Positive Control System Erratic Operation.

[Caribbean Aviator]

Hi guys! Today while flying straight and level with the PC engaged my plane started turning left by itself. Almost at the same time I got a High Vac Light  warning. Actual suction was in the green pretty much in the middle and no other instruments failed. I disengaged the PC and tried to re engage with the same results. Has anyone experienced this issue or has an idea of what the problem could be? Any feedback will be greatly appreciated. My plane is a 69 M20F.

[McMooney]

sounds like a leak in a servo, same symptoms as mine.

 

[McMooney]

 

Just now, McMooney said:

sounds like a leak in a servo, same symptoms as mine.

 

Reminds me, anyone have a spare servo ?

[chriscalandro]

I have one.  Where are you located?

 

[McMooney]

57 minutes ago, chriscalandro said:

I have one.  Where are you located?

 

Houston, how much are you asking ?

[chriscalandro]

120?  I still have to take it out of the wing. Not 100% sure of condition but I know it works.   If it’s beat up a bit, less. If you come to Miami and take it out yourself, even less than that. 

[takair]

14 hours ago, Caribbean Aviator said:

Hi guys! Today while flying straight and level with the PC engaged my plane started turning left by itself. Almost at the same time I got a High Vac Light  warning. Actual suction was in the green pretty much in the middle and no other instruments failed. I disengaged the PC and tried to re engage with the same results. Has anyone experienced this issue or has an idea of what the problem could be? Any feedback will be greatly appreciated. My plane is a 69 M20F.

I have had the disable switch leak such that it mimicked pushing the disable button.  The result was that the aircraft, which was not quite rigged perfectly without the PC would bank one way.  The high vacuum light may be the result of the PC being disabled and not using its share of the vacuum.  Started by looking at this. Old aircraft had a pneumatic solenoid, newer have an electric solenoid.  Both shut off vacuum to the system.

[0TreeLemur]

15 hours ago, Caribbean Aviator said:

Hi guys! Today while flying straight and level with the PC engaged my plane started turning left by itself. Almost at the same time I got a High Vac Light  warning. Actual suction was in the green pretty much in the middle and no other instruments failed. I disengaged the PC and tried to re engage with the same results. Has anyone experienced this issue or has an idea of what the problem could be? Any feedback will be greatly appreciated. My plane is a 69 M20F.

There is a lot of discussion on this site regarding diagnosing and repairing PC system problems.   Every question you will ask has probably answered on this site.   Use google to search.   Type into google.com things like: "PC system repair site:mooneyspace.com"   The site:mooneyspace.com will limit your search results to this site.   You will find many threads discussing how to fix the PC system.  Good luck.

[Pasturepilot]

Check your left wing servo, the red lines, or the servo in the tail that's fed by the red line (pretty sure it's the forward one). Just found a leak in the left gear well causing similar problems, but I don't have a high vacuum light installed in my '65C. 

[McMooney]

On 7/31/2020 at 8:51 AM, chriscalandro said:

120?  I still have to take it out of the wing. Not 100% sure of condition but I know it works.   If it’s beat up a bit, less. If you come to Miami and take it out yourself, even less than that. 

@chriscalandro pm sent

[Caribbean Aviator]

On 7/31/2020 at 12:32 PM, takair said:

I have had the disable switch leak such that it mimicked pushing the disable button.  The result was that the aircraft, which was not quite rigged perfectly without the PC would bank one way.  The high vacuum light may be the result of the PC being disabled and not using its share of the vacuum.  Started by looking at this. Old aircraft had a pneumatic solenoid, newer have an electric solenoid.  Both shut off vacuum to the system.

Thanks! I will have to check that out. I inspected all the servos and they are in perfect condition.

[Caribbean Aviator]

On 8/2/2020 at 9:21 AM, Pasturepilot said:

Check your left wing servo, the red lines, or the servo in the tail that's fed by the red line (pretty sure it's the forward one). Just found a leak in the left gear well causing similar problems, but I don't have a high vacuum light installed in my '65C. 

Thanks! I will have to follow this lead also. I inspected all the servos and they are in perfect condition. Subsequently I did two flights with similar results. On both after climb out and level off I engaged the PC. It works for about 15 minutes with no problems but eventually it starts a turn to the left that can’t be corrected with the trim knob on the turn and bank indicator. Turning system off for a few minutes and turning back on resulted in the same left turn. I turned the system off for the duration of the flight. 
 

On my return flight I repeated what I had done before with pretty much identical results. System was engaged after level off but after approximately 15 minutes the aircraft started an un commanded turn to the left. Turning PC off and back on later during the flight produced the same results.
 

 

[Pasturepilot]

34 minutes ago, Caribbean Aviator said:

Thanks! I will have to follow this lead also. I inspected all the servos and they are in perfect condition. Subsequently I did two flights with similar results. On both after climb out and level off I engaged the PC. It works for about 15 minutes with no problems but eventually it starts a turn to the left that can’t be corrected with the trim knob on the turn and bank indicator. Turning system off for a few minutes and turning back on resulted in the same left turn. I turned the system off for the duration of the flight. 
 

On my return flight I repeated what I had done before with pretty much identical results. System was engaged after level off but after approximately 15 minutes the aircraft started an un commanded turn to the left. Turning PC off and back on later during the flight produced the same results.
 

 

I missed the part about 15 minutes of normal operation before it headed off onto the weeds. Mine was having left banking issues constantly, but only barely so. 
 

I used to have an attitude indicator that did that after an hour or so.... it’d start a slow diving turn although I was level. That may well be a failing  TC but I have no knowledge of those.  My PC and TC are independent. 

[MBDiagMan]

On 7/30/2020 at 9:18 PM, McMooney said:

 

Reminds me, anyone have a spare servo ?

I have a spare boot.