Autopilot

The real KLN 90B does not have an integrated autopilot. Therefore, this simulation does not include a custom autopilot either. There are different ways how the autopilot can be interfaced with the KLN-90B:

Follow the needle

Older and simpler autopilots would simply follow the needle. If the needle is to the right, the aircraft will turn right. This type of autopilot will only work correctly, when roughly on course and will require the pilot to make larger course changes manually. This type of autopilot could be implemented by observing GPS WP CROSS TRK

Roll steering

Modern autopilots support roll steering commands from GPS units. The KLN-90B sends roll commands via ARINC 429 Label 121. There are adapters, that convert this digital bank signal into an analogue heading signal for older autopilots. This roll steering command is simulated with the LVar L:KLN90B_RollCommand. The unit is degrees. The range is -30 to 30. Left bank is positive, right bank is negative. The values can have large deviations and may require smoothing in the autopilot code.

Implementation

There is no information about the behavior of the roll steering command in the real KLN-90B. If you know anything about the autopilot behvaiour, please get in touch we me. I implemented it like this: If the aircraft does not intersect the leg or is far away, it will turn towards the leg in a 45° angle. It plans to intercept the track with a 25° bank angle and will turn towards the track with a maximum bank angle of 30° once in range. Once established on the track, it will only command minor course changes.

Default autopilot

If you do not wish to implement a custom autopilot, you can still use the default autopilot from the sim. As mentioned before, the autopilot itself will not be touched by the KLN-90B. Some values like GPS WP BEARING have been tweaked to allow improve performance of the default autopilot.