Product Overview

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 sense twice as much azimuth as roll rate) cannot do this. Instead, in turbulence, yaw disturbances 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 beyond question 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 within a single panel-mounted programmer/computer package all the electronic and sensing elements needed for the roll and pitch functions and interfaces to a rate-gyro-controlled yaw damper.

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. It is likely that the DG heading bug will become obsolete. In the GPS NAV mode of operation the system responds to digital guidance information so as to fly a complex navigation program. This function has also been referred to as GPS Steering.

The vertical portion of the system contains a digital altimeter and associated altitude selector capable of selection in increments as small as fifty feet. Altitude transitions can be made either by airspeed or vertical speed selection. If an upward vertical speed is selected which is beyond the capability of the aircraft, there will be no stall. Instead, the autopilot will cause the aircraft to climb at a pre-set minimum safe airspeed. This is the only known system to provide this safety feature.

The programmer has an illuminated digital display that shows modes and related numerical data. Controls consist of an ON/OFF button, a MODE button, an ALT (altitude) button, a rotary/push selector for numeric functions and data entry, and buttons for VS UP and VS DOWN. Operation is self-explanatory when these controls are used in conjunction with the display.

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 engineers we tend to be consumed with the technology challenge of creating the very best product, but extensive experience in this field has shown that a company can have the best product and still not excel without good customer relations. At Trutrak Flight Systems the customer will be well treated and not ignored after the sale. Our upgrade policy exemplifies this. If you buy a single-servo system and expand the installation later, you will only pay the difference in system price. Any unit may be exchanged at any time for one with more features, for the difference in published price at the time of exchange.

Except for the Digiflight series, all programmers fit a 3ATI panel cutout or within the avionics stack. The Digiflight is in a flat package measuring 1.6" H x 4.2" W. The servos employ a digital stepping torque motor operating through a single gear pass to drive the output shaft. With no brushes to wear out, this is the most reliable mechanical servo available, one that should outlast the aircraft in which it is installed. To accommodate variations in aircraft requirements, Trutrak provides a choice of four different torque capability servos, which are mechanically interchangeable. So the human pilot can override the autopilot with the least possible effort, the maximum torque capability of the servo is then electronically set to the lowest value that allows the autopilot adequate control authority. This is more accurate than the conventional mechanical clutch.

For simplicity and reliability the digital servo remains coupled to the control system when not active and does impose a small residual torque load. This is why the smallest servo with adequate torque capability should be chosen. The chart below lists the four servo sizes and related torque and weight information.