M20C positive control system

[pilot-as14]

h

Hello everyone, thanks to your help I've gotten a little further. I received a junk Mooney and am trying to restore the plane. A lot is broken. This positive control system looks very bad. I wouldn't even repair it. How is it in the US, does the system have to work, or can the plane operate without it?

Thank you for the reply

Alex

[Rjfanjet]

Mine was removed years before I became the owner. It is not required to fly the plane. Just have to hand fly everywhere since I don't have an autopilot either.

[Igor_U]

6 hours ago, pilot-as14 said:

 This positive control system looks very bad. I wouldn't even repair it.

Alex

 

Please describe in more details. Used parts are available as owners are removing their PC for new autopilot... It's a very good and simple system that is working well when sorted out. Also inexpensive to maintain but some parts are hard to get...

[Fly Boomer]

9 hours ago, pilot-as14 said:

h

Hello everyone, thanks to your help I've gotten a little further. I received a junk Mooney and am trying to restore the plane. A lot is broken. This positive control system looks very bad. I wouldn't even repair it. How is it in the US, does the system have to work, or can the plane operate without it?

Thank you for the reply

Alex

Parts are difficult to find, but those who have them working seem to love them.

[Bob R]

On 2/21/2023 at 2:54 PM, Fly Boomer said:

Parts are difficult to find, but those who have them working seem to love them.

They are not required. I have the pilot side yoke, disengagement button, pilot control valve(very recently overhauled), tubing and hardware. It’s a pretty simple system and works well keeping the wings level.

[Walk]

Can someone point me in the direction of a thread that discusses positive control malfunctions or failures? I have a 1974 M20 c that has a PC system that doesn’t seem to do anything. In fact, the aircraft doesn’t want to maintain a heading but instead tends to roll one way or the other fairly consistently. Thanks for any advice.


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[Bob R]

10 minutes ago, Walk said:

Can someone point me in the direction of a thread that discusses positive control malfunctions or failures? I have a 1974 M20 c that has a PC system that doesn’t seem to do anything. In fact, the aircraft doesn’t want to maintain a heading but instead tends to roll one way or the other fairly consistently. Thanks for any advice.


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I've been all through mine and they are pretty simple, differential vacuum system. More than likely, one of the boots (actuators) is torn in the wing or needs to be resealed with electrical tape of all things. Could be a couple of other things as well like the TC, vacuum hoses, poly lines, pilot valve.I have a freshly rebuilt pilot valve it it turns out to be that and also have the poly line and connectors which are readily available through a Parker dealer. Just don't tell them it's for an airplane.

Where is the gyro located for the TC? On the TC or remote?
 

 

[Bob R]

17 minutes ago, Walk said:

Can someone point me in the direction of a thread that discusses positive control malfunctions or failures? I have a 1974 M20 c that has a PC system that doesn’t seem to do anything. In fact, the aircraft doesn’t want to maintain a heading but instead tends to roll one way or the other fairly consistently. Thanks for any advice.


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Forgot to tell you, look in the download section as there are schematics.

[Shadrach]

41 minutes ago, Walk said:

Can someone point me in the direction of a thread that discusses positive control malfunctions or failures? I have a 1974 M20 c that has a PC system that doesn’t seem to do anything. In fact, the aircraft doesn’t want to maintain a heading but instead tends to roll one way or the other fairly consistently. Thanks for any advice.


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It is unlikely a hardline problem.

Could be Servos, could be the head unit,  could be hoses behind the panel.

First thing I would do is some low speed taxi tests. Find a place where you can make tight turns. The yoke should bank in the opposite direction of the ground turn on either direction. If it does not, something is wrong. Next remove the soft vacuum hoses from the hard lines (red and green) at their couplings which are mounted to the left sidewall under the instrument panel. Verify both right and left side will hold vacuum. Next check the condition of the hoses behind the panel, they will likely be deteriorated if >5 years old. Not much left after that, but the instruments. The pilot valve simply shuts the system on and off. It pretty much acts like a vacuum operated relay.  It is actuated by yoke mounted thumb switch or a panel mounted switch which when activated dumps vacuum at the pilot valve taking the system off line.

[Hank]

In my C, the system was leaking at the joints in the lines. Replacing all of the fittings was tedious, but it worked great after that.

The most common issue is probably leaks at the servos. The approved way to attach the rubber boot to the servo is to put the boot on at least 1"; put a thin o-ring on to hold it in place; fold the end if the sleeve back over the o-ring; and wrap Scotch 33 electrical tape around it to attach the rubber sleeve to the servo body. That's happened to me a couple of times, too.

[DCarlton]

4 hours ago, Walk said:

Can someone point me in the direction of a thread that discusses positive control malfunctions or failures? I have a 1974 M20 c that has a PC system that doesn’t seem to do anything. In fact, the aircraft doesn’t want to maintain a heading but instead tends to roll one way or the other fairly consistently. Thanks for any advice.


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It doesn't take much of a vacuum leak to cause it to act very lazy.  I was able to test my Red / Right Turn (mounted in left wing) and Green / Left Turn (mounted in right wing) servos and vacuum circuits using one of these:  

https://www.harborfreight.com/mityvac-vacuum-pump-39522.html

I was able to find a leak in my right rudder servo seal (located near the battery).  Ken Westbrook (former Brittain tech) repaired it for me.  My wing leveler works great now.  I'm currently troubleshooting another issue though; mine is not following the DG heading bug when the heading function is activated.  With a little help over the phone (again from Kevin) and a few schematics, I was able to confirm that the Inverter, DG Adapter, and DG were functioning satisfactorily.  We isolated the problem to the electrical portion of the pneumatic valve on the back of my Turn Coordinator.  Unfortunately the Turn Coordinator now needs to be repaired for the DG heading function to work properly.  I'll likely send it to Porter Strait in Tulsa to have Kevin repair it later in the fall.  

Folks might be able to help more if they knew which system you had in your airplane.  There are several configurations.  Or you could call Kevin.  He's always willing to help.