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FSX Re : Nervous trim Tab ??

Hello Forum,

Running Fsx/P3d in Windows 7/64 - and I am experiencing a bit of aggravation - I have looked around and can't seem to find an answer - it looks to be a common problem ??

When I set the auto trim to true - in any plane - the vertical trim wheel and the trim tab get very nervous - just flipping up and down ?? - when autotrim is set to false things smoth out and act normal .

un fortunately I enjoy flying with auto trim on - saves a lot of aggravation - chasing the aircraft all around - constantly trimming - would really appreciate an answer to this !!

Thanks in advance


I might Add that I am setting the Auto Trim ( True/False ) in the FSX/P3d ( *.cfg ) Configuration File.

Am I the only Simmer that this Bothers ??

I know nothing about an autotrim... but, if it's name is exactly what it implies... the 'nervous' behavior is the autotrim constantly adjusting to control the aircraft's trim.

Sounds like an autopilot to me.
Hello WarpD,

Thanks for Your Reply - Checking into it further - I find A. Not all Aircraft do it - default planes OK - Planes built for P3d look OK - All FSX/FS9 Planes seem to do it ??

Also B. Sitting on the end of the runway - Trim Wheel and Trim Tab Nervously Twitching - Kick it in the Guts - and as You Pick up Airspeed - things start to smooth out.

I'm just wondering if there is some Magical Config file setting - that would settle it down - It is a handy Flag !!

Thanks Again !

Johnman :)
Hello WarpD,

Check in Your C:\Users\Username\AppData\Roaming\Lockheed Martin\Prepar3d\prepar3d.cfg - File under - [REALISM]

This is with older simulators so it may not work for you.
I found that if the trim effect per notch is too high, you will often experience this type of "nervous behaviour" especially as airspeed increases.
The problem (less than rigorous explanation) is that the autopilot cycles at a certain rate and tries to adjust trim to a neutral direction.
When you are slow, the effect of each notch of trim is less, so there may actually be an equilibrium setting.
As you go faster, the effect of each notch is greater and for Longitudinal trim, one notch might put you in a climb and one notch below that would put you into a dive so the autopilot keeps flipping back and forth.

If the trim effect per notch is too low (Longitudinal again), you might see the aircraft go into a divergent oscillation because by the time the autopilot can crank in enough trim to bring vertical speed down to zero, it has cranked in so much trim that the attitude rate of change is very high.

Hope this helps.
- Ivan.