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flyforever

throttles and autopilot

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I just started flying the falcon. When on autopilot and cruise speed, the plane suddendly pitches up as soon as I pull back on the throttles before starting my descent. I don't understand why a throttle movement would cause an extreme aircraft pitch behavior. I've checked for spikes and everything is calibrated correctly.

Does anyone else experience this? P3D , separate trim wheel, separate throttle quadrant, win 7.

thanks

tony

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Not normal behavior...never seen that here.

Sounds like you may have a "phantom" assignment of a throttle axis to the elevator, trim, speed brake, etc.  It could be in the sim, or in FSUIPC if you use that.  Check the assignments for every controller listed in the P3D Controls menu and in FSUIPC that there are no unintended axis assignments.  Odd, though, that you don't see it before that point.  It may also be possible, though not likely, that an out-of-limits aft CG (eg from a nonstandard fuel burn) could manifest itself that way when the nose-down moment from the tail-mounted engines is reduced when pulling power for the initial descent.

I'd also watch the trim gauge to see if there's a big and/or sudden change at that point, and watch the yokes to see if there's a large autopilot input.

 


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1 hour ago, flyforever said:

When on autopilot and cruise speed, the plane suddendly pitches up as soon as I pull back on the throttles before starting my descent.

I don't see this, and don't recall any other similar reports. I use win10 and P3Dv4.5. If ALT hold is on, the a/c will slowly pitch up as the airspeed falls in an attempt to hold the altitude at lower airspeeds.

Al

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If it's an actual control surface deflection (Watch the yoke to see if it's pulling back) then check that you haven't assigned the axis to both FSUIPC and P3D - they'll fight eachother.

 

Otherwise I would suggest verifying the AP mode you're in, if you have IAS and ALT hold on, chopping the throttle in cruise will cause a pitch up and perhaps porpoising while the AP tries to find the right pitch attitude to maintain your selected altitude.


James Burke

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31 minutes ago, paradoxbox said:

.........  if you have IAS and ALT hold on, chopping the throttle in cruise will cause a pitch up and perhaps porpoising while the AP tries to find the right pitch attitude to maintain your selected altitude.

I don't think you can have ALT Hold and IAS on at the same time with the autopilot. IAS, like VS, is a pitch mode for climbing or descending, not for cruise at a fixed altitude. Perhaps you meant ALTSEL, because if in a stable climb or descent with IAS (or VS) and ALTSEL,  chopping the power will necessitate pitch changes by the autopilot as it tries to maintain the climb or descent IAS (or VS).

Other thoughts welcome,

Al

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