My TBM is still Oscillating

[SHaines]

Just want to throw a note into the pile here regarding a strange phenomenon I am seeing, still, in my TBM900 flight performance. After resetting my yoke to allow 30% less control sensitivity, which I thought would solve this issue, I still see my airplane "bobbing" up and down in level flight, at nominal speed, with no external (weather) conditions. I call it "oscillating" but maybe there is a better term. Regardless how you describe it I would like to know if it is intentional, i.e. "supposed to look that way to simulate normal aircraft behavior" or something that is out of the ordinary requiring external adjustment. Any takers on this? Appreciate advice on how this may, or shouldn't be corrected. 

[jfjoubert]

Make sure you have Experimental Flight Model enabled.

[SHaines]

Thank you Jean. I DO have that enabled. Are there any other suspects? I tried setting my yoke sensitivity to 50% but that had no effect (and might effect other controls.) To be clear, it's not a "violent" shaking or anything like that. It's just that instead of a nice steady view from inside the aircraft, or a nice steady view of the aircraft from outside, I get a repetitive up and down motion that causes the landscape to constantly bob up and down in the windscreen and the airplane to do the same from outside. Can't that setting as I do have that checked.  

Thanks for the reply, Jean. I am willing to try anything here. And to clarify... it's not a critical issue. It's just something I notice which i would like to cure if possible. 

—SteveH

[Rossco]

Iv'e seen this happen a few times mainly on climb or descent & I believe it occurred after I used my Saitek Trim Wheel. I believe it gets out of coordination with the electric trim so I tend not to use the wheel anymore. Thought I'd throw this in as it might help. You might have two trim bindings that are clashing? 

[Goran_M]

5 hours ago, Rossco said:

Iv'e seen this happen a few times mainly on climb or descent & I believe it occurred after I used my Saitek Trim Wheel. I believe it gets out of coordination with the electric trim so I tend not to use the wheel anymore. Thought I'd throw this in as it might help. You might have two trim bindings that are clashing? 

That actually makes sense, because I haven't seen this problem in every system.  Only a select few.

[jfjoubert]

The only time I had this "issue" was when my joystick (a classic Sidewinder FF2) was ever so slightly off centre on the pitch axis. Moving it back to centre stopped the "bobbing".

This was however without the EFM.

[SHaines]

I appreciate the reply. Not sure it applies in my case. I use a CH Eclipse yoke and have mapped an unused lever to handle rudder trim. And it works quite well. For vertical trim I use the #1 and #2 keys on my keyboard. And they work well also. I will try the #3 and 4 keys for rudder and see if that works as well and if it resolves this issue. As for the issue itself, it seems to occur during straight cruise flight, though I will check on that today to verify. And as I said, it is not a dramatic "shaking" or anything like that. It is rather a slight but noticeable "oscillating" of the nose/tail up and down, perhaps 2 or 3 cycles per second and about .5º of pitch. I will tinker with it further to refine exactly when I observe it and if any adjustments, particularly to pitch access, have an effect. Thanks for the replies. 

[SHaines]

@jfjoubert

I think you may have nailed it. I was just doing a flight and got distracted so I never checked during the short cruise phase. However during the descent I noticed the airplane doing it's "bobbing" motion as you describe it. Since we were on autopilot I didn't want to mess with the manual trim so i just tried first gently pushing then pulling back on the yoke. Two tries back and the bobbing stopped. Now my Eclipse yoke is anything but accurate so it entirely possible that it was just "fighting" the autopilot which kept trying to trim the aircraft up properly while the yoke kept trying to push it down. Ergo "bobbing" or "oscillation". Now it's nice and smooth. So thank you for that tip, Jean. It worked! 

Be well. —SteveH

[jfjoubert]

@SHaines

Glad I could assist...

I assume most users with yokes won't have this issue if the yoke has a spring detent for the pitch axis. I now make a point to check that the joystick is centered.

[SHaines]

Yes. Full disclosure... shortly after I purchased my yoke I decided to "modify" it by replacing the springs for the roll axis with rubber bands. They produced a much smoother action. I left the springs in place for pitch but the friction of the yoke shaft (which I periodically lubricate) occasionally causes it to stick, resulting in the behavior described. Now that I see the result I will pay more attention to this detail.