Hi, I recently purchased the Qualitywings 787 for P3DV4, and I am more or less enjoying it so far. One of the things I am seeing is when I engage the autopilot and turn a random heading, and FLCH to 10,000 ft, it puts severe inputs into the control column, causing the nose to violently push up and down. It never reaches the altitude. Can anyone help me with this?

Had me worried for a moment looking at your post title.  A quick Google Search indicated a correct Aviation terminology.  Whew! 😱  Sounds like a bad case of rollercoasteritis.  There is an 11 or 12 page (by now) topic about the QW 787.  Any mentions in there about what you are seeing?

Hi, thanks for responding, for the "QW787 P3DV4 - first impressions?" forum, I don't see anything except for VNAV TOD problems; but even with autopilot on FLCH, VNAV, or V/S, it is still the same. It also could be an autothrottle problem, because it loses speed and I stall every time.

Have you reported what you are seeing to the Quality Wings site?  They may already know about it and are working on a fix.  Waiting for someone to report available patches or fixes here on the AVSIM forums may take longer.

I have, they said just wait for the next patch, but I don't think that is the issue.

Just to split hairs, what you are seeing is not a phughoid but a limit cycle :)

The phugoid is an aerodynamically driven oscillation, while the oscillations you are seeing are due to instabilities in a control system (the autopilot).

I see. A phugoid cycle is a manual input.

I wonder if anyone has thought to see this from an "autopilot/FMS that cannot interpret W&B properly or well" angle. The way I see it, the simulation of an advanced FMS/AP coupled with an advanced weather generator (ASP4 or other) in our P3D, requires that the FMS/AP be just like or extremely close to the real world or it simply will misbehave. Leaving out FMS wind data for example, when there is plenty of realistic wind layers, then throw in W&B not precisely (enough) taken into account, so things like this become more likely rather than rare. Temperature also can play a part, but does the FMS "know" this.

I wonder if someone could present this to QW as a possibility in the 787 Forums.

I intend to D/L and read the manual and tutorial, to see if there are specific cautions or advice about how to avoid A/P FMS LNAV VNAV issues.

I truly want to buy this plane, but not if there are blatant blunders.

I updated to 1.10 and none of the models worked :(

My 787 (1.13) also does phugoid motion, unable to maintain FL400

Version 1.13 is pretty out of date. I have had good luck with the current version, 1.2-ish.