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Dec 16, 2015, 04:34 PM
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Converting Gas Planes to Electric?


Just getting back into the hobby after about 18 years. I've got three kits that I assembled most of. Well two that I almost finished and one still in the box. The first is a PT40. The second is a P51 Mustang Funscale. Can't remember the brand name but it's also sized for about a .40 engine. I have no real interest in flying gas so I was thinking about converting them to electric, since the technology has come so far. My question is basically, is this a common thing or a waste of time? I built them so I'd like to fly them, but if it makes more sense to sell them as-is and then build electric equivelents then I'd do that instead. But hey, they're already built. Thanks for any help on this in advance.

Oh, the third is a Piper Cub kit, still in the box. I'd probably just sell that but not worried about that right now.
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Dec 16, 2015, 04:43 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Vriendelijke groeten Ron
Dec 16, 2015, 04:45 PM
aka: A.Roger Wilfong
gnofliwr's Avatar
Yes, it's very common; although less since more planes are designed explicitly for e-power. Check out the glow to elecyric forum, https://www.rcgroups.com/glow-to-ele...nversions-247/ , yo may find a thread on your specific plane.

Also check out Ken Myer's EFO web site, http://theampeer.org/ , for help on selecting a power system. BTW, you select a power system (motor, prop & battery) with electrics, not just a motor as you would for glow.

Lastly, this forum is a great resource. Questions usually get a plethora of answers.

Welcome back, and good luck with the conversions.

- Roger
Dec 16, 2015, 04:57 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by retrodog
Just getting back into the hobby after about 18 years. ...
... since the technology has come so far.
Please, do your RC equipment, wallet, ego, house/garage/car a big favour ... get a watt-meter. It will more than pay for itself, will save you at least one fried motor and one fried controller. Will also help you finding the best setup.


Some reading for rainy/windy days. Will save you, and us , a lot of questions.
Will also prevent you from burning up several controllers and/or motors and/or battery.
  • Advice for Getting Into Flying Radio Controlled (RC) Airplanes - The Ampeer
  • Gibbs Guides
    → Articles
  • E-flight 101 by RCG member Ken Myers, will at least save you a ruined LiPo (or worse!), a burnt motor and a fried ESC:
    The Ampeer

    → Articles: Electric Power Basics (Ken Myers)
    Table of Contents, a.o.
    • Recommended First Purchase - Power Meter & How to Use it
    • About Chargers & LiPo Batteries
    • Power Lead Connectors and Wire
    • Brushless Electronic Speed Controls (ESC) Basics, LVC and BEC
    • Motors for Electric Flight, Kv, Timing, Efficiency, Props
  • Excellent watt-meter instructions and explanations, about charge, current, voltage, resistance, power, energy
    www.rc-cars-planes.com/docs/wu100v2_user_manual.pdf
    Chapter 4 Basics of electricity
    → page 7-10
  • The Ampeer
    → Articles: Everything youw wanted to know about e-flight (Ed Anderson)
    Table of Contents, a.o.
    • What You Need To Know About Receivers
    • Battery Basics, Battery Chargers
    • Amps Versus Volts Versus C
    • Understanding the Electronic Speed Control (ESC)
    • Sizing Power Systems for Electric Airplanes, Prop Versus Amps
    • What Do the Kv Numbers On Motors Mean?
    • Who Needs a Wattmeter/Powermeter?
      (Everyone! But don't buy one if you plan on sponsoring motor and ESC manufacturers RvS)
  • Simulator, lets you play with throtle, voltage, current, resistance, power, capacity (Ah), load etc.
    www.rc-electronics-usa.com/ammeter-simulator.html
  • Pleasepleaseplease, do your RC equipment, wallet, ego, battery, controller, motor, house/garage/car a big favour ... get a watt-meter. It will more than pay for itself, will save you at least one fried motor and one fried controller. Will also help you finding optimal setup.

    E-calculators get you in the ball park. Without a watt-meter you are in the dark. Until something starts to glow
  • 'Multiple choice' wiring diagrams, charger selection tools, instructive demo's, calculators ...
    Script Asylum

    → RC calculations
    → electrical
    system wiring
    respectively ...
    LiPo pack wiring
    respectively
    chargers (2 menu items)
    The other menu items and demos are also veeeeery handy/instructive for e-folk, add site to your favourites?

    Brian G. pulled the plug on his ScriptAsylum site, I copied it.
    Statement:
    www.rc-monster.com/forum/showthread.php?p=431754
  • It is a good practice to have some headroom built in ...
    About derating motors, controllers, and batteries, electronics in general:
  • Motorcurrent does not behave like the current through a simple resistor. E.g. double voltage and current will quadruple.
    • extra current with one or two cells added, simple table
    • Motor/battery-current is proportional to voltage squared and proportional to Kv cubed ! Way more than one would expect, a disproportionate increase in current and power. (Worst case, ignoring voltage losses/sag due to the higher current ).
      Whether motor can handle those current- and powerlevels is a different story.
    • A motor's Kv constant says nothing about ... max.current and max. power a motor can handle, it is no indication for efficiency, rpm, quality, torque, propsize etc. Kv is only about matching prop rpm and battery voltage.
    • Simple instructive table giving the extra current when you add one extra cell to a pack
      (a.k.a. "why did my motor and/or controller and/or battery go up in smoke ???")
      Another excellent explanation.
    • The Kv motorconstant is not a rating, not a figure of merit, in that higher or lower is better, it's just a characteristic. More windings will give lower Kv, less windings will give higher Kv, that's all there is to it. No big deal, anyone can rewind a motor with more (thicker) copperwire. Will give you a more efficient (Pout/Pin), more powerful and cooler running motor.
    • Motors have just one Kv, not e.g. 1400Kv's.The motor Kv constant is a physical quantity (length, weight, time, current, ...) measured/expressed in rpm/volt. It is not a physical unit (meter, kg, s, ampère, ... ). Therefore, Kv=1400rpm/volt.

Vriendelijke groeten Ron
p.s. took some liberties with the tables of contents, they are abridged/compacted a bit.
Last edited by Ron van Sommeren; Apr 05, 2019 at 04:35 PM.
Dec 16, 2015, 05:41 PM
Registered User
Thread OP
Thansks for the info and links guys. just what I needed. I've got a little research to do. I'd like to use the planes since I spent so much time assembling them... years ago. My first plane was actually an electric. I think it was a Mirage 550, if memory serves.

My background is an Electrical design engineer for over 32 years. And I work for one of the big airplane companies so I never get too far away from aviation in one form or another. Although the last 24 years has been on the space station. And it doesn't really fly so there's that. Anyway, lots of new stuff to learn so thanks for all the help. Much appreciated.
Dec 16, 2015, 06:45 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Keep in mind that planes designed for IC power are designed for a motor hammering away at the airframe, they weigh more than when designed for e-power. Try to lighten your planes if/where possible.


  • Motorcurrent is proportional to voltage squared, Ohm's law does not apply,and proportional to Kv cubed!
    Motorpower is proportial to voltage cubed.
    Way more than one would expect. Worst case, ignoring voltage losses/sag due to the higher current. Whether motor can handle those current- and powerlevels is a different story.
  • Simple instructive table giving the (worst case) extra current when you add one extra cell to a pack
    (a.k.a. "why did my motor and/or controller and/or battery go up in smoke ???")
    Always check current with a watt-meter, it will pay for itself, and will help finding the best setup.
    In depth discussion
    www.theampeer.org/ampeer/ampnov15/ampnov15.htm#ADD
  • Both a 10watt motor and a 10kilowatt motor can have the same Kv motorconstant.
    A motor's Kv constant says nothing about ... max.current and max. power a motor can handle, it is no indication for efficiency, rpm, quality, torque, propsize etc.
  • The Kv constant is not a figure of merit, in that higher or lower is better, it's just a characteristic. More windings will give lower Kv, less windings will give higher Kv, that's all there is to it. No big deal, anyone can do that.
    Rewinding a motor with more (thicker) copper will give you a more efficient (Pout/Pin), more powerful and cooler running motor.
  • Motors have just one Kv, not e.g. 850Kv's.The motor Kv constant is physical quantity (length, weight, time, current, ...) measured/expressed in rpm/volt. It is not a physical unit (meter, kg, s, ampère, ... ). Therefore, Kv=850rpm/volt.
Vriendelijke groeten Ron
Last edited by Ron van Sommeren; Dec 16, 2015 at 06:53 PM.
Dec 16, 2015, 09:31 PM
Registered User
E-Challenged's Avatar
There is a separate forum for converting IC models to electric power. Choosing the right size of brushless motor, speed control, battery pack and propeller is a complex question. You can get advice from Lucien Miller on his thread on the Power Systems forum. There are free download software programs to help you choose the right power system based on model parameters and desired flight performance. Many of us simply copy what others have used successfully in similar models. E-Flite has some IC to electric motor equivalency information on their website. There are crude rules of thumb i.e 75 watts per pound for trainers, 100 watts per pound for scale models, more watts per pound for aerobatic models, etc.
Generally brushless motors and battery packs weigh less than IC engines and fuel, so it's necessary to locate motor batteries and RC gear more forward to minimize need for nose ballast. Try to keep tail structure as light as practical for the same reason. I don't know of any good books how to convert IC powered models to electric power. I helps to be an experienced electric powered model builder first and then take on converting models to electric power.

Most IC powered model structures do not have convenient motor battery compartments and access hatches. It is usually necessary to modify the top nose structure to add a battery compartment and hatch (or) to remove the wing to change battery packs (or) invert the model and access the motor battery from a hatch in the bottom of fuselage.
Last edited by E-Challenged; Dec 18, 2015 at 12:47 PM.
Dec 16, 2015, 11:56 PM
Registered User
scirocco's Avatar
If you can tell us how much the models weigh (just airframe with servos will do) and what the max prop diameter that fits with ground clearance that you're comfortable with, we can give you lots of options.
The hardest part will be for you to figure out battery location and access
Dec 17, 2015, 06:02 AM
Learn to build with wood.
Tucci's Avatar
The PT40 is easy. 46 sized electric (Hobby King G46 or equivalent), 4 cell lipo and 12x8 or 13x6 prop. Easy conversion too.


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