SB M20 208

[hoot777]

Has anybody had corrosion on the tubular structure ?  I have a 68 M20G. The ad was address in the logbooks.  Any thoughts ?

 

[67 m20F chump]

I would look myself.  It’s not hard to do.

[carusoam]

We have had a few examples of rust failed tubes and their repair posted on MS...

A typical candidate at risk.... often has a few things not going for it...

• stored outside without a cover... allowing contact with rain.
• Windows not replaced... allowing rain to get past old seals.
• original insulation.... holding water in contact with tubes.

Tube replacement is an expensive exercise for a casual owner.

If the AD was complied with, that removed the offending insulation. If the plane has been stored indoors... that keeps rain from getting in...

When buying a plane... Trust, but verify. The PPI is good for things like this...

ongoing maintenance for tubes... they are two sided... outside gets painted...inside probably gets fogged with an anti corrosion spray...

PP thoughts only, not a mechanic...

Best regards,

-a-

[DXB]

When purchasing my C model, I had it flown into a reputable MSC.   The MSC owner immediately made it a point to show me two C models flown into his shop for prebuy that now would never fly again because of tubular frame corrosion he found. I think he was looking forward to keeping his recent streak of declaring C models unairworthy alive on my prebuy plane and practically said as much. The dealer selling the plane was there,  didn't know much about Mooneys, and was visibly sweating at this point.  He had obviously never looked at the frame himself before taking the plane into his inventory in a recent exchange for a Bonanza.  I'm surprised he didn't end the deal right there rather than let us pull the interior.  The MSC owner found lots of other smaller issues, but it was corrosion free. The dealer then seemed pissed at him for having been put through the stress and was in no mood to negotiate on the other stuff.  The whole interaction seems rather amusing in retrospect, though it probably cost me a few bucks on the deal .

Edited May 8, 2019 by DXB

[Sabremech]

This S/B is recommended to be complied with at each annual. I wonder how many people actually do it versus those who think it’s a one time only S/B? 

 

[tigers2007]

Okay lets say there is a shocking amount of rust on a section of tubing. Is the aircraft unsafe to fly because it will crumble apart and the aircraft will implode? Has this ever actually happened?

Is there a way to fog the inside of the tubes with ACF-50 or CorrosionX?

[Prior owner]

37 minutes ago, tigers2007 said:

Okay lets say there is a shocking amount of rust on a section of tubing. Is the aircraft unsafe to fly because it will crumble apart and the aircraft will implode? Has this ever actually happened?

Is there a way to fog the inside of the tubes with ACF-50 or CorrosionX?

Not all of them but some of them.

[yvesg]

Mine is inspected every annual. Two years ago they found some corrosion on the pilot side. It was properly and legally fixed by an authorized reputable aviation welding shop. I think having SB 208 done every annual allows finding corrosion starts early that otherwise would eventually require major repair work.

Yves

[Prior owner]

3 hours ago, yvesg said:

Mine is inspected every annual. Two years ago they found some corrosion on the pilot side. It was properly and legally fixed by an authorized reputable aviation welding shop. I think having SB 208 done every annual allows finding corrosion starts early that otherwise would eventually require major repair work.

Yves

Just out of curiosity- were they able to do your repair without removing any of the skin? I have often wondered whether this is possible in some instances, as the only repair I have seen was when a member here posted his complete roll cage replacement that was paid for by his insurance company...and that required major disassembly of the aircraft. Thanks 

[yvesg]

5 hours ago, PilotCoyote said:

Just out of curiosity- were they able to do your repair without removing any of the skin? I have often wondered whether this is possible in some instances, as the only repair I have seen was when a member here posted his complete roll cage replacement that was paid for by his insurance company...and that required major disassembly of the aircraft. Thanks 

Rust went through a tube at one location only and they had to open a fairly small section under the belly in order to have room to weld. They did not need to replace any skin... just spread some sheet to have access all around the culprit tube. Maybe a dozen of rivets from memory? I will try to find the repair picture and post it here.

Yves

[Prior owner]

20 minutes ago, yvesg said:

Rust went through a tube at one location only and they had to open a fairly small section under the belly in order to have room to weld. They did not need to replace any skin... just spread some sheet to have access all around the culprit tube. Maybe a dozen of rivets from memory? I will try to find the repair picture and post it here.

Yves

I would really like to see that- thank you.

[yvesg]

Here is before and after pictures:

 

[Prior owner]

Excellent. Thank you very much for sharing that. I’d like to see more of these vintage M20’s being saved this way!

[Paul_Havelka]

@yvesg

 

Just curious but was that portion of the tube replaced or was a tube placed over it and subsequently welded? That hole looks to be really close to the joint

 

 

Sent from my iPhone using Tapatalk

 

[Shadrach]

On 5/8/2019 at 8:39 PM, tigers2007 said:

Okay lets say there is a shocking amount of rust on a section of tubing. Is the aircraft unsafe to fly because it will crumble apart and the aircraft will implode? Has this ever actually happened?

Is there a way to fog the inside of the tubes with ACF-50 or CorrosionX?

I have never heard of a cage failing in flight due to corrosion. 

[EricJ]

32 minutes ago, Creekrat said:

@yvesg

 

Just curious but was that portion of the tube replaced or was a tube placed over it and subsequently welded? That hole looks to be really close to the joint

 

I'm curious as well.   I suspect they'd have had to take the wing off to get at the other side of that.    It looks like the section of tube was taken off and the splice is to put in the new section, with the other end going to the joint.   Not sure how they managed to re-weld over the old joint, though.

Interesting, though.   The splice is straight out of 43.13.

[Shadrach]

4 hours ago, yvesg said:

Here is before and after pictures:

 

Was this performed with the skins in place?  That looks reasonable and robust. I have heard horror stories about tube repairs and I always wondered why it had to be so painful.  So many things utilize steel in the structure and it can be readily replaced and repaired by a competent welder.  With a Mooney though it seems that it needs to cost a minimum of $8,000...

[tigers2007]

If it was experimental: Weld it shut. JB weld on a metal sleeve wrap. Maybe weld on some gussets. Fly. 

[Prior owner]

The interior area of the repaired tube is not accessible from the rear bolt hole where the SB instructs you to pass a magnet through the lower tube.... so no matter how many times someone may have complied with the SB, it would have made no difference at all regarding the development of corrosion in that tube.

The SB only provides for prophylactic measures to deter external corrosion on all the tubes and internal corrosion in only a short section of lower tube.

Complying with the SB is a good idea, but I think that the above instance shows that the SB only benefits a very small section of the steel cage- the rest of the interior tubing is going to do whatever it wants to do.

Edited May 10, 2019 by PilotCoyote

[cliffy]

It used to be normal procedure to finish welding a fuselage, drill a small hole in each section of tube and inject a small quantity of linseed oil and then weld the hole closed. Kept the tubing from rusting from the inside out. Don't know if Mooney followed this procedure or not.  

It used to also be normal procedure for mechanics to make up fuel and oil hoses in house and do cylinder work in house. Had to learn how in A&P school many decades ago. Like other things its all lost to time.  

[carusoam]

Cliffy,

The updated procedure probably has boeshield and or corrosionX in place of linseed oil...

Long term protection of the inside surface is a very good idea still.

-a-

[Prior owner]

I’m very curious as to what Mooney is doing now as a preventative measure. 

[Shadrach]

On 5/17/2019 at 2:33 AM, PilotCoyote said:

I’m very curious as to what Mooney is doing now as a preventative measure. 

Well for one, they stopped using loose fiberglass insulation which held any moisture that entered the against the cage. For another, coatings have come a long way since the sixties and seventies. Whatever the are using now is likely a lot more robust than the enamel they once used.

[Guest]

On 5/10/2019 at 1:16 PM, EricJ said:

I'm curious as well.   I suspect they'd have had to take the wing off to get at the other side of that.    It looks like the section of tube was taken off and the splice is to put in the new section, with the other end going to the joint.   Not sure how they managed to re-weld over the old joint, though.

Interesting, though.   The splice is straight out of 43.13.

You can see the shop floor through the spot where the shop removed the lower wing skin to belly fairing.  It looks like a nice repair.

Clarence