S-Turns and zigzagging around LNAV path

[themasterWookie 17]

Hey guys,

I know that this has been a known issue with PMDG aircraft for quite a while, but I only recently started experiencing this in my sim. I run FSX SP1+2 with AS16. Mostly near cruise altitude, my aircraft can hardly ever maintain stable flight. It 'zigzags' around the LNAV path, first either turning to the left or right and then turning in the other direction to compensate for its earlier deviation. 

Now, I've read a lot of forum threads about this issue, and unfortunately, most of them are quite outdated and only deal with Active Sky Evolution/2012 settings. I have, however, tried all the 'solutions' listed in these threads; I've checked and unchecked suppress turbulence, variance, gusts, upper level gusts, wind smoothing, and 'allow changes to FS own weather' in the FSUIPC wind menu. I've changed the TurbulenceRate and TurbulenceDivisor values in FSUIPC.ini, dragging them down to lower levels, and put the "TurbulenceScale" to 0.50000 in fsx.cfg. With AS16, I've dragged my Turbulence effect scale, Updraft, Downdraft and Cloud Turbulence levels all down to 0. I've even tried fixing FSX's registry through Flight1's registry repair tool. Unfortunately, none of these edits have resulted in any change to the aircraft's LNAV performance. 

I've noticed similar LNAV performance in my NGX, 777 and MD-11. It is by far the worst with the MD-11, in which it almost feels like the aircraft is Dutch rolling. 

In case anyone might be knowing about clashes with other addons, these are the non-aircraft, non-scenery addons I use:

FSUIPC 4 (registered), EZDok Camera Addon v2, Active Sky 16, REX Essential Plus.

 

Thank you in advance! 

 

[downscc 1,327]

Wow..., first you claim this is a known issue with PMDG aircraft then cite as reference "outdated ... ASE/2012.." You should not assume this is a common problem.  It is not.

I can suggest several items to look at but in the end this is a problem with your configuration.  First, ensure your controls are calibrated and do not use FSUIPC to calibrate, use the recommendations in the Introduction regarding FSUIPC.  Second you want to ensure that the gust and wind variance settings in AS16 are at a realistic setting. This varies with user and configuration, for comparison I set those to about 20%.  Third, make sure the roll trim is zero and finally ensure that you are not using panel states or saved flights from previous PMDG versions.  Hope this helps.

[PerWel 23]

I have FSX:SE, FSUIPC (reg version) and AS16+ASCA and do NOT have any problems with zigzagging. I have all PMDGs aircrafts and all works as they should.

Remove EZDoc it is known to create a lots of strange things. Disable it and try again, if you still see zigzagging I have no idea what is wrong.

If you see the zigzagging in 777 and ngx and now 747 it must be something external like EZDoc, check PMDGs forums for EZDoc. Have been some issues with it.

I use Opus FSI for cameras, very good. I used FSI for weather before I got AS16.

[paradoxbox 13]

In the MD11 it appears to be version dependent. I can't remember which version has the trouble unfortunately. On my old setup, I never ever had LNAV zigzagging in the MD11. In my new one, I do have zigzags especially when close to the next waypoint.
 

I used to use the MD-11 version that did not have the "L/H configuration) in the loadout manager. This version did not have problems zigzagging regardless of whether Activesky was enabled or not.

[kevinh 409]

9 hours ago, paradoxbox said:

In the MD11 it appears to be version dependent. I can't remember which version has the trouble unfortunately. On my old setup, I never ever had LNAV zigzagging in the MD11. In my new one, I do have zigzags especially when close to the next waypoint.
 

I used to use the MD-11 version that did not have the "L/H configuration) in the loadout manager. This version did not have problems zigzagging regardless of whether Activesky was enabled or not.

I've never had S turn problems with PMDG sims, or anyone else's complex sim addons. The only time I've seen anything like it was when I was using FSX real time weather, which has sudden and violent windshifts which, in combination with the way FSX applies wind, messes up LNAV control. The fact that no one seems to be reporting it in forums recently (apart from you), suggests that if it was a problem relating to weather simulation it has been solved by improvements in weather simulation.

AS16 needs no modification or assistance from FSUIPC, and that might even be making things worse for you.

[themasterWookie 17]

Guys, 

Seems the problem doesn't lie with any weather engine. I fixed my S-Turn issue following Dan's suggestions and the PMDG 747 intro. All I did was recalibrate my joystick using its own drivers and the aircraft now fly flawlessly. @James: If you use a joystick, recalibrate it from its own drivers that were shipped with the hardware. Also, if you use EZDok, drag down the camera effect processor for weather components to 0. That may also help to an extent.

Thank You, guys!

[VHOJT 172]

3 hours ago, themasterWookie said:

Guys, 

Seems the problem doesn't lie with any weather engine. I fixed my S-Turn issue following Dan's suggestions and the PMDG 747 intro. All I did was recalibrate my joystick using its own drivers and the aircraft now fly flawlessly. @James: If you use a joystick, recalibrate it from its own drivers that were shipped with the hardware. Also, if you use EZDok, drag down the camera effect processor for weather components to 0. That may also help to an extent.

Thank You, guys!

Thanks for posting your solution.

And yes - EZDok does do some very strange things before you turn off those effects - that is good advice.  I don't like many effects, and it took me a day to figure out why all my planes were going along the runway as if it had huge potholes.  Good advice.

Cheers,

[paradoxbox 13]

I think I remember what is causing this problem.

Slight null zone issues in your controls set up will cause this. I can't say for certain but I think that the PMDG code controlling null zone / autothrottle behavior changed in some update. Settings that worked previously may cause the porpoising behavior in both lateral and vertical autopilot modes in the updated version.

Changing the sliders in the PMDG menu may solve this, as will changing your controller null zones in FSUIPC or the sim itself should fix this as well.

[elmucki 32]

99% of the time its not the products fault, but user error in one way or another.

[downscc 1,327]

9 hours ago, paradoxbox said:

I think I remember what is causing this problem.

Slight null zone issues in your controls set up will cause this. I can't say for certain but I think that the PMDG code controlling null zone / autothrottle behavior changed in some update. Settings that worked previously may cause the porpoising behavior in both lateral and vertical autopilot modes in the updated version.

Changing the sliders in the PMDG menu may solve this, as will changing your controller null zones in FSUIPC or the sim itself should fix this as well.

I can't follow that logic..., simply because the s-turns are occurring in A/P modes and any interaction by controller would disconnect the A/P.  Also, how is the module being controlled aware of any null zone?  A null zone is where the input to the module being controlled is unchanged by input to the controller.  I suspect the source of the problem in this specific case was the camera/weather.  That add-on can create havoc if not set up properly.

[kevinh 409]

I'm utterly mystified how moving the camera position, which is all Ezdok does, can possibly affect how the sim flies.

[paradoxbox 13]

4 hours ago, downscc said:

I can't follow that logic..., simply because the s-turns are occurring in A/P modes and any interaction by controller would disconnect the A/P.  Also, how is the module being controlled aware of any null zone?  A null zone is where the input to the module being controlled is unchanged by input to the controller.  I suspect the source of the problem in this specific case was the camera/weather.  That add-on can create havoc if not set up properly.

i don't use ezdok.

i am certain it is a controller thing because the problem can be immediately rectified by adjusting the pmdg nullzone, and reintroducing it by reverting the settings.

i don't pretend to know why, but i do know that this fixes the problem.

it may be good to set up a small null zone in your basic FSX or fsuipc controls as well.

 

perhaps it is not a bug, but it is an unwanted behavior and it is definitely caused by the controller sending tiny inputs while engaging autoflight or while it's already engaged. seeing as there are almost no controllers in the consumer world that don't have some center slop or noise, and considering pmdg even put a null zone tool in the software, i think it's fair to say this is part of the aircraft behavior with consumer hardware, and there are tools provided with the aircraft to stop it.