP = 19g, 10x5 APC E = 16g, 10x6 GWS HD = 9g

11x5.5 EMP = 22g, 11x5.5 APC E = 20g, 11x7 GWS HD = 12g

12x6 EMP = 31g, 12x6 APC E = 23g, 12x6 GWS HD = 15g

13x8 EMP = 32g, 13x4 APC E = 27g, 13x6.5 APC E = 26g, 13x8 APC E = 27g

I started with the 4.1x4.1 EMP, for comparison with the 4.1x4.1 APC E. I set up a Grayson Hobby SuperSonic v2 (~U2212/6) motor on the stand, with a Markus 45A ESC, since I figured this ~2180Kv motor would give a 4.1x4.1 a good run, yet be able to spin the next size up (the 6x4) at below 25A which is the limit of my Zurich DM304 power supply.

I ran the 4.1x4.1 EMP, and then the 4.1x4.1 APC E for brief (~15sec) bursts to WOT, at my usual voltage intervals (Set at 7v-11v on the Power Supply) - recording volts/amps/watts/rpm/thrust/temp.

I then "filled in the graph" for each prop by running each at incremental throttle (on 7v) from "idle" to "WOT" recording amps, but more particularly, watts/thrust/rpm. Thus for each prop I ended up with at least a dozen points along the curve for graphing "RPM versus Watts-in" and "Thrust from Watts-in". The third graph "Thrust from Watts-in" is essentially a measure of "efficiency g/W" - clearly these two props are very close - the EMP simply draws more current and, by doing so, delivers a bit more thrust.

Even to the casual eye these EMP props have broader blades (and thus more blade area) than the comparable APC E prop... so it was no surprise to see that the 4.1x4.1 EMP drew more amps, attained fewer rpm, yet generated more thrust than its APC E counterpart. As far as "efficiency g/W" goes, the EMP prop returned a slightly lower figure than the APC E (2.47g/W;2.75g/W).

I then ran my series of 6x4 props - the EMP, an APC E an APC Sport and a stray HobbyZone one I had picked up at Hobby Town!).

On the 11v run, the EMP and the HZ drew the highest current (23.90A/253W), but the EMP generated a LOT more thrust (868g;780g). The HZ prop is not as rigid as these others (gray 'plastic') and at >16000rpm it produced some weird sounds as though it was reaching its rpm limit - yet it became far quieter at the max. rpm it reached - 18840rpm). The 6x4 APC Sport drew almost as much (22.70A/242W) but produced the lowest thrust (735g). The APC E drew the least, yet generated the highest rpm, but the thrust was relatively low (748g) - fully 120g (~14%) less than the EMP produced! I have not yet done the incremental runs with these 6x4 props, so there are no graphs for them just yet! As far as "efficiency g/W" goes [with far higher thrust, even though at the fractionally lower pitch speed] the 6x4 EMP is clearly superior to all of the rest.

I've attached the data tables for the SuperSonic v2, with all six props tested in this session. There are graphs of "RPM from Watts", "Thrust from RPM" and "Thrust from Watts".

Please keep in mind that, to be useful, any of these estimates of efficiency in terms of g/W require a component of pitch speed - and we are all hog-tied by the fact that we don't actually KNOW what the pitch of any particular prop is (we can only go by what is printed on it - and that may well be incorrect - viz. GWS HD). Estimates of g/W are useful if we are comparing two motors with the same prop, but [because of the "unknown pitch" problem], less useful for comparing, even on the same motor, two props of allegedly comparable size (but different makes).

Lots more to come in the fullness of time!

Cheers, Phil
Last edited by Dr Kiwi; Jan 22, 2009 at 07:36 PM.
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Jan 21, 2009, 04:12 PM
Fly me to the moon...
Atom1025's Avatar
Interesting........ As I prefer thrust over top end the numbers are looking good to me. Thanks for your troubles Doc.
Jan 21, 2009, 06:25 PM
I like the violent stuff!
Thanks for the time and effort. I tried the 10x4.7SF on my Flash, the performance seemed pretty close to the APC . I did notice however it seemed to spool up a little slower on certain 3D maneuvers. Is there any way you can verify this on your thrust stand? Thanks!
Jan 21, 2009, 08:19 PM
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Dr Kiwi's Avatar
Originally Posted by Wingin' Wayne
Thanks for the time and effort. I tried the 10x4.7SF on my Flash, the performance seemed pretty close to the APC . I did notice however it seemed to spool up a little slower on certain 3D maneuvers. Is there any way you can verify this on your thrust stand? Thanks!

Now are you comparing a 10x5 APC E with a 10x4.7 APC SF? The SF will suck more amps, get you more thrust, and probably spool up more slowly because of its wider blade area.
Jan 22, 2009, 06:15 AM
Rejisterd Youzer
SU Jags's Avatar
Thanks for the info Doc! I was just wondering if these props were any good; I think I'll order a few.
Jan 22, 2009, 07:32 AM
Registered User
Dr Kiwi's Avatar
I tested the 7" and 8" props last night and I'll write 'em up today, but the bigger stuff will have to wait - I think it is safe to say the trend is clear - they draw more than say APC E (sometimes a LOT more) but they deliver commensurately more thrust too, at only marginally lower pitch speed.

One word of warning before you purchase - you may need to be careful in your prop size selection, since the 7" and 8" props may draw fully 40-50% more than the same sized APC E!
Jan 22, 2009, 04:24 PM
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Dr Kiwi's Avatar
Here are the figures and graphs for the 7" and 8" props:

The 7x4.5 EMP was a real surprise - it draw more than the 7x6 EMP, yet generated less thrust at lower pitch speed... that's a lose, lose situation! I was so astounded by the measurements that I thought I might have inadvertently mixed up the props or transposed the results - so I re-ran both props in exactly the same regime (making certain of the 7x4.5 and 7x6 embossed upon them) - well, all that proved was that my test stand is consistent! I got the same result the second time around, with plus or minus just a watt or two, a few grams or a few rpm here and there.

Another significant finding was that the EMP props drew a LOT more than the APC E props - yes, they did generate more thrust, but this really emphasizes the fact that, if one is cognizant of amp/watts limits of one's motor, one CANNOT simply substitute different brands even if they are the same pitch and diameter. The 7x4.5 EMP drew 56% more than the 7x5 APC E and the 7x6 EMP drew 30% more than the 7x6 APC E.

The 7x6 EMP is a very good prop because, as seen on the "Thrust from Watts" graph, it generates more thrust than any of the other props (admittedly at fractionally lower pitch speed), yet still is more "efficient" than them!

The 8x4 EMP really sucks some amps (>40% more than the 8x4 APC E), but it does generate a lot more thrust (765g @ 35mph). If you can fit nothing bigger than an 8" prop on your plane, yet need lots of thrust - this is the boy for you! But, beware of casually switching an 8x4 EMP in place of your 8x4 APC E - your amp draw will go from <10A to >14A!

At the other end of the spectrum the MAS Electric Only again demonstrates its inferiority! It draws a lot of amps, but doesn't deliver a heck of a lot of thrust (only 4.78g/W)! In comparison with its sibling 8x4 MAS G/F 3, it draws 25% higher current and delivers only 13% more thrust, at lower pitch speed.

The GWS HD, at its amp-miserly, lower power level, appears to be easily the most "efficient" but of course this depends on the true pitch, doesn't it!


Cheers, Phil
Last edited by Dr Kiwi; Jan 22, 2009 at 04:51 PM.
Jan 22, 2009, 06:56 PM
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Dr Kiwi's Avatar
Since you guys may not know what these EMP Scimitar props look like, I thought it might be useful if I posted some "comparison" photos to illustrate the wide variation that exists in props with the same basic numbers (diam x pitch). I could have thrown in Graupners and Aeronauts and APC SF .... but that would just have confused the issue further!

Note that the 6x4 EMP is actually 6.1" diameter (~155mm), whereas the others are all around 5.9"-6.0" (~151mm-152mm).

Here are the 4.1x4.1 and 6x4 props together, then the 7 inch props, then the 8x4's.
Jan 22, 2009, 10:09 PM
I like the violent stuff!
Doctor, I was comparing the 10x4.7SF APC to the 10x4.7SF EMP. The EMP is stiffer, heavier and from what I can tell slightly less efficient. I hope you get a chance to compare SF props. I tried the 12x6E EMP on my 3DHS 40" Edge, it shook the plane. So I balanced it, pretty far off. Have not tried it yet. Looking foreward to your further reports.
Jan 23, 2009, 07:41 AM
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Dr Kiwi's Avatar
I haven't seen any of the EMP SF props (yet).

I found that all these Scimitar props needed balancing - some (the 8x4 especially) were a LONG way out! But, hey, what's new - every APC E (and indeed virtually every prop I've ever handled) needs balancing too.
Jan 23, 2009, 06:25 PM
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Dr Kiwi's Avatar
The plot thickens!

Today I received from HobbyCity a package of props I had ordered a few weeks ago - I had ordered several sizes of their TGS Sport propellers.

It would seem Hobby City is even more devious than we had suspected - the package came marked as a "Gift" with a declared value of "$13" - since it was clearly a commercial transaction it should have been marked as "Goods", and the declared value as the correct "$29"... I guess that's one way of defrauding the mail service and customs. Moreover there was no invoice included, so the real value of the goods could not be determined, even if the parcel were opened.

But it gets better! The props (all 10 of them) came in plastic sleeves which had been opened by removing the staples. Each sleeve had within it the appropriate "tree' of prop adapter rings and a red and yellow slip of paper headed with Caution......., but none of the sleeves had the cardboard closure piece on which would have been printed the makers name and the prop size.

I guess we know why that vital piece of red and checkerboard cardboard is missing - it would have been printed with EMP and had stick-on label which would have read, for example, Electric Model Power 11*5.5E, and a bar code.

These props are in fact EMP props identical to those sent to me by Steven Chao at Cermark, and advertised on the Cermark website. quite properly. as being from ElectricModelPower.

It would seem that HobbyCity is simply selling EMP props [which they would probably argue, "fell off the back of a truck somewhere"] under its own name (TGS Sport).


Cheers, Phil
Last edited by Dr Kiwi; Jan 23, 2009 at 08:29 PM.
Jan 23, 2009, 06:52 PM
Registered User
Ken Myers's Avatar
I'm not sure what is surprising about this. Their motors "appear" to be EMP products as well.
Jan 23, 2009, 08:34 PM
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Dr Kiwi's Avatar
I was just disturbed by the fact that any labels which might have indicated the origin of the product were quite clearly deliberately removed. Why go to that trouble, and advertise them as your own product by a completely different name, if there was not something "fishy" in the wind.
Jan 23, 2009, 11:43 PM
Team Hitec, Customer Support
Xpress..'s Avatar
^They're chineese, what can you expect?

Soo, from your testing (and me not wanting to read all the data right now- it's late) are they better or worse in performance then APC E props?
Jan 24, 2009, 05:42 AM
I hole jumped him!!!
Lance's Avatar
Originally Posted by Dr Kiwi
The plot thickens!

It would seem Hobby City is even more devious than we had suspected - the package came marked as a "Gift" with a declared value of "$13" - since it was clearly a commercial transaction it should have been marked as "Goods", and the declared value as the correct "$29"... I guess that's one way of defrauding the mail service and customs. Moreover there was no invoice included, so the real value of the goods could not be determined, even if the parcel were opened.

My expierence with Hobby City has been the same. I recently placed and order with them and just received it. The order was roughly $200, and the shipping alone was $32. The small battered cardboard box that arrived...(something I could probably ship priority at the post office for about $8~9)
....the box had a chinese label on it with no packing slip. The slip had very little english on it, but it did say the contents were "Toys" and that the value was $17. A bit surprising since most of the order was small lithium batteries. From China to me in a few days, so I assume it went via airmail.
Now don't get me wrong...I'm happy/satisfied that the package arrived. BUT I have to wonder what the outcome would be if it had not. Would I be eligible for only the declared value of $17?

Now wonder their economy is spanking our domestic market. They don't pay their fair share of taxes/tarrifs to us. The other edge of the sword is that they can sell us good and vastly undercut our domestic market price. Sometimes it's a tough decision.

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