I've been enjoying the JS41 for just over a year now, but something has come up that is a bit annoying and I would love to be able to fix it. In the beginning, I was amazed at this bird's autopilot system. I would intercept the LOC (on a reasonable intercept angle) with absolutely no overshoot and it would track the LOC and GS down to the DH without even a hint of deviation on the needles, literally none to be seen. At that stage, the Jetstream was my only add-on apart from IVap client.

 

These days things aren't going so smoothly. The GS tracking became worse up to the point where it would deviate up to 1 "dot" close to DH. A few weeks ago I did an FSX rebuild and things are looking slightly better, but not as good as in the beginning; I still see a bit of an overshoot even on normal LOC intercept angles and there are small deviations on the GS needle.

 

Things I've added to my FSX since starting with the JS41 is the PMDG NGX as well as FS2CREW for both the NGX and the JS41. I run a pretty standard FSX apart from that, as my rig is pretty old, I run on low settings for the most part except that which is needed to get enough out of the wonderful cockpits of these PMDG planes.

 

So my question is: what could have changed to make the JS41 behave slightly less perfect than it used to? I've had a look at the aircraft.cfg file and it looks like the autopilot gains are user changeable, although I would really like to avoid this approach as I do not want to mess with what PMDG has gifted the Simming world (and they may frown upon me messing with their control design). Messing with these would also mean a lot of experimenting which I would rather avoid.

 

Carl Kohrs

This might sound crazy, but have you defragged recently, or is your available disk space getting low? If your system is having a hard time pulling all of the pieces together, or has less space to stick data, it will take more time to process. If that's true, the calculations will be slower and turns may be delayed, which would result in overshoots.

 

Inside the sim, are you trying to intercept at higher speeds? Is the angle less than about 30 degrees?

Hi. Thanks for the hints. I will try a defrag, haven't done one in a while. Intercept speeds and angles are the same if memory serves correctly, also, I do not believe these can be the only culprits as I believe the problems are related to the way the PID controller controls the plane, as it seems everything is slightly off; I did a quick check again and I even get overshoots on ALT SEL. It would slow down close to the selected Alt, but not stop completely and go to 10 or 15 feet above.

 

If this is the case, I guess my system performance may be the issue. It is possible that if there are fewer resources, the PID controller error check iterations rate are reduced and then it will take longer to correct errors, and may even result in overcorrections, which will explain some of the behaviour seen before my FSX rebuild. Will give it a try and if it works I'll mail you a beer, because this has been bugging me a while now.

 

Carl Kohrs

Are you using different weather settings than what you use to? I found that using REX made a difference to the stability of my landings because there is more wind/turbulance in my flghts now. Maybe try a "calm" weather setting and see if that makes a difference.

Will give the calm weather a try as well. No weather add-ons. Really, its just the NGX, J41, FS2crew for both and Ivap. Does anyone have any suggestions on the legality, advisability of playing with the autopilot controller gains?

 

Carl Kohrs

Does anyone have any suggestions on the legality, advisability of playing with the autopilot controller gains?

 

I'm not going to play armchair lawyer here, but from the side of usability and avoiding destroying things, I'd avoid it at all costs. If it has worked before (as you stated), it's clearly not an inner workings issue.

OK so I've done a defrag and did a flight with clear skies: no change.

 

I'm wondering whether I'm expecting too much. I seem to remember clearly it aligning perfectly with the LOC with (as mentioned) no overshoot AT ALL. But maybe I remember incorrectly. It was my first add-on and I was still trying to get my head around the sheer magnificence of it that a very slight overshoot seemed perfect compared to the stock-standard FSX wrecks I had flown before, which seem like they barely stabilize on the LOC before touchdown. How do you guys find it? Does it get on LOC without any overshoot and stays nailed to the LOC and GS all the way down? Does it overshoot alt's on autopilot, or lose about ten feet in turns, or does it stay perfectly on the desired alt? Of course on all of these I am asking considering the limitations of the plane, i.e. I'm not asking whether it overshoot from a 4000ft/min descent.

 

Basically: am I being too hard on the bird, or am I picking up something slightly out of the ordinary?

 

Carl Kohrs

I haven't flown JS41 for a while but IIRC the AP on that plane is not as precise as on other aircrafts (i.e. MD-11 or NGX) and I have a memory that there were sometimes deviations on the GS up to even a dot. Should take some time to check that up in the sim though.

Have you tried this at a couple different airports?