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A/C goes nose up when activating autopilot


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I can add that I am having the same issue as the OP. I typically arm HDG and SPD on the ground and set the speed target during the initial climb (either 250 if I plan to activate AP below 10k, or 290 if I'm handflying for longer).  Once I take off and get the aircraft into a stable climb at target speed, I trim to remove control forces and then activate AP. I immediately see the AP running the trim at a high rate and see an immediate pitch up. If I do not intervene, I see 50-60 kt loss of speed before the AP starts trimming nose down. If I intervene and push forward on the yoke, I get an autopilot disconnect due to the control forces required.

 

I've learned to live with the pitch up, since I know it will fix itself, but I'd prefer not to have that worry as it gets down near Flaps 1 maneuver speed before pitching down.

 

I'm always flying with "live" weather and the 550 model. I saw this in 1.0.4.0, 1.0.5.0, and 1.0.6.0

 

Bill

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I can confirm that this issue is indeed present in SU5. Me and other 2 guys in VA that fly CRJ 7 V1.0.6 where able to EXPERIENCE and reproduce this issue. For me it occurred after I decided to fly SID manually… took off…captured altitude at 12000 ft. Fully trimmed with FD(very satisfying ) next step I engage AP, and immediately after, excessive nose up (NU)… trim goes NU very very rapidly… I tired toggling it few times same response no mater if you’re in NAV OR HDG mode. The only thing that helped me so far is to fight it with stick ND like so one suggested before. I also noticed that trim input is increased in v1.0.6 was anything changed with that?  Maybe that has do do with the violent AP NU.

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3 hours ago, Mathijs Kok said:

We'll keep an eye on this but at this moment we simply do not see this behavior.

 

I'm also having this odd trim behavior.

Easy to reproduce steps:

1- Trim the CRJ before take off in a value other than 7.5

2- Take off

3- Trim the nose down as speed increases

4- Turn on the auto pilot and see the trim value jump instantly from wherever the aircraft was trimmed to 7.5

Consequences: sudden nose up when engaging the auto pilot while it trims the nose down all the way from 7.5.

Conclusion: Autopilot mode is resetting the trim to 7.5. when it is engaged regardless of previous trim setting.
 

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I can confirm the issue as well.

 

I usually hand-fly departures, and thus, activate the AP quite late. But I can observer exactly the same behavior.

 

Most of the time, I'm in SPD/NAV mode, IAS and speed bug are both at 250kt, the plane is trimmed for hands-free flying, and the center of the PFD is aligned with the FD cross. When I activate the AP, the planes pitches up followed by pitching down to the previous/correct attitude.

 

This is nothing severe or game-braking and can be compensated by pushing the yoke a little bit. But I guess this is not the intended behavior and it makes the transition to AP a little bit unsmooth.

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Here is a video by CptCanada showing what happens (at 35:45). You can also see what he's doing with the yoke. It's certainly not the latest version of the plane and MSFS, but it's still exactly the same with 1.0.6.0 and SU5. It hope this helps you investigating the issue.

 

 

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vor 2 Stunden , Mathijs Kok sagte:

Okay, we'll have a serious look at this.

Mathijs, 
i have seen exactly this behaviour and reported it as well. This was in the first days of the CRJ.
It happend basically from AP-controlled flight to manual flight, while trying to catch the aircraft back due to pilot error.

 

Having it under control, level flight and controlled speed, if you revert back to AP controlled (Heading/Alt)  the trim was out of bounds and the a/c pitched up.

 

As one said here, it looks like TRIM is not resetting from an old setiing or to a default TRIM (UP 7.x)

I still consider this a bug and a serious one , too

 

AND, havent tried it lately, but is FD SYNC working at all ??  I remember it failing some times

 

Oliver

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To evidence enrichment here is a short video looping 3 times when the issue happens and zoomed in showing the stab trim bar.
On the video I hand flown after departing for a few seconds. The more you trim for speed the bigger the issue becomes as it resets to 7.5 instantly as sown.

Video is set to unlisted.
 

 

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This just happened to me for the first time today. I was trimmed at 290 knots with the HSI centered, enabled the speed and nav modes and engaged the autopilot at which point the plane started pitching up and reached a climb rate of over 10,000 ft/min before I alt-f4'd.

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vor 2 Stunden , SinusJayCee sagte:

Hitting the AP disconnect button would have worked as well ;)

The problem remains, once in level, trimmed flight, you activate the AP, the a/c goes haywire again ... . Pitches up, about 7.5+ deg.

 

To be precise: it does not trim up continuesly, it basically switches to a (given, default ?)  value immediately

 

Oliver

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vor 2 Minuten, JetNoise sagte:

The problem remains, once in level, trimmed flight, you activate the AP, the a/c goes haywire again ... . Pitches up, about 7.5+ deg.

Yes, this of course true. My point was that this is no reason to quit the game by hitting Alt+F4. You can simply push the yoke a little bit until the AP has trimmed the plane correctly or, if it is really serious, you would disconnect the AP.

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gerade, SinusJayCee sagte:

Yes, this of course true. My point was that this is no reason to quit the game by hitting Alt+F4. You can simply push the yoke a little bit until the AP has trimmed the plane correctly or, if it is really serious, you would disconnect the AP.

LOL, of course ... 😉

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5 hours ago, JetNoise said:

The problem remains, once in level, trimmed flight, you activate the AP, the a/c goes haywire again ... . Pitches up, about 7.5+ deg.

 

To be precise: it does not trim up continuesly, it basically switches to a (given, default ?)  value immediately

 

Oliver

 

7.5 to be precise. The problem is exacerbated the farther you are from 7.5 (default) trim as the autopilot needs to bring it back to trimmed from all the way from 7.5. I hope there will be a fix on the next update for this as it negates a good experience of hand flying it before enabling autopilot. It is quite bad.

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9 hours ago, SinusJayCee said:

this is no reason to quit the game by hitting Alt+F4

 

It is for me. It's so immersion breaking (even though it could technically happen in real life too) that I couldn't even be bothered to continue the flight.

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vor 8 Stunden , Puuhbear sagte:

I don’t see this behavior. 
 

Do you follow the FD when switching the AP on? 
 

I always try to not just level the aircraft but have it stable on the path given by the flight director. 

If I got that right, you should be able to use pitch sync (yoke) .

But for me that doesn't always do the job as it should. Pitch sync may be bugged too. Indication "Sync" is displayed on the PFD only once or twice and then never again.

 

Oliver

 

 

 

 

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On 31.8.2021 at 10:31, Seekay sagte:

reached a climb rate of over 10,000 ft/min

 

vor 15 Stunden , Seekay sagte:

It is for me. It's so immersion breaking (even though it could technically happen in real life too) that I couldn't even be bothered to continue the flight.

 

I get your point. But I also have to say that I never have seen such a severe behavior with a climb rate if 10,000ft/min. I usually get an increase to about 5,000ft/min, which is still not nice but less immersion breaking imho. For 10,000ft/min, the CG must have been totally out of range or your current attitude was far away from the FD.

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11 hours ago, Puuhbear said:

I don’t see this behavior. 
 

Do you follow the FD when switching the AP on? 
 

I always try to not just level the aircraft but have it stable on the path given by the flight director. 

 


Yes. On the flight director.


Steps to reproduce a dangerous situation:

-Hand fly the aircraft towards 250 knots

-Trim for speed throughout the whole flying.

-Turn on the autopilot while keeping your input neutral.   Inconsistent.

 

Flight director doesn't matter. The auto pilot will go off the flight director while it will try to bring back the trim to the current air speed.

Edit: I ran a quick test from the ready to taxi state to 250 knots and trimmed. There is different behavior, but not quite "perfect" (?). The trim movement was significantly smaller.
Something still feels off.
Video updated.

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18 hours ago, SinusJayCee said:

 

 

I get your point. But I also have to say that I never have seen such a severe behavior with a climb rate if 10,000ft/min. I usually get an increase to about 5,000ft/min, which is still not nice but less immersion breaking imho. For 10,000ft/min, the CG must have been totally out of range or your current attitude was far away from the FD.

 

I got my fuel and weights from Simbrief, the flight plan indicated that they were within limits, and I loaded the plane using the EFB's ZFW mode which (presumably) should set the CG correctly and notify me if there's a problem. I don't pay much attention to the CG indicator, I just trust the numbers Simbrief gives me, but I'm absolutely certain that I've never seen the indicator go beyond the takeoff, landing and approach CG limits.

 

I didn't check the attitude but I was climbing straight ahead with the HSI centered at 290 knots and had the autopilot speed bug set to 290 so I should've been right on the FD, no?

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2 hours ago, Seekay said:

 

I got my fuel and weights from Simbrief, the flight plan indicated that they were within limits, and I loaded the plane using the EFB's ZFW mode which (presumably) should set the CG correctly and notify me if there's a problem. I don't pay much attention to the CG indicator, I just trust the numbers Simbrief gives me, but I'm absolutely certain that I've never seen the indicator go beyond the takeoff, landing and approach CG limits.

 

I didn't check the attitude but I was climbing straight ahead with the HSI centered at 290 knots and had the autopilot speed bug set to 290 so I should've been right on the FD, no?

If you use the original SimBrief profile for the CRJ, you will get the wrong ZFW. SimBrief set the passenger weight differently than the CRJ which again conflict with the EFB and FMS. SimBrief passenger weight includes bags, but the CRJ adds more weight in addition to the passenger weight and therefore the ZFW will be wrong.

If you set passenger weight in Simbrief profile to 186 pounds/ 84 kg it will be correct. 
When I set this correct my plane stopped the odd behavior when turning AP on and I got correct ZFW in EFB.

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