Let’s review. We have the servos
moving in the correct direction and have
centered the servos and adjusted the
travel to get the recommend travel on all
controls. We are ready to fly, right?
Well, maybe not. There are a few
more features that you need to be aware
of that can help make the model easier
and more fun to fly.
Let’s discuss dual rates. This program
allows a pilot to adjust the total travel of
a specific control surface with the flip of
a switch. A good example of this is on
the elevator. Most aircraft instructions
will come with travel recommendations
for both high and low rates. Previously
we set up the high-rate travel. Now, you
can adjust low rates.
Referring to the radio manual, select
the dual-rate program and choose
elevator. Find the switch that controls the
elevator dual rates. When the switch is
flipped up toward the top or back of the
transmitter (depending if it is mounted
to the front or top of the transmitter),
that is usually the high-rate position. You
won’t need to make any adjustment for
this switch position.
Now flip the switch down or back
toward yourself. That will be the low-rate position. Referring to the radio
manual, reduce the 100% setting to
roughly 70%, or whatever measurement
for the control travel at low rates. Adjust
the percentage until you achieve the
desired amount of travel.
Now, if you hold full up on the
elevator stick and flip the switch back
and forth, you will see the travel of the
elevator change. This allows you to select
more or less throw while flying in order
to complete a specific maneuver. In the
case of elevator, it usually takes more
elevator to perform snap rolls or spins
that you would want to use in normal
flight, so you take off and land and do
most of your flying at low rates.
When you want to perform a spin or
snap, flip the switch and you have the
control you need to do the maneuver.
Afterward, switch back to continue
flying. Very handy indeed! Go through
the rest of the channels and set them up
as well. Dual-rate rudder can be helpful
to keep you from oversteering on takeoff
by switching to low rates when you
start the takeoff roll.
Exponential is something that I think
most newcomers don’t understand.
Exponential changes the response of
the servo from linear (proportionally
following the exact motion of the stick),
to a nonlinear response.
Taking elevator and aileron control
as examples, most aircraft are sensitive
around the neutral point, so only a small
amount of control movement is needed
to make minor corrections in flight.
This is where typical use of exponential
comes in. Adding some exponential to
the control will make the servo move
less when the stick is moved around the
neutral point and more when the stick is
moved near the end of its travel.
Depending upon the radio system
and how it is set up, you can select
exponential as part of the dual rate
program, so that you can have different
amounts of exponential with different
amounts of travel as selected by the
dual-rate switch position. Again using
elevator as the example, enter the
radio program for exponential and
select elevator. By flipping the dual-rate
elevator switch, you can determine
where you need to make the change in
the exponential program.
At high rates, you will normally want
a higher amount of exponential—40%
to 70%. Check your manual for
recommended amounts. At low-rate
elevator, you will normally set a lower
amount, maybe 20% to 50%. With these
values entered, slowly move the elevator
stick from neutral to full up.
You will notice that the control
surface moves very little around
neutral, but then moves much farther
as you get to full stick deflection.
Again, do the same for all of the other
controls. Sometimes exponential
can help with glow and gas engines,
because most have almost no power
increase from 70% to full throttle.
Adding exponential will give a more
linear engine response to your throttle
In some instances, you might find that
your setting actually results in making
the travel around neutral greater and
the travel at the end smaller. In this case,
you will need to go the reverse direction
(negative number) on your exponential
input. That is, instead of 40%, make it
-40% on the screen. This information is
usually in your radio manual, so check
that before you start making changes.
Using exponential on ailerons and
elevator are a must for me! It makes
all of my models—from trainers to jets
to 3-D machines—easy to fly. I can fly
lazily around, or switch to high rates and
high exponential to hover or perform
3-D maneuvers. With many of my
models, I don’t even use dual rates, only
exponential. Then I don’t have to flip
switches or remember to flip them when
I am flying!
Finally, I’ll touch on mixing. Most
fliers will not get into mixing at all, but
some will find it makes certain models
easier to fly. Take a J- 3 Cub, for instance.
Most will turn better using both rudder
and ailerons to bank. The full-scale J- 3
Cub definitely requires rudder to turn
Using a mix to allow a small amount
of rudder to automatically move
whenever you use the ailerons can make
flying easier, especially for inexperienced
pilots. Simply follow the programming
instructions and select aileron as the
master channel and rudder as the slave.
Set the mix to 10% or whatever is
recommended in the aircraft manual.
Make sure that the rudder is moving
to the right when you are giving right
aileron input! If it is backward, simply
reduce the number until it reads -10%.
There is normally a switch that turns
this mix on and off, so you can steer
normally on the ground, but switch the
mix on in flight. In crosswind landings,
sometimes it is important to be able to
turn the mix off to compensate for wind.
I hope this brief introduction into
basic radio programming helps you
better understand your radio and how
its features can enhance you model
flying experience and even aid in quickly
setting up a new model!
See you at the field!
RB4 Model Aviation JULY 2017 www.ModelAviation.com