M20C Spar Corrosion - options?

[DaV8or]

Under normal use maybe not , but load up the wing and EVERY component of the wing is stressed , and corrosion on a spar cap will cause a failure , its just a matter of how much and when.... 

 

See, I have to challenge this idea. Can you find any record of a failure of a Mooney wing spar cap failure while in service? I don't mean failure and rejection after inspection for corrosion. The Mooney wing spar is so beefy, that I would bet the wing spar cap could fall off altogether and you could easily fly on for years. This is not an ideal situation I agree, but again, some perspective. A little pimple that digs into the metal .030 of in inch, isn't going to kill anyone.

[tony]

the wing spar does look like it was designed by a bridge builder and not an aeronautical engineer....  my gut tells me that there is a lot of design margin there.

[Alan Fox]

See, I have to challenge this idea. Can you find any record of a failure of a Mooney wing spar cap failure while in service? I don't mean failure and rejection after inspection for corrosion. The Mooney wing spar is so beefy, that I would bet the wing spar cap could fall off altogether and you could easily fly on for years. This is not an ideal situation I agree, but again, some perspective. A little pimple that digs into the metal .030 of in inch, isn't going to kill anyone.

I am going to give you the benefit of the doubt here , But I have cut these up before...the wings weigh about 90 lbs each , don't think that they are  indestructible , they are not....They are the equivalent to the strength of an egg , one imperfection in the wrong place , and the whole structure fails, and it fails miserably.....

[carusoam]

The key words are "stress magnifier” an "crack propagation".

These are the engineering mechanisms that allow a minuscule problem to become disastrous.

This is the same explanation that keeps us polishing out nicks in our prop. Done properly, the prop lives on. Improperly, the prop cleeves and departs... Followed by vibration that are strong enough to break an engine mount...

Has a Mooney ever lost an engine overboard???

It's best to follow known procedures when to properly correct known issues...

The alloys in this case are chosen for ther strengths. Their weaknesses are, corrosion of spar and cap materials and denting of prop materials.... Try and avoid, followed by fixing properly, don't wait...

No fear, just sharing some ideas...

Best regards,

-a-

[javidan]

Do we know how common it is to find this type of corrosion of spar and cap? Do we have somewhere data on the subject 

[DaV8or]

Do we know how common it is to find this type of corrosion of spar and cap? Do we have somewhere data on the subject 

 

No data, but it is something to check for on the pre buy. This kind of corrosion is most common on planes that have spent a lot of time parked on the ramp.

[Alan Fox]

Unfortunately the Mooney uses a LOT or steel fasteners in the wings especially near the caps , which causes a mooney wing to be more succeptible to corrosion...(dissimilar metals)

[M20F-1968]

I have a nice clean Mooney wing from a 1967 F.  No corrosion. 

John Breda

(617) 877-0025

johnabreda@yahoo.com

[The_Wrench]

There are hundreds of high-shear pins in the Mooney spar.  They can be easy to install but you have to remember one very important thing.  These are a precise press fit.  Any hole that a high-shear pin falls into is not acceptable.  These pins need to be drilled undersize, then reamed to an interference fit.  If they are not a press-fit installation, they wont hold.  Your spar will start to smoke over time and the joint will weaken.  Not good.  make sure your mechanic uses a jig to drill the hole perfectly straight, then ream to fit.  If the pin goes in at an angle, its useless too.

[Shadrach]

There is no way in hell that a Mooney wing will survive 12 Gs.....Where do you guys come up with this stuff??? 

 

To quote you... I believe I have the last word on this one...study NTSB report.

 

Wing may not have been in airworthy condition after the event, but it got the pilot back on the ground uninjured... I count that as survival.

 

"The pilot executed a precautionary landing at the nearest suitable airport...

...A Mooney Airplane Company representative reported that the damage to the airplane indicated that the airplane experienced about 12g's of force during the recovery from the turbulence event."

 

 

 

http://www.ntsb.gov/aviationquery/brief.aspx?ev_id=20050428X00524&key=1

.

[Alan Fox]

If you read between the lines , you realize two things , 1) the wing did indeed fail , 2) the event must have been extremely short , ... You cant remain conscious at 12 Gs without a G suit ,     when a wing fails , the strength is compromised ...... This guy is the luckiest guy in the world , I wonder if the 10 K loss of altitude was from a loss of consciousness , or a stall spin event , or a combination of both.....I also wonder if the damage was from the turbulence or the recovery..... Pretty scary stuff....

[Alan Fox]

There are hundreds of high-shear pins in the Mooney spar.  They can be easy to install but you have to remember one very important thing.  These are a precise press fit.  Any hole that a high-shear pin falls into is not acceptable.  These pins need to be drilled undersize, then reamed to an interference fit.  If they are not a press-fit installation, they wont hold.  Your spar will start to smoke over time and the joint will weaken.  Not good.  make sure your mechanic uses a jig to drill the hole perfectly straight, then ream to fit.  If the pin goes in at an angle, its useless too.

I have replaced huck bolts and Hilocs on the spar before , and surprisingly they are not pressed in (or interference fit) I was actually surprised that they were not .......

[Matt Michael]

Howdy all, new guy here.  Been reading for a few weeks.  I restored an all metal 2 seat sailplane a few years ago.  It had a bunch of surface corrosion requiring abrasion, alodine, and painting. Now I'm considering buying a 64 M20C that by all accounts is in excellent condition.  I'd like some info and guidance on doing a pre-buy corrosion inspection or contact info for someone in the Iowa/Missouri area who could help me do it.

Thanks!

Matt

[Alan Fox]

The first places to look are at the front and back of the wing inside the cabin under the interior panels where the frame tubes come together and bolt to the wing.....This is common an explained in SB208 , the second place is in the wings on the back of the spar in the wheel well where the fixtures for the gear bolt to the wing spar......and generally around the spar in the wings , there are enough panels to make a decent assessment of the rest , pay a MOONEY experienced guy to do the prebuy , may be the best money spent... 

[sleepingsquirrel]

Does anyone have knowledge of the main spar alloy?

[RobertGary1]

Don't give up on it yet! Also, your GNS-430 will be worth more than $3500, or you could sell it in less than an hour for that price.

Twice that if it's waas