PC system still not working smoothly after repair

[salty]

Hi everyone, been lurking for awhile, flying with a friend that owns a '65 C that I might buy a share of or buy outright someday.

Anyway, we recently replaced all the servo boots and everything was great for a few flights, but then all of a sudden, they started binding. When checking controls free and clear, the ailerons got stuck, the PC button didn't help, muscling it broke it free, but then it would "stick" again when trying to move full aileron.

I pulled the wing panel by the boot off to see what was happening, and it seems like the boot isn't quite aligned straight and when you pull against the suction the rubber rubs against itself and "grips" causing the binding. It was a little cold (here in florida that means 50's) that morning, but otherwise nothing was different from other flights that didn't have the binding.

If the boot were aligned perfectly, I don't think the binding would occur, but it seems installed correctly, it's not crooked, it's flush to the mounting bracket. But, it also seems like just a little lubrication would solve the problem too. And it seems like it would be good for the life of the rubber, especially in warmer climates. The maintenance documentation mentions nothing of lubrication though.

Just looking for thoughts. Does anyone treat their rubber parts in general?

A bad attempt to show the alignment I'm referring to:

[cliffy]

The hole in the spar for the servo mount needs to be exactly perpendicular to the mid tangent point of the arc inscribed by the movement of the bellcrank arm.  That gives the least amount of sideways movement of the servo bag.

[salty]

Yeah, that's what I thought too. But, these servos are installed exactly like the originals. Not sure how the old ones could have ever worked, or how these could be aligned properly.

[ryoder]

Hmm.  Definitely a head scratcher.  That friend of yours sounds like a super awesome guy though.

[takair]

The hinge point on the servo where the chain attaches needs to turn 90 deg so that it allows the chain to pivot at the clevis.  The way it is set up now, the metal piston will torque under tension and wedge between the boot and the housing.  With the pivot oriented corectly it will better handle the angle between the link and the servo.  I have also treated my new boots with tire tube pure talcum powder, but only on the outside.  I know mine have also inadvertently been treated with Corrosion X with no negative affect, but I would think that fresh talc and corrosion X may make a mess.

[cliffy]

I have seen the hole in the spar drilled in the wrong place before. The boot needs to be pulled directly in line out of the can and not pulled by dragging it sideways in the can. The hole in the spar makes all the difference. On one I saw they replaced the boots every year  because they were dragging them out sideways. and cutting the boots. Once the servo was realigned properly it went 10 years with no issues. 

[takair]

9 hours ago, cliffy said:

I have seen the hole in the spar drilled in the wrong place before. The boot needs to be pulled directly in line out of the can and not pulled by dragging it sideways in the can. The hole in the spar makes all the difference. On one I saw they replaced the boots every year  because they were dragging them out sideways. and cutting the boots. Once the servo was realigned properly it went 10 years with no issues. 

Proper orientation of the clevis should help with some of the misalignment.  Perhaps worth a try prior to elongating a hole in the spar.  Even with a well aligned servo is only aligned at the mid position, rotation of the bell rank will move that point, which is another reason the clevis needs to be rotated.  I also seem to recall that you can get misalignment of the servo if the pneumatic fitting gets hung up and the servo does not sit flush.  

[salty]

11 hours ago, ryoder said:

Hmm.  Definitely a head scratcher.  That friend of yours sounds like a super awesome guy though.

Anybody that lets me fly their plane is a super awesome guy.

[salty]

12 minutes ago, takair said:

Proper orientation of the clevis should help with some of the misalignment.  Perhaps worth a try prior to elongating a hole in the spar.  Even with a well aligned servo is only aligned at the mid position, rotation of the bell rank will move that point, which is another reason the clevis needs to be rotated.  I also seem to recall that you can get misalignment of the servo if the pneumatic fitting gets hung up and the servo does not sit flush.  

I thought about spinning the clevis too, but it seemed like the chain will not accept a spin, The chain doesn't spin, so it seems like the clevis has to be aligned like it is now so that the bolt will go through the chain properly.

When the new boots were first installed, the fittings did prevent proper fit and this problem was much worse, but that was resolved and we're still seeing this problem.

I'm not following the "elongating the hole in the spar". Not sure what that means or how what I think you mean would help.

Edited February 6, 2016 by salty

[takair]

i was simply responding to the possibility that the hole in the spar is not in the right place, I was not advocating that.  I see what you mean about the chain and can't recall how to overcome that, but the misalignment is very likely the issue here.  When you pull on the chain at that angle it creates a lever arm that wedges the servo.  I had thought the chain had just enough play to allow the 90 degree rotation.  Maybe your chain is shorter.  Might also be worth checking that the servo sits flush.  As I recall it is hard to tell and easy for the pneumatic fitting to hang it up.  If I have time, I will pull the panel on mine and take a picture.

[salty]

I'm pretty sure the fitting is no longer an issue and the servo is flush. That's what Ryan and I thought was the problem originally, so I checked that pretty closely. But, maybe i"m wrong.

 

[TWinter]

This is a big reach here. You installed new boots. The rubber is going newer (stiffer as well). Have you checked the vac on the lines. Possible vacuum leak? I'm thinking maybe when you first installed the new boots they worked for a few flights because the old lines could handle the extra pressure for a short few flights, but actually the boot being stiffer and new  was in fact really creating a higher vacuum pull on old lines. The lines may have been strong enough for a few flights, but suddenly developed a leak (dry rot lines). I know it's a reach and might not fit your problem scenario, but I do know my lines were in of replacement bad. They worked until I had a boot develop a tear. In the trouble shooting process the lines were checked and several would almost tear and crumble with any slight movement. It was a wonder they could hold any pressure at all. 

As far as your binding I think it is only because the boots are new. I think with proper vacuum and alignment you would be working. I'm not sure that's the culprit, but I'm just a pilot not a MX. Just a thought..  

Good luck,

 

-Tom

[salty]

23 minutes ago, TWinter said:

This is a big reach here. You installed new boots. The rubber is going newer (stiffer as well). Have you checked the vac on the lines. Possible vacuum leak? I'm thinking maybe when you first installed the new boots they worked for a few flights because the old lines could handle the extra pressure for a short few flights, but actually the boot being stiffer and new  was in fact really creating a higher vacuum pull on old lines. The lines may have been strong enough for a few flights, but suddenly developed a leak (dry rot lines). I know it's a reach and might not fit your problem scenario, but I do know my lines were in of replacement bad. They worked until I had a boot develop a tear. In the trouble shooting process the lines were checked and several would almost tear and crumble with any slight movement. It was a wonder they could hold any pressure at all. 

As far as your binding I think it is only because the boots are new. I think with proper vacuum and alignment you would be working. I'm not sure that's the culprit, but I'm just a pilot not a MX. Just a thought..  

Good luck,

 

-Tom

I'm not following how a vacuum leak would cause the system to bind. 

Also, if I push the piston into the servo and then move the aileron (with no vacuum on the system), the servo binds as described above, so I don't think vacuum is the issue.

[MyNameIsNobody]

Send the photo to Brittain.  Kevin or Jerry will know what is going on. They build/repair/install and troubleshoot these systems.  It appears to be a chain/servo position issue.  Ring them up.  They are GOOD people.

[salty]

Just now, MyNameIsNobody said:

Send the photo to Brittain.  Kevin or Jerry will know what is going on. They build/repair/install and troubleshoot these systems.  It appears to be a chain/servo position issue.  Ring them up.  They are GOOD people.

Yeah, I tried to get them yesterday but they were gone for the day. 

[Yetti]

who is going to go out and take some access panel screws out and take a picture?

[carusoam]

'Binding' and 'controls' are usually a show stopper for me.

'maintenance manual' and mechanic are usually the solution.

'we recently replaced' is missing some important detail.

Both the airplane and wing leveler are such well proven systems. When they are both fully worn out there isn't any binding that is normal.  Having a small amount of binding can lead to an unknown amount of binding.

The good news is...

1) the companies are all still in business supporting their products.  Manual printing companies make copies of old manuals.

2) getting boots OH'd is well documented around here.  Low cost and fast turn-around.

3) reinstalling the parts shouldn't have any mystery to them.  Get the manuals so your mechanic can set the system up properly.

4) I like Yeti's idea for reference.  Controls are just too important to have mystery involved.  

5) friends don't let their friends fly planes that have unknown suspect conditions.  

6) my 65C's wing leveler never worked in my decade of ownership.  BMS... Before MooneySpace.

7) Is the wing lever simply not being turned off, and fighting for control?  Are you using the button on the yoke? Thumb, Rubber band or film canister?

Or did I miss something in the conversation.  Sometimes I'm much older than my driver's license says I am...

Best regards,

-a-

 

[MyNameIsNobody]

59 minutes ago, Yetti said:

who is going to go out and take some access panel screws out and take a picture?

Asked and answered.  There is a photo earlier in thread of the perpetrator.

[N601RX]

It's been a couple of years since I've had one out, but are you sure there isn't a 2nd hole in the bracket the servo mounts to? If I remember correctly it mounts to a riveted bracket and not directly to the spar.  Compare it to the other side and look for any obvious difference. 

[Yetti]

40 minutes ago, MyNameIsNobody said:

Asked and answered.  There is a photo earlier in thread of the perpetrator.

I was suggesting a non perpetrating install picture.....

[salty]

1 hour ago, carusoam said:

'Binding' and 'controls' are usually a show stopper for me.

'maintenance manual' and mechanic are usually the solution.

'we recently replaced' is missing some important detail.

Both the airplane and wing leveler are such well proven systems. When they are both fully worn out there isn't any binding that is normal.  Having a small amount of binding can lead to an unknown amount of binding.

The good news is...

1) the companies are all still in business supporting their products.  Manual printing companies make copies of old manuals.

2) getting boots OH'd is well documented around here.  Low cost and fast turn-around.

3) reinstalling the parts shouldn't have any mystery to them.  Get the manuals so your mechanic can set the system up properly.

4) I like Yeti's idea for reference.  Controls are just too important to have mystery involved.  

5) friends don't let their friends fly planes that have unknown suspect conditions.  

6) my 65C's wing leveler never worked in my decade of ownership.  BMS... Before MooneySpace.

7) Is the wing lever simply not being turned off, and fighting for control?  Are you using the button on the yoke? Thumb, Rubber band or film canister?

Or did I miss something in the conversation.  Sometimes I'm much older than my driver's license says I am...

Best regards,

-a-

Yeah, I was doing the run up checklist with instructor to get my complex endorsement when I felt the binding and we scrubbed the flight and I pulled the panel to see what was going on. The mechanic we used isn't experienced with the Mooney PC system, but we do have the manuals.

The button on the Yoke didn't have effect, because the problem is the physical binding of the servo. I can duplicate the problem without the engine (vacuum) running. 

[N201MKTurbo]

Takair has it right...

[N601RX]

Be sure the hose is routed through the hole in the bracket.  It seems like it isn't setting flat against the bracket.

[takair]

Pulling the panel refreshed my memory.  The chain that Mooney used is more appropriate for a toilet, but can work.  I recall I had to compromise between the ideal rotation of the clevis and the chain.  As I recall, I rotated as far as comfortable with the chain at full extension.  So, it is not quite horizontal, but close enough that it allows movement.  I think I had this problem when the bellows was new, so it was rotate the clevis and add tire talc.  If I still had the problem I would be tempted to remove the chain and add some twist to it or find a different kind.  Wish my aluminum looked as fresh as Salty's...

[FloridaMan]

Did you check for friction on the ailerons against the gap seals? I've seen it happen where the tape disappeared and the ailerons were binding against the gap seals, completely unrelated to the PC system. Remaining adhesive could increase this friction. Try putting some oil on a rag and rub it on the aileron where you see the friction to see if it makes it go away.