Black Tiger 4250C

[Matt Piatkowski]

I am looking for somebody who bought this motor from RSM Distribution and tested it in flight.
I bought the entire package (Black Tiger 4250C, 65 Amp Speed Controller, 13x4.5 APC E prop, KR governor and 5S 2600 30C battery and bench tested yesterday.

The test was short but I believe quite representative. Please see the eLogged data (attached).

The results are rather disappointing with max. power around 420 Watts (!!) with RPM set by RSM Distribution as ~9,200 ( actual RPM ~9180 measured using the tachometer) and the static current only about 24 Amps.

I believe this motor must be run at much higher current, probably about 50 static Amps that can be done by loading it properly using 6" or even 7" pitch.

50 static Amps corresponds to the in-flight average current of, say 40 Amps and the time of flight will be (2.6/40) x 60 =3.9 minutes. My guess is that to get full 5 minutes of flight with this motor, the battery must be in 3300-3500 mAh range.

I have contacted Eric Rule with questions and concerns but your suggestions, opinions and friendly critique is always appreciated.

Regards,
Matt

[Motorman]

Call Bob Hunt.


MM

[eric rule]

Matt;

Why post this here?

After all of your e mails asking questions about various topics and all of the time I have taken answering your questions and the way I handled your problem with the KR Gov I would think that I have proven beyond any doubt that the products I sell and my after sale service is exceptional. When you couple this with RSM's guarantee of satisfaction or your money back there is simply no need for you to post something like this that calls into question one of my products.

The reason you could not find anything about the Black Tiger motors on the web is that they are manufactured exclusively for RSM to my specifications. As such they are only sold by me and a few of my dealers. For the record here are the specs for the Black Tiger 4250C motor.

Name BK4250C, kv rating 780.
Amps 55, Max Watts 1200, efficiency 85%, thrust per gram 1500-2300, battery 4-6 cell. weight 190 grams, stator diameter 42 mm, stator length 50 mm, outer shaft length 20 mm

You will get maximum watts if you turn the rpm up to maximum and use a 6 cell battery. Since you are likely to use a 5 cell battery and run the motor in the 9100-9600 rpm range you will record a lower wattage.

The important thing is that you can generate sufficient power to allow the model to perform the aerobatic pattern well while keeping the electric components cool. The Black Tiger 4250C in the application you purchased it for will do this. If you still feel that this product will not perform properly for you just send it back to me. I will be happy to refund your money.

[William DeMauro]

I am looking for somebody who bought this motor from RSM Distribution and tested it in flight.
I bought the entire package (Black Tiger 4250C, 65 Amp Speed Controller, 13x4.5 APC E prop, KR governor and 5S 2600 30C battery and bench tested yesterday.
PUT IT IN A PLANE AND GO FLY IT!!! I BET YOU WILL BE MORE THAN PLEASANTLY SURPRISED!!!
The test was short but I believe quite representative. Please see the eLogged data (attached).

The results are rather disappointing with max. power around 420 Watts (!!) with RPM set by RSM Distribution as ~9,200 ( actual RPM ~9180 measured using the tachometer) and the static current only about 24 Amps.
9180 vs 9200 FIND ME A TACH THATS EVEN THAT ACCURATE I've said many times the RPM reading is just a rough guidline IT'S THE LAP TIMES THAT COUNT!!!!
I believe this motor must be run at much higher current, probably about 50 static Amps that can be done by loading it properly using 6" or even 7" pitch.  NO NEED TO RUN IT AT A HIGHER CURRENT!!! I doubt very much that you will never take that set-up over 9500-9600 RPM in a stunt plane with that prop. If 24 amps or so is the current you need to get there then that's what you need and NOT more.

50 static Amps corresponds to the in-flight average current of, say 40 Amps and the time of flight will be (2.6/40) x 60 =3.9 minutes. My guess is that to get full 5 minutes of flight with this motor, the battery must be in 3300-3500 mAh range.
The 5s2600 battery may be a bit small in a 65-70 oz stunt plane flying a full 5.5 min flight and the whole pattern. I think that in most cases a 5s 3000-3300 would be the best choice in size if you wanted to stay with a 5 cell set up. Otherwise a 6s 2500-2700 should work fine too

I have contacted Eric Rule with questions and concerns but your suggestions, opinions and friendly critique is always appreciated.

See my comments in red above. Those numbers are pretty close no matter whose power system you use in your plane. I've personally tested some of Eric's stuff for a past Stunt News Article and can say it WORKS AS ADVERTISED and I had NO issues using or setting up his stuff. there is no universal RPM or power setting but we do have guidelines regarding certain commonly used props and batteries. When Eric sets them up he uses those guidelines. When someone calls me and asks me where to start on a certain set up I can usually get them close, once I know the motor, prop and plane, I can give them a close RPM. Mine, like Eric's, may not be exact but I bet its within 300-500 RPM in most cases. I think its pretty good. All power systems need to be tweaked due to conditions, plane, etc.
William
P.S.
I am not writing this to defend or put down anyone(Eric or Matt). Those are numbers that are well tested and work regardless of who's electric set up one uses. Go through the "List your set up" here you will find many using that prop and RPM setting. I don't care what motor or speed control you have it attached to(as long as its capable of spinning the prop without burning up). The RPM doesn't vary whether you use a 4,5,6 cell setup. I also paid for any of the test set ups that I kept so I was not paid to write my article and the opinions stated there and here are just that. MY OPINIONS.

[Matt Piatkowski]

Hi William ( or can I call you Bill?),

I do not have a plane to put it in,yet.
The plane I am designing will weight RTF about 57 oz and will be very similar to Juri Yatsenko Shark (http://discovery-aeromodels.com/en/andrey-yatsenko-mace-r2-shark-f2b-model.html).

I can fly 57 oz stunt plane with 5.3 s laps and good tension OH on 65-66' long lines using any 60-76 size glow engine for 5 minutes, almost anybody flying stunt can do it - the trick is to find the electric motor and battery combination that will give just that and will not be in the Plettenberg price range.

I bought the RSM6174SYSC based on the following description:
" RSM .61 - .74 Competition Level Power System Equal to .61 to .74 glow power. Includes a RSM Black Tiger 4250C Motor, 65 Amp Speed Controller, KR Flight Manager, 2600 mAh 5 cell 30C Battery & 13 x 4.5 Pusher Prop. Comes with all programming installed. This power system is ready to be installed in your model. Just flip the switch and fly!    $299.99".

Here comes the main point:
During bench testing of the above parts, I have found that the power of this "61 - .74 Competition Level Power System Equal to .61 to .74 glow power" is only 420 Watts ( 17.5 V x 24 Amps).
This means that the RTF weight of the "very competitive" model using this system cannot be more than 420/11=38 oz.     

I have a RTF 38oz. trainer-stunter that uses EVO 36 C/L, has the wings area 523 sq.in. and flies exceptionally well.

Now...I did not buy the "61 - .74 Competition Level Power System Equal to .61 to .74 glow power" to fly the 36 size plane - I bought it to fly the 57-60 oz plane for at least 5 minutes. To fly the 57 oz. plane competitively, I need at least 630 Watts (57 x 11 ). Where are they?

I will bench test Black Tiger 4250C using 12x6 or 13x6 prop with provided 2600 mAh 5S battery and I bet the cherry lollipop that I will get around 50 Amps draw, but the time of flight will be about 3 minutes what is not really "competitive".

I have not decided yet what to do with the system I bought from Eric. If, in order to use it "competitively" ( meaning: for more than 5 minutes ) I have to use the 21 oz. battery, the RTF weight of my full size stunter will go up to 65 oz. and this is no good.

If I use my Ro-Jett 76 the RTF weight will be 57 oz. and the 8 oz. makes all the difference in the world.
Regards,
M





 



You see my point?

   

[William DeMauro]

Matt,
   We have flown Sharks with similar power systems. Orestes is flying a shark with a similar sized Cobra in it and Igors active system, with a 5s 2700 Thunderpower battery. Igor's system uses more that the set up that you will use and he is just making it with the 2700 battery. I know that the set up that you bought will more than fly your plane with power to spare. I do question the capacity of the 5s 2600 and feel that you need at least a 5s 3000. I will upload a log file from back in may when I first started experimenting with Alan Resinger 3 blade props This is a 4s setup but you will see my average amp draw is about 30 amps at 10300 rpm and I peak at about 50 amps in maneuvers. With a 5s system the amp draw will be lower. My plane also weighs 65 oz. This was a test flight so I do peak the RPM a few times. I am using a Cobra 3520/10 which size wise is similar but its a 4 cell kv.
William
PS. I agree with you YOU CANNOT USE A 21 OZ BATTERY, BUT you can find 5s systems in the 10.5 to 14 oz range very easily which will keep your plane 56-60 oz.

[Matt Piatkowski]

William,
I have found my Watts.
A moment ago I bench run the Black Tiger with 13x4.5 APCE prop and 5S2600 battery and got the following readings:
1. RPM: 10320-10350
2. Current: 35-38 Amps
3. Voltage under load: 17.9-17.0 Volts
4. Power: (17V x 37A) = 630 Watts
5.Time of run: 3 minutes 50 seconds (!!)

The battery was completely drained in the end ( my meter reported 2715 mAh used - not good!).

630 Watts/11 Watts per oz = 57.3 oz - close to the target but I will not make it. Like you wrote, I would need larger battery. How much larger? 2700 seems to be sort of standard for many models but I will not make 5 minutes with it at these RPM. 10,000 with this pitch may not give me enough tension.

Hmm...

The entire electric system (motor, 5S,2600 mAh battery, ESC, prop, KR Governor, cables, velcro ) weights 24 oz. The battery standalone is 11.68 oz.

I have found on this forum that Peter German ( Location: LSZH) built some time ago 60.1 oz plane (Sultan-e) with AXI 2826/12 Kv=760 motor ( identical to my Cobra 2826/12) and used 5S 2600 25C battery, obtaining the total flight time of 5:20 and lap time 5.5s.

Perhaps going with 4250 motor requiring large and heavier battery to achieve 5+ minutes flights is not a good idea if my Cobra 2826/12 can fly 60 oz. RTF plane??

Decisions,decisions and more decisions.
Regards,
M

[Target]

I think you will see a large reduction in amp draw in flight....
Also, lower pitch uses more power. You might try a 12x5, or 12.5x 5, and that might also save some amps, and still accomplish what you want power wise.
My oriental is only drawing 19a and at 48 oz, averaging 314w, so 105w/lb, and I'm about to lower the on the ground rpm a touch.
Good luck. Give this a chance, I think you'll be pleased after getting dialed in. Nice not to clean the plane ever.
R,
Chris

[Dennis Toth]

Matt,
I think you are over estimating the flight rpm you need. The 4.5" pitch x 13" diameter only needs around 9200 - 9400 to do lap times that will get through the wind consistently. On paper you think you need to be 9800 plus rpm for the lower pitch but in actual conditions it needs less. Look in the "list your setup" and you can see what has been working for your expected size/wt ship.

RPM cost amps. This is the weakness in ECL. You are stuck with rather big jumps in battery pack size and weight. For your ship with the 2600 pack to get the 5.5 min flight with 20% headroom you need around 21 amps average max this would be a static draw of 26 ish.

Best,   DennisT

[Matt Piatkowski]

Hi Dennis,
Thank you for using numbers - this makes everything easier.
You wrote about two extremely important things: one is the ratio of the in-flight average current (lets call it Ai) to the static current (As), the other is the actual RPM needed to fly w/r to the theoretically needed RPM.

You wrote that Ai/As = 21/26 = 0.8

Some time ago, I started suspecting that this ratio is always constant for the electric C/L flight.
In other words, no matter what the motor, battery, ESC, prop. line length, lap time and the stunt plane geometry, this ratio always stays around 0.75-0.80.

Can we all call it a "The Law of 3/4 "? Using eLoggers will allow to verify this in any plane and collect the statistically credible data.

Using Eric Rule setup of KR governor, I got 24 static Amps at 9180 RPM of 13x4.5 APCE on my Black Tiger 4250C with 5S 2600 mAh 30C and thought is was not enough because 24 static Amps at 17.5 Volts under load translate to 420 Watts and 420 Watts translated to 420/11 = 38 oz. - not enough for the full size plane.

Comment: from Chris' response I calculated 6.5625 Watt/oz and this is only 60% of 11 watts/oz. I am using (!!!).

Perhaps 11 Watts/oz. ( 175 Watts/lb.) is excessive and I have based my entire calculation on the power requirements that are too high?

I have been using the bold numbers below ( from http://www.wattflyer.com/forums/showthread.php?t=24238), assuming that it must be unlimited performance and taking a buffer for the lines drag.
 
70-90 watts/lb. Trainer and slow flying aerobatic models.

90-110 watts/lb. Sport aerobatic and fast flying scale models.

110-130 watts/lb. advanced aerobatic and high speed models

130-150 watts/lb. Lightly loaded 3D models and ducted fans.

150-200+ watts/lb. Unlimited performance 3D models.

If, following Chris' numbers, I start using 6.5625 Watts/oz. instead of my 11 Watts/oz., the entire problem I had with the Black Tiger 4250C lack of power is gone and I not only have more than 5 minutes of flight on 2600 mAh battery but also can fly 60+ oz. plane easily with ~9,300 RPM with Ai=21-22 Amps.

Guys...this is extremely interesting and important for me to hear WHAT IS THE AGREED UPON NUMBER REPRESENTING THE ACCEPTABLE, AVERAGE POWER CONSUMPTION PER WEIGHT OF THE PLANE IN THE C/L STUNT.

Thanks,
Matt

[William DeMauro]

Matt,
  I'm sorry I'm not better at explaining the numbers thing but I do know what works and what doesn't. I did forget to mention that the numbers do drop in flight as the prop unloads. I never bench test with my "fly" prop I always drop it a size or 2. I would still watch my usage with the 2600 mah pack. Remember you only want to use about 80% out of the pack in flight. If it takes much more than 2100 then you may have to consider a larger capacity pack.
William

[Target]

I think it's always good to have a slight excess of power available, and in fact the kr timer has the gain function to give a boost when loaded on maneuvers.
I would think however, that 420w would fly the plane. It seems about on line with my smaller plane running at 314w average. (Actually, exactly on line for a 4lb plane vice my 3lb example)
I'm curious about your voltage, it seems a little low for 5s, but maybe it's about right. I can measure my 4s pack with my watt meter if you want and see what the sag is loaded.
I'd like to be helpful if I can.
R,
Chris

[Matt Piatkowski]

My no load voltage just after the 5s 2600 mAh battery is fully charged is 21.00 Volts and all cells are charged exactly 4.2 Volts.
17.5 - 17.6 Volts is the total average battery voltage after the motor started running and reached the operational RPM I set using the KR governor.
Operational RPM yesterday: 10320-10350
Current: 35-38 Amps
Voltage range under load: 17.9 (just at the beginning of the run) to 17.0 Volts ( shortly before the RPM went down in the end of the run)
Power (conservative calculations): (17V x 37A) = 630 Watts
Time of run: 3 minutes 50 seconds (!!)

After Chris' revelations ( "My oriental is only drawing 19a and at 48 oz, averaging 314w, so 105w/lb, and I'm about to lower the on the ground rpm a touch") I know now that I do not need such high RPM and current.

Chris, could you please confirm the 105w/lb value that translates to 6.5625 Watt/oz?
This is the most important number that defines everything in my future large plane.
Regards,
Matt

[Target]

I think I'm actually down into the sub 100w/lb category.
Maybe my math or technique is incorrect, please follow my findings below-
Plane has a 4s 2500 pack.
My timer is set for 5m30s (330s)
My batteries are taking 1650ma to fully charge after each flight.
That means 300ma/min, 18a/hr. So, my average pull is 18amps.
My glow engine loving flying buddy flies the full stunt pattern on this draw.
18a x 16.8v (max voltage possible from my packs) = 304w
My plane is 48oz rtf with the pack aboard.
So, if all that makes sense, I'm at 101w/lb average for a stunt flight.
I'm using a 10x5 apc tractor prop, not sure what the take off rpm is, but my laps are 5s on 60' lines.
We intend to lower the rpm a little too slow down a tiny bit, then come up on the gain a click or two (currently at default of 4) for a bit of boost in maneuvers.
I can hook up the watt meter if you want, but I'm sure static will be different than the easy cruise we appear to be getting in the air.

[Matt Piatkowski]

I am pleased to inform that the problem with the Black Tiger 4250C combo has been solved.

Firstly, I have to apologize to Eric Rule (RSM Distribution) for doubting the quality of his stuff.
It was my mistake to use the wrong Power/Weight parameter and, consequently, to expect about 40% more power from the electric setup.

The Power/Weight parameter I used in my calculations and initial sizing of my next three electric planes was 11 Watts/oz. (176W/lbs).
(ref: http://www.wattflyer.com/forums/showthread.php?t=24238)

At the time I discovered this number, and it was about three months ago, I knew very little about electric C/L flight and 11 Watts/oz seemed reasonable while expecting "the unlimited 3D aerobatics" including the drag effect of the lines.

Since August 2015, I have learned a lot and gathered practical experience flying my experimental paper and foam Little Great White (LGW) with Cobra 2808/22.

I have also purchased new engines and electric motors and the complete electronics package to check and test whatever requires checking and testing.

Purchase of the Black Tiger 4250C with the rest of the 61-74 class combo from RSM Distribution was the last step to be properly equipped before "building and basement life" season ( alternate name: winter) in Toronto.

I would like to thank many people who shared their electric setup data with me but special thank you goes to Chris Behm and Keith Renecle who provided their Power/Weight parameters.

The low number is 101 Watts/lbs (6.3125 Watts/oz.), the high one - 130 Watts/lbs. ( 8.125 Watts/oz.).

Now, I can easily match my electric motors to batteries and future planes.

Two static tests today using Black Tiger 4250C with 5S 2600mAh 30C battery, 13x4.5 APCE pusher, 60Amps ESC and KR Governor.
Initial voltage = 21.00 Volts
RPM = 9430 - 9450
Static current = 28.8 - 26.7 A.

Comment: using my "Law of 3/4", the average in-flight current of whatever is flying C/L stunt will be 0.75-0.80 of the static current, in this case 21.6 to 23.04 Amps and  20 to 21.36 Amps. I feel the 0.75-0.80 is a constant of the electric stunt.

Time of run achieved: 5.0 minutes with proper warning in the end.
Battery capacity used: 2350 MAh ( 90%) - a little high.

Black Tiger 4250C electric setup above will competitively fly any stunt plane having 59-60 " wings span, 630-700 sq. inch. wings and flaps area and RTF weight 59-64 oz.

Regards,
Matt
 

[Target]

That all sounds pretty reasonable, Matt.
I suspect you may record even lower numbers, especially if you drop some diameter and add some pitch (may not be ideal for what you're after).
I'm 99% certain that I'm not getting the full 4.2v/cell to my motor, so that puts my watt figure even lower.
I haven't tried a larger diameter prop with less pitch, but from what I'm told, less pitch and higher rpm draws more amps...
So far, I'm perfectly happy on the 10x5, so I'm not inclined to change what appears to work really well.
I'm interested in your findings with the black tiger. I'm sure it will serve you well, Eric has a terrific work ethic, so you can trust whatever he sells and recommends.
I hope to build a larger stunter in the next year or two. It'll need a similar power plant.
Regards,
Chris