S-TEC 55x Role Rate Parameters

[Jeff_S]

Hey all,

I'm trying to address an issue that has been slightly vexing since I bought this airplane.  The S-TEC 55x is a fine A/P for its generation...although I've already inquired from Mooney if there is ever going to be an upgrade path to the new Garmin GFC600 or Genesys digital A/Ps...their response was "we'll look into it."  So maybe someday.

In the meantime, I would like to address what has always been a slow roll-rate for GPSS.  On any kind of hold or course turn, the roll rate is slow to develop and I always fly outside the designated flight path and then angle my way back onto it.  While installing the GTX345, my avionics guy showed me how to access the STEC config page of the G1000 and there is a setting for roll rate. It was set to -17, which he said was the maximum "inhibitor" setting meaning that would make roll the slowest. We set it to -13, but I can't tell if that's had much effect. My question to anyone with knowledge about STECs in general, or this G1000 configuration, is what settings they use or have experimented with.  Has anyone tweaked these settings before to improve roll rate? If so, where did you end up?

This may apply equally to the other S-TEC models, so if you've made changes to a -30 or other model I'd be interested to hear how that worked. Thanks!

Jeff

[jasona900]

I have found the roll rate and angle of bank is rather "brisk" when I select GPSS on my 55x.  Mine is being fed by a GNS-480, and to my knowledge, there is no roll rate setting on that unit.  I have noticed when I select HDG or NAV, the roll rate is much slower.  I have not yet tried a hold with the AP, as my purchase was also rather recent.

On a side note, and defiantly not trying to steer the thread in a different direction, but I cannot dim the display on the 55x during night operations.  Wondering if that is something that should be wired into the instrument dimmer, or if I am missing something.  Searched on google with no luck, so I'm guessing it is either not wired correctly, or not possible.

[carusoam]

From outside experience...

really good process controllers have three variables that they use...  P, I, & D (proportional, integral, derivative)

https://en.m.wikipedia.org/wiki/PID_controller

I would expect that are APs are pretty good controllers using feed back from our attitude indicators...

New controllers are self tuning.  Old controllers were set up by engineers following the tuning process.  Every plane would have to go through this tuning process.  Some planes like all M20Js may be close enough to share their settings...

nothing beats a smart self tuning controller...

the variables essentially adjust how quickly the controller reacts, how large a step it takes, how close it gets in its solution with overshooting...

Great theory, hope you get a solution without having to go this far...

essentially our APs are nice process controllers with attitude sensors and servo motors for control.  Tune them properly they should be able to fly to a spot and join the magenta line perfectly.  If it flys through the spot and oscillates all over the magenta line there is room for tuning improvement...

lesser controllers are P, and PI.  The best ones are PID...

Best regards,

-a-