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pilotandre

737NGX Autopilot Problem

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Hi

I have had this issue since I bought the 737ngx

The problem is when I am on my cruiseing altitude

And I speed it up to 16x when a turn come the plane

Seems to don't hang on and takes the turn to late.

And after that the plane just can't get back on course

It just turn to the right and then to the left but not straight.

When I put it back on normal speed the autopilot turns back

On course.

Any one knows about this problem?

Thanks/André

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And I speed it up to 16x when a turn come the plane
Seems to don't hang on and takes the turn to late.
16X is a problematic acceleration rate for the NGX. There are too many things occurring for it to operate correctly. If you need to use acceleration try 4X and see how that works. You don't need 16X in a short haul aircraft.

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It would be a problem for any sim trying to follow an FMC route at 16x. The autopilot control laws simply aren't able to cope with the high rates of change involved. Small errors lead to large corrections and overshoots. Hence the weaving around and missed waypoints.

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Somewhere in the documentation PMDG gives an x8 maximum I belive.  Slightly off topic:  My NGX on my system will perform flawlessly at x2 and x8 but at x4 it will always start a yaw oscillation. I know it is just a quirk in my setup but wondering if anyone else observes something similar?  Maybe too far off topic since I just noticed the OP claimed an AP problem when in fact it is simulation rate problem.

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I always have problems slewing even at 4x, especially when sharp turns in LNAV are involved. The autopilot just looses track of things.

 

I try to slew if I have to only and on straight long legs.

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If you really must use 16x, bypass the intermediate waypoints and make it a long straight direct leg. That should avoid steering problems and it can't miss a waypoint. Not very realistic, but if you are using 16x acceleration you won't have time to be concerned with ATC or following airways.

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