its aircraft speed controls’ maximum current
ratings require the speed control to be “in
contact with a 5mph airflow of 25°C (77°F)
or cooler air.” That’s not a very fast airflow.
Warmer ambient temperatures or higher
temperatures in the speed control would, of
course, require more air movement.
If the air needs to go to specific areas in the
fuselage with higher velocity, it might help to
install baffles or guides to direct the airflow
more accurately. These guides can be made
out of whatever material is appropriate: thin
plywood, shaped balsa, flexible plastic, or foam.
Many ARF models designed specifically for
electric power have taken cooling airflow into
consideration and come out of the box with
well-designed vents, baffles, and power-component mounting areas.
Get the heat Out
The exit for the heated air can be just about
anywhere in the rear of the fuselage or cowl
that makes sense. For a model with a speed
control mounted in the engine compartment, a
simple cutout in the lower rear part of the cowl
is all it takes. For models with the speed control
inside the fuselage, cutting the covering or
sheeting from the space between a couple of
rear formers works pretty well.
The primary goal of the exit vent is to create
a low-pressure area so that the higher-pressure air in the fuselage wants to move
toward it. An easy way to do that is to make
sure that the total area of the exit vent is about
three times the area of the total inlet area.
KnOw the ScOre
Whether before or after setting up a cooling
airflow in a model, it’s handy to know what the
temperatures you’re dealing with actually are.
There are several ways to check temperatures:
an infrared thermometer, telemetry systems
for your radio, and speed-control data logging.
The most versatile of the three methods is
the infrared thermometer. This is a handheld
device that you simply point at the surface that
you want to measure the temperature of. You
can check the temperatures of any component
that you need to with this device—motor,
battery, speed control, wires, and plugs—so
I recommend having one of these in your
Many radio manufacturers offer telemetry systems as options for
their radio systems. These transmit data from various sensors to the
transmitter, and all of them have at least one temperature sensor
that can be attached to any component that you need to know the
temperature of. An advantage of using telemetry is that you’ll be able to
see the temperatures change as a flight progresses instead of checking
after the landing.
Speed-control data logging is available from several manufacturers.
These speed controls keep a running log of selected data throughout a
This Castle Creations speed-control data log graph shows a temperature plot for a short test flight. The
maximum temperature of 313°F is well over Castle’s recommended maximum of 212°F and is a sign of a serious
overload in the power system.
flight, and you can download the resulting file to a computer for viewing
afterward. Opening the data in a graphing application provides a great way
to see what’s going on.
Heat in an RC electric-power system can be fairly straightforward to manage.
Choosing the components of the system conservatively can reduce
the amount of heat generated in the first place, and well-placed inlets,
components, baffles, and outlets can help your airplane keep its cool.
This Castle Creations data log chart shows a temperature plot from a 30cc Spitfire powered by an E-flite Power
160 motor, Castle Creations Edge 120 speed control, 10S 4000mAh battery, and an APC 19x10 propeller.