GRT Autopilot Post-Installation Checkout All GRT EFIS Models April 2011 Grand Rapids Technologies, Inc. 3133 Madison Avenue SE Wyoming MI 49548 616-245-7700 www.grtavionics.com
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GRT Servo Post-Installation Checkout Procedure This procedure is to be performed when access to the servos is easily available. This allows for detailed inspection, and any necessary troubleshooting. Warnings GRT Avionics has mounting kits and is currently developing specific instructions regarding the installation of servos in various aircraft. We do not represent that we are experts or that our advice should be solely relied upon to accomplish a safe installation of the servos. We encourage the installer to consult with us, as well as the aircraft designer, and any other expert that is appropriate, to evaluate the safety of the installation. Our mounting kits, while specific to many aircraft, is not assurance that the installation accomplished with it is safe. There are many variables, various and possible unknown versions of each type aircraft that may or may not be known to us, as well as alterations that may be made to an aircraft by the builder, or installation variations or errors that we can not be aware of that can adversely affect the safety of the installation. The flight control system of the airplane is one of the most critical aspects of the airplane. Failure of the flight controls is likely to result in death. Appropriate attention must be paid to assure the servo installation does not adversely affect the integrity of the flight controls. Visually inspect the servo installation to confirm the following: WARNING: Movement of the flight controls results in no binding, and the servo arms are at all times more than 30 degrees of rotation away from an over-center condition. This must be verified by moving the flight controls (aileron and elevator) to all possible positions, including full up and right, full up and left, full down and right, full down and left, and all other positions. Failure to comply with this requirement can result in locked flight controls, which if were to occur in flight, would result in certain death. WARNING: Verify the servo is mounting is secure and all mounting hardware has been safety-wired, uses castled nuts with cotter pins, or uses self-locking hardware as is appropriate. Similarly, any hardware associated with the flight controls that are altered to accept the servo installation must be replaced with similar hardware that includes the same type of locking for the nut. Inflight failure of the flight controls due to hardware that become disconnected or jammed will likely result in death. GRT Autopilot Post-Installation Checkout pg. 1 Initial Release
WARNING: Rod ends must include large washers through the mounting bolts, such that if the rod end was to fail by the bearing separating from the rod end housing, the rod end housing is retained by the large washer so that the pushrod can not become loose in the airplane. The rod ends have the minimum number of threads in the pushrods, and they have been secured with stop nuts. Air may circulate around the servo to allow adequate cooling. Wiring to the servo is secured so that it can not interfere with the flight controls, and does not touch any moving parts. The total amount of slop (also called, lost motion or dead band) in the linkage, from the control surface through all linkage, to the servo arm, should be minimized. Excessive slop can result in degraded autopilot performance. Airflow around the servo is not restricted to allow convection around the servo to allow it to cool. If the servo is allowed to get too hot, the torque it can supply will be limited. Configuring the Display Unit to Drive Servo(s) 1. Use the soft keys, select the Set Menu, and then "General Setup". 2. Refer to GRT A/P and your specific wiring diagram. Configure the serial input and output wired to the servos as "GRT Autopilot Servo", and set the rate to 9600. 3. Set the "Autopilot Engage Switch Configuration" to "Single Switch for Pitch and Roll" if one engage switch is used for pitch and roll, or "Separate Switch for Pitch and Roll" if wired with one switch for each axis. When power is turned on to the servo(s), the serial port input counter will advance rapidly (more than 200 counts per second). Since both servos use multiplex communication on the same serial input to the display unit, this does not assure that both servos are working. See the checkout procedure. Electrical Checkout Procedure: 1. Select the "A/P Maintenance" Page from the "Set Menu" using the display unit soft keys. 2. Turn on power to the servos using the servo Power/Servo Disable switch specified in the wiring diagram. 3. Serial communication to each servo can be verified by observing the "Roll Software Version" and "Pitch Software Version" is not grayed-out, and a software GRT Autopilot Post-Installation Checkout pg. 2 Initial Release
version is indicated for each servo. If this is not observed, check power and serial connections to the servo. 4. Set the Roll and Pitch Torque to the highest setting. 5. Select the "Roll Servo Direction" setting and press the knob. Select "YES" in response to the "Run Servo Direction Test?" The roll servo should move. 6. Allow the servo to move until it moves the aileron to its stops. Depending on the design of the airplane's flight controls; it may be necessary to manually assist the servo by applying pressure to the control stick. 7. Verify that the servo does not go anywhere close to over center when the servo is at the limit of its travel. Verify also that the mounting of the servo is rigid such that its mount does not bend, or deflect in such a way that the servo can move its output arm after the aileron linkage has reached its stop. 8. Repeat this test in the other direction by pressing the "REVERSE" soft key. Again, verify the mounting of the servo is rigid such that its mount does not bend, or deflect in such a way that the servo can move its output arm after the aileron linkage has reached its stop. 9. Before exiting this test, use the "REVERSE" soft key as necessary to set the correct servo direction according to the directions on the display unit screen, and press "CONFIRM" when complete. 10. Repeat steps 5-9 for the pitch servo. 11. Verify the operation of the engage/disengage momentary switch(es) by observing the affect the engage discrete status for the servo(s). 12. If the disengage discrete is connected, verify its operation by observing the disengage discrete status for the roll servo. 13. Verify the pitch torque sensed does not change when the engage/disengage or disengage switches are activated. The pitch servo must not have a disengage connection, as this would interfere with its torque sensing. Pitch Trim Calibration This calibration may need to be repeated if the servo torque setting is changed. For the initial calibration, set the pitch servo torque setting to 11, as described below. Select the "Set Menu" from the soft keys, and "A/P Maintenance" page. Select the "Pitch Trim Calibration" from this menu. This page displays a value that represents the torque being sensed by the servo. It also shows the minimum and maximum values sensed. These values are reset each time this page is selected. To calibrate the pitch trim sensing: 1. Set the pitch servo torque to 11. 2. Press the "Start Cal" soft key. 3. The pitch servo will engage, and will automatically be set to torque setting that is a set percentage of the maximum. GRT Autopilot Post-Installation Checkout pg. 3 Initial Release
4. Apply a very slight back pressure to the control stick. Very slowly increase the back pressure applied until the servo slips. 5. Repeat step 4 several times until the minimum/maximum no longer changes. 6. Repeat steps 4 and 5, but this time applying forward pressure. 7. When the test is complete, press the "Store Trim Cal" soft key. (If you forget to press this soft key, you will be prompted before you exit the page.) Flight Testing Flight testing is required to adjust the gains for optimal autopilot response. Optimal response will provide: Minimal oscillations in pitch and roll. Rapid acquisition of the selected targets (such as the selected heading and altitude, GPS course, etc.) Comfortable ride quality in turbulence. The first two characteristics are trade-offs. If the gain is set very low, the autopilot will have a slow, deliberate response, without oscillations, but the acquisition of the selected targets will be very slow. Conversely, a high gain might allow rapid response, but with oscillations and overshoots. When the gain is adjusted properly, it will also be noted that the autopilot provides a comfortable ride in turbulence, while still accurately controlling the airplane. If the gain is too high, it will feel as if turbulence is amplified by the autopilot. If the gain is too low, the airplane will be slow to respond to turbulence and will not hold an altitude or vertical speed, or track a GPS course or heading. The pilot should keep these trade-offs in mind when adjusting the autopilot. These qualities dictate proper autopilot response. In summary: Condition Slow to acquire, or inaccurate tracking of a selected heading, gps course, etc. Oscillations or overshoots in roll significant enough to reduce ride quality. Turbulence seems to be amplified (made worse) by the autopilot. When in turbulence, the airplane does not hold a selected altitude, or pitch attitude deviates significantly Meaning Roll Gain is too low. Increase gain. Roll Gain is too high. Reduce gain. Roll and/or Pitch gain is too high. Reduce gain on one or both axis until roll and pitch response to turbulence is optimized. Pitch gain is too low. Increase gain. GRT Autopilot Post-Installation Checkout pg. 4 Initial Release
when in vertical speed mode. (Do not use the climb/descent on airspeed function to adjust or evaluate pitch gains.) When in turbulence, the airplane does not hold a selected heading, or does not track a GPS course accurately. Roll gain is too low. Increase gain. The recommended steps for adjusting the autopilot are: Before Flight: 1. At the bottom of the "General Setup" menu, set all autopilot gain adjustments to 1.00. This is the default gains for each of the individual autopilot functions. These settings may be adjusted after the "Roll and Pitch Autopilot Gains" are adjusted. 2. Using the "Autopilot Settings" menu, set the roll and pitch "Gain Settings" to "0-Nominal". 3. Turn off the servo power until in-flight so the autopilot is not inadvertently activated before it has been adjusted. In Flight 1. Climb to a safe altitude, away from obstacles. Trim for hands-off level flight. 2. Turn servo power on. 3. Press the engage/disengage button to activate the autopilot. 4. Select "Straight & Level". The autopilot will now be attempting to hold the current altitude and heading. 5. If flying in turbulence, try various pitch gains * to evaluate the performance of the autopilot at holding altitude. If in smooth air, change the selected altitude by 50-100 feet, and evaluate the response of the autopilot. Use the table above to adjust the pitch gain settings on the autopilot settings menu. 6. Similarly, use the heading select function to evaluate roll gains*. If in turbulence, evaluate the ride quality and performance at holding the selected heading. If in still air, change the selected heading by 15 degrees, and evaluate the response. 7. Optimum gain settings will probably require flying the airplane in both smooth and turbulent air to evaluate various gain settings. * When changing gains, choose a gain that is double or half of the current gain. For example, if the pitch gain was at the default setting of "0-100% (default), and the gain seems too low, change the setting to 4-200%. Similarly, if is still too low, then try "8-400%". Once the approximate gain is determined, small GRT Autopilot Post-Installation Checkout pg. 5 Initial Release
adjustments can be made. Typically, little change in response will be noted if unless the gain is changed by double or half. GRT Autopilot (Using GRT Avionics Autopilot Servos) The GRT Servo/Autopilot provide for full autopilot functionality in both roll and pitch for all phases of flight, including coupling to lateral and vertical navigations sources (Optional GRT Sport software required). The autopilot includes many safety features, including the ability to override the servo by applying force to the control stick at any time. Safety features are also built into the servos to prevent them from jamming the flight controls in the rare case of a mechanical failure of the servo. Autopilot Operation The wiring of the GRT autopilot servos includes a servo power switch, an engage/disengage momentary pushbutton, and an optional disengage momentary pushbutton. Servo Power Switch This switch provides electrical power to the servo. Normally power is turned on just after takeoff, and turned off just before landing. The servos will not engage (become active) when power is applied. The servos will only engage if they are powered and the EFIS commands them to engage. The power switch is also an important safety feature, as removing power from the servo will always disengage them and return full control of the airplane to the pilot. Future versions of the EFIS software may provide an option for automatic envelope protection features. This feature would only be functional if the servos are powered. Engage/Disengage Pushbutton This button commands the autopilot function to engage the servo and control the airplane. The first press of this button will engage the autopilot, and simultaneously display the autopilot shortcut menu. Pressing this button again will disengage the autopilot and return control of the airplane to the pilot. The airplane may be wired with one "Engage/Disengage" button for each axis, or it may include one switch for both axis. Disengage Pushbutton GRT Autopilot Post-Installation Checkout pg. 6 Initial Release
This switch is wired only to the roll servo. When activated, this button always disengages the autopilot. Often this button is located on the control stick to provide a convenient means of disconnecting the autopilot. Autopilot Operation The autopilot is engaged by momentarily pressing the "engage/disengage" pushbutton. The autopilot will begin operating, with its mode set to vertical speed hold and heading hold. Selected heading and altitude will not apply. In this mode, the autopilot will simply attempt to hold the current vertical speed and heading indefinitely. The autopilot shortcut menu will appear, and further autopilot modes may be selected from this menu, as described below. See the "Autopilot Shortcut Menu" for more information about the various autopilot modes. Response to Unusual Attitudes during Autopilot Engagement and Operation Roll Engaging the autopilot with a roll angle exceeding 10 degrees will cause the autopilot to first roll wings level before entering the heading hold mode. Pitch The autopilot cannot control altitude or vertical speed when the roll angle exceeds 65 degrees. If the autopilot is engaged with a roll angle exceeding 65 degrees, the pitch control will be suspended (the pitch servo will not be engaged) until the airplane has rolled to less than 60 degrees of bank. Similarly, if the autopilot is operating, and the roll angle exceeds 65 degrees, the autopilot will suspend pitch control and disengage the pitch servo. When the roll angle is reduced to less than 60 degrees of bank, it will resume normal operation. While the pitch function is suspended due to excessive bank angle, the EFIS will show the pitch autopilot mode as "SUSP". GRT Autopilot Post-Installation Checkout pg. 7 Initial Release