Pitch Axis Wonky on Descent

[SWA4420]

Hi All - after 2 full flights, I have encountered the problem both times of extreme porpoising when engaging either VS or FLCH during descent.  VNAV descent is still not what it should be.  Has anyone else encountered this problem?  That is the main problem I'm having....other than that, it's good to have her in XP12.  Also, looking forward to improvements/bug fixes listed, and being able to load the plane and get CG from the menu, and NOT to have to use XP's W&B menu!

Thanks for bringing this bird to XP12!
Jim

 

[Cameron]

Hi Jim,

Thank you for your feedback. It’s essential to clarify that this initial release for XP12 mirrors the system functionalities present in the X-Plane 11 version. We acknowledge the VNAV system requires further refinement, and this is on our roadmap for future updates. We ask for your patience and understanding as we work to enhance the product. Your continued support and enthusiasm for the aircraft are greatly appreciated.

[SWA4420]

Hi Cameron - this has always been one of my favorite planes, and I know a lot has changed with XP12.  I was wondering if anyone else has reported the problem I mentioned during descent using VS/FLC?  I know this is the initial release for this platform, and as such, has a few bugs to be squashed!

Thanks!
Jim

 

[Litjan]

Hi JIm,

what kind of porpoising did you see? What were the conditions? Real weather, speeds, weight, CG? If you could post a picture (or a series) of the instrument panel of when it happens, that would be great, a video would be even better!.

We had to retune the PID values for most of the autopilot and there may be some fringe cases when the dampening doesnt work as it should, so I would be very interested to understand (and fix) your problem.

Cheers, Jan

[SWA4420]

Hi Jan,

Nose/plane rocking up and down severely, immediately upon initiating descent by VS (also with FLCH).  The plane did descend, though.  VNAV descent is still not working right for me.
Real weather, 290 knots, 107.7 lbs, CG 22.1.  I haven't had a chance to do another flight today to provide pics/vid.

Something else I forgot about my initial flight KLAX-KLAS --> RNDRZ2 arrival to ILS 26L.  At HOGOG, for the ils, the plane stayed on 083 heading and did not turn left to KODSE 020, nor left again at HUXAR 259 degrees.  I went to HDG mode and tried to turn, to no avail, so I had to disconnect the AP and fly it manually.

Second flight KLAS-KLAX the straight in approach to 24R was ok...no 180 turn needed.

You may want to run those two test flights yourself: KLAX-OSHNN1 MISEN RNDRZ2 ILS26L KLAS, and KLAS-RADYR2 BLAQQ SHTNR ANJLL4 ILS24R KLAX.  FL250 eastbound, FL240 westbound, real weather.

Thanks,
Jim

 

Edited September 19, 2023 by SWA4420

[Litjan]

Hi Jim,

thanks for the report, I will do those flights and see if I can reproduce your issue!

Is there a chance that the wind was fluctuating on your descent? Did it look like the plane was chasing the value it was supposed to keep (i.e. the vertical speed) or did it stray from the set value by it´s own (inappropriate) inputs?

Thanks again, Jan

 

[SWA4420]

Hi Jan,

The winds stayed pretty consistent as I recall.  When I initiated the descent, the plane dove at over 4000 FPM while rocking up and down, then slowly adjusted to the VS value set in the MCP.

I hope you will have the same situations happen when you do those flights!

Thanks,
Jim

[Litjan]

On 9/19/2023 at 5:04 AM, SWA4420 said:

At HOGOG, for the ils, the plane stayed on 083 heading and did not turn left to KODSE 020, nor left again at HUXAR 259 degrees. 

Just flying your route, @SWA4420,  could it be that you did not remove the route discontinuity after the RNDRZ2 arrival terminates at BERBN? It actually ends in "radar vectors" and ATC would expect you to keep flying straight (away from the airport) - you are only allowed to turn onto the ILS if you are cleared for the approach, in that case move "SHAND" onto the "vectors" line to "close" the flightplan.

[Litjan]

Regarding the "pitch oscillations" - I have not been able to reproduce those YET, but this could be due to environmental conditions like turbulence, etc.

If you use FL CHG when descending from a higher altitude like FL240, the target speed will revert to a Mach number (if you have been on VNAV before) and since the true airspeed for a given mach number increases rapidly with decreasing altitude, a jet will really "dive down" if you initiate a constant Mach descent.

Modern airliners are better at mitigating this, but nevertheless, descent rates are high) 5000+ feet/min. Use V/S to initiate the descent - I did (with -2000 fpm) and the plane pitched down smoothly without overshooting and maintained 2000.

Cheers, Jan

[SWA4420]

Hi Jan,

I just completed a successful flight (KLAS-KLAX @ FL240) with no pitch problems, using VS to initiate and modify FPM when needed to maintain the proper glide, so that seems to be the key/best way to manage descent....which is basically the same way I do it in XP11.  Roger that about FLCH!

Thanks,
Jim