Aft Spar Web SB Doublers M20-217

[TravelingIA98]

Hello, my 65 M20E never received the doublers from M20-217 to address the cracking on the aft spar splice. I’m very familiar with the Mooneys and I’m an IA and would love to get these installed, but don’t know the dimensions of the doublers to fabricate them, nor can I find any for purchase. Does anyone have a good source for them or drawings I can produce them from? More than happy to just buy a set from someone if available! 
thanks! 

Edited October 16 by TravelingIA98

[PT20J]

I’d contact Frank Crawford at Mooney. fcrawford@mooney.com

[Andy95W]

LASAR makes a kit (or sells the Mooney kit).

[Shadrach]

Is your stub spar cracked? We inspect ours annually. In 3300hrs, no visible cracks as of yet.

 

[TravelingIA98]

13 hours ago, Shadrach said:

Is your stub spar cracked? We inspect ours annually. In 3300hrs, no visible cracks as of yet.

 

Ours isn't cracked, however I do prebuys on a fair amount of vintage Mooneys and see this problem far too often. Just trying to get ahead of it

Edited October 17 by TravelingIA98

[MB65E]

From reference when people have done the SB in the past I believe it’s .032 material. Mine has been stop drilled and hasn’t cracked in 10y. 
-Matt

[Shadrach]

7 hours ago, TravelingIA98 said:

Ours isn't cracked, however I do prebuys on a fair amount of vintage Mooneys and see this problem far too often. Just trying to get ahead of it

Understood. Just throwing out some unsolicited advice from someone who has also been maintaining a nearly 60 year old M20 airframe for the past two decades.

If the rear spar has not cracked in 59 years of service, it seems unlikely that it's going to any time soon...unless abused.  I believe that these cracks develop as a result of multiple overspeed events and that once a crack is initiated, it propagates under normal usage. It's a good sign that it yours is still in good shape.

Installing the doubler is a 10 to 12 hour job that will require removing the rear seat as well as re-rigging the flaps.  Have you considered all of the other things that might benefit from 10-12hrs of your time?  When was the last time the elevator trim gear box was disassembled, cleaned and lubed?  Have you removed the wing root fairings to ensure everything is still sealed? The interior compartments of the trailing edge of the wings at the root tend to accumulate dirt and debris which holds moisture. The same for the bottom, inside of the empennage.  Every year I check these areas and if needed pressure wash them with mineral spirits and finish them with a vacuum (after fumes dissipate).  It's not on the annual checklist, but these are extra things that I do to maintain the integrity of the airframe.  If this airplane was not previously A&P owned or owner maintained, I can almost guarantee these areas have seen little attention. Also, If it has a Brittain wing leveler/autopilot, there is a better than 50/50 chance that the vacuum hoses are rotten, but will only appear so when stretched.  It's likely that SBM20-208 has been complied with, but have you removed the interior and put eyes on steel tubing from top to bottom, inside and out?

I say all of this not to deter you from complying with the SBM20-217, but because in my experience there are areas of the airframe that are often neglected and prioritizing them might yield a better return on your maintenance efforts than installing a doubler on what seems to be a healthy rear spar.  If all of those other things have been addressed, then please disregard.

[Andy95W]

I mostly agree with what Ross said, above.  One additional piece of information is important, though- if the rear spar splice is not cracked, there is only one doubler to install. It is relatively straightforward. If that piece of metal IS damaged, the SB repair becomes much more involved and requires a second doubler be riveted in place inside the rear spar center splice box.  That’s a big increase in work.

Finally, a lot of people call it the “stub spar”, but it’s not.  The Stub Spar is actually the rear attach point of the landing gear and runs under the rear seat back.

[Shadrach]

1 hour ago, Andy95W said:

I mostly agree with what Ross said, above.  One additional piece of information is important, though- if the rear spar splice is not cracked, there is only one doubler to install. It is relatively straightforward. If that piece of metal IS damaged, the SB repair becomes much more involved and requires a second doubler be riveted in place inside the rear spar center splice box.  That’s a big increase in work.

Finally, a lot of people call it the “stub spar”, but it’s not.  The Stub Spar is actually the rear attach point of the landing gear and runs under the rear seat back.

Thanks for the clarification Andy,  I could not find an easily viewable copy of SBM20-217 perhaps I have the wrong number.   A cursory look at the IPC diagram could lead to mistaking the stub for the rear spar. I have seen it written so many times that I just adopted the terminology.  After reviewing the IPC, it's clear that the flap actuator is attached to the rear spar center splice.   I will edit. Thank you! 

 

 

[PT20J]

1 hour ago, Andy95W said:

Finally, a lot of people call it the “stub spar”, but it’s not.  The Stub Spar is actually the rear attach point of the landing gear and runs under the rear seat back.

Yeah, it's like most refer to the part of the nose gear that gets damaged as the truss when it's actually the leg.  

[TravelingIA98]

4 hours ago, Shadrach said:

Understood. Just throwing out some unsolicited advice from someone who has also been maintaining a nearly 60 year old M20 airframe for the past two decades.

If the rear spar has not cracked in 59 years of service, it seems unlikely that it's going to any time soon...unless abused.  I believe that these cracks develop as a result of multiple overspeed events and that once a crack is initiated, it propagates under normal usage. It's a good sign that it yours is still in good shape.

Installing the doubler is a 10 to 12 hour job that will require removing the rear seat as well as re-rigging the flaps.  Have you considered all of the other things that might benefit from 10-12hrs of your time?  When was the last time the elevator trim gear box was disassembled, cleaned and lubed?  Have you removed the wing root fairings to ensure everything is still sealed? The interior compartments of the trailing edge of the wings at the root tend to accumulate dirt and debris which holds moisture. The same for the bottom, inside of the empennage.  Every year I check these areas and if needed pressure wash them with mineral spirits and finish them with a vacuum (after fumes dissipate).  It's not on the annual checklist, but these are extra things that I do to maintain the integrity of the airframe.  If this airplane was not previously A&P owned or owner maintained, I can almost guarantee these areas have seen little attention. Also, If it has a Brittain wing leveler/autopilot, there is a better than 50/50 chance that the vacuum hoses are rotten, but will only appear so when stretched.  It's likely that SBM20-208 has been complied with, but have you removed the interior and put eyes on steel tubing from top to bottom, inside and out?

I say all of this not to deter you from complying with the SBM20-217, but because in my experience there are areas of the airframe that are often neglected and prioritizing them might yield a better return on your maintenance efforts than installing a doubler on what seems to be a healthy rear spar.  If all of those other things have been addressed, then please disregard.

I’ve been doing some pretty extensive maintenance on this bird getting it up to my standards. I have removed every bit of interior (especially to clean the smell of cigarettes off it) and seen every inch of the steel structure. Fuel tanks are free of leaks, gear pucks are in great shape, and I’ve gone through every applicable SB, this is the only one outlying. First annual I spent two weeks cleaning the internal structure and addressing a lot of overlooked items. The bird isn’t 100% perfect but it’s getting there. I currently have no cracks so I’d rather install the single doubler than do the internal one as well and risk eventual damage to the rib. Just staying on top of a 1965 airplane, unfortunately a good amount of A&Ps don’t even reference the MM when doing an annual so I often see neglected birds, especially Mooneys unfortunately.

[Shadrach]

3 hours ago, TravelingIA98 said:

I’ve been doing some pretty extensive maintenance on this bird getting it up to my standards. I have removed every bit of interior (especially to clean the smell of cigarettes off it) and seen every inch of the steel structure. Fuel tanks are free of leaks, gear pucks are in great shape, and I’ve gone through every applicable SB, this is the only one outlying. First annual I spent two weeks cleaning the internal structure and addressing a lot of overlooked items. The bird isn’t 100% perfect but it’s getting there. I currently have no cracks so I’d rather install the single doubler than do the internal one as well and risk eventual damage to the rib. Just staying on top of a 1965 airplane, unfortunately a good amount of A&Ps don’t even reference the MM when doing an annual so I often see neglected birds, especially Mooneys unfortunately.

Good deal! Sounds like you’ve got everything on the proper trajectory. If you’re able to fab a doubler and feel like making a second while you’re at it, I’ll buy it from you. It’d be good to have on hand.