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Matt_thePilot

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About Matt_thePilot

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  1. Matt_thePilot

    Saab Climbout on Autopilot oscillates/porpoises

    I've done numerous flights in the last couple of days and for me having Autocoarsen and CTOT off doesn't seem to have a specific effect. About every other flight the progressive oscillations occur - usually after the aircraft has passed a turn of more than 30 degrees or so. I always keep my speed around 40-50 kts below the barber pole, so it shouldn't be overspeed induced. It seems there are issues with damping the oscillations whenever VS goes over 1500 fpm during a turn. It can sort of stabilise when the VS is smaller but anything over that and it keeps progressing until pitch is going up and down over 20 degrees and there is no other way than to disengage the A/P, manually stabilise and re-engage the A/P.
  2. Matt_thePilot

    Saab Climbout on Autopilot oscillates/porpoises

    I have an issue with the oscillation as well and I won't start a different post. I'm flying level at FL170, the A/P is keeping track and altitude just fine, then there's about a 30 degree turn and the A/P loses maybe 100-150 ft of altitude during the turn. Speed is around 200 kts IAS, 45kts below the barber pole (shouldn't be too fast). The A/P compensates heavily for the altitude loss, starting off with VS +/- 2000 feet, then increasing the oscillations more and more until VS is +/- 6000ft up and down. This sort of dynamically unstable behaviour would end with a stall. Tried reducing power just in case but that had no effect. Had to disengage the A/P, manually level the aircraft and only then re-engage the A/P and the aircraft would continue flying level. That's probably not normal behaviour, is it? I have screenshots of the plane at the extremes of the oscillation and logfiles, should those be necessary for investigation of the matter.
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