What you should consider
before converting your rc airplane gas engine to an electric motor
system.
With the changes in rc
electric motor technology it is possible to fly ANY size model using
rc plane electric motors. The biggest leap in making this possible
has been two fold. First we have model airplane electric engines
that are powerful enough, not to mention much more efficient, that
they rival or even surpass gas/slimers/smokers/nitro hogs, or
whatever else you may call rc airplane gas engines.
In fact you can expect to
see an increase in the performance of a model airplane in several
areas. Your take-off is shorter, climb rate will increase
and you can now fly in areas that have noise
restrictions.
The debate between the
benefits of rc plane electric and gas motors are as controversial as
those between pc and Mac users. It will continue for as long as they
are both in existence.
Some questions you might be
asking before you convert your rc model airplane's gas engine to an
rc electric motor...
How long will the battery
allow me to fly? With today's Lithium Battery technology, you can
easily expect 10 minute flights, even in bigger aircraft. The days
of overheating the batteries and fire hazards are almost
non-existent. There are many add on features that you can now
purchase that all but eliminate battery hazards. Such as temperature
monitors and voltage indicators.
Here are some questions to
ask before you start buying any components. These questions will
help determine what components to buy.
1. What is the radio control
plane that you are wanting to convert? Is it a trainer, sport plane,
3D etc.. This is important because you will need to determine the
electric motor based on your models capabilities, and what you want
it to do.
Example: Hangar 9
Arrow with a .40 size gas engine.
Would require an electric rc motor
equivalent to a
AXI 2826/12 External Rotor Brushless.
This motor would allow this
model to perform basic aerobatics with
its semi-symmetrical wing.
Specs of the Hangar 9 Arrow
You will need these numbers
to help determine the motor, battery, and prop requirements.
Wingspan: 63 in
Overall Length: 52.5 in
Wing Area: 710 sq in
Flying Weight: 5.7 lb (as a
radio controlled gas plane)
Engine Size: converting a
standard .40 size rc gas engine to an rc
electric motor.
Now
you need to determine what type of batteries you will need. This is
based mostly on your budget and time till land variable. In other
words, how long do you want to fly for and still get performance.
The most obvious choice is
going to be a Lithium Polymer battery, this is the most advanced
battery technology available for rc model airplanes. They are also
the most expensive. Other older battery technologies are available,
such as, lithium ion and nickel metal hydride. They can do the job,
but at a weight cost and flying time consideration. So choose
carefully.
In the Arrow Example: We
will use a 4200 mAh 11.1V Li-Poly Pack.
This was determined based on the flight performance we were after,
some aerobatics, but mainly stable easy going flying. Nothing too
extreme.
As with any gas rc plane
conversion to electric (or any electric radio controlled airplane
for that matter), you will have to consider an ESC (electronic speed
control). This hooks up to the motor, battery, and receiver. You
will need to pick one that can handle the required number of battery
packs, servos and have programmable features. This will make life
easier for you if you pick one that is feature rich. Of all the
components, this is one to spend a little more on. You will be glad
you did.
For this example, we used a
40 Amp Brushless Controller with Program
features. There are lots of manufacturers of ESC's so take the time
to research them.
Prop Selection is an
important consideration. You need to be aware that with an electric
conversion there is a possibility that your model plane will not
have enough clearance when using an electric motor prop. It may need
modifications to the landing gear (making them longer) so that the
prop has clearance.
For the Arrow example we
used a APC 13x10 propeller. Most electric
motors now have a table that you can find on their website that will
recommend the propeller range to stay within.
One final consideration with
rc gas planes converted to electric. You always need to factor in
cooling of the battery pack and esc. In fact many modelers,
including myself, put the ESC on the outside of the plane, usually I
mount it under the engine on the firewall. You also need to make air
vents to cool the battery inside the model. Without this, you run
the risk of overheating batteries and ESC's.
