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Need some help with a conversion

Old 09-10-2018, 02:31 PM
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Snoopy47
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Default Need some help with a conversion

I have a vintage Jemco P-47 that used to be glow. I am thinking of trying electric for the first time. Can anyone tell me what all exactly I will need to do this conversion? It is a 54" wingspan, .40-.60 size glow engine with retracts.

Thanks,
ZM
Old 09-13-2018, 11:22 PM
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Joseph Frost
 
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Get yourself "Eflite46" motor or similar, 80-100Amp/ESC and couple of 5 or 6S/4000/50C+mA batt, subj. to what size prop you like to spin, you'll be laughing!
Old 09-14-2018, 06:00 AM
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Originally Posted by Joseph Frost View Post
Get yourself "Eflite46" motor or similar, 80-100Amp/ESC and couple of 5 or 6S/4000/50C+mA batt, subj. to what size prop you like to spin, you'll be laughing!
Sounds good. I will probably give that a try. Laughing???
Old 09-12-2019, 05:50 AM
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Know the prop clearance available and choose the correct motor with the proper KV for most efficient operation.
This is where buying a "one size fits all" such as the Eflight 46 may not be the best choice.
Check with Lucien Miller at innov8tive designs for advice on a motor with the proper KV.
Innov8tive Designs/Scorpion products
Old 09-12-2019, 05:58 AM
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Snoopy47
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Originally Posted by jollyroger View Post
Know the prop clearance available and choose the correct motor with the proper KV for most efficient operation.
This is where buying a "one size fits all" such as the Eflight 46 may not be the best choice.
Check with Lucien Miller at innov8tive designs for advice on a motor with the proper KV.
Innov8tive Designs/Scorpion products
Thank you. I will check with them,.
Old 09-12-2019, 01:38 PM
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ron_van_sommeren
 
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Originally Posted by Snoopy47 View Post
... .40-.60 size glow engine with retracts. ...
Careful, engine↔motor cubic inches equivalencies restrict your choice of motors needlessly, motors are more versatile than engines. Ignore shops that try to give you advice that way, they don't know their business.

Plane type and mass are leading when choosing power. See quote below.

Planes don't care about voltage or Kv. They care about power though, bigly.
Choice of voltage mainly depends an what you already have, and on what equipment is available.

Below an excellent quote about motor selection.
From
brushless motors Kv?.
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. On the other hand, 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, e.g. limited prop diameter, if it's a pusher configuration, or if you already have a bunch of 3S packs and don't want to buy more, and so on.

Minor lay-out changes by RvS

Last edited by ron_van_sommeren; 09-13-2019 at 12:17 PM. Reason: Ignore engine -> Equivalancies
Old 09-12-2019, 03:45 PM
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46 still hanging on.
Quote-Ignore enginemotor cubic inches equivalencies, they restrict your choice of motors needlessly. Ignore shops that try to advice you that way, they don't know their business.
Ignore people who never fly and don't know anything about flying! Best advice, visit your flying field and ask the for help from the ones that know what they are doing.
Old 09-13-2019, 05:06 AM
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Great info guys. Thank you. I will pursue my needs based on the info in post #6.
Old 09-13-2019, 10:51 AM
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Originally Posted by Snoopy47 View Post
... .40-.60 size glow engine ...
I added that quote to my earlier post to clarify what I was referring to with regard to ic-engine↔e-motor equivalencies being too restrictive.

Originally Posted by jollyroger View Post
... Check with Lucien Miller at innov8tive designs for advice on a motor with the proper Kv.
Innov8tive Designs/Scorpion products
Lucien does all the testing himself, he knows his business, you can take his motor-prop numbers to the bank

And there are also (garbage in, garbage out)
e-flight calculators (compilation) - RCG
E.g. eCalc, DriveCalc, ScorpionCalc c.s., MotoCalc.

Originally Posted by scirocco View Post
... Decide your peak power requirement based on the weight of the model and how you want to fly it. ...
Plane type and mass are leading when selecting power (in watt). Hence these rules of thumb for electric power:
Magic numbers for e-flight - WFF

Note that Kv (in rpm/volt) says absolutely nothing about motor max.power, max.current, torque, efficiency.
Kv only depends on desired rpm and battery voltage. It does effect current and power drawn greatly though, both are proportional to Kv cubed.

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Last edited by ron_van_sommeren; 09-13-2019 at 12:29 PM.

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