This guide will help you choose the correct Brushless motor for your Airplane project.

Nowadays, figuring out a high-quality power system for your RC plane’s motor is more complicated than what it sounds like overall. That’s because it requires a certain amount of educated guesswork when you are trying to figure out the best RC plane motor for your RC plane.

While you could take the time to calculate each bit of information you’d need to figure out the best power system for an RC plane model, it’s almost more comfortable to use the approach of an educated guess.

To help you understand how you can go about making your educated guess concerning your RC plane’s motor, you’ll have to learn some new knowledge. That’s what our guide will focus on below.

First, we have to cover some basics regarding physics, science and construction.

1. TYPES OF MOTORS

The main Motors used in RC today are Brushed, and Brushless types. Brushed motors are typically 

DC motors with low efficiency. Modern Brushed motors are 3-wire AC motors. (This is not too important, as the electronic Speed Control (ESC) will take care of sending the right "signal" to the motor to get it turning at the right speed). In this article, we will focus on BRUSHLESS motors only.

Brushless motors are typically divided into 2 types, In-runners and Out-runners. Simply put, in-runners look like a typical electric motor, with the inside of the motor turning. These motors normally produce high RPM values, but with little torque. They are nomally used in geared applications, such as RC cars and boats.

Most Aircraft and drone applications use Out-runner brushless motors. The OUTER casing turns, while the inside (stator) remains stationary. This produces more Torque at lower RPMs and this is ideal for swinging a propeller.

2. All those numbers!

When confronted with a typical brushless motor, there are several tech specs to take into consideration.

• Motor Size

A number like BL3526/12 -1200 on the motor means different things to different manufacturers. Unfortunately not all manufacturers label their motors using the same conventions or standards.

The numbers are supposed to indicate the measurements (in mm) of the Rotor. As an example, the first 4 numbers of the motor mentioned above would be 35mm motor diameter, and 26mm length.
Unfortunately some manufacturers give the measurements of the rotor, others define the stator, or even a combination of both! Use these numbers purely as a guide, or just as a means of identifying the motor, so you can look up the important bits, which we will discuss later in this article. The "/12" in the above example simply denotes the number of wire turns per stator winding. This has the primary effect of changing the KV value of the motor, which is the next spec we will discuss.

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• KV Value

Looking at our example of BL3526/12 -1200 ,  the -1200 at the end denotes the KV value of the motor. Not to be confused with a POWER value electricians use, this value indicates the SPEED the motor will turn. Simply put, the number indicates the RPM PER VOLT value.

In our example, 1200 means 1200 RPM per volt. on a 3S (11.1V) battery, the motor will thus turn at 1200 x 11.1 = 13 320 RPM at full throttle. 

This value is an important consideration when choosing either the correct motor for the battery you want to use, or conversely the correct battery to use with the motor.

As a rough guide, you can use the following table to narrow it down :