DUAL RATES AND EXPONENTIAL CURVES
A53
Dual Rates and Exponential curves can be very effective
in setting up an aircraft to “feel” the way you would like
it to feel when performing different types of maneuvers.
You can essentially change the aircraft’s personality just
by flipping a switch, causing the aircraft to take on traits
that make certain maneuvers easier for the pilot. At times
you may want the aircraft to feel very crisp, such as when
performing point rolls and sided-loops and then feel
softer for other maneuvers, such as rolling circles and
consecutive rolls, and yet other times when you would
like the aircraft to be very crisp but without a the tendency
to be over-controlled, like in performing snap rolls. Dual
Rates and Exponential curves can be combined to produce
these traits for most any aircraft. When programming a
Dual Rate and Exponential curve, always think about what
kind of maneuver or flying style you plan to accomplish
with it.
Dual Rates (D/R) limit how far a control surface travels.
Without dual rates your control surfaces deflect to their
full travel – the travel that you previously established with
the TRVL ADJ. function and linkage setup. When a D/R is
programmed, it limits the amount of deflection that occurs
when the stick is moved to its extremes. For example, if
you set an Elevator D/R to 75%, the Elevator will only
deflect 75% or 3/4 of its full travel; if set to 50%, it will be
limited to ½ of its full travel; and so forth. A D/R setting of
100% results in full travel again, as though there were no
D/R programmed at all.
An example of programming a D/R for the Ailerons
would be to set up an Aileron D/R for flying consecutive
rolls by setting the Aileron D/R to 25% (actual percentage
will vary). At this setting, moving the Aileron stick full
left or full right would result in a roll rate of about 1 roll
per second. This allows you to deflect the Aileron stick
all the way and just hold it there while concentrating on
Elevator and Rudder inputs – flying consecutive rolls
just became easier.
EXPONENTIAL (EXP) does not limit the total deflection
of a servo/control surface – the surface still moves
100% of its travel. It does, however, determine how the
surface reaches its full travel, or how the control surface
moves relative to the stick. When Exponential is not used,
the servo response is said to be linear. That is, every
movement of the stick causes the same movement in the
servo--if the stick moves 20%, the servo moves 20% and
the control surface follows the stick throughout the entire
travel range. When plotted on a graph where the X-axis
(left and right) = stick movement and the Y-axis (up and
down) = servo movement, the result is a straight line that
is at 45 degrees.
When using Exponential, a positive (+) exponential
percentage causes the servo to move less when the stick
is close to the neutral point, and to move more as the
stick moves further from the neutral point. For instance,
the stick is moved from neutral to 30% and the servo
only moves from neutral to 10%. As the stick is moved
further from center (from 30% to 50%), the servo moves
further and faster (from 10% to 35%). The further the
stick is moved away from center, the higher the rate of
servo movement. The larger the positive (+) Exponential
percentage, the further the stick must be moved from
center before the servo rate increases, and the faster the
servo rate becomes when it gets close to the end of its
travel. When stick travel (left and right) versus servo
travel (up and down) is plotted on a graph, the result is a
“curve.” The curve stays close to the X-axis at the center
(small servo movement) and moves away from the X-axis
at a greater rate (more servo movement) as the stick is
moved further off center.
Exponential is typically used to reduce sensitivity or
otherwise dampen movements around the neutral stick
position without sacrificing full servo travel. This provides
the pilot with very smooth and precise control of the
aircraft while allowing relatively large movements in the
control stick. It becomes easier to make very smooth and
precise corrections that are difficult to detect.
If negative exponential is used, it has the opposite effect.
Servo travel is increased around center and slows towards
the ends. Care must be taken with negative exponential,
as an aircraft that is already overly sensitive may become
uncontrollable with negative exponential. It can prove
useful, however, when hovering a 3D type aircraft.
To Next Page
Loading...
Need help?
General
