Getting Started with R/C Airplanes
Radio Equipment
Aircraft radio
systems consist of a transmitter (or controller), a receiver, one or more
servos, and batteries. Servos are the part of the airborne radio system that
convey mechanical movement. Each moving part will need a servo to make that
part move. Radio systems are available with a wide variety of features.
However, they all share similar quality and basic functions.
When you first look at a radio system, you'll see how many channels it has
and then what channel it's on. The word channel is used two different ways:
firstly, an airplane radio is very often a 4-channel radio. This means that
it controls four functions on the plane (ailerons, elevator, rudder,
throttle); secondly, it refers to the actual radio frequency the radio
transmits. There are several frequencies legal to use for R/C airplanes and
each one has been assigned a channel number.
When deciding on a radio, it is important to decide on how many channel
functions you want. Most airplanes use four channels. However, some
aerobatic, scale, and sport planes use five or six channels (adding flaps
and retractable landing gear). So, you may want to think about the future
and what plane you want next, and buy a radio that will control all
anticipated functions.
Frequencies
The FCC has set aside 50 frequencies in the 72 MHz band (channels 11-60)
dedicated to aircraft use only. No license is needed to operate these
radios. However, if you have an amateur (ham) radio operator's license you
may be able to use a radio in the 50 MHz band. Also, there are six
frequencies set aside in the 27 MHz band that are legal for any kind of
model use (surface or air). Just remember, whatever channel your radio is
on, check the field where you fly for any other radios on the same channel
and do not use your radio when theirs are on!
Many fields have a frequency control system. Before you use your radio, be
sure you understand the system and are using it correctly.
AM vs FM / PCM vs PPM
This refers to the signal type (or modulation). A radio wave of any
frequency can have different signal types.
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PPM (pulse proportional modulation) is usually an analog system. This is
very precise (but not digitized). This equipment is more economical than PCM.
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PCM (pulse code modulation) signals are digitized and provide the most
accurate signal. A dedicated computer in the transmitter and receiver
actually use binary code (pulses) in the signal.
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AM signals are always PPM. AM is more subject to interference than FM and
does not allow for the use of a "Buddy" cord.
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FM signals are either PPM or PCM. Usually, only pilots flying competitively
in precision aerobatics or scale use PCM.
Control Features
The following features can be found on many economically priced 4 and 6
channel units:
Servo Reversing
Due to servo rotation and control linkages, control inputs can end up
reversed (i.e. moving the transmitter stick to the right, viewed from
behind, the rudder moves to the left). To remedy this, the transmitter has
servo reversing switches. Just flip this switch and everything moves the
right way.
Adjustable Travel Volume (ATV)
ATV limits the amount of total servo movement. This eliminates excessive
control travel and stress on the servo.
Dual Rates
These switches, usually found on the TX face, allow two different total
travels for ailerons and elevator and can be switched in flight. For some
aerobatic maneuvers, planes need increased control movement, but for normal
flight they don't, thus dual rate is used.
End Point Adjustment (EPA)
EPA is an advanced feature that allows each direction of movement to have a
different travel. For example, if your plane banks too quickly to the left,
turn down the left aileron EPA dial. This will not change the amount of bank
control to the right.
Exponential
Some planes (especially racers) need more control travel at low speeds and
less at high speeds where control response can be overly sensitive.
Exponential changes the relationship between transmitter stick motion
(linear) and the control servo response (non-linear). This feature can be
used to "soften" plane response near the center of stick motion without
lessening the overall amount of control at full stick deflection.
Mixing
Many planes benefit from mixing two functions together. In fact, for planes
like flying wings or V-Tails, mixing is mandatory. For example, a flying
wing's elevators are also its ailerons (these are called elevons). When the
radio has mixing, one servo will be installed for each elevon. Mixed
together, these servos will respond correctly to both the elevator and
aileron inputs.
Computer Radios vs. Standard Radios
A computer radio allows more adjustments and channels to be mixed in a more
precise way. Computer radios also have more trims and setup adjustments
making the radio installation and flight-trimming process of the plane
easier and more precise. Also, the settings can all be saved to memory and
settings for more than one plane can be saved. In more advanced computer
radios, the mixing is programmable, actually allowing custom combinations of
channels and movements (and even control inputs). Competition pilots find
this kind of adjustability a must. Many beginners simply find computer
radios too complicated.
Standard radios have basic mixing but it is not as precise nor as adjustable
as a computer radio. Also, the setting cannot be saved for more than one
plane. However, these radios are simpler to use and are less expensive.
NEXT
- PLANE TYPES
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