What Does an RC System Do? | The First Thing You Should Do | How Are RC Systems
Classified? | RC Operating Frequencies | Remainder of RC System Components | Sizing RC-
System Components | Dual Stick Transmitter Control | Trim Levers | Servo-Reversing
Switches | Conclusion
Last month I introduced the subject of learning model aviation “from the ground up.” As the
name implies, this is a beginner series that will be devoted to people at the entry point of
our wonderful hobby. The sequence of articles planned for this series follows a logical order
to allow you to enjoy the learning process. After all, it is a hobby and it is supposed to be
fun.
Since approximately 90% of model-flying enthusiasts resort to Radio Control (RC) systems
for flight control, this was judged the best starting place. The article has literally been
developed from square one. If you already have some knowledge of RC devices, you might
consider our presentation too basic. We will try to describe all aspects of RC for the benefit
of the entry-level hobbyist.
What Does an RC System Do? The basic idea is that you—the pilot—stand on the ground
holding a radio transmitter. The transmitter operates as any broadcasting-type device,
except in this instance voice is not transmitted; a coded signal is sent to the model aircraft
up in the air.
On board that aircraft is a radio receiver that receives these coded signals without the need
for interconnecting wires. The received signal is decoded or processed then passed on to
individual motor-driven actuators (servos) that physically move the aircraft control surfaces
and adjust (or change) the engine speed settings (known as throttling). The radio
transmitter (which the pilot holds) and the receiver/servos in the model are powered by
batteries. So as a newcomer, you must become familiar with the RC system and the
batteries that power it.
The entire thrill of RC flying is the ability to control the model’s attitude in flight, sometimes
at distances of several hundred feet away, maneuvering the airplane and landing it close
by, just like a full-scale aircraft. Judgment, experience, and skill development enter into the
equation when it comes to the model aircraft’s flight.
The First Thing You Should Do: Before you purchase anything, you owe it to yourself to visit
a local RC flying field. A hobby dealer in your area should be able to steer you in the right
direction. A referral to a local RC club can also prove helpful. The idea is to get you and
possibly other family members out to see these models in flight firsthand.
You may be able to talk with some of the experienced fliers and get a rough idea of what is
involved. These same people should be able to make initial recommendations concerning
types of RC systems, popular system brand names, model aircraft suitable for initial flight
instructions, engines to power the airplanes, and the necessary supporting equipment to
get you started. All of these elements will be discussed in-depth as this series grows month
by month.
How Are RC Systems Classified? RC systems in the most basic sense provide control of the
aircraft rudder (for steering left and right), elevator (for pitch control or up and down
motion), and engine throttle (control engine speeds from idle up through full power). Each of
these basic flight-control functions are classified as channel functions (rudder, elevator, and
throttle). Keeping that in mind, RC systems are classified by the number of channel
functions offered—two, three, four, and in the cases of the most advanced systems, upward
of eight to 10.
When you go out to shop for your first new RC system, you will see a few basic two-channel
systems (rudder and elevator); they are only suitable for flying model gliders or sailplanes,
where engines are not employed, therefore a throttle is unnecessary. Since two-channel
function control is limited in application, the initial point of consideration when buying your
first radio is a three-channel-function RC system.
A three-channel RC system provides basic rudder, elevator, and engine control (sometimes
called throttle). Several manufacturers, including Futaba and Hitec, make excellent, easy-to-
use three-channel RC systems which are also inexpensive. Since so much can be done with
a three-channel RC system, it will probably never become obsolete. Many of us who fly
sophisticated radio systems still own and regularly use three-channel systems because they
are easy to operate.
Looking ahead, there are four-channel RC systems which comprise the most popular
category. With four channel functions, the added control is ailerons, which are located on
the wing and permit the model to bank in flight. By adding aileron control to rudder, elevator,
and engine control, you have essentially the same form of control as used on full-scale
aircraft. As you progress in the RC hobby, you will sooner or later want to expand your
horizons and use all four basic channel functions.
Your first choice for an RC system should be a three-channel-function radio. That will hold
your initial investment to a minimum. If you enjoy the hobby and want to grow with it, it would
be best if your second radio system were what we call a “full four-channel” system.
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RC-System Operating Frequencies: After selecting the number of channel functions, your
next choice is what frequency to operate on. This discussion is most important because it
involves a basic safety requirement you must always observe as an RC pilot.
Years ago the model-aircraft hobby was granted a series of 50 specific frequencies for RC
use by the Federal Communication Commission (FCC). Just as the FCC assigns radio and
television stations, it has assigned our frequencies which exist in a band that runs from
72.000 megahertz (MHz) to 73.000 MHz. Each of the 50 FCC-approved frequencies (such
as 72.010 MHz, 72.030 MHz, etc.) has been assigned a “channel number” for easy
identification purposes.
The term “channel number” has nothing to do with the channel control functions I just
discussed. I mention this because that point has caused initial confusion for many beginners.
Each RC channel (number) is essentially the same as a radio-station number or call sign. If
you purchase an RC system on channel 11, it will broadcast a signal on that exact channel
(or frequency). In this regard, channel number and frequency are one in the same.
When you purchase your radio system, there will probably be a label on the box containing
the frequency (expressed in MHz, such as 72.010 MHz, and its equivalent channel number
(in this case CH11). When you open the box, the RC transmitter and receiver will probably
be stamped with the operating frequency and the channel number.
Keeping this in mind, RC receivers on the same frequency/channel can receive the same
signal. This is important. If you own an RC system that operates on CH11 and another
modeler shows up at the flying field with the same channel number, you can’t operate or fly
at the same time. Attempting to do so will lead to possible radio interference and could
result in one or both models crashing. This is your first safety lesson as an RC pilot.
If two modelers show up at the field using the same channel, each must wait his or her turn
so that only one model is operated at a time. To simplify the control of these RC channel
numbers, a two-digit-numbered flag is supplied with every RC system. That flag must always
be prominently displayed on the transmitter antenna for all to see. More will be written about
flying-field safety procedures, but for now I want you to know about the basic controls that
are usually in effect throughout our country.
Each RC flying field usually has a display board that contains a group of numbered
clothespins or clips. There will be 50 of these pins or clips running from CH11 to CH60. The
drill is simple; when you want to turn on your RC transmitter at the field, you must first go to
this channel-control board. If the clip for your channel is on the board, that means it is not in
use. Remove that clip and attach it to the transmitter antenna. At this point you may turn on
the power to that transmitter for test or flying purposes.
While you are “on the air,” if any other modeler intends to operate on the same channel
number and goes to the board, the missing clip will alert him or her that that RC channel is
in use. That person must wait until you are finished flying, have turned off your transmitter,
and have returned the channel clip to the control board. It’s a simple drill, but if followed
faithfully it will prevent any chance of interference or model crashes. There are more
detailed subtleties to these procedures, but I will leave that until later.
FM, PCM, and AM Modes of Transmission: Since we are dealing with “radio,” you should be
familiar with the terms “AM,”or Amplitude Modulation, and “FM,” or Frequency Modulation,
when it comes to listening to broadcast radio stations. Except for the station numbers or call
signs, you can usually receive both broadcast modes on the same radio, and for the most
part they sound the same. Sure there are subtle differences, but the bottom line is that they
serve the same purposes.
In the RC hobby we can use AM, FM, and a special form of FM called “PCM,” or Pulse Code
Modulation. The most popular operating mode today is FM—much like in broadcasting. The
majority of RC systems sold are FM; it has been that way for the last 20 years. FM provides
good, reliable control and can be purchased at reasonable prices. Few RC systems are still
offered on AM.
Some sophisticated RC systems are offered on a special PCM mode. It adds a proprietary
digital code on top of the FM signal, such that it can offer more protection from outside
interference. PCM-type modulation is only found on the more advanced and more costly
systems.
As a beginner, the one important thing you must keep in mind is that you can’t mix
modulation types between a transmitter and receiver. An FM transmitter will only operate an
FM receiver, and only if both are on the same frequency (or channel number). You will
never be able to have an FM transmitter operate an AM receiver or vice versa.
Taking this a step further, PCM RC systems must be of the same type and manufacturer.
Each manufacturer employs different digital codes. Even within a manufacturing company,
several codes relating to control resolution might be indicated (such as the expression 512
PCM and 1024 PCM). For now let’s concentrate on regular FM, which is in the majority.
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Remainder of RC System Components: So far we have discussed only the RC transmitter.
When you purchase a full RC system, included in the box will be what we call the “airborne
components” (the equipment that must go in your model) and supporting equipment
necessary to make the system operate.
Airborne RC equipment includes the receiver, a set of servos (usually one for each channel
control function), a battery pack, a switch harness—usually with a charging jack—and an
aileron extension cable.
A four-channel-function RC system will usually be supplied with four servos. On some
economy-priced systems, you might see a four-channel transmitter with only three servos
supplied. This would allow you to start with three channel functions at a slightly lower price,
then you could purchase that fourth servo later. I mention this marketing technique so you
are not surprised when you open your first system box.
The aileron extension cable is supplied because in most cases the aileron servo is mounted
in the wing structure. The receiver, located in the model’s fuselage, may be farther away
than the regular servo cable length. The extension cable comes in handy for this
application. Almost all RC systems include servo-mounting hardware and extra output arms
(for different applications).
In addition to the airborne components, you will receive an all-important dual-output battery
charger. Some basic, inexpensive RC systems are supplied for use with alkaline,
nonrechargeable batteries. Although these systems work well, this can cost more money in
the long run. For that reason, most RC systems are supplied with nickel-cadmium (or Nickel
Metal Hydride) rechargeable batteries.
Generally, eight cells are installed inside the transmitter and four more are used inside the
model. Systems that include rechargeable batteries also provide the necessary charger.
Most chargers are wall-plug devices. You plug the transformer (black box) into a 115VAC
electric outlet. Two cables exit the charger; one goes to the transmitter and the other goes
to a charging jack, which you may be able to locate externally on the side of the aircraft
fuselage. Leaving this charger plugged in overnight will completely charge both battery
packs.
The other RC-system supporting items include the frequency or channel-number
identification flag (already discussed) and hopefully a well-written (most are) operating
instruction manual.
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Sizing RC-System Components to the Expected Size of Your Model: Another choice when
buying an RC system is the size of the airborne components. In RC we can have Giant
Scale models that weigh upward of 20-40 pounds and we can have what we classify as
“park flyers”: models weighing roughly 6-10 ounces. The larger models can employ larger
and heavier receivers, servos with strong outputs to move the large control surfaces, and
battery packs of high capacity that can cope with the required extra power.
Large RC components such as this might weigh 20 ounces or more; that would be twice the
weight of an entire park flyer. The size of the airborne RC components must be geared
toward your specific model requirements. The average RC system generally includes
airborne components that weigh approximately 10-12 ounces which are capable of flying
average models ranging from 20-size engine power upward of 60-size engine power.
If you are interested in starting with park-flyer-size models, your hobby dealer or distributor
should be able to steer you to substantially lighter-weight equipment for that application.
The purpose of this discussion is to make sure you don’t accidentally end up the first time
with a 20-ounce airborne radio that is intended to fly a 10-ounce total-weight park flyer.
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Dual-Stick Transmitter Control: Throughout the years the popular means of imparting
control-signal commands from the RC transmitter has been through “control stick
assemblies.” These control sticks provide two-axis type control; we can obtain two discrete
controls from one stick. If you grip the stick with the fingers of one hand and rock it side to
side, you can obtain left or right rudder or possibly left or right aileron control on the model
end. Moving the stick fore and aft at the same time will prompt elevator or pitch control,
making the model move up or down.
If you purchase a three-channel RC system, the transmitter will have a single two-axis
control-stick assembly. This will provide rudder or aileron control along with elevator control.
A small lever on the front, side, or rear of the transmitter case will allow you to operate
engine throttle on the model.
A four-channel RC transmitter will have two two-axis control-stick assembles. With this
popular configuration you grasp the transmitter case with both hands such that each thumb
rests on the top of a stick. Each stick will move in two directions. As you will soon learn,
moving a control stick to a corner will impart a certain amount of control to two channels at
the same time. The control will be in proportion to the amount you displace or move the
control stick. That is why it has always been referred to as dual, simultaneous proportional
control.
The four-channel transmitter usually has what we call a Mode II control-stick configuration. It
is safe to say that 99% of all RC-system transmitters sold are with that configuration. With
respect to the two control-stick assemblies, the right-side assembly controls aileron (left or
right) and elevator (up and down). The left-side stick assembly controls rudder (left and
right) and engine throttle (up and down, or actually low throttle at the bottom and full throttle
at the top position).
The throttle stick does not have a spring return to the neutral position, as do the other three-
channel functions. Instead it has a soft detent effect that makes a clicking sound as you
slowly advance or retard the throttle. When you take your finger off the throttle stick, it will
stay where you left it.
If you bought a full four-channel RC transmitter at the start, you could initially use it to
control only three airborne control functions. In that case the right stick assembly would
operate the rudder and elevator, and the left stick would only control the throttle. The fourth
channel function would be ignored.
At your local hobby shop or in RC-system catalogs, you may see that certain transmitters do
not have control sticks; they have steering wheels. These radios have been designed
expressly to control surface vehicles such as RC cars and boats. Per FCC regulations, they
do not operate on the 50 channels (CH11 to CH60) which have been set aside for model
aircraft. These surface vehicles operate on channels 61 through 75, along with some other
channels in another band.
You should never use one of these steering-wheel RC transmitters to operate a model
aircraft. Likewise, you should never attempt to use a dual-stick transmitter, operating on
CH11 to CH60, to control a surface vehicle. This is a federal law!
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Trim Levers: One of the basic controls you must learn early on involves the use of trim
levers. There is usually one for each channel number. These trim levers are located close
to the transmitter control sticks. They usually follow the same path as the control stick. On
the right stick assembly below the stick there will be a small protruding lever that moves left
or right, duplicating the same motion as the rudder-control stick. This lever will be tied to the
left-to-right steering action which might be rudder or aileron, depending on your application.
When you move this lever, the neutral position of the rudder control surface shifts slightly.
Full excursion of a trim lever generally imparts a total of 15% of the normal control throw.
The idea of using trim is to be able to “zero out” your aircraft’s attitude in flight so that it will
track straight and level with your hands off the control stick. Full-scale aircraft have the
same type of trim control.
Most beginner and basic sport-type RC transmitters use a basic mechanical-type trim
function. The levers have a light detent action that helps hold the last trim position. The
lever’s position can usually give you an idea of how much trim is being employed and to
which side (left or right, up or down, etc.). Some newer RC transmitters employ a digital-type
trim function. You probably won’t see this on a basic system, so I’ll leave that discussion for
another chapter.
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Servo-reversing switches are another basic control feature. In subsequent installments you
will read about many extra control features. Some are even available on basic radio
systems, but we want to give you this information gradually so you can absorb everything.
Servo reversing can be found on almost any RC transmitter, and it can be a real
convenience. Somewhere on your transmitter case—in the lower front (exposed or under a
flip cover), at the rear, or even under the battery pack—you will find a series of tiny
switches—one for each channel function. Flipping one of these switches will reverse the
direction of a servo located inside your model.
Why is this important? When you make that initial control installation in your model, the first
time you power up the system you might find that your left rudder is actually going right and
vice versa. If you have servo-reversing switches, you can flip the switch for the channel
involved and the servo will switch directions. Then when you apply left rudder at the control
stick, the rudder will move for left control on the aircraft. There will be more about this later.
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That concludes this installment. As basic as all this may sound, I’m sure you will have many
good questions. We learn from asking questions and getting the right answers. This sort of
thing is done on Web-site chat groups; that kind of service may be offered eventually. In the
meantime, write your specific questions to “From the Ground Up” in care of Bob Hunt, Box
68, Stockertown PA 18083; E-mail: robinhunt@earthlink.net.
Along with the monthly articles in this series I hope to publish product reviews covering items
that would especially be of interest to the RC beginner. This would include such things as
basic RC systems, ARF (Almost Ready-to-Fly) training models, basic model engines,
personal-computer simulators, training programs, field-support equipment, etc.
As this series progresses, Model Aviation hopes to publish articles about constructing
models from kits. Later it expects to go further and publish construction articles for simple
aircraft trainer designs so the beginner can get the thrill and experience of building a model
from raw materials (like from scratch!).
The photos accompanying this article were taken with equipment in my possession. The fact
that a particular brand is not shown should not be construed as a “rating” on my part. At the
end I have listed all the RC manufacturers, their addresses, and their Web sites when
available. All the RC systems work well and are easily on par with one another. Your
purchasing decisions will likely be predicated on your personal requirements rather than the
brand name.
Next month I will get into RC-system installations, system operation, and briefly discuss
some of the more advanced systems. I also expect to cover purchasing aftermarket-type RC
components to be able to operate more than one aircraft from one transmitter. MA
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