TBM's Nose Bobbing Up and Down on ILS Approach

[ark 1,290]

Has there been a fix for the TBM 930's nose bobbing up and down during an ILS approach with the autopilot on? I find this happens both with the original G3000 and the latest G3000 mod, and I can see the elevator trim wheel cycling back and forth. I also noticed the throttle power lever jumping around a few times although the torque value on the MFD did not change. The a/c did seem to generally track the ILS, however.

Thx,

Al

Edited October 20, 2020 by ark

[Flyfaster_MTN002 412]

Get it with the CJ4 as well, however the latest G3000 mod caused issues and removed it immediately. Suggest you do the same.

Edited October 20, 2020 by Flyfaster_MTN002

[captain420 3,099]

Must be an Asobo issue then.

[marsman2020 1,310]

No autothrottle on the TBM.  If you are seeing the throttle jumping around, you might want to check your controller axis for any noise.

The pitch is an Asobo flight model/AP issue, although if controller noise is causing throttle changes that might also contribute.

[Alvega 2,124]

12 minutes ago, captain420 said:

Must be an Asobo issue then.

No problem here, so I guess it's not an Asobo issue.

[fppilot 4,371]

42 minutes ago, ark said:

Has there been a fix for the TBM 930's nose bobbing up and down during an ILS approach with the autopilot on? I find this happens both with the original G3000 and the latest G3000 mod, and I can see the elevator trim wheel cycling back and forth. I also noticed the throttle power lever jumping around a few times although the torque value on the MFD did not change. The a/c did seem to generally track the ILS, however.

Thx,

Al

No way to assess unless you provide detail on how you have configured at the time.  Power, airspeed, flaps, gear.  And when and how deployed for each.

[ark 1,290]

21 minutes ago, fppilot said:

No way to assess unless you provide detail on how you have configured at the time.  Power, airspeed, flaps, gear.  And when and how deployed for each.

Seems to happen when tracking the glide slope -- typically when inside the FAF with gear down, full flaps, and 85 knots -- so the standard approach configuration.

Al

Edited October 20, 2020 by ark

[ark 1,290]

I think I may have figured out what is causing the TBM nose bobbing when on approach with the autopilot on -- me!  🤔

As has been discussed at some length in this Forum, the default a/c controls are over sensitive, and one of the suggested 'fixes' to reduce the elevator sensitivity was to reduce a parameter in the [FLIGHT TUNING] section of the a/c flight_model.cfg file called elevator_effectiveness (I've done this in FSX/P3D). In the TBM's case I reduced this value from 1.0 to 0.5.  I think an unintended consequence of this is that this made it harder for the elevator trim system to 'keep up' with necessary changes in pitch, and so it tended to lag behind as indicated by the seemingly excessive action of the trim wheel in the TBM. When I changed the elevator_effectiveness parameter back to 1.0, the TBM nose bobbing was just about totally reduced. I then again set the  elevator_effectiveness to 0.5, but also increased the  elevator_trim_effectiveness parameter from 1.0 to 1.5. This again significantly reduced the nose bobbing problem. So I think the issue is the autopilot system is tuned to work with these parameters and you have to be very careful when making changes.

So that's my nose bobbing theory at this point. I'm sure @robert young  who gave us the outstanding Bonanza G36 Turbo, could shed some light on whether this makes any real sense.

Al 

Edited October 20, 2020 by ark

[marsman2020 1,310]

The trim tab moves the elevator, so if you reduce the effectiveness of the elevator, you'll need "more" trim tab to move the elevator through a larger distance to get the same control authority with the autopilot.

Personally I'd adjust the control sensitivity in the joystick settings, not mess with the aircraft models.

[ark 1,290]

23 minutes ago, marsman2020 said:

The trim tab moves the elevator, so if you reduce the effectiveness of the elevator, you'll need "more" trim tab to move the elevator through a larger distance to get the same control authority with the autopilot.

Personally I'd adjust the control sensitivity in the joystick settings, not mess with the aircraft models.

Yes, that is exactly my point, and is why increasing the elevator trim effectiveness helps to offset the reduced elevator effectiveness. In FSX/P3D I used FSUIPC to setup two levels of trim effectiveness -- for low and high speed -- for certain jet a/c like the Lear35. What worked well at the lower speeds, like on approach, was to sensitive at cruise speeds if hand flying. Never had any a/c 'nose bobbing' issues, however.

The problem with adjusting the sim's sensitivity curves for the controls, as Robert Young pointed out, is that the sensitivity becomes exponential-like as you move the controls much past their midpoint. You can also use FSUIPC to adjust primary control sensitivity.

Thx,

Al

Edited October 20, 2020 by ark

[EvidencePlz 276]

5 hours ago, ark said:

TBM 930's nose bobbing up and down during an ILS approach

you mean like this? 😁

 

[EvidencePlz 276]

5 hours ago, marsman2020 said:

No autothrottle on the TBM.  If you are seeing the throttle jumping around, you might want to check your controller axis for any noise.

 

well spotted

[ark 1,290]

5 hours ago, marsman2020 said:

No autothrottle on the TBM.  If you are seeing the throttle jumping around, you might want to check your controller axis for any noise.

Yep, I took the Saitek TQ apart once before to clean the contacts on the pots, don't want to have to do that again. Fortunately the problem has not reoccurred -- yet.

Al

[ark 1,290]

14 minutes ago, EvidencePlz said:

you mean like this? 😁

😊

[ThomseN_inc 1,128]

I have the same issue everytime i am @FLC and the wind changes in direction/speed. Its a constant wobbling and bobbling.The TBM seems very unstable at the moment.