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Spar Corrosion


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Mooneys aren’t the only ones with spar corrosion issues.  I’ve inspected two Piper Arrows, both 1973 200HP models 135 serial numbers apart, both with cracks in the aft spars caused by dissimilar metal corrosion between the aluminum spar and the steel attachment plate.

Clarence

B45BA08D-CABA-4F74-8633-0CC2BCFEBD5A.jpeg

171D7E85-6BD3-44CB-9674-58ECF99A813D.jpeg

D8D59135-EFA0-4E74-B0E8-1B19AF5B2582.jpeg

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That’s crazy. 
Williams airmotive in Indiana has a great YouTube video on the Piper spar corrosion Issues. They have a kit to fix it. 
I watched Paul, The founder, cut, match drill, and roll a center Mooney wing skin all by by hand one afternoon. Neat experience that I’ll remember forever. 
-Matt

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5 hours ago, EricJ said:

Oof!  I'm guessing the economical repair for that would be a replacement (junkyard) wing?

 

No, there is a kit to replace the inner 11”.  It’s about $1200 for the kit for left and right wings plus labour.  
 

Clarence

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47 minutes ago, N201MKTurbo said:

Is there any way to inspect that if they don't have the inspection plate installed?

On the Arrow there is an inspection plate in each wheel well for access.  Some in the Cherokee series had an inspection cover on the lower wing surface by at the rear spar, for those that don’t there is an SB to install one.  Even without the inspection cover you can remove the lower wing root strip and use a light and mirror thru lightening holes in the butt rib or slip a borescope in the same opening.

Clarence

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9 hours ago, bradp said:

And we wonder why piper wings fall off. 

The failure that took place in Florida a few years ago was the main spar and is subject to a soon to be revealed AD.  In the mean time Piper has released SB1345 calling for eddy current inspection of the spar.

Clarence

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1 hour ago, M20Doc said:

On the Arrow there is an inspection plate in each wheel well for access.  Some in the Cherokee series had an inspection cover on the lower wing surface by at the rear spar, for those that don’t there is an SB to install one.  Even without the inspection cover you can remove the lower wing root strip and use a light and mirror thru lightening holes in the butt rib or slip a borescope in the same opening.

Clarence

Thanks, sense I got my IA everybody is pestering me to do annuals. I’m doing a PA-28-180. Spent more time studying than inspecting.... 

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Wow...

There wasn’t much of the aluminum left that was in contact with the steal piece...

It doesn’t look like inspection can work in a timely fashion...

A significant amount of corrosion is in place before it becomes noticeable... on the outside...

I was expecting a method of insulating the two different metals from each other...

Possibly the next steps are replacing with a similar metal... (?)

PP thoughts only not a mechanic...

Best regards,

-a-

 

If anyone didn’t see the video posted by brad... the first one shows wear of a hole in an aluminum plate that has a steel bolt holding the wing attached...

A student tugged on the wing, pre flight... and it moved...   :wacko:

Good catch!

Thanks for sharing the details gents...

Best regards,

-a-

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6 hours ago, M20Doc said:

The failure that took place in Florida a few years ago was the main spar and is subject to a soon to be revealed AD.  In the mean time Piper has released SB1345 calling for eddy current inspection of the spar.

Clarence

Is that an easy thing to do?  Is the equipment relatively inexpensive?  I ask because would that be something someone would want to do on a Mooney, maybe even during a prebuy?

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6 hours ago, carusoam said:

Wow...

There wasn’t much of the aluminum left that was in contact with the steal piece...

It doesn’t look like inspection can work in a timely fashion...

A significant amount of corrosion is in place before it becomes noticeable... on the outside...

I was expecting a method of insulating the two different metals from each other...

Possibly the next steps are replacing with a similar metal... (?)

PP thoughts only not a mechanic...

Best regards,

-a-

 

If anyone didn’t see the video posted by brad... the first one shows wear of a hole in an aluminum plate that has a steel bolt holding the wing attached...

A student tugged on the wing, pre flight... and it moved...   :wacko:

Good catch!

Thanks for sharing the details gents...

Best regards,

-a-

The new parts in the repair kit from Piper have a layer of sealant type of material between the steel and aluminum.  There are a number of places in the Cherokee series where Piper used painted steel against bare aluminium.  My guess is the corrosion is caused by paint stripper entry during painting, then water, moisture and time doing the rest.

Clarence

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4 hours ago, ArtVandelay said:

Is that an easy thing to do?  Is the equipment relatively inexpensive?  I ask because would that be something someone would want to do on a Mooney, maybe even during a prebuy?

The inspection requires removal of 4 bolts then inspection of the bolt holes with Eddy current, it requires equipment and training to compete.  The wings on Mooney airframes don’t have the same installation method as the Cherokee series so it’s not applicable.

Clarence

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One of the reasons I elected to purchase a Mooney over others was the way it was constructed. I had considered a PA32R or a BE-36. I decided on the Mooney for both performance and structural reasons. The Cherokee wing attach method is not a "50 year" method. It is sad, because the old high wing Pipers had a simple, effective and durable system. I also shy away from Beechcrafts with "bathtub" spar attachments.

Believe me, the Beechcraft "bathtub" fitting is no fun.. I had a King Air which was one of the first to get the production installed Monel bolts inspected at the 5 year mark. Deciding I did not want to be on the "bleeding edge" I elected to replace the bolts rather than NDT the factory installed units. When we went to pull the old bolts out found the factory had installed the chamfer washer backwards and gouged the bathtub fitting beyond repair. Ended up hanging a new wing on the airplane. A lot of Beechcrafts out there with mis-torqued and mis-installed wing attach bolts. The methodology required to properly attach the wing is too error prone.

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On 5/12/2020 at 9:50 AM, M20Doc said:

Here is what the Piper rear spar repair looks like.

Clarence

47BB0EF1-70C8-4DB0-B842-54B164DC0DE7.jpeg

That assembly attaches to the existing spar?   So you have to remove a significant chunk, eh?

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2 hours ago, EricJ said:

That assembly attaches to the existing spar?   So you have to remove a significant chunk, eh?

The instructions say just under 11” have to be cut off.

Clarence

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