TruTrak Digiflight II Operating Manual - Manual (Page 3)

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General Introduction
The TruTrak autopilot can be defined as being an orthogonal rate system.
This means that gyroscopic rate sensors are installed so as to sense motion
about each of the major axes (roll, yaw, and pitch). These sensors generate
the fast signal responses necessary to create an autopilot with the best
possible dynamic performance.
To fly an aircraft well about the axis controlled by the ailerons, velocity
of aileron movement must be directly proportional to the rate of roll for small
movement. This means that aileron position corrections do not lag behind
motion of the craft about the roll axis. Aileron control systems that use a
turn coordinator, which senses twice as much azimuth as roll rate, cannot do
this. Instead, yaw disturbances in turbulence cause undesired aileron
movement. In some aircraft this effect is so severe that the controls may
even move momentarily in the wrong direction.
The challenge at TruTrak is to create systems with the very best
dynamic performance available—systems that need not be disengaged in
turbulence, but instead provide function when most needed.
The complete TruTrak flight control system combines all the electronic
and sensing elements needed for the roll and pitch functions and interfaces to
a rate-gyro-controlled yaw damper within a single panel-mounted
programmer/computer package.
Basic directional control is provided by digital selection of a GPS track
to be flown. This replaces heading selection on the DG and eliminates drift
as well as crosswind correction. In the GPS steering mode of operation, the
system responds to digital guidance information to fly a complex navigation
program.
The vertical portion of the system contains a pressure signal source for
altitude and vertical speed information, an airspeed signal source, and a high
performance pitch rate gyro. These signals are combined to provide
performance equal to that of the most expensive autopilots. Also by having
airspeed information the system is stall proof.
For any set of features, all TruTrak computers are identical. Servos
likewise are identical in velocity response. Servos do differ according to
total torque required. By providing setup functions in the programmer for
system activity and torque, one TruTrak programmer-servo combination can
fly any aircraft.
As a starting point in understanding how to operate the TruTrak system,
the following describes the presentation of data, the operating controls, and
the procedures for selecting modes of operation.