Having the optional Dynon AP Panel module installed in the DOG Aviation RV-12 necessitates that the autopilot be configured using Van’s “expert mode” configuration files for the autopilot. This is because the AP Panel module requires the SkyView’s autopilot’s settings be set to expert mode to function correctly. This also makes it necessary to perform a calibration of the autopilot’s Auto-Trim function. Why is it necessary to go through the trim calibration process if the anti-servo trim tab moves in the correct direction when the panel mounted trim switch is activated?
JUST BECAUSE THE ANTI-SERVO TRIM TAB MOVES IN THE RIGHT DIRECTION WHEN THE PANEL MOUNTED TRIM SWITCH IS ACTIVATED, DOES NOT MEAN THE AUTO PILOT PANEL MODULE IS CONFIGURED CORRECTLY … THE AUTO-TRIM FUNCTION STILL NEEDS TO BE CALIBRATED.
The reason for the above statement is because there are two trim control circuits at work here. The panel mounted switch is one circuit available to manually trim the aircraft using the panel mounted trim switch. PLUS, there is an additional trim control circuit built into the AP Panel module that can “Auto-Trim” the aircraft during flight when the autopilot is engaged … (I believe this is based on feedback from the autopilot’s pitch servo motor). The Auto-Trim calibration process makes sure the Auto-Trim circuit built into the AP Panel module will move the anti-servo trim tab in the correct direction when the AP Panel module calls for an Auto- Trim correction when the autopilot is engaged.
Calibrating the Auto-Trim is a piece of cake and begins with positioning the anti-servo trim tab approximately in the center of its range of motion prior to entering the Auto-Trim calibration menu in the SkyView. As usual, the Set Up menu is entered by depressing buttons 7 & 8 simultaneously. Using the left joystick, cycle down the list to highlight Hardware Calibration.
The calibration for the autopilot’s auto-trim feature can be accessed from the Hardware Calibration menu highlighted in this photo after joggling the left joystick to the right.
As can be seen in the photo below, one of the options in the Hardware Calibration menu is Trim Motor Configuration. Highlighting the Trim Motor Configuration by moving the left joystick down then joggling the joystick to the right will enter the Trim Motor configuration menu.
The trim motor calibration menu has two choices Motor 1 and Motor 2 … the RV-12 only uses Motor 1.
Selecting Motor 1 will open the options menu for motor 1. The Auto-Trim function is the first item in the list. Note in the photo below that Auto-Trim Function is set to None ... this is because the calibration test has not yet been performed.
With Motor 1's Auto-Trim Function highlighted, joggling the left joy stick to the right will enter the calibration test menu. The test will begin then the “Start” button is pressed.
With the Auto-Trim Function highlighted for Motor 1, as in the photo above, joggling the left joy stick to the right will open the calibration test menu. The testing will begin when the start button is pushed. When the test begins, the AP Panel module will activate the trim motor and move the anti-servo trim tab. The user is to select which “trim” was called for by the AP Panel module based on the direction the aft edge of the anti-servo trim tab moved. In my case, the anti-servo trim tab was moved DOWNWARD … this is “Nose Up” trim. (Remember the trim tab moves opposite of the desired trim, so nose down trim moves the trim tab UP and nose up trim moves the trim tab DOWN). Anyway, the user interface asks which trim was called for and in my case I selected “PITCH NOSE UP” and pressed the OK button.
The test began by the AP Panel module moving the anti-servo trim tab DOWNWARD. This equates to calling for PITCH NOSE UP trim so that entry was highlighted before pressing the OK button to continue the calibration process.
After pressing OK, the AP Panel module moved the anti-servo trim tab in the opposite direction moving the anti-servo trim tab UP this time. On the screen, the user interface asks which trim was called for and in my case I selected “PITCH NOSE DOWN” because the anti-servo tab was moving UP. After highlighting PITCH NOSE DOWN and pressing OK the calibration process is completed … the Auto-Trim feature is now calibrated.
The calibration continued by the AP Panel module moving the anti-servo trim tab UPWARD. This equates to calling for PITCH NOSE DOWN trim so that entry was highlighted before pressing the OK button.
Taking note of the text on the left side of the screen in the above two photos, one can see there are additional trim control settings that can be manipulated. As an example, should the pilot feel that the trim is a little too sensitive at speeds above 100 knots, using the trim speed settings in this menu, the actuation speed of the trim motor can be slowed down if the aircraft is flying faster than the predetermined speed entered in the menu. If the aircraft is moving faster than the predetermined speed, the trim motor will run slower thus the anti-servo trim tab movement will be slowed down thus making the trim “feel” less sensitive above 100 knots. Elected to leave these settings alone for the time being until I get a better feel for the trim ... which can only come after flying the RV-12 for a while. However, it is nice to know the option is there to customize the trim settings should one desire to do so.