This guide is intended to help give aero-modelers enough simplified knowledge to choose from the bewildering array of components available, and to assemble appropriate power systems for their model aero planes. This guide is not intended as an answer to everyone’s questions, but as a basic introduction so that we have a reference to help understand this subject.
Read this before using guide
Choosing a power system is a more complicated procedure than I first thought when I started putting this guide together. Often choosing a power system includes a fair bit of educated guesswork. Although it is possible to accurately calculate every important bit of data to determine the optimum power system for a model, most of us will prefer the “educated guess” approach. Unfortunately there is some knowledge required to make an “educated guess”, and that is hopefully what this guide will provide.
For those completely new to the world of aeromodeling who also intend building a new model, I suggest starting from the beginning of this guide. Even if it doesn’t all make sense at first, it will eventually. Some trial and error might not seem like the most economical way of learning but it can sometimes be the most effective.
Many people will only want to access certain information, so each topic has a heading. Scroll down to see if you can find the information you need.
What is Wing Loading and Stall Speed ?
Wing loading is the loaded weight of an aircraft divided by the area of the wing. It is broadly reflective of the aircraft's lift-to-mass ratio, which affects its rate of climb, load-carrying ability, and turn performance.
Many aero modelers try their hardest to make models as light as possible. This is because a model with a light wing loading is easier to fly as it has a slower stall speed. In a banked turn an aeroplane is subjected to a gravitational force (G) which increases its weight, the same as a weight on the end of some string gets heavier if you spin it around like a lasso. The heavier the wing loading in a banked turn, the higher the stall speed gets. Other factors that can affect the stall speed of a model aero plane are aerofoil shape and aspect ratio. The only way of giving a heavy model a light wing loading is to increase the size of the wings. So a model with a high wing loading will have a high stall speed, which will become even higher in high G maneuvers. Because we land our models at or slightly above their stall speed, a model with a high wing loading will have a high landing speed which can call for some very good piloting skills.
Wing loading is usually calculated in the form of oz/ft² or gr/dm²,1 dm² = 15.50003 inch². If you want to calculate the wing loading of your model, try this calculator http://www.coloradogliders.com/wingloadingcalculator.htm.
Relationship between Volts, Amps and Watts - Explained
The most important terms you need to understand when choosing components for your electric model are Volts, Amps and Watts. Here is the "Hydraulic analogy" from Wikipedia which explains these terms in a simple way.
"The hydraulic analogy is sometimes used to explain electric circuits by comparing them to water-filled pipes, voltage is likened to water pressure - it determines how fast the electrons will travel through the circuit. Current (in amperes), in the same analogy, is a measure of the volume of water that flows past a given point, the rate of which is determined by the voltage, and the total output measured in watts. The equation that brings all three components together is: volts × amperes = watts".
As we will see, the size and efficiency of a motor and the load imposed on it by the propeller affects the Volts and Amps. The idea is to choose a motor, battery, esc and propeller combination that will fly your model in a desired manner within the specifications of the components, preferably at around the peak efficiency of the motor. This will be covered in more detail in the following sections.