Moar Right Rudder 10 Posted May 2, 2022 Share Posted May 2, 2022 I've been experimenting with the CRJ 900 at slow speeds recently, and it doesn't seem like the autopilot has enough pitch authority to maintain altitude. In the real aircraft, the autopilot will continue increasing pitch in order to hold altitude until the stick shaker activates. Once the shaker activates, the autopilot will disconnect automatically and the cavalry charge aural will sound until one of the pilots selects AP/SP DISC on the control wheel. In the MSFS CRJ, the aircraft begins a slow descent almost immediately upon power reduction. Speed continues to decrease until reaching ~150 KIAS and then stabilizes with the aircraft descending somewhere near 3,000 fpm, but never reaching the low speed cue (red/black checkerboard) and stick shaker. Video of the behavior beginning from M0.77 and 37,000 ft around 75,000 lbs: An oddity that suggests this might also be related to thrust occurs at 1:10. The thrust levers are increased and the aircraft stops its descent and begins a slow climb at 200 KIAS. Steps to Reproduce: 1. Engage ALT or ALTS on FMA and allow VS and airspeed to stabilize 2. Reduce thrust to idle 3. Observe decreasing altitude and descent rate while airspeed stabilizes around 140-160 KIAS 4. Observe aircraft does not follow flight director above ~7.5 degrees pitch nose up Link to comment Share on other sites More sharing options...
Deputy Sheriffs Secondator 643 Posted May 3, 2022 Deputy Sheriffs Share Posted May 3, 2022 This kind of behavior is known to us but it's highly unusual to fly an aircraft at such slow speeds in normal operations without extending some flaps. We will see if we can improve the altitude hold further at some point but right now it isn't the highest issue on our priority list. 1 Link to comment Share on other sites More sharing options...
jstnj 102 Posted May 16, 2022 Share Posted May 16, 2022 On 5/3/2022 at 11:48 AM, Secondator said: This kind of behavior is known to us but it's highly unusual to fly an aircraft at such slow speeds in normal operations without extending some flaps. We will see if we can improve the altitude hold further at some point but right now it isn't the highest issue on our priority list. (Read: this will never be addressed) Link to comment Share on other sites More sharing options...
Richard Dastardly 108 Posted May 17, 2022 Share Posted May 17, 2022 That sort of behaviour turns up in a lot of aircraft - whether it's an asobo AP problem or just a lot of people not tuning the AP right I don't know. How's the real jet at slow speed on AP, if anyone's actually got it in that state? Link to comment Share on other sites More sharing options...
KuntaKinte 210 Posted May 18, 2022 Share Posted May 18, 2022 10 hours ago, Richard Dastardly said: How's the real jet at slow speed on AP, if anyone's actually got it in that state? As long as the AP is activated, the real aircraft would never start a descent or climb due to airspeed changes. It would increase/decrease pitch to maintain altitude. At low airspeeds this would go as far as stick shaker onset. The same is true for climb with V/S or PITCH mode. When the aircraft approaches a high angle of attack, the stall protection computer will: warn the crew of an impeding stall through the stick shaker, activate the engine auto-ignition system and disengage the AP On 5/3/2022 at 3:48 PM, Secondator said: it's highly unusual to fly an aircraft at such slow speeds in normal operations Agreed. But overall, the AP/FD is relatively sluggish and inaccurate both in lateral and vertical modes. Link to comment Share on other sites More sharing options...
Moar Right Rudder 10 Posted May 21, 2022 Author Share Posted May 21, 2022 Quote As long as the AP is activated, the real aircraft would never start a descent or climb due to airspeed changes. It would increase/decrease pitch to maintain altitude. At low airspeeds this would go as far as stick shaker onset. The same is true for climb with V/S or PITCH mode. When the aircraft approaches a high angle of attack, the stall protection computer will: warn the crew of an impeding stall through the stick shaker, activate the engine auto-ignition system and disengage the AP This is accurate (and verbatim from the FCOM no less). On 5/17/2022 at 6:03 PM, Richard Dastardly said: That sort of behaviour turns up in a lot of aircraft - whether it's an asobo AP problem or just a lot of people not tuning the AP right I don't know. How's the real jet at slow speed on AP, if anyone's actually got it in that state? We train to this specific configuration and scenario during our Extended Envelope Training in the CRJ. On 5/16/2022 at 11:26 AM, jstnj said: (Read: this will never be addressed) I believe Aerosoft will address this eventually. They have higher priorities with the aircraft at the moment and that's ok. The majority of end users aren't testing the flight model and AP at the edges of the aircraft's flight envelope. I primarily brought this forward because I felt it might hold some additional information regarding other autopilot issues users have been experiencing lately. 1 1 1 Link to comment Share on other sites More sharing options...
Richard Dastardly 108 Posted May 22, 2022 Share Posted May 22, 2022 Thanks, both of you. Presumably it's much the same if you're not wings-level too? Link to comment Share on other sites More sharing options...
Moar Right Rudder 10 Posted May 22, 2022 Author Share Posted May 22, 2022 Assuming you mean the real aircraft (I haven't tested this with turns in the sim), yes it's much the same. The autopilot does a surprisingly nice job of holding altitude at high AOA. 1 1 Link to comment Share on other sites More sharing options...
Richard Dastardly 108 Posted June 26, 2022 Share Posted June 26, 2022 As of update the A/C will do it's best to hold attitude down to stall speed, but then it starts sinking instead of disconnecting the AP. Add power & it'll overshoot the selected altitude before settling back down again - the trim runs awfully slowly. It is a little improved, i think - certainly couldn't get down to 120-ish kts on the AP ( in a -900 ) before it started dropping, previously. Edit: I take that back, it's sinking at 140 kts again. Link to comment Share on other sites More sharing options...
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