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pitch oscillation

C

cgw44

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7
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us-connecticut
I have a payware aircraft that after a certain amount of time during flight
starts to pitch up and down on autopilot. I assume this has to due with weight
change from fuel being used up.

What parameters do I need to change to fix this?

Thanks for any response.
 
If would help if you stated in which autopilot mode you see this happening and whether the model suffers from such oscillation when not in autopilot.
Most of the time you get some form of pitch oscillation in autopilot it is at high altitude in height hold mode.
A brute force method of reducing these oscillations is to increase empty_weight_pitch_MOI in the Weight and Balance section of the aircraft.cfg file.
Roy
 
Roy Holmes said:
If would help if you stated in which autopilot mode you see this happening and whether the model suffers from such oscillation when not in autopilot.
Most of the time you get some form of pitch oscillation in autopilot it is at high altitude in height hold mode.
A brute force method of reducing these oscillations is to increase empty_weight_pitch_MOI in the Weight and Balance section of the aircraft.cfg file.
Roy
Click to expand...
It does happen in alt hold at high altitude but not in manual flight.
 
The FS autopilot uses elevator trim for pitch changes. Altitude hold works through pitch changes generated by an altitude error compared to the selected altitude.
When the error exists, the autopilot attempts to correct it and tends to overshoot the correction leading to an oscillation.
At high altitude and high true air speed inertial forces are strong, but aerodynamic damping is reduced since it comes from forces generated by indicated air speeds, which are lower.
This is why you get the oscillation at high altitude only.
Unfortunately there is no way to simply control the stock autopilot in pitch.

That leaves you with having to increase the pitch damping or as above, increase the longitudinal moment of inertia so that the resistance to pitch changes is increased.
If you are familiar with the air file and aerodynamics, I would suggest getting Yves "Flight Dynamics in Microsoft Flight Simulator" and study section 6.3.2. You might then decide to increase pitch damping Cmq.
Roy
 
Roy Holmes said:
The FS autopilot uses elevator trim for pitch changes. Altitude hold works through pitch changes generated by an altitude error compared to the selected altitude.
When the error exists, the autopilot attempts to correct it and tends to overshoot the correction leading to an oscillation.
At high altitude and high true air speed inertial forces are strong, but aerodynamic damping is reduced since it comes from forces generated by indicated air speeds, which are lower.
This is why you get the oscillation at high altitude only.
Unfortunately there is no way to simply control the stock autopilot in pitch.

That leaves you with having to increase the pitch damping or as above, increase the longitudinal moment of inertia so that the resistance to pitch changes is increased.
If you are familiar with the air file and aerodynamics, I would suggest getting Yves "Flight Dynamics in Microsoft Flight Simulator" and study section 6.3.2. You might then decide to increase pitch damping Cmq.
Roy
Click to expand...


Thanks for your info. I will look into applying these suggestions.
 
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