investigating FCS pitch stick command

[Ahmed]

Hi,

Running a test to investigate the issues trying to maintain on-speed during turns in not-auto flaps up operation, I noticed the following:

1. Started test by setting on-speed (~152 KCAS)

2. Entered turn, applied aft stick input up to maximum (limited to 3.55 inches aft in not auto flaps up logic, and also to a ~70% of travel in DCS)

3. Noted that pitch stick command and pitch trim bias allow to pull up to ~14º AOA (stab deflection up to 24º teu). All within expectation.

4. Accelerated to ~230 KCAS, trim untouched, entered turn attempting to capture on-speed.

5. Max pitch stick command won't achieve the previously trimmed 8º AOA, max resulting stab deflection is now only 6º teu.

6. Finally, accelerated to ~243 KCAS to force transition to auto flaps up logic. On transition, noted big AOA and pitch rate spikes as the FCS command transitions between 6º teu and up-to-24. (Note that these spikes will also happen in case of only applying the ~70%/3.55" stick limit mentioned above, and smaller deflections too -- this is not in the attached track, where I used full deflection, but the result will be similar)

I'm unsure of what exactly is wrong here. The pitch stick command, trim bias, and aircraft sensor feedbacks are scheduled by airspeed in not-auto flaps up operation, and the gains and limits may benefit from some tuning. I couldn't find a reference to the 6º teu limit observed above at higher speeds anywhere. The aircraft seems to have very little pitch authority in the above test conditions with the current gains. I'd appreciate if you can run this report by your dev team FCS expert, as this particular test case may have slipped through them.

 

FCS_PA.trk

Edited March 25 by Ahmed