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Old Jan 31, 2013, 11:56 AM
Fylingdales Flyer
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Yorkshire Coast. United kingdom
Joined Apr 2008
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Similar in size to the Halfax Spartan and Simplex, my Flair Junior 60 is equipped with an Axi 2820/10, Jeti Eco 40 Esc and a 3S 2,300 LiFe battery which gives about 10 minutes flight with an APC 12x6 Electric propeller.
My Ben Buckle Southerner 60 has an exactly identical power train, but is waiting for suitable weather for the maidan flight.
Graham
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Old Feb 18, 2013, 12:37 PM
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Canada, ON, Hamilton
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What Size Motor Do I Need?

What Size Motor Do I Need?

See

http://www.rcgroups.com/forums/showt...even+aeromodel


2000 watts per cubic inch is a good average.

.049 Glow = 98 watts of input power

.10 glow = 200 watts of input power

.25 glow = 500 watts of input power

.40 glow = 800 watts of input power

.45 glow = 900 watts of input power

.60 glow = 1200 watts of input power

.90 glow = 1800 watts of input power and so on.
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Old Feb 18, 2013, 03:06 PM
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Converting ic into watts can get complex, take a look at this chart on the.049 glow http://www.rcgroups.com/forums/showp...23&postcount=4 The tee dee has twice the output of the babe bee, so if the chart says a .049 has x watts output which 049 do they mean .
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Old Feb 18, 2013, 08:06 PM
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For too many people the mere mention of watts become either the scare or put off. Shouldn't be but unfortunately this glazed look appears over faces no matter how basic (those of us who know) the explanations are.

I suppose I'm either lucky or too much of a nerd but after 20+ years of electrics I just know what I'll fit in a model. So, the easiest way I now do it for local fliers is to recommend a specific set up or suggest looking on the Hobby City site, choose their appropriate "engine equivalent" sizes and then pick one that will handle your proposed prop size, battery preference and pocket.

These suggestions are not always optimum but invariably get the flier into the air with success. Once he has got a handle around his first or second electric the light will (with luck) hopefully come on and he/she may make better selections as time and models progress.

And no, I don't understand why electric should seem to be such a black art.
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Old Feb 18, 2013, 09:05 PM
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Quote:
Originally Posted by David Hipperson View Post
For too many people the mere mention of watts become either the scare or put off. Shouldn't be but unfortunately this glazed look appears over faces no matter how basic (those of us who know) the explanations are.

I suppose I'm either lucky or too much of a nerd but after 20+ years of electrics I just know what I'll fit in a model. So, the easiest way I now do it for local fliers is to recommend a specific set up or suggest looking on the Hobby City site, choose their appropriate "engine equivalent" sizes and then pick one that will handle your proposed prop size, battery preference and pocket.

These suggestions are not always optimum but invariably get the flier into the air with success. Once he has got a handle around his first or second electric the light will (with luck) hopefully come on and he/she may make better selections as time and models progress.

No, and I don't understand why electric should seem to be such a black art.
Alot has to do with where you started. If your roots are in glow-powered models then you also dealt with higher wing loaded models of the same era. IC engines also have relatively narrow power bands (as compared to BL electrics) which combined with this generation of heavier models made glow people 'sensitive' to engine choice. If you made a less than ideal IC choice you would often end up with a model that barely flew (if IC too small) or a lead-sled (if too big). With BLMs and Lipos and the associated lighter airframes, you can put a much wider range of electric power systems in any model and get excellent performance. Significant performance changes from there can be had simply by changing prop and/or cell count. If anyone doubts this, witness the size range (extremely small and large models) and model types powered routinely by electric systems that where only dreamt of in IC only days
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Old Feb 18, 2013, 09:49 PM
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You’re correct Colin. There can be a big difference between engines having similar displacement.
My friend and myself each built a small “Wild Thing”. He had an Enya .15 (2.5 cc) and I had the faster Webra Speedy 1.8cc.
Small Cox Baby Bees seem to produce more power if allowed to rev on a smaller prop. A 5x4 will give more thrust than a 6x4 on mine. I flew my reed valve “Space Hopper” U/C on 42 ft lines. It put out close to 16 oz static thrust. A great little engine. Regardless of what engine you use, it’s really hard to beat the throttle response of an electric.
Good comments David and John.
Yes, the electrics are built lighter and can operate with perhaps a wider power range. Looking back, my glow powered models that were built on the lighter side always were more enjoyable to fly. Using the Wild Thing for an example, it had 350 sq in wing area. One built and flown with a Cox .09 at 30 oz was a lot more friendly than another weighing 35 oz and flown with an MVVS 2 cc engine (see Blue Flame in my blog).
I really don’t know why anyone flying an electric doesn’t have the amp/watt/volt meter that just plugs in after the battery. You know right away what power is being drawn and you should know what the power limits are of the equipment you are using, hence you should be able to balance everything up, at least to the point that you don’t over load it and burn it out.
John
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Old Feb 18, 2013, 11:43 PM
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Originally Posted by JohnAV8R View Post
....I really don’t know why anyone flying an electric doesn’t have the amp/watt/volt meter that just plugs in after the battery....
That's why I like to use ESC's like the Castle ICE. Built in logging tells you everything you need to know. Just give it a quick test and read the data.
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Old Feb 18, 2013, 11:54 PM
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I used to be an IC flier using diesels, sparkies, glow in both two stroke and four. I can't say I ever loved two stroke glows but four, yes and nothing beats the smell of a diesel. However once I changed to electric I never had a serious urge to go back to IC. I'm also no into trying to convert others. What you choose is your business.

In our club most of the people are IC fliers but a great number of them have one or more ARF electrics in the car along with their "normal" model(s). Because of this there is no friction between the club members. Curiously though a significant number of the IC fliers have spent little or no time on ensuring that their engines are at optimum. Too many seem to trail along with same fuel, same prop, same whatever. To be fair the engines are good enough to accept, more or less, anything thrown at them,

Does this mean that it isn't just a matter of not understanding electrics but bothering tio understand anything?
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Old Feb 19, 2013, 09:15 AM
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Could be. Just go out and “do it” the same old way every time. Don’t try something new. Then there are those that get a model working fairly well and are afraid a change will either cause a problem, not be worth the effort, or actually might cause a crash. It’s amazing that more modelers don’t even try different prop combinations!
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Old Feb 19, 2013, 09:27 AM
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Yes, different power from the same "size" ?

Yes, Colin, there can be quite a power spread across the same displacement engine. Same can probably be said for electrics. Just looking at the physical size may not tell you very much about the power. However, if you are familiar with one particular power unit, then you have a starting reference point. The next “step” could either be ahead, or backwards. You just won’t know until you take it.
John
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Old Feb 19, 2013, 11:59 AM
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It really is a state of mind I think. For me, the 'discovery' of new technology and how to use it effectively in new and different airplane projects is a very enjoyable and satisfying aspect of the hobby.

One of my best personal examples of how BLM & Lipos have changed what's possible is the Hobbyking 1875mm Memphis Belle B-17. Always had a love affair with B-17s and off/on over the last 2 decades seriously considered building a large gas/glow powered version but never did. A huge investment of time and money and you still have to be maticulous every time you fly it that all 4 engines are running perfectly or you could loose it. Even with all that, they would be heavy and fly at above scale speeds. Fast forward to 2 years ago. For roughly $225, I have a beautifully detailed, 6ft wingspan, lightly wing loaded scale flyer with virtually no worries of an engine or two quiting in flight; all because of BLMs and Lipos. If only to be a kid again with all this technology. Fortunately, I've a few years left (I hope) before my eye sight and/or wits go the way of the doo-doo bird
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Old Feb 19, 2013, 03:09 PM
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Quote:
Originally Posted by JohnAV8R View Post
Yes, Colin, there can be quite a power spread across the same displacement engine. Same can probably be said for electrics. Just looking at the physical size may not tell you very much about the power. However, if you are familiar with one particular power unit, then you have a starting reference point. The next “step” could either be ahead, or backwards. You just won’t know until you take it.
John
Yes John, I believe you are right,Adding more to this you can also have a vast power range from any 1 electric motor , I think it is better to have a motor slightly bigger than is needed and run it at a max of say 80%... this way it should last longer and the same for the esc. You are also right about having a meter to check amps.. watts.. volts etc, i use a watts up meter from HK for this. I fly my Playboy in Duration pulling about 600 watts with 4 cells and also fly Texico pulling only 75 watts with 2 cells with the same motor ( i also change the prop).

These figures are from my Playboy using my Watts Up meter
PROP AMP WATTS THRUST Oz
10 x 6 .. 21 .... 246 ..... 37
10 x 7 .. 22 .... 245 ..... 37
11 x 4 .. 17 .... 200 ..... 37 .. MOTOR TURNIGY 35X48.900Kv.
11 x 5 .. 22 .... 250 ..... 44
11 x 6 .. 30 .... 330 ..... 49
11 x 7 .. 33 .... 370 ..... 54 .. 3 CELL X 2200 Mah Battery
12 x 6 W. 31 .... 355 ..... 55
12 x 7 W .35 ....395 .....58
12 x 8 W. 42 .... 410 ..... 67



11 x5 .. 36 .... 540 ..... 70
12 x 6w . 44 .... 630 ..... 74 .. 4 cell x 1800 Mah Battery

11x4 .. 9.6 .... 75 ..... 17 .. 2 cell x 800
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Old Feb 19, 2013, 03:16 PM
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Quote:
Originally Posted by ColinNZ View Post
Yes John, I believe you are right,Adding more to this you can also have a vast power range from any 1 electric motor , I think it is better to have a motor slightly bigger than is needed and run it at a max of say 80%... this way it should last longer and the same for the esc. You are also right about having a meter to check amps.. watts.. volts etc, i use a watts up meter from HK for this. I fly my Playboy in Duration pulling about 600 watts with 4 cells and also fly Texico pulling only 75 watts with 2 cells with the same motor.

These figures are from my Playboy using my Watts Up meter
PROP AMP WATTS THRUST Oz
10 x 6 .. 21 246 37
10 x 7 22 245 37
11 x 4 17 200 37 MOTOR TURNIGY 35X48.900Kv.
11 x 5 22 250 44
11 x 6 30 330 49
11 x 7 33 370 54 3 CELL X 2200 Mah Battery
12 x 6 W 31 355 55
12 x 7 W 35 395 58
12 x 8 W 42 410 67



11 x5 36 540 70
12 x 6w 44 630 74 4 cell x 1800 Mah Battery

11x4 9.6 75 17 2 cell x 800
Great example of the range of models a single BLM/ESC can service. I have the same HK wattmeter; an invaluable tool for determining the output/efficiency of your setup

John
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Old Jun 30, 2013, 08:06 PM
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Canada, ON, Hamilton
Joined Oct 2005
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I tried one of these for indoor flying. Seems to work very well on a 2S 300 ma LiPo.


Small BL motors size and power listing .
Rim Fire
http://www.electrifly.com/motors/gpmg4505.html


RIMFIRE

RimFire 200


Description Stock No. Diameter Length
kV Constant Watts Burst Watts Weight Shaft Diameter (mm) Voltage Range
Sport 3D Power System Recommendation
ESC LiPo Prop
RimFire 200 GPMG4455 18 mm
(0.71 in) 18.8 mm (0.74 in) 2400 36 47 12.4 g
(0.44 oz) 2 mm
(0.079 in) 7.4 / 2S LiPo 177 g
(6.2 oz) 110 g (3.9 oz) 6 Amp 2S 7x3.5 electric


RimFire 250
Description Stock No. Diameter Length
kV Constant Watts Burst Watts Weight Shaft Diameter (mm) Voltage Range
Sport 3D Power System Recommendation
ESC LiPo Prop
RimFire 250 GPMG4502 28 mm
(1.1 in) 13 mm
(0.51 in) 1750 90 120 20 g
(0.71 oz) 3 mm
(0.12 in) 7.4-11.1V / 2-3S LiPo 225 g
(8 oz) 140 g (5 oz) 8 Amp 2S 7x6 to 8x4 Slow-fly
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Old Jul 01, 2013, 04:03 AM
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Must admit I'm guilty of using the old 'if it works stick with it' way of thinking. Advantage is I've never had any problems with any of my electric planes as it's all well tried and tested components.

I have a lot of electric outrunners...but they're all really only 2 types; ones I use in my 30" sports models and ones I use in my 36"-40" scale WW1 models, which is as big as I build.

I even stick to the same batteries! (400-800mAh in the 30" planes and 1000-1500mAh in the bigger ones). I do experiment with props though, so I'm not a total 'stick in the mud'..buying a Watts Up meter was the best thing I did.

This is a great hobby for tinkering though, isn't it

Regards
Harry
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