pc autopilot question

[MATTS875]

I have a question that hopefully someone can answer. When I am flying my plane it tends to want to go to the right. I have the basic wing leveler brittain autopilot. I have turned the screw on the pilots yoke but nothing happened..still wants to go left. any solutions or anyone had the same problem?

[butchgilbert]

On a Vintage (older) Mooney, just like mine, I believe you definitely have vacuum problem.  You need to find a skilled Mooney mechanic who has the knowledge to track down the leaks in the system and seal them up.  It the vacuum lines are cracked or broken (or even disconnected like mine), they'll need to be repaired/replaced.  The bad news is that the bellows in the wings are probably rotted and needed to be replaced as well (they move the ailerons to turn the airplane).  The good news is the Brittain is alive and well in Ada, Ok.  Google Brittain and contact them once the system has been troubleshot by a good Mooney mechanic. Good luck.

[Mooneymite]

Before you spend money on your problem, I'd check the boots on the servos....if one is leaking too much, the vacuum system can't compensate and the aircraft turns.

Usually, the boots have been sealed with tape; either the tape has pulled away, or the boot has a crack in it.  Re-taping is pretty easy if that's the issue.

Don't forget to check the ones in the tailcone!

 

 

[robert14]

I had the same problem with my 65 M20E. It turned  out to be the gyro. My mechanic called the Brittian (sp) folks and returned the gyro for repair. It took about 2 weeks and cost about $200. I was impressed. the system works great now.

[robert14]

FYI, sometime in the distant past, before I bought my 65 M20E, someone had installed a small pneumatic push-pull switch on the panel that performs the same function as the button on the yolk. Without that switch, I do not know how folks would comfortably fly the plane. Do you have such a switch on your plane?

[Cris]

Quote: Mooneymite

Before you spend money on your problem, I'd check the boots on the servos....if one is leaking too much, the vacuum system can't compensate and the aircraft turns.

Usually, the boots have been sealed with tape; either the tape has pulled away, or the boot has a crack in it.  Re-taping is pretty easy if that's the issue.

Don't forget to check the ones in the tailcone!

 

 

[Shadrach]

Matt,

On my F model, there are 2 flexible tubes that are slipped over hard fittings mounted on the inside pilot's side fuselage wall just above towards the fire wall from the the bottom of the pilots side outside instrument access panel. If anyone has been inside recently, it is concievable that one of the tubes was inadvertantly loosened or removed. This happened to me one year after annual presumably while a mechanic was inspecting my ignition switch. when I took off, the plane consistantly wantet to drop the left wing ~20 degrees.  

When you're on the ground, what does the yoke do while you're steering? The yoke should bank away from your ground turn. If it does not the system has a leak. Check what's easiest first.

I replaced all of flexible tubing for my PC last year. It took me about 2.5 hours (I'm flexible) and cost ~$100 from Lasar. A lot of shops put this off at annual as it can be a PIA from a labor standpoint. PM me if you need more technical info, I have the Brittain MX manual and operating hand book. It's not that hard to trouble shoot and is quite reliable. Ours has had zero failures in 44 years of service... A very elegant and simple yet effective device.

[Jerry 5TJ]

You may have a leak at the PC valve on the left end of the pilot's yoke.   I had to rebuild mine as the PC action was "sloppy" due to a low-level leak there.  The airplane's heading would tend to drift off in one direction. 

Rebuilding the PC valve involved pulling it out of the seat, taking the button and plunger apart, replacement of the internal spring, and cleaning out 40+ years of gunk.  After that the wing leveler was more effective and the centering knob worked positively.

Checking the electrical tape on the pneumatic servos is an annual inspection item.   It is easy enough to pull off the old tape and wind on new if needed. 

 

[Steve65E-NC]

A small hand vac pump with gage is invaluable in checking for boot or tube  leaks.  I think a good one goes for about $90 at an auto parts store.  They are used to check vac systems under the automobile hood.    You have to fiddle around to find the right barb connection for the tubing, I think I found the right attachment at Ace.  I can check all four boots through the rear battery access, though some may be easier with the bottom off.  You just id the tube running to each of the four boots.  Pull them one at a time and suck down the boot, don't get to aggressive, you are just looking for boot leaks.  Once you have the boot sucked down moniter the  meter for a leak.  A slow leak that takes a minute or so to lose vacumn may not be a show stopper.  I found the people at New Brittian to very helpful.  If you should need a new boot, they can exchange the entire bellows canister assembly, they no longer sell just the boot.  I have had tubes inadvertently pulled off in the cockpit.  I have had tubes running down the cockpit pierced by panel attachment screws.  I have had to replace tape on boots.  Once since 1992, I had to replace a leaking bellows.  I try to work on one connection at a time.  A few digital color photos can help get things back right.  

[AmigOne]

I recently visited Central Florida Avionics and Instruments at KLEE near Orlando, FL, to diagnose and repair the older a/p in a Cessna Centurion I will be ferrying this month to South America and to my surprise the manager told me that they also work on Mooney's PC system, including o/h of the turn coordinator.  Till then I thought that the guys at Brittain in Tulsa were the only ones that worked on these autopilots.  I own a 68 C model with a PC a/p and from time to time is prone to wander right or left.  It may be a leak issue but for sure the TC should get an o/h soon since I found no record in the logbooks that one has ever been done.