I recently purchased the RXP GTN 750 and have installed it into Prepar3D v2.5 and v4.2.  This is an amazing product and I am so glad that I purchased this unit.  So far, I have installed it into 2D Windows for the Lear 45, Baron 58 and Mooney Bravo.  Of all the things that I love about this unit, there is one problem that I am experiencing with each aircraft.  During flights that require course changes of 30 degrees or more, the aircraft starts preforming S-Turns and has difficulty tracking and locking on course.  The P3D standard G1000 that I used before I purchased the GTN 750 did not have this problem.  It seems to me that the GTN 750 over responds to course changes greater than 30 degrees.

Is anyone else having this tracking issue?  Is there a way to correct this problem?

Thanks for your help.

Hi,

If you use time acceleration at 4 or more, it is more than possible it causes this. At 2x is should be fine enough.

The only limiting factor to the A/P coupling performance is the A/P settings in the aircraft.cfg. These are usually the ones about how fast the autopilot reacts to F/D changes and what is the maximum bank angle. The default B58 should be ok, the default Mooney more or less ok as well.

Otherwise, you might want to fine-tune and see if you can enhance these aircraft?

http://www.prepar3d.com/SDKv4/sdk/simulation_objects/aircraft_configuration_files.html#autopilot

notably:

• max_pitch_acceleration
• max_pitch_velocity
• max_bank_acceleration
• max_bank_velocity
• max_bank

And for the PIDs:

• nav_proportional_control
• nav_integrator_control
• nav_derivative_control
• nav_derivative_control
• nav_derivative_boundary

About PID:
https://en.wikipedia.org/wiki/PID_controller
http://www.pidlab.com/en/

Thanks for your good advice.  I kept the Autopilot settings standard in the Aircraft.cfg file with one exception - for the Lear 45, I adjusted the nav_proportional_control from 11.0 to 9.0.  It didn't seem to help.  I'll adjust the time acceleration from x4 to x2.

Thanks for your help.

 

Hi, just to let you know, the latest GTN v2.5 (and GNS V2 v2.4) are now compatible with host simulator time acceleration, up to 128x. 

I can tell you I was even skeptical at first during beta tests, but it is amazingly tracking the flight plan including turns!

Thank you for your feedback, it has been in our list since day 1 but we've never had the chance to further this capability before.

Edited April 15, 20188 yr by RXP

GTN 750 v2.5 has completely resolved my tracking issues.  With the Lear 45 set at 300 kts [GS@380 kts], I can make enroute turns at x16 and x32 without any issues.  Significant improvement in tracking,  good job RXP.

Thanks for your assistance with this issue.

Yes it makes a whole lot different indeed, and like I said above, I was even skeptical this would track this good at these time acceleration factors. It is nearly amusing to see the GTN (and the GNS V2 has the same capability in v2.4 too) make the aircraft turn so fast and align so promptly to the track!