strange behavior, when chaning weather conditions (inflight)

[JackJones 3]

Hello everyone,i noticed very strange behavior of the aircraft (in this case B737) inflight, after the wind changes from head to cross wind (FL380).The aircraft tries to stay on LNAV path by tumbling from left to the right. It was so extreme that "bank angle" warning was to hear.I limited the bank after t/o to 25° with no resultPS: FSUIPC is a reg. version with wind limitation enabled....

[DaveCT2003 1,820]

Very interesting. Over 30+ flights in the NGX I've encounter something similar on just two occasions. It's only happened twice. I wasn't watching the winds that closely, so I don't know if it was caused by an abrupt wind change. I have Active Sky Evolution and the registered version FSUIPC, using the settings recommended in this forum.During both instances the aircraft snapped to the left so fast (first was under 1 second and the other took about 1 second) so I don't believe it was autopilot input that caused either event.The first event occurred when I was landing (don't remember where) and the aircraft was at approximately 50ft, on profile, with Autoland engaged. The aircraft snapped 45 degrees to the left with no warning and without changing aircraft attitude. It occurred in less than 1 second and I was able to correct as I had my hands on the controls.Conditions:-Landing (don't remember which airport).-ILS Approach-Autoland engaged (both auto pilots engaged)-No control input (I wasn't touching any of the flight controls)-Aircraft was at approximately 50ft AGL-No system failures before or after-No Cautions or WarningsThe second event was far more severe. The aircraft snapped left 240 degrees in about 1 second at 36,000ft. As with the first event, aircraft attitude did not change.Conditions:-KBWI to KSDF (was about 1/3 of the way there).-Autopilot Engaged-LNAV-VNAV-Cruise at 36,000ft-No control input (I wasn't touching any of the flight controls)-Had been at cruise altitude for approximately 20 minutes.-No system failures before or after the event-No Cautions or Warnings

[martin-w 3,235]

S-turns and sudden wind shifts are an FSX issue.The fix, is wind smoothing enabled in FSUIPC, something like 8 seconds per knot, and the suppress turbulence box ticked to stop the s-turns.Works perfectly with REX weather, although I believe ASE requires further tweaking.

[737727Nut 12]

I have had the same thing happen several times and it started after SP1! Plane banks so hard it cause Over bank alert to sound. If I go to any default weather theme all is ok. I use REX for weather and also real weather. Very frustrating indeed.

[DaveCT2003 1,820]

Yeah, same for me, only occurred after SP1.Hey, how about some photos of your Sim?

[DaveCT2003 1,820]

S-turns and sudden wind shifts are an FSX issue.The fix, is wind smoothing enabled in FSUIPC, something like 8 seconds per knot, and the suppress turbulence box ticked to stop the s-turns.Works perfectly with REX weather, although I believe ASE requires further tweaking.

Martin,Yeah, looks like the first poster was talking about S-turns.... sorry about that.

[JackJones 3]

Martin,Yeah, looks like the first poster was talking about S-turns.... sorry about that.

Yes, thats correct! and @ Martin: read my post again please....FSUIPC is reg. an winds changing is enabled (4 sek. for each knot)I use the FS orginal weather...

[JackJones 3]

The bank angle selector has NO effect on LNAV.It is used for HEADING SELECT & VOR only.http://forum.avsim.n...answers-thread/

Ok, thats an explaination, but in my eyes this behavior is very strange...Maybe PMDG can try to terminate this behavior !?

[martin-w 3,235]

Yes, thats correct! and @ Martin: read my post again please....FSUIPC is reg. an winds changing is enabled (4 sek. for each knot)I use the FS original weather...

Jack... I did read it...But did you tick the "suppress turbulence" box?You didn't say.What you describe is the classic and much discussed s-turn issue.It's "suppress turbulence", along with the two boxes next to it that I have ticked. Although I believe it's just the suppress turbulence box that does the trick.Turbulence can also be reduced in the FSX CFG if you still have issues.As I say, it's an FSX issue, not a PMDG issue.

[JackJones 3]

Ok, sry for that!The tubulence box was unchecked...now it is enabled and i will have a look at that.THX

[martin-w 3,235]

Hopefully that should do it Jack.Tick the two boxes next to it as well, just in case.I would change your wind shift to 8 knots per second as well. That way you have the same settings as me, that i know work.Good luck, and don't forget to report back so we know how you got on.