Century 31 A/P Pitch Oscillations

[Piloto]

For about two years I had my C31 A/P doing occasional pitch oscillation or sudden pitch changes. I had the AI overhauled by Auto Pilot Central, after six month the A/P started pitch oscillating. On my last flight to KAGC I noticed there were no oscillations below 8,000ft but at -20C OAT this turns to about a DA of 6,000ft. The vacuum pressure was consistent at 4.5"hg (the bottom edge of the blue arc). I decided to increase the vacuum. I removed the vacuum regulator and found it was limiting the vacuum to 4.5"hg by sucking on it while measuring the inlet port. The placard on the regulator indicate a setting of 5.5"hg. So I adjusted the regulator to 5.6"hg. Reinstalled the regulator and checked all the vacuum lines. After 1 hour at 10,000ft at 7F OAT not a single event of pitch change. Pitch was super stable. It appears that Century gyros do not perform well at low vacuum.

José

[carusoam]

Interesting observation, José!

Thanks for sharing that.

Best regards,

-a-