In-flight oscillation

[65Rangoon]

The malfunction is: The civ acft develops a brisk but minimal up/down oscillation shortly after reaching level flight. Changes in MP, AS, nor altitude for that matter, have any effect on the oscillation. Engaging the auto pilot does not help eliminate the problem either, but it does reveal the elevator trim wheel briskly oscillating forwards and backwards. However, in the external view, the elevator is stable, with no discernible movement at all. Disengaging the auto pilot quiets down the elevator wheel, but the oscillation remains. I have not flown the mil version to determine if it too suffers the same sickness. The oscillation does seem to disappear at some point during the course of entering the landing circuit.

Thoughts, cures???

[Lewis - A2A]

Hello,

first thing to check is to ask if you are all updated? Are you an Accu-sim user?

Also double check to ask which product this is for I am assuming you are using the P-51 Civ with the Century AP?

thanks,
Lewis

[Tomas Linnet]

Do you have the fuselage tank installed if so how much fuel?? If you have to much fuel you can't use the autopilot because the CoG is behind limits

[65Rangoon]

To answer your questions Lewis; I am an Accu-sim user and it is up to date. And yes the AP is Century. I did re-run the core update, flew the acft, the problem still exists.

In response to Tomas' inquiry, yes I do have the fuselage tank but keep it empty (I'm aware of the CoG issue), so I can depart from 'straight & level', to rolls, loops, or whatever else I can think of to bore holes in the sky, minimizing the risk of a virtual crash not withstanding my own lack of acrobatic talent.

[Nick - A2A]

If it's not the CoG being out of limits, do you have any hardware controlling the pitch trim which could be responsible? If so, I'd recommend disabling or even unplugging it to test if it's the culprit.

Nick

[Dominique]

If the aft tank is empty, it sounds like a calibration issue. Verify that you don't have a double assignment. I love my P3D but each iteration has a tendency to mess up things in this regard and calls for a thorough check.

[Nick - A2A]

[...] it sounds like a calibration issue.

Yes, this is a good point as unlike the A2A GA autopilots, the primary hardware control for pitch (i.e. joystick or yoke) isn't disconnected when the autopilot is engaged. Therefore controller noise or a double assignment may produce just the effect on the pitch trim wheel described.

At any rate, in FSX-SE no problems encountered with the P-51 pitch stability in cruise or autopilot.

Nick

[65Rangoon]

If it's not the CoG being out of limits, do you have any hardware controlling the pitch trim which could be responsible? If so, I'd recommend disabling or even unplugging it to test if it's the culprit.

Nick

Only a hat switch on my X55 HOTAS. I'll disable it to see if it is the problem source.

[Dominique]

[...] it sounds like a calibration issue.

Yes, this is a good point as unlike the A2A GA autopilots, the primary hardware control for pitch (i.e. joystick or yoke) isn't disconnected when the autopilot is engaged. Therefore controller noise or a double assignment may produce just the effect on the pitch trim wheel described.

At any rate, in FSX-SE no problems encountered with the P-51 pitch stability in cruise or autopilot.

Nick

No such problem in P3D either. Tell me Nick, if the throttle pot spikes a little with too little a calibrated null zone, wouldn't it generate porpoising too ?

[Nick - A2A]

Tell me Nick, if the throttle pot spikes a little with too little a calibrated null zone, wouldn't it generate porpoising too ?

I reckon you'd need some pretty big spikes (and slow ones too) in terms of throttle response to cause any noticeable porpoising Dominique. With the control surfaces on the other hand, I'd guess noisy pots could have more of a noticeable effect at cruise speeds, especially if the autopilot is active and they're 'confusing' it.

Assuming it's not the hat switch which is responsible, I'd suggest for the OP to completely eliminate the HOTAS from the enquiries by unplugging it once in level flight. Then if the problem remains, at least we know it's not the hardware.

I'd say next on the list of stuff to eliminate would be any weather add-ons which may be active.

Nick