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WWI Era Discuss all your favorite WWI warbirds here!

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Old 05-11-2017, 05:57 PM   #1
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Default Electrifly 1/4 Eindecker Style

Hi,

My project : A 95"/1550 sq in/15 lbs (in flight order, I hope so) monoplane !
It actually just needs a prop and motor and have no really clear idea about what should work.
I want it scalish so don't need extra speed with plenty of flight time.
Some of you, thinking of Ron, like a 6S motor G160-245 (or SK3) with a 25% wingspan prop (23"in my case)

So feel free to share your experience
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Old 05-13-2017, 08:04 AM   #2
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Here it is.


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Old 05-17-2017, 07:15 AM   #3
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Hi

I obviously made a mistake choosing this forum having met not much interest.
So I think I should have a try in the "Power systems" perhaps better suited to my needs
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Old 05-17-2017, 03:31 PM   #4
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The entries in scirocco's blog will surely help you
www.rcgroups.com/forums/member.php?u=3045

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Old 05-17-2017, 05:45 PM   #5
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Thanks Ron for your link, appreciate !
By the way, according to you does the principle of a big prop (22") linked to a small pack (6S) seem a good means for scale flying this thing ?
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Old 05-18-2017, 07:33 PM   #6
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(I have asked the moderators to move this thread to the Power Systems subforum (via click on the icon, report post).

Going to higher cell numbers reduces the current through battery, wire, controller and motor. But this lower current only effects wires and controller. Less losses in wire, connectors and controller.

For battery- and motor-choice the lower current makes no difference.
  • Battery
    System voltage has little effect on choice of required battery energy and on battery mass, e.g. with a 6s pack you would need 5000mAh capacity, with a 12s pack you would need 2500mAh capacity.
  • Motor
    A 6s pack with a motor wound for say Kv=300rpm/volt and a 12s pack with a motor wound for Kv = 150rpm/volt behave the same as far as motor rpm, power, current, temperature and efficiency are concerned.
    (Provided both versions of the motor have the same amount of copper.)

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Old 05-18-2017, 07:36 PM   #7
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Kv is only about matching system voltage and desired rpm, it says nothing about max motor.power or max.current.

Originally Posted by scirocco View Post
While an absolutely critical part of the system ...
Kv is actually the item one should choose last.
  1. Decide your peak power requirement based on the weight of the model and how you want to fly it.
  2. Pick a preferred cell count (voltage) and pack capacity for how to deliver the power.
  3. Pick a prop that will a) fit on the model and b) fly the model how you want - often as big as will fit is a good choice, but if high speed is the goal, a smaller diameter higher pitch prop will be more appropriate.
  4. Look for a size class of motors that will handle the peak power - a very conservative guide is to allow 1 gram motor weight for every 3 watts peak power.
  5. Then, look for a motor in that weight range that has the Kv to achieve the power desired with the props you can use - a calculator such as Ecalc allows very quick trial and error zooming in on a decent choice. For a desired power and prop, you'd need higher Kv if using a 3 cell pack compared to a 4 cell pack. Or for a desired power and cell count, you'd need higher Kv if driving a smaller diameter high speed prop compared to a larger prop for a slow model.
The reason I suggest picking Kv last is that prop choices have bounds - the diameter that will physically fit and the minimum size that can absorb the power you want. OTOH, combinations of voltage and Kv are much less constrained - at least before you purchase the components.

So Kv is not a figure of merit, in that higher or lower is better, it is simply a motor characteristic that you exploit to make your power system do what you want, within the constraints you have, eg limited prop diameter if it's a pusher, or you already have a bunch of 3S packs and don't want to buy more, and so on.

Minor lay-out changes by RvS

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Old 05-19-2017, 06:52 AM   #8
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Thanks Ron !

Great links especially the Noflyzone's mini how to !
My thinking is to begin the process with the size of the prop as you want it big enough to fit the scale of your model and for WWI aircraft biggest is the best.
From this statement it appears that a low voltage pack is the answer to low speed flights with a low wing loading.
Too bad WOC is no more available : is there something in the same spirit ?
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Old 05-19-2017, 09:12 AM   #9
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Sorry PandaE ....

Wattflyer is your best place for this sort of discussion and Power listing might be appropriate.

OK ... lets look at some fundamentals ...

You are building a 95" Eindecker. This is a slow flying high lift machine. It would be best to have a high thrust low rpm type prop. That means a large diameter and reasonable pitch. To accommodate such prop as you guessed is best with a low KV motor.

I put your data into eCalc and the attached is the output using the G160-245 motor.

OK ... I am at odds with a statement put out earlier .... increasing Volts does NOT automatically mean LOWER amps ... in fact it leads often to INCREASED amps as the motor is forced to work harder to swing the prop at the increased RPM created by the higher volts to KV factor.

eCalc shows that a 6S pack and a 20 x 12 wood E prop would fly your Eindecker ...

Please note that often eCalc underestimates flight results - so if it says it will fly - there's a 99.9999% chance its good to go and BETTER than listed.

It is well worth the few cents to register with eCalc and you can play around with numbers / settings to arrive at your needful. The beauty of such program is you don't need techno babble ... you just put in the numbers and press "calculate" ....

I will be following this thread to see how you get on ...

Nigel


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Old 05-19-2017, 01:39 PM   #10
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Originally Posted by solentlife View Post
Sorry PandaE ....


You are building a 95" Eindecker. This is a slow flying high lift machine. It would be best to have a high thrust low rpm type prop. That means a large diameter and reasonable pitch. To accommodate such prop as you guessed is best with a low KV motor.
I put your data into eCalc and the attached is the output using the G160-245 motor.
eCalc shows that a 6S pack and a 20 x 12 wood E prop would fly your Eindecker ...

Please note that often eCalc underestimates flight results - so if it says it will fly - there's a 99.9999% chance its good to go and BETTER than listed.
Nigel
Hi Nigel,

I already work with E-Calc and I get of course same results as yours.

Now since I have a good margin for prop clearance, I would look for something bigger if I follow Noflyzone'rule :
("The only thing left for us to do now is measure how much ground clearance we have for our plane's prop. And this is going to determine just how big a prop we can stick on our plane. Why? Because we want the largest diameter prop that will fit on our plane! Ideally, we want a prop with a diameter that is about 1/4 the wingspan of our plane".)

Not so easy now if we want to keep a safe pitch speed with a 1/4 Wingspan 23" prop.
As said before target is the biggest prop with the smallest power for flying
safe of a steep bank stall.
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Old 05-19-2017, 02:21 PM   #11
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Problem you are getting here is falling foul of Pitch Speed vs Flight Speed as you probably saw with the 23" prop and lesser pitch. You need to up the motors KV to counter the pitch problem ... which in turn means power.

It is always a compromise but I find that I can 'stretch' eCalc results.

My Zlin gace results of about 0.9Power to weight and 4.5 mins flight on the 6S and 5050 motor ... 15x10 prop.
It actually climbs into the clouds without stop ... flies for nigh on 9 mins with throttle use ... on those items.

So get near to what you want in eCalc and its likely you get actually what is asked.

Nigel

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Old 05-19-2017, 02:31 PM   #12
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Now, what do you think of this 1/4 BUSA DR1 , it seems incredible

"If you are 15 pounds, the G110, or the E-flite Power 110 will be way more than enough power for you . I have forgotten exactly, but I believe scale prop size is 24"
At 24" on 6 cells, you could use 24X10 E-flite Power 160 and 6 cells. That combination flew my DR1 for a season, until I obtained the 63/74. the only reason I put the 63/74 in was because I wanted to swing a scale sized prop....the Power 160 was more than enough power.... prop was just too small for scale.
"
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Old 05-19-2017, 05:47 PM   #13
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If he says it works ... who am I to argue !!

To be honest I was having trouble finding a combo to work with the 23" based on 6S ...

Nigel

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Old 05-19-2017, 06:00 PM   #14
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Originally Posted by solentlife View Post
If he says it works ... who am I to argue !!
To be honest I was having trouble finding a combo to work with the 23" based on 6S ...
Nigel
The same.
It would be great to have Ron from Canada to give us more details about his way of powering his DRI.
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Old 05-20-2017, 02:48 PM   #15
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Originally Posted by PandaE View Post
... From this statement it appears that a low voltage pack is the answer to low speed flights with a low wing loading. ...
Not necesarily, low(er) rpm is what you need, and that can be achieved by lower voltage and/or lower Kv.

Originally Posted by solentlife View Post
... OK ... I am at odds with a statement put out earlier .... increasing Volts does NOT automatically mean LOWER amps ... in fact it leads often to INCREASED amps as the motor is forced to work harder to swing the prop at the increased RPM created by the higher volts to Kv factor. ...
Of course, for a given motor, motorcurrent is proportional to voltage squared and proportional to Kv cubed .

However, my answer in post #6 deals with post #5 about choosing a system voltage, before choosing a motor, for a given performance, rpm, power. In extremis, just for the fun of it, there would be no difference between 0.1volt and 1000volt systemvoltage as far as choice of motor (only needs different number of windings) and choice of battery-energy are concerned.

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Old 05-25-2017, 06:43 AM   #16
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Hi

I'm looking at this motor : Sk3 6354-260 from HK with a 22x12 prop on 6S 5000 mAh.
Could some one test this set through motocalc and tell me what he gets
Thanks for your help !
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