Electric RC Motors & Power Systems: Complete Selection Guide

Updated August 2026

An electric RC airplane power setup works as a system: motor, propeller, battery, ESC, BEC, wiring, cooling, and the airplane’s finished weight. You can’t safely choose one part without considering what it will do to the rest of the setup.

I’m going to walk through how brushed and brushless motors work, what KV and wattage actually tell us, what the ESC is doing, and how to put together a practical power system for anything from a trainer to an electric conversion.

Table of Contents

The Short Answer: How to Choose an Electric RC Power System

Start with the airplane. Write down its ready-to-fly weight, how much propeller clearance and battery room you have, and the way you want the airplane to fly.
Estimate the required power. Watts per pound will get you into the right range, but it’s only a starting point. It doesn’t prove that a setup will work.
Choose battery voltage and motor KV together. Cell count, KV, and propeller load all work together to determine the actual RPM and current.
Select the propeller from tested motor data. Going up in diameter or pitch can raise the current a lot more than you might expect.
Size the ESC and BEC with margin. Make sure it can handle the battery voltage and measured full-throttle current, has enough cooling, and has a BEC that can support the servos and accessories.
Verify the complete system with a wattmeter. Before you fly it, test the exact motor, propeller, battery, and ESC together.

One thing to keep in mind: Stay within the aircraft and motor manufacturers’ limits whenever they give them. Propeller load, battery condition, cooling, and even the way everything is installed can make two setups that look the same behave very differently.

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Frequently Asked Questions About RC Electric Motors

❓ What is KV in an RC motor?

KV tells us the motor’s approximate RPM per volt with no load on it. For example, a 1400KV motor supplied with 10 volts would have a theoretical no-load speed of about 14,000 RPM. Once we put a propeller on the motor, we’ve added a load, so the actual RPM will be lower. It will also change with the battery voltage under load, the propeller, the motor, and the rest of the installation. KV helps us match a motor, battery, and propeller, but that number by itself does not tell us the loaded propeller RPM or how much torque the motor will make.

❓ How many watts per pound do I need for my RC airplane?

It depends on the type of flying you want to do:

– Trainer: 80 watts per pound

– Sport: 100 watts per pound

– Sailplane: 80-150 watts per pound

– 3D: 200 watts per pound

– EDF jet: 200-300 watts per pound

These numbers are only rough starting points, not hard rules that fit every airplane. Multiply the airplane’s expected ready-to-fly weight by the appropriate watts-per-pound figure to get a starting target, then consider the aircraft type, propeller efficiency, desired performance, installation, and the aircraft and motor manufacturers’ tested data.

❓ What’s the difference between a brushed and brushless RC motor?

Brushed motors have physical carbon brushes inside that wear out over time and are less efficient. Brushless motors have no brushes, last much longer, run cooler, and are more efficient. Almost all modern RC airplanes use brushless motors. You can identify them by the number of wires — brushed motors have 2 wires, brushless motors have 3.

❓ What size ESC do I need for my motor?

Pick the ESC based on the current you measure with the actual motor, propeller, and battery—not just the maximum-current number printed for the motor. Stay within the motor, ESC, battery, and propeller manufacturers’ limits, allow a suitable safety margin, and make sure the ESC has adequate cooling. Verify full-throttle current with a wattmeter before flight; changing the propeller or battery can change current substantially.

❓ What is a BEC and do I need one?

A BEC (Battery Elimination Circuit) can power the receiver, servos, and accessories from the main flight battery, eliminating a separate receiver battery. Whether an ESC’s built-in BEC is suitable depends on its type and rating, the flight-battery voltage, servo count and current demand, accessories, cooling, and installation. A properly selected high-current switching BEC may be suitable even in a larger airplane; other installations use a separate BEC or a dedicated receiver battery.

❓ Can I convert my nitro RC plane to electric?

Yes! Electric conversions are very popular and not that difficult. The main steps are removing the engine, fuel tank, and associated plumbing, mounting the electric motor with a proper standoff distance, finding a good battery location, and — most importantly — rechecking and adjusting the center of gravity since the weight distribution will change.

❓ What battery do I need for my electric RC airplane?

Flight time depends on the average current you use during the flight, not just the motor’s maximum current or the current at full throttle. If you have a realistic average-current estimate, use: (flight time in minutes × average amps) ÷ 60 = amp-hours used. Allow a reserve rather than planning to use the battery’s entire rated capacity. If you use the full-throttle current in that formula, you’ll get a conservative example, not an accurate prediction of how long a normal flight will last.

Definitions

Before we describe electric motors and discuss how they work, we need to define some words we’re going to use so that we’re all clear on what we’re talking about.

Volts – a volt is the SI unit of electric force, the difference of potential that would drive one ampere of current against one ohm resistance. In simpler terms, a volt is what pushes the electrons through an object.
Current – an electrical current is the rate of flow of the electric charge that passes through a certain point.
Amps – an amp is short for ampere, which is the measurement of the amount of charge flowing through an electrical circuit over a period of time. Current is measured in amps.
Watts – a watt is equivalent to one joule per second. It’s a measurement of power, or energy per unit time. It measures how much actual electricity is being consumed by a device. A watt is equal to one amp under the pressure of one volt.
Resistance – simply put, electrical resistance is the measurement of an objects opposition to the flow of electric current. Resistance is measured in Ohms.
P = V*I – power(watts) = volts multiplied by current (amps)
E = P*T – Energy = Power(watts) x Time
Stator – the stator is the stationary part of an electric motor.
Rotor – the rotor is the rotating part of the motor.
Inrunner motor – On an inrunner motor, the rotor, or rotating part of the motor is on the inside, so you will normally only see the inner shaft spin when you spin an inrunner motor. Inrunners can normally spin much faster than outrunners and are mostly seen in smaller aircraft. These can be mounted from the front of the motor since the only part of the motor that spins is the shaft.
Outrunner motor – Outrunner motors are more common in bigger rc aircraft. With an outrunner motor, the center of the motor is stationary and the outside can rotates around the stator. These are generally lower revving motors, but they produce more torque which makes them great for spinning a propeller.

The Garden Hose Analogy

These terms are going to come up a lot in this article, so let’s try to explain these concepts. Having a basic understanding of this makes it easier to understand how our rc airplane electric drive system works. It’s a lot easier for me to grasp this stuff when I relate it to a garden hose, so let’s make some comparisons.

Volts are supplied by our battery. Volts are what pushes electricity. Think of volts as the pressure you have from your spigot before the valve is turned on. It’s the stored energy you have access to.

An amp is a measurement of current, so that will be the water flow through the garden hose. The higher your amps, the bigger your hose.

Resistance is going to be anything that slows down the water flow, so your spigot valve, the hose nozzle, and even the size of your garden hose, both diameter and length. This is measured in ohms.

You’ll also hear about voltage drop across wire. I saw a prime example of “water hose voltage drop” the other day when my wife was watering her garden. She just bought 3 – 50 ft sections of that expandable garden hose, the kind made out of the surgical tubing. She turned the hose on and all 3 of the hoses expanded to their full length and then she walked out to the garden with the nozzle.

As soon as she pulled the trigger on the hose nozzle, the hose started to shrink and get shorter and the pressure coming out of the end of the hose was lower. So the voltage, or the pressure of the water dropped because of the resistance of the garden hose, and because of that there wasn’t enough pressure to keep the hose fully inflated, or to keep the flow coming from the nozzle at the same rate. The longer the hose, or the longer the electric wire, the higher the voltage drop will be.

If she was watering with a 25 ft hose, the water flow at the end of the nozzle would be much greater than if she used her 150 ft hose, and if she connected more together to make it longer, the flow at the nozzle would be much less.

Electrical power is the product of the voltage and current, and is measured in watts. Think of watts as the amount of water that comes out of the end of our garden hose to water plants, but the water is measured in gallons instead of watts.

Brushed Motors

Brushed RC motor — A brushed motor. This one is out of an old Traxxas RC car.

Brushed motors only have a few parts, so let’s talk a bit about each one. They consist of stator magnets which are stationary and permanent magnets, and they are mounted inside the shell of the motor.

Permanent stator magnets inside a brushed RC motor — The stator and stator magnets from the above electric motor

The armature which is also known as windings, a commutator, and as the name suggests, a set of brushes.

brush for an electric motor — A brush from the inside of the above electric motor

Brushed motors have 2 external wires that you connect to your power source. As these wires are electrified with dc current, the electricity runs through these brushes to the commutator.

Brushes inside motor — The wires connect to the brushes send power to the armature through the commutator

I always had a problem remembering what the commutator did, but one day it hit me that the commutator communicates the electricity from the brushes to the windings. That helped me a lot! But, the commutator is a little electrical pad inside the motor that is connected to the windings, and the windings create an electromagnetic field.

Brushed Armature — The armature from inside of the above motor

This field is what interacts with the stator magnets in the motor shell, and that’s what causes the rotation of the motor. As the motor spins, the brushes make contact with different parts of the commutator, which reverses the polarity on the windings and pulls the motor farther through its rotation. This continues on and on and that’s what makes these little motors rotate. The problem with brushed motors is that they’re not as efficient as brushless, and they don’t last nearly as long because of the physical interaction of the brushes riding on the commutator; therefore brushes are a wear item, and the commutator can also go bad. That’s about as deep as I want to go into how brushed motors work because for the most part, many of the electric airplanes we deal with today are brushless.

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Brushless Motors

Brushless motors are different from brushed motors, both in the way they are constructed and the way they work. Brushless outrunners will be the most common type of motor we see in the hobby so let’s talk about them. So the reason brushless motors run without the use of a brush is because the armature is no longer the spinning part of the motor, and because of that there’s no need to electrify a piece that is moving.

Brushless motor stator — The stator from inside the above brushless outrunner motor

We’ll talk about ESCs later, but the reason these motors are able to operate is because the electronics advanced to where they became in a loose sense a computerized brush. Let me explain and let’s see if that makes any sense. In a brushed motor, the armature had to be the part that was electrified because there was no other way to reverse the polarity of the electromagnetic field to keep the motor spinning. If you were unable to switch the polarity then the motor would just move to the position that the magnets were attracted to and not continue on with it’s rotation. Since the armature and the commutator spun, the electricity delivered to it by the brushes was able to reverse polarity and continue to spin the motor.

Brushless motors don’t have that issue because the electromagnetic field is controlled by the ESC, and since the electromagnets are on the stator and the permanent magnets are on the rotor, there’s no need to transfer any electricity to a moving part.

brushless motor rotor — The rotor from the above brushless outrunner motor

Therefore, the biggest limitation to brushed motors was eliminated. So no more brushes, no more commutator, no more friction between the brushes and commutator to slow the motor down. No more sparks to foul up the connection between the brushes and commutator. So, a brushless motor is really a simplified brushed motor, almost an inside out brushed motor. Or at least flipped, I guess not quite inside out. Brushless motors last longer since really the only wear item is the bearings on the front and rear of the motor. Brushless motors come in many different sizes, and they each have some specs that are good to know about. So, what do all the numbers mean in the specs?

This is where it can get confusing, so let’s go through it step at a time. We’ll read the numbers from the motor that’s pictured above.

The numbers on the above motor are A2212 1400kv

A = the letters don’t really denote anything specific about the motor setup. They usually are a manufacturer’s brand number, or series number of the motor. Sometimes they’ll be labeled with an S for a short can or an L for a long can, but on the whole, nothing really to be concerned with.
2212 = This gets a little tricky since there’s not a standard for these motors. This 4 digit number is really a set of numbers that get broken down to 2 separate sets of 2 numbers. The first two numbers, the 22, tells either the exterior motor diameter or the rotor diameter, and the second two numbers, the 12, tells either the motor height or the rotor height. Since there’s no standard in these motors, the only real way to know what the numbers refer to are by looking at the spec sheet or the description of the motor. The spec sheet for this motor tells me that it is a 28mm can, or the outside diameter is 28mm, so that means the numbers written on the outside of the motor are talking about the rotor diameter since the first two numbers are 22, not the motor measurements itself. If it was talking about the motor, it would start with 28 instead of 22.
1400kv = The kv of a motor tells us, under no load, how many times the motor will spin in one minute with 1 volt applied, so it’s the rpm rating of a motor. Our motor here will rotate 1400 times in one minute with one volt applied. The specs for this motor say it’s designed to be ran with a 2s or 3s lipo, so doing the math, since a 2s lipo is 7.4 volts, this motor will spin at 10,360 rpm on a 2s battery, and at 15,540 rpm on a 3s 11.1 volt battery. Remember, those numbers are all no load numbers, so you won’t get that rpm, but it should be close enough for our purposes.

The spec sheet for this one also tells us some other important information.

Max efficiency = 80%. The higher the efficiency, the more efficient the motor is at spinning a propeller, which means less wasted energy. The lower efficiency a motor is the more heat it produces since heat is the by-product of an inefficient electrical system.
Max efficiency current – 4-10A (>75% throughout that range)
Current capacity -12A/60S, so it can handle 12 amp bursts for one minute.
No Load current at 10V – .5A So when it’s just sitting idle, it uses half an amp at 10V.
Number of cells – 2-3 Lipo.
Motor dimensions – 28mm x 30mm
Shaft diameter – 3.17mm
Weight – 47g.

Let’s look at the numbers from a different motor. It’s labeled CF-2822/14 1200kv. There’s a little difference between it and the last motor we talked about. There’s an extra number in there. So, let’s take it piece by piece.

CF – doesn’t really tell us much of anything
2822 – tells us the motor or rotor diameter is 28mm, and the 22 tells us either the height of the motor or the rotor. Since we don’t have the motor spec sheet in front of us, we can measure the can to find out what the numbers are referring to. It measures 28.54mm, so these numbers are talking about the can size, or the actual measurement of the diameter of the motor.
/14 – The next two numbers were not on the first motor we talked about. The /14 refers to the number of turns in the motor. The higher the turn number, the lower the KV of a motor. The turns refer to the number of times the copper wire has physically been wrapped around the stator of the motor.
1200kv – this is the rpm/volt of the motor, so for every 1 volt applied, the motor will spin 1200rpm under no load.

So, like I said, higher turn motors have lower KVs, but they have more torque. Because of that they are able to spin larger props. Also, as the physical motor size increases, most of the time the KV of a motor decreases because of the way it’s constructed. But that’s okay, because the bigger, lower KV motors run on higher voltage batteries, so even though the KV is lower, the overall performance increases.

Let’s look at one last motor.

Sometimes a motor will not give you very many specs, but instead it will be labeled with the size nitro motor it is designed to replace, like the below Super Tigre .10, which is designed to replace a .10 sized nitro motor.

Super Tigre Stator — The stator from the Super Tigre .10. Notice how much shorter the magnets are compared to the other brushless motor stator pictured above

Super Tigre .10 rotor — The rotor from the Super Tigre .10

How can you tell a brushed motor from a brushless motor?

If you have a motor sitting around, or you see one and you’re not sure if it’s brushed or brushless, the easiest way to tell is by how many wires are coming out of it. Brushed rc motors have 2 wire leads, and brushless rc motors have 3 wire leads.

What if I hook up a brushless motor and it spins backwards?

One last thing on a brushless motor. To change the rotation of a brushless motor, simply swap any two of the three wires going to the motor from the speed controller. So, if you hook your motor up and it spins backwards the first time you power it up, don’t fret. Just switch two of the wires then you’re all set!

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Electronic Speed Controllers, or ESCs

So, now that we know all about our brushless motors, we need something to make them spin. The brushless electronic speed controllers, or ESCs that we all know and love take the direct current, or DC, from the battery, and convert it to the 3 phase alternating current, or AC, that the motor needs in order to spin. The terms ESC, speed controller, and electronic speed controller are all interchangeable. ESCs interpret the PWM signals, or the pulse width modulation signals from the receiver. That means the width of the signal pulse determines how fast the ESC spins the motor. The ESC sends the electricity to the motors at different frequencies based on what speed the motor needs to spin based on the signal from the receiver. The motors are in sync with the frequency being produced by the speed controller, which is why the motors are called synchronous motors.

Speed controllers are pretty complicated little electronics, but we really don’t need to concern ourselves with how they work, we just need to know what to look for when deciding on which one we need. Most speed controllers have a few settings that can be programmed based on your application, and the programming instructions will either come in the package with the ESC when you buy it, or will be available on the website where it came from. Each ESC’s programming sequence is going to be different. Some are programmable from the transmitter, some have a little card that plugs into it to program it, some connect to a computer for programming, and there are some that aren’t programmable at all. Sometimes there’s nothing really that you need to change so programming isn’t necessary and it’ll work just fine for what you’re doing straight out of the package. You’ll have to refer to your manual, or look at the manual online for specific directions for a particular ESC.

A very important thing to know is the current, both the continuous and peak ratings that an ESC is rated for. You also need to know what battery voltage it is designed to handle and whether it has a BEC (battery elimination circuit). If it does, check the BEC type, output voltage, and current rating. A BEC can eliminate the separate receiver battery we use in our nitro airplanes by powering the receiver, servos, and accessories from the main flight battery. In a typical electric setup, the battery plugs into the ESC, the motor connects to the ESC, and the receiver lead plugs into the throttle port. Electricity from the BEC then powers the receiver and servos through that lead. If you remember from our receivers episode, we talked about how the receiver’s power bus can take input voltage through a servo port, so you don’t necessarily need anything plugged into the battery port. Whether a BEC is suitable is not determined by airplane size alone. You need to consider whether it is a linear or switching BEC, its input-voltage and output-current ratings, the number and type of servos, possible servo stall current, retracts, lights and other accessories, cooling, and the installation. A properly selected high-current switching BEC may be suitable in a larger airplane. In other installations, a separate BEC or a dedicated receiver battery is the better choice. Tom’s Christen Eagle is set up with a separate receiver battery, so even though it’s fully electric, he charges and takes care of that battery the same way he would in one of his nitro planes. A separate BEC is another voltage regulator between the main battery and receiver, and some are rated for more current and higher input voltage than the BEC built into an ESC. Do not assume either type is suitable from its name alone—check the manufacturer’s ratings. If an ESC has a built-in BEC but you plan to power the receiver another way, follow the ESC and external-power-system manufacturers’ instructions for isolating the built-in BEC’s positive lead. Don’t connect two receiver power sources together unless the equipment is specifically designed for it.

Some ESCs have brakes on them, and the brake is normally able to be switched on and off in the programming. Sometimes the brake is used on airplanes with foldable props, like for glider pilots that turn off their motors to glide.

ESCs for RC airplanes usually have a built in safety feature that will turn off the electric motor once the battery gets too low, but it will continue to power the radio and servos through the BEC. This is called the LVC (low voltage cutoff). Some ESCs are programmable and can be set to different voltages, and some are set from the factory and can’t be programmed. It’s a better idea to fly with a timer and use this safety feature as a last resort, but it’s a nice feature to have to save your li-po batteries from accidental over discharge without turning the whole airplane off.

Let’s take a look at a speed controller and see what it says. It is an inexpensive hobbyking ESC. It’s labeled with HK-30A ESC, has a big 25 printed on it, with a small 30 in subscript below it. It says Cells 2-3s(auto detect), Max Current 30A, BEC 3A. It does not say if it’s for a brushed or brushless motor on the label, but we can figure that out by looking at it. Since it has 3 wires on the motor side, we know it’s designed to run a brushless motor. If it only had 2 wires on the output side, it would be for a brushed motor. Now, that’s a lot of information on the label, but it’s important information to understand.

HK-30A ESC -This is the model number of the ESC. Not all speed controllers will have a model number on them, so if yours doesn’t, it’s okay.
25 – Now, the big 25 printed on it is telling me what it’s constant current rating is, which is 25 amps.
30 – The subscript 30 , along with the max current info printed on it, tells that it has a 30 amp burst rate, so for short bursts of time, 15-20 secondsish, it can handle 30 amps without being damaged.
Battery – 2s or 3s, auto detect -The label also tells us that it is designed to be ran on either a 2 cell lipo battery, or a 3 cell lipo battery, and it can auto detect which one is plugged in so it knows when to enable its low voltage cutoff, since the low voltage cutoff will obviously be at different voltages between 2s and 3s lipo batteries.

Can you use the same speed controller for a brushless motor as a brushed motor?

Something we’ve been asked is whether or not you can use the same speed controller for brushed motors as you can for brushless motors. And generally speaking, the answer is no. Brushless motors work in a completely different way than brushed motors, and because of that require a special speed controller to drive them. Brushed motors run on dc, or direct current. Brushless motors, on the other hand, are 3 phase ac synchronous motors. I say generally speaking because there are very few that can handle either type of motor based on firmware. The speed controllers that can do both are not common, but not unheard of.

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Selecting the right motor

So now that we know and understand the basics of brushless motors and speed controllers, let’s put it to use and figure out how to figure out what electric setup you need for your airplane.

Remember the garden hose from earlier? Let’s use that analogy again to quickly walk us through what we’re going to do to figure out what electric motor, battery, and speed controller we need for our airplane.

First thing we need to figure is the motor size. We’ll talk about that in a minute, but once we know the size motor we need we have a starting point for the rest of the setup. For the water hose analogy, let’s say we need to fill a 1 gallon bucket with water every minute to do whatever it is that we need to do. Now that we know what our goal is, we can work backwards to figure out the rest of the equation. The next thing we would figure is how much pressure we need from the spigot to do that, and remember the spigot pressure is our voltage from our battery. And the last thing to do is figure out what kind of hose we need to get to be able to continually supply that water at that pressure, or how many amps our ESC needs to be. So, without knowing what our end goal is, we can’t pick any of the components of our system. You wouldn’t use the same water hose or pressure from the spigot if you needed to fill a 55 gallon drum in 30 seconds.

A Full electric airplane power system — An electric airplane power system

Let’s talk watts for a minute. What are watts, and how do those numbers relate to their capability? Watts = voltage x amps. The higher the number, the more powerful the motor will be. Think of it like a car motor. To get more power out of one of those, basically, you need to be able to get more fuel through the engine to burn (more cylinders, bigger displacement). The watts are a bit like that. The higher the wattage, the more power the motor makes, but it will also drain the battery, aka your fuel tank, faster, so you’ll need a higher capacity battery in order to get a longer flight.

RC Plane Electric Motor Size Calculator

This gives you a sensible wattage target to start shopping. It does not choose the propeller, battery, or ESC for you, and it does not replace the motor manufacturer’s tested setup information.

Ready-to-fly weight
Weight unit
Flying style

Before flying: Check the exact motor, propeller, battery, and ESC together with a wattmeter. Stay within every manufacturer’s voltage, current, RPM, and propeller limits.

Okay, so, we start with picking the right motor for our airplane. To do that, we need to know a couple of things. Let’s use my Kavalier as an example and work through the numbers. Just remember that this gets us in the ballpark. We’ll still need to check the actual setup before we fly it.

First thing we need to know is the weight of the airplane. According to the manufacturers website, it’s weight will be between 5.5 and 6 lbs, so we’ll use 6 pounds for our calculations. The next thing you want to do is figure what kind of flying you’re going to be doing.

The old fashioned general rule is to stick with the following guidelines.

Trainer	80 watts per pound
Sport	100 watts per pound
Sailplane	80-150 watts per pound
3D	200 watts per pound
EDF	200-300 watts per pound

Watts per pound based on the type of flying you want to do

I want to fly it in a sport manner, so I’m going to aim for 100 watts per pound. Taking 100 watts per pound and multiplying it by the 6 pounds my airplane should weigh, I will need a motor capable of producing around 600 watts. Another thing to consider is prop RPM. Nitro engines give or take spin around 10000 rpm in the air.

Unfortunately, you can’t just google a 600 watt rc airplane motor and find the motor you need. After digging around online, I found a couple motors, so let’s look at them. First thing I found was an E-flite 4250 brushless motor, 540kv. Unfortunately, it didn’t give me enough useful setup information on the page I was looking at, so that one’s out of this planning exercise. The next one I found was a Tom Cat G46 5020-680KV outrunner. Let’s look at this a little closer. It was described as a comparable replacement for a .46 glow engine and rated at 900 watts maximum, so it looked like a candidate worth investigating. The 680KV rating means approximately 680 RPM per volt with no load on the motor. Once we put a propeller on it, the motor will not turn that exact RPM. Dividing a desired 10,000 RPM by 680 gives about 14.7 volts, which points us toward a 4S battery. That still doesn’t prove the loaded propeller RPM or current will be right. In the same way, 600 watts divided by 14.8 volts gives us about 40.5 amps to use for planning. That is not a guarantee that the motor will actually draw 40.5 amps. We still need to choose the propeller from the manufacturer’s data and check the current, power, and RPM with the actual motor, propeller, ESC, and battery.

Next is to pick the battery we want to use, and flight time is part of that decision. Normally, I like to fly for about 7 minutes per flight. The basic calculation is flight time multiplied by average current, divided by 60. If we use the 40.5-amp planning number as though the motor ran at full throttle for the entire seven minutes, the result is 4.725 amp-hours, or 4725 mAh. Allowing a reserve brings that theoretical example to roughly a 6000 mAh pack. That gives us a conservative full-throttle example, though. It is not an accurate prediction of a normal flight because we won’t spend the whole flight at full throttle. Actual duration depends on average in-flight current, throttle use, propeller load, battery condition, and the airplane. The discharge rating on the label is still a manufacturer’s rating, so we can’t assume every battery will perform perfectly in every installation.

When it’s time to pick the ESC, start with the manufacturer’s limits and tested propeller data. Then use a wattmeter to check the full-throttle current with the actual motor, propeller, battery, and ESC together. Choose an ESC that supports the battery voltage, has a suitable current margin above the measured load, and can be cooled properly in the airplane. The motor’s maximum-current rating does not tell us exactly what the complete setup will draw. Just adding 15 percent to a calculated number isn’t enough to prove that an ESC is the right one.

To recap, we started with the airplane’s weight and used the watts-per-pound rule to get ourselves into the right range. That gave us a motor and battery combination worth looking into, an estimate for voltage and power, an idea of the battery capacity, and a starting point for the ESC. There’s a lot to it, I know. The math helps narrow down the choices, but it doesn’t prove the setup will work. Before flight, the final propeller, current, and power must be checked against the manufacturers’ data and verified with a wattmeter using the actual motor, propeller, ESC, and battery.

Nitro conversions

If you’re converting a nitro powered plane to electric power, or EP, after you follow the steps we just talked about for picking the right electrical setup for your plane, there’s really not a lot that goes into switching out the motor and electronics. Obviously, you’re going to pull everything out of the frame that was used for the nitro engine. So, the engine comes off, the motor mount comes off, the throttle servo comes off, all of the linkages come off, the fuel tank comes out, and all of the plumbing for the fuel comes out. When it comes to mounting your shiny clean new electric motor to the front of your airplane, you can either buy a pre-manufactured electric motor mount, or make you own, which is what I prefer to do. You’ll need to measure the stand-off distance so you make sure the propeller sits at the same distance from the firewall as it did when it was hooked up to that dingy, dirty, smelly ole nitro motor. After you have the distance measured out from the propeller to the firewall, you can measure how long the motor mount needs to be and design one up. Motor mounts aren’t all that tricky, and since we’re going electric, they won’t be subjected to the high vibrations that a nitro engine produces, so they don’t have to be built as strong. You’ll need to find a place to mount the ESC, and a place that’s easily accessible to mount the battery. Depending on the airplane, you may want to cut a hatch somewhere. It will most likely go in the same place that the fuel tank was removed from. After you have it all laid out and put together, you have to, and I can’t stress this enough… It is imperative that you recheck the center of gravity and make any necessary adjustments. The weights of the nitro gear versus the electric gear aren’t going to weigh the exact same amount, so the cg is going to change and it has to be addressed.

Troubleshoot an Electric Power-System Problem

If something isn’t working right, start with the symptom instead of changing the motor, propeller, battery, and ESC all at once. Use ESC beeps but the motor will not start, motor or ESC gets hot, motor cuts out in flight, or electric flight time is too short. Start with what the airplane is actually doing, check the whole power system, and then decide whether you really need to buy replacement parts.

Once the power system is matched: use the RC Airplane Setup & Preflight Center to verify motor rotation, propeller installation, radio setup, balance, and the final walk-around.