The first thing that you need to understand with electric
airplanes is that you have to look at the entire power
system as a whole—one that will work together for
maximum power and efficiency for the plane you are
flying, and with that, you have to understand how much
power will be needed to fly your plane safely. Whether
you’re flying a lightweight micro indoor flyer or a large
Electric motors, propellers, and battery packs, along with
a suitable electronic speed controller, make up your power
system. But, you have to use the correct combinations
of equipment for your system to operate properly. To
determine the power of your model’s power system, you
need to measure the voltage and current while the motor
is running. The three important parts of the power formula
are amps (A), volts (V), and watts (W). But before we can
talk about selecting power systems, we need to understand some very basic things about electric power.
A watt is the unit of electric power in the same way
that horsepower is used to
express power for an internal combustion engine. You
produce a certain number of
watts by moving electricity
through a device that converts it to power. Movement
of electricity through a
power system is described
by the term ampere (amp),
and the force that causes it to move is the volt. The basic
relationship between these units can be described with
the equation watts = volts x amps (W=VxA). The most
important thing for modelers to understand is that you
can produce watts by using a lot of volts and just a few
amps, or you can use a small amount of voltage and lots
of amps. It all works together. What this means is you can
use a small amount of battery voltage and a large propeller diameter/pitch size or a larger battery voltage and a
smaller propeller depending on the requirements of your
model. And to properly power our models, we can use a
simple rule called the “watts per pound” rule.
3D aerobatic plane, its performance is based on the
amount of power it develops relative to its ready-to-fly
weight. If you get an ARF model airplane, then everything will be included and you’re good to go, but if you
are putting your plane together with separate airframe
and power system components, then you have to know
what will work together.
The most important thing for modelers
to understand is that you can produce
watts by using a lot of volts and just a few
amps, or you can use a small amount of
voltage and lots of amps.
Power meters that are connected in between your batteries and your esC are great for evaluating your power system’s setup.
above: The first step when
you are putting an electric air-
plane together is to figure out
how much power you actually
need. There’s a formula for
that (see text).
Below: Brushless motors like
this Power 100 from e-flite
are very popular. They come
in several sizes and power rat-
ings to fit just about any size
plane you like.
2watts Per Pound This categorization is a loose, flexible way to estimate the amount of power needed for a specific size airplane while giving the performance required for safe flight. The rule is really just a guideline to determine how many watts
of power are needed per pound of airplane weight and is
expressed as W/lb.
50w/lb. or less—Very lightweight micro RC and slow
50-75w/lb.—Sport-powered sailplanes and gliders,
basic trainers, lightweight scale planes, vintage RC and RC
assist-free flight designs.
75-100w/lb.—Basic sport flyers, intermediate aerobat-
ics, scale low-wing designs, and medium-size warbirds.
100-150w/lb.—Advanced aerobatics, pattern flying, 3D
planes, larger warbirds, and EDF jets.
150-200 plus w/lb.—Unlimited 3D aerobatics, warbirds,
and large jets.