Trim in the PMDG NGX

[webmaximus]

Currently I’m not using hardware trim since doing that causes the yoke to “drop” to the left/right whenever I let go of it already when sitting at the gate. Not sure why that is really or how it’s related to the selected trim method in CLS2Sim.

All in all this works pretty OK I think but there are two things I would like to ask about.

First question is when checking the flight controls after setting the t/o trim I notice how the elevator isn’t centered according to the status page in the NGX but instead it’s indicating about 25% pitch up. This is when using a fairly normal t/o trim around 5 units. Looking at the physical yoke (as well as the NGX virtual yoke) they are what I would estimate about 75% pulled back.

Second question is when I disconnect the A/P on short final I need to be very careful to apply some forward pressure on the yoke before actually disconnecting to avoid “ballooning” since the trim at this stage always seem to be very much pitch up.

Thanks in advance for any advice how to best handle/set up the trim in the NGX.

[Diego Bürgin]

Hi webmaximus

Currently I’m not using hardware trim since doing that causes the yoke to “drop” to the left/right whenever I let go of it already when sitting at the gate. Not sure why that is really or how it’s related to the selected trim method in CLS2Sim.

Can you recreate the situation and make a screenshot of the upper half of the profile manager? I’ll have a look then.

First question is when checking the flight controls after setting the t/o trim I notice how the elevator isn’t centered according to the status page in the NGX but instead it’s indicating about 25% pitch up. This is when using a fairly normal t/o trim around 5 units. Looking at the physical yoke (as well as the NGX virtual yoke) they are what I would estimate about 75% pulled back.

There are multiple possibilities. Please disable the yoke physics (top-left checkbox in the general tab) and tell me how the behavior changes.

Second question is when I disconnect the A/P on short final I need to be very careful to apply some forward pressure on the yoke before actually disconnecting to avoid “ballooning” since the trim at this stage always seem to be very much pitch up.

I understand that the behavior is sub-optimal, but with the experimental AP fix for the elevator movement Stefan sent you, this is the trade-off at the moment.

[webmaximus]

Did some testing and took a couple of screenshots attached below.

With HW trim enabled the elevation center issue is gone and the yoke is perfectly centered looking at the flight controls status page as well as the actual location of the physical yoke along the pitch axis. Quite fun to see how the yoke moves a bit forward to a centered position as soon as you enable HW trim and vice versa moving back towards you as soon as you disable HW trim. Also worth mentioning is the stab trim value doesn’t affect the physical elevator and thus the deflection of the yoke in the real aircraft since the elevator and stabilizer are two separate parts. This was explained to me over in the PMDG support forum.

Looking at the roll axis with the HYD system pressurized and with HW trim enabled the yoke “drops” to the left/right as previously described almost like if the forces had been reversed where the yoke returns to full left/right rather than center when you let go of it.

Here are the screenshots.

[webmaximus]

I edited my previous post once when I realized Google Drive links don’t work in here but when I just tried to edit my post a second time to add descriptions for each screenshot since the descriptions I added during the image upload process seem to have disappeared the edit button is no longer visible so will have to add the descriptions in this post instead.

The first image is hardware trim and no HYD pressure.
The second image is hardware trim with HYD pressure.
The third image is No hardware trim and no HYD pressure.
The fourth image is No hardware trim with HYD pressure.

Also I forgot to mention that the yoke is pulled forward option under Yoke physics under the general tab is disabled in all examples above.

[webmaximus]

Just installed the latest version of CLS2Sim (4.2) to confirm the issue is still present.

Were you able to figure anything out from the screenshots I posted?

Right now with HYD system pressurized in the NGX and hardware trim in CLS2Sim not enabled the yoke centers fine on the roll axis but instead the pitch position indicates a positive value of 2982. If I enable hardware trim the pitch position value in CLS2Sim changes to 1 indicating close to perfect centered position but instead the yoke now “drops” to full left/right on the roll axis.

So in short with hardware trim enabled the pitch center position is perfect but the roll center position is totally off to the far left or right when the HYD system in the NGX is pressurized. With hardware trim not enabled but with the HYD system in the NGX still pressurized it’s the other way around where the pitch center position is pitching up (indicated by the positive pitch position value of around 3000 in CLS2Sim ) while the roll center position now is working normal without the yoke dropping to the left/right.

Please let me know if you have any additional questions or if I can help you in any way with further troubleshooting by doing more testing.

[jovabra]

On this side, I have the same experience and i’ve got also an elevator movement during the use of the rocker-trim switch on the yoke. This is not normal for the 737 NGX and other “big aircrafts”.
I’ve installed just now the latest update version of the PMDG 737NGX for FSX. At this moment i have no strange roll commands and the yoke (pitch) is not moving any more.

Is it the update of the NGX or is it the the “WIN10 ghost”. Sometime you think the FSX software is switch off but it take some time for a real shutdown.
Add inf: Don’t forget, after a new installation (according the PMDG rules) to add in the 737NGX_option.ini file:
[SDK]
EnableDataBroadcast=1
Regards
John

[webmaximus]

Not sure if there’s a difference here between FSX and P3D. I’m currently on P3Dv3.2.3 and I’m using the latest version of the NGX and I’ve verified I have the EnableDataBroadcast=1 set.

Edited to add that as for Windows version I’m on 10.0.15063.

[Diego Bürgin]

Hi webmaximus

Just letting you know that I haven’t forgotten you.

I made time for a short test but could not confirm the behavior.
I didn’t have enough time time do a detailed analysis, so maybe i did something wrong.
Unfortunately I’m fully planned out with a deadline until the end of the week.
Then the company will be closed due to summer holidays for two weeks until 6. of August.
After that I’ll be able to allot more time.

Sorry for the delay

[Diego Bürgin]

@jovabra

As to my knowledge the controls transmit aerodynamic forces, I assumed reversible controls. The yoke movement is due to changing the force neutral point when trimming.

[webmaximus]

Thanks for the update Diego.

No rush what so ever. I’m currently busy playing around with XP11 for a change. Figured I’ve been in the FSX/P3D pool for so long now that it was time to try something different 🙂

Have a great summer vacation!

[Diego Bürgin]

Hi webmaximus

I’m back in the office today and had a look at the described behavior regarding the yoke moving to one end on the roll axis.
I could see from the screenshots that there is AP roll or trim input causing this.
Now I’ve tried for hours, but I can’t reproduce the behavior no matter what I do.

So I would like to ask, would you willing to write me a step by step guide or record a video on what exact steps you take to produce the behavior?
The focus would be the manipulations in the virtual cockpit / instrument panels.

Thanks

[webmaximus]

Welcome back and hope you had a great time off 🙂

As for the yoke moving along the pitch axis when changing the stab trim I think the problem is what aircraft type you’re in. As described in post #431, in a B738 changing the stab trim won’t affect the elevator since the elevator and stabilizer are separated.

As for the issue where the yoke drops to the right/left with HW trim enabled in CLS2Sim and ELEC HYD PUMPS ON in the NGX I recorded a short clip to demonstrate this. What I forgot to show in the clip is how having HW trim enabled/disabled also affects the pitch axis where the yoke is perfectly centered with HW trim enabled while with HW trim disabled the yoke will always pitch up also seen on the SYS page in the NGX using a neutral stab trim value of 5. The yoke will also move back to a centered position without HW trim enabled if the HYD system in the NGX is not pressurized.

Here’s the clip.

https://youtu.be/VNYoe_RL_iw

[jovabra]

Same experience on this site
Regards John

[jovabra]

Hi all,
I few minutes ago i installed an old CLS2sim version (3.24.2) and i used this for testing with the default profile. In the trim-tab field you must disable the
“use hardware trim” option. This is the way how it works for a 737. I checked this with the PMDG 737-800 Prepar3dV4. So no more uncontrollable roll movements
In a 737 only the horizontal stabilizer is moving up and down when you use the trim rocker switch on the yoke.
So the column must be kept in there position when using the trim. This is not the case, in general, for the most GA aircrafts.
Regards
John v Braam

[jovabra]

Add info.The best way is also to disable PITCH (trim) check mark

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