M20F rusty tubing

[Seth Miller]

Mooney M20F with a short section of rusted through tubing located under the instrument panel near the firewall. I've included a couple pictures. Was previously covered up with electrical tape and zip-ties. I think its been there a while. I'm looking for some advice from someone who's been there on how to make this thing airworthy.

 

Thanks

 

[RLCarter]

Not good, 1st pix upper left corner is the engine mount bolt

[Andy95W]

That can be fixed.  Not easy, but not a huge issue for someone who is good with a TIG welder in tight spaces.

   This is from AC 43-13.  It’s a fairly standard repair.

[philiplane]

that's a highly unusual place for tubing rust, since it's coming from inside. Before repairing, you'll want to check uphill from there for a water source.

Repairing is done using a sleeve over the affected area. The methods are laid out in AC43-13-1A. The welding is the hard part since you have to clear a path for the welder, and protect everything in the area from sparks. Meaning you'll have days of prep, and then reassembly, for what is essentially a one hour welding job.

[Guest]

From the IPC and SB M20-208 you can determine the tube part number and material required for the repair.

https://www.mooney.com/wp-content/uploads/2020/12/SBM20-208B.pdf

Clarence

[PT20J]

Might want to check if water got inside and rusted the inside of other tubes.

[Gary0747]

The removable covers directly above the hydraulic pot on these early models are notorious for leaking.   Has the airplane spent much time tied down outside?  

[carusoam]

Welcome aboard Seth.

That is a most unusual first post...

Rusty tubes are something that often gets checked for during the PPI...

The most common location to find rusty tubes, is below the windows...

Look for sources of water entry to cause a challenge like this...

The common secondary cause of the rust... was the insulation next to the tubes... the insulation kept the water next to the tube...

 

What was the electrical tape and wire ties doing there?

PP thoughts only, not a mechanic...

Best regards,

-a-

[A64Pilot]

I’m astonished it rusted through with so little surface rust, are we looking at the bottom of the tube, could it have rusted from inside out?

I have a rusted tube in a similar location, but it appears to be just surface rust, it’s not through, I don’t have an ultrasonic thickness gauge though, but it passes the ice pick test, I need to pull the seats and convert the rust and zinc chromate it soon

‘if you look at the pic, I have way more surface rust, which is why I wonder if your rust is from inside?

 

 

Edited April 20, 2021 by A64Pilot

[PT20J]

One of the biggest issues is a leaky seal on the pilot's window. In airplanes that have not had the fiberglass insulation replace with foam, the water soaks the fiberglass which is against the steel tubes and can rust the tubing from the outside. A more insidious problem is that there is an aluminum channel for the purpose of attaching the plastic trim which is attached to the tube just below the pilot's side window with PK screws. On older airplanes, these screw heads were not sealed and if water leaked onto the channel it could rust them out after which it dribbled into the tubes and found its way through the structure to the bottom tube where it rusted from the inside.

Skip

[Seth Miller]

This all beats me. There was nothing in that area that I could see that would cause this. It's an 1966 M20F converted. Has the sloped windshield mod along with several other mods. I've known the airplane to be hangared for the last several years. I assume the tape was hiding this defect, and I think it's been there for a long while. Nice airplane that just got bladders put in. As they say, it's flown just fine for many years like this . I'm not up to tackling the repair, or at least doing the welding. Any suggestions on where to go to accomplish the fix would be appreciated. I'm located in KY.

 

Thanks

 

[TomM20F]

Anything can be fixed as others have stated. My concern is that this is that someone knowingly decided to conceal it from you. What I would want to know before throwing money at this problem is the condition of the rest of the tubing structure. Personally I would want to get an experienced Mooney person to go through the air frame and tell me what I am dealing with (pull the interior apart yourself and let the expert inspect it).  I am new 67F Mooney owner but not new to aviation or aircraft ownership. If we were talking about Cessna 140, 170, 180, j3 and super cubs I could offer you some credible information but I can't on a Mooney. From experience I would suggest take a step back and find what you are dealing with in total so you don't chase one problem after the next. Please don't be discouraged by mt rant, my wife will tell you I am the pessimist that assumes for the worst only to have the issue be much smaller than I worried about. You own a Mooney, get it right, and fly it. There are a lot of very knowledgeable people on this forum to help you.

[Andy95W]

4 hours ago, Seth Miller said:

This all beats me. There was nothing in that area that I could see that would cause this. It's an 1966 M20F converted. Has the sloped windshield mod along with several other mods. I've known the airplane to be hangared for the last several years. I assume the tape was hiding this defect, and I think it's been there for a long while. Nice airplane that just got bladders put in. As they say, it's flown just fine for many years like this . I'm not up to tackling the repair, or at least doing the welding. Any suggestions on where to go to accomplish the fix would be appreciated. I'm located in KY.

Don’t despair!  This will get better.  It’s going to cost money, but it’s just work.  A few hours to remove the components in the vicinity, a few hours to prep the repair, an hour to weld the new tube.  After that, a few hours to paint and replace all the removed components.

Biggest question right now is what does your local mechanic say?  This doesn’t necessarily have to be flown to a special shop, it just needs an A&P that knows the regulations, understands AC 43-13, and who can supervise a welder who can work in tight places.  That A&P will then sign off the repair.

Keep us posted, sorry you have to go through this.

[carusoam]

Great support, Andy!

Thanks for sharing those details...

11 hours ago, A64Pilot said:

I’m astonished it rusted through with so little surface rust, are we looking at the bottom of the tube, could it have rusted from inside out?

I have a rusted tube in a similar location, but it appears to be just surface rust, it’s not through, I don’t have an ultrasonic thickness gauge though, but it passes the ice pick test, I need to pull the seats and convert the rust and zinc chromate it soon

‘if you look at the pic, I have way more surface rust, which is why I wonder if your rust is from inside?

 

 

Often, tubes can rust through from the inside... ours aren’t very thick...

In some applications, tubes get painted on the inside...

Mooney steel frames need to be kept dry...

expect that modern steel frames have drain holes at the bottom... to allow air and moisture to escape...

 

So... moments ago... I asked BK if his new engine mount was going to get painted on the inside of the tubes...

Probably not needed... but a nice to have...

 

Chances of finding a tube getting thin, before it fails... is a tough one...

Exhaust tubes on TC’d engines come to mind...   they erode slowly in the transition from engine to turbo...

Somebody posted a pic of a Bravo exhaust... they stuck a tool through the tube wall... it was thiiiiinnnnn...

Best regards,

-a-

[Marauder]

This all beats me. There was nothing in that area that I could see that would cause this. It's an 1966 M20F converted. Has the sloped windshield mod along with several other mods. I've known the airplane to be hangared for the last several years. I assume the tape was hiding this defect, and I think it's been there for a long while. Nice airplane that just got bladders put in. As they say, it's flown just fine for many years like this . I'm not up to tackling the repair, or at least doing the welding. Any suggestions on where to go to accomplish the fix would be appreciated. I'm located in KY.
 
Thanks
 

You didn’t say which window mod you had. The SWTA 201 windshield mod has two small access panels. Those panels need to be tightly sealed or water will leak into the areas up by the foot wells.

Good luck with the repair. As Andy says, “Don’t despair, it can be repaired!”


Sent from my iPad using Tapatalk Pro

[A64Pilot]

The industry standard going back for Lord knows how long has been to fill tubes with boiled linseed oil and drain it. Bell 206 engine mounts will have rivets in the tubes, that’s where they drilled a hole to put the oil in and drain it out, then seal the hole with a Cherry Max. I’m almost positive my 1946 Cessna engine mount was filled and drained with linseed oil, I’d guess this started literally about 100 years ago?

In manufacturing you have to have all process specs approved, I’m sure there are better products than Linseed oil, but it works and is pretty much guaranteed to be approved without question by the FAA as its been the standard longer than any of them have been alive, to get something new approved will probably take time and money.

‘It took I’d guess about two months getting powder coating our fuselages approved and several Engineering reports addressing questions / perceived problems.

‘If you want something new, you have to prove it will do no harm, interestingly they really don’t care if it’s better or not

‘I’ve never heard of painting the inside of a tube, doesn’t mean it’s not done, just I’ve not seen it

‘I have during tube replacement of rusted tubes, sprayed liberal amounts of Corrosion-X in the adjoining tubes hoping to prevent further corrosion, but that was a repair and seemed logical to do. I think it helps.

‘Unless it’s a long tube like a fuselage longeron for example, I’ve found it easier usually to replace a tube as opposed to repairing it, although a proper repair is actually stronger than a new tube, it just looks better if it’s replaced.

[Seth Miller]

So I'm back to getting around to the repair. Going to have a welder come in and tig it. I was wondering if Mooney ever put out the specifications for tubing size and thickness, kind of like the do for the skin sections of aluminum? There is nothing in the service manual. Outside diameter is a given but I kind of would like to know the wall thickness if possible.

FYI 340117-49 is the tube part number that is being repaired 

Thanks

[Rwsavory]

24 minutes ago, Seth Miller said:

So I'm back to getting around to the repair. Going to have a welder come in and tig it. I was wondering if Mooney ever put out the specifications for tubing size and thickness, kind of like the do for the skin sections of aluminum? There is nothing in the service manual. Outside diameter is a given but I kind of would like to know the wall thickness if possible.

FYI 340117-49 is the tube part number that is being repaired 

Thanks

This service bulletin does not have your exact part number, but you could probably extrapolate from the various dimensions of tubing that are listed.  http://www.mooney201.de/files/M20-208B.pdf

[EricJ]

26 minutes ago, Seth Miller said:

So I'm back to getting around to the repair. Going to have a welder come in and tig it. I was wondering if Mooney ever put out the specifications for tubing size and thickness, kind of like the do for the skin sections of aluminum? There is nothing in the service manual. Outside diameter is a given but I kind of would like to know the wall thickness if possible.

FYI 340117-49 is the tube part number that is being repaired 

Thanks

The usual way to determine thickness is to drill a hole in it.

[Tcraft938]

I hope that's not a bad and costly repair for you.  My non A&P thoughts, but based on things my A&P has mentioned during annual.  If you do not have the 201 windshield, make sure your avionics bay (long narrow sheet metal) has some sort of caulk like tape under it.  Don't just screw it down metal to metal.  If like mine there are two small holes at the bottom for some reason and the metal to metal doesn't make a water tight seal.  He had me get a 3M product from Spruce I believe.  It comes in sheets and you peel off a gooy caulk like material and put around the opening.  It squeezes down when tighten screws and does an excellent job of sealing the area (plane quieter too and lower CO reading too).  The other thing is condensation.  If you have a hangar that sometimes gets very wet, or a wet floor, condensation will happen inside the plane.  I have that issue for 3 days every spring.  I love it because my A&P told us the best thing is to fly it a lot and blow it out.  So for weeks after that time my Wife has a To Do List item for me to "fly the plane to clear it of moisture.  I saved gas money honey, fly it two hours every day if you can".  DARN IT!!!! Okay if I have to.  :-)

[M20F-1968]

Seth,

Where are you located?

As part of my rebuild, I changed the structural cage to look like the new models.  I did so with a DER and a DAR did the welding.

The DAR was Lucky at Dallas are salvage.  

You can give him a call.

John Breda

[A64Pilot]

1 hour ago, EricJ said:

The usual way to determine thickness is to drill a hole in it.

There are ultrasonic thickness gauges that I have used on fuselages before that work well. I prefer NDI whenever possible.

‘The generic answer is your allowed 10% of the tubes new thickness loss to corrosion, and while I don’t know these tubes thickness, I don’t believe it’s very much. Even if you drill a hole good luck measuring to a tight tolerance through a small hole, and of course that’s the thickness of the tube at that hole.

‘The old school inspection method was via ice pick. if it didn’t break through, your good. Looking at one of the holes it looks maybe like a screwdriver tip?

When you replace that tube, I’d spray a liberal coating of Corrosion-X inside of it, and if it connects to any others them too.

Edited May 26, 2021 by A64Pilot

[PT20J]

I’d call Mooney and have them look up the specs for the tube from the manufacturing drawing.

[carusoam]

If looking for actual Mooney tubing...  of the pre-flown variety...

I know a guy.... a reaper....   see @Alan Fox.

Be on the lookout for open ends or drain holes...

But, as Doc John mentioned... not all tubes are the same dimensions...

PP thoughts only...

Best regards,

-a-