Autopilot Parameters
Posted: Sun Feb 29, 2004 11:25 amA very interesting auto pilot analysis by lilo
This is the narrative from Official FS Site 2. Go there to see the screenshots.
From: lilo_we Sent: 2/28/2004 6:32 PM
Hi,
in FS2K4 there are new settings in the aircraft.cfg file which allow you to change the behavior of the autopilot. For example, these are the original parameters for the Beechcraft Baron 58:
...
[autopilot]
...
nav_proportional_control=9.00
nav_integrator_control=0.25
nav_derivative_control=0.00
nav_integrator_boundary=2.50
nav_derivative_boundary=0.00
gs_proportional_control=9.52
gs_integrator_control=0.26
gs_derivative_control=0.00
gs_integrator_boundary=0.70
gs_derivative_boundary=0.00
...
"nav_" stands for navigational control and "gs_" for glideslope control. According to the Aircraft Container part of the FS SDK 2004 these parameters are the constants of a PID feedback controller. If you are unfamiliar with PID controllers seach the Web for "PID feedback controller" and you will find a lot of related introductions, summaries and tutorials. In short the proportional part reduces the time to reach the desired output for the first time and increases the overshoot. Unfortunately it doesn't eliminate the steady state error. The integral part eliminates the steady state error but increases the overshoot as well as the time to settle down to the desired output. The derivative part mainly reduces the overshoot. All three parts interact with each other. So if you want to change one parameter you also have to change the other two to find the perfect combination. You can even ommit one part by setting the corresponding constant to zero to create a P, PI or PD controller.
If I am not totally wrong by default both the NAV and the glideslope controllers work in PI mode for all aircrafts. Which means the derivative part is inactive resulting in overshoots.
So I started with an experiment. I created a test flight with ABL-script to make the flights reproducable. The flight starts some miles east of EDDE heading 45
This is the narrative from Official FS Site 2. Go there to see the screenshots.
From: lilo_we Sent: 2/28/2004 6:32 PM
Hi,
in FS2K4 there are new settings in the aircraft.cfg file which allow you to change the behavior of the autopilot. For example, these are the original parameters for the Beechcraft Baron 58:
...
[autopilot]
...
nav_proportional_control=9.00
nav_integrator_control=0.25
nav_derivative_control=0.00
nav_integrator_boundary=2.50
nav_derivative_boundary=0.00
gs_proportional_control=9.52
gs_integrator_control=0.26
gs_derivative_control=0.00
gs_integrator_boundary=0.70
gs_derivative_boundary=0.00
...
"nav_" stands for navigational control and "gs_" for glideslope control. According to the Aircraft Container part of the FS SDK 2004 these parameters are the constants of a PID feedback controller. If you are unfamiliar with PID controllers seach the Web for "PID feedback controller" and you will find a lot of related introductions, summaries and tutorials. In short the proportional part reduces the time to reach the desired output for the first time and increases the overshoot. Unfortunately it doesn't eliminate the steady state error. The integral part eliminates the steady state error but increases the overshoot as well as the time to settle down to the desired output. The derivative part mainly reduces the overshoot. All three parts interact with each other. So if you want to change one parameter you also have to change the other two to find the perfect combination. You can even ommit one part by setting the corresponding constant to zero to create a P, PI or PD controller.
If I am not totally wrong by default both the NAV and the glideslope controllers work in PI mode for all aircrafts. Which means the derivative part is inactive resulting in overshoots.
So I started with an experiment. I created a test flight with ABL-script to make the flights reproducable. The flight starts some miles east of EDDE heading 45