Was wondering if anyone else has a problem with autopilot porpoising?
longer video with electric trim on and off:
Took this video of the Saratoga's S-Tec 55X autopilot oscillating during flight for maintenance review. Took the video on an Angel Flight mission return climbing and level at 10,000 and 17,000 feet. It does it at all altitudes--intermittently. Also, in the climb. Did a number of tests during oscillations with electric trim on and off. I think the CG location may have some part of the intermittent porpoising. Was told that a Piper Navajo had a similar problem but only if it had passengers in the rear. So, they just placarded it as “autopilot will oscillate when carrying passengers.”
From previous owner.
Former owner had a little porpoising since the time he bought the airplane—4 years. It got progressively more pronounced with time starting in 2019. Avionics team removed slack in cables and that helped a lot but then returned. There have been numerous long flights with no noticeable porpoising at all. Most flights it settled down after awhile. Also rebuilt pitch servo in last annual.
Adjusted Auto Pilot servo bridal cable tensions IA W S-Tec
Field Install manual ST-536-1 Rev. 14
5/13/2022
Removed and send 0 108-PI ser # 0608-157 18CDEFGK Autopilot servo to
Genesys 15452 - Airport Drive Aerosystems under SRO # RI 02968 for repair and service.
Same unit re-installed into aircraft after service.
Slowing working through system checks but getting plane in for detailed trouble shooting is a problem with scheduling. S-Tec provided some guidance:
1. Cable tensions (servo bridle and aircraft primaries).
2. Start up voltage on the servos (less than 2V for 28V A/C and 1.5V for 14V A/C).
3. Auto-Trim induced pitch porpoise (turn off trim to identify).
4. Strapping/securing of the computer mounting rack (vibrations into the computer).
5. Static system leaks (<100ft/min @ 18,000ft), moisture in the system.
6. S-TEC altitude pressure transducer (see attached chart).
7. Friction in the aircraft control system.
8. Electrical interference (AC ripple from alternator).
9. Seating of the computer into the rack/wiring harness.
10. Wasted armature motion in Pitch Servo before making contact with Trim Sensors.
11. Servo Clutch not set to specification.
longer video with electric trim on and off:
Took this video of the Saratoga's S-Tec 55X autopilot oscillating during flight for maintenance review. Took the video on an Angel Flight mission return climbing and level at 10,000 and 17,000 feet. It does it at all altitudes--intermittently. Also, in the climb. Did a number of tests during oscillations with electric trim on and off. I think the CG location may have some part of the intermittent porpoising. Was told that a Piper Navajo had a similar problem but only if it had passengers in the rear. So, they just placarded it as “autopilot will oscillate when carrying passengers.”
From previous owner.
Former owner had a little porpoising since the time he bought the airplane—4 years. It got progressively more pronounced with time starting in 2019. Avionics team removed slack in cables and that helped a lot but then returned. There have been numerous long flights with no noticeable porpoising at all. Most flights it settled down after awhile. Also rebuilt pitch servo in last annual.
Adjusted Auto Pilot servo bridal cable tensions IA W S-Tec
Field Install manual ST-536-1 Rev. 14
5/13/2022
Removed and send 0 108-PI ser # 0608-157 18CDEFGK Autopilot servo to
Genesys 15452 - Airport Drive Aerosystems under SRO # RI 02968 for repair and service.
Same unit re-installed into aircraft after service.
Slowing working through system checks but getting plane in for detailed trouble shooting is a problem with scheduling. S-Tec provided some guidance:
1. Cable tensions (servo bridle and aircraft primaries).
2. Start up voltage on the servos (less than 2V for 28V A/C and 1.5V for 14V A/C).
3. Auto-Trim induced pitch porpoise (turn off trim to identify).
4. Strapping/securing of the computer mounting rack (vibrations into the computer).
5. Static system leaks (<100ft/min @ 18,000ft), moisture in the system.
6. S-TEC altitude pressure transducer (see attached chart).
7. Friction in the aircraft control system.
8. Electrical interference (AC ripple from alternator).
9. Seating of the computer into the rack/wiring harness.
10. Wasted armature motion in Pitch Servo before making contact with Trim Sensors.
11. Servo Clutch not set to specification.
