How To Deal With Major M20 Airframe Corrosion Repairs

How To Deal With Major M20 Airframe Corrosion Repairs
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First off, take this type of repair seriously. Generally speaking, we will categorize serious corrosion repairs in two categories, 4130 tubular rust and/or M20 spar area corrosion. While significant expense can be attributed to general airframe corrosion repairs, unless widesprad, replacing exterior sheet metal is generally something which isn't as economically threatening or doesn't turn-up unannounced. Generally, corrosion occuring in the interior/exterior lap and rivet areas manafest itself slowly. In fact, as the Mooney fleet ages, general airframe corrosion and especially corrosion in the skin lap areas will play a larger part of threatening the fleet. The good news however, is that this type of corrosion is perhaps the most easily detected and prevented. The bad news is that in order to affect OEM quality repairs to skins, it takes a greater amount of expertise in sheep metal repairs and rivet workmanship than most shops possess.

Sheet Metal Repairs: The Difference Between Typical "Field repairs" and OEM Factory (quality) Repairs Can Be Real....
When picking a shop to do M20 skin sheet metal repairs of any kind (especially corrosion repairs), ask to see examples of their workmanship as to rivet and "fit and finish". Ask for references and for examples. Generally speaking, the Mooney factory used more precision riveting and skin fitting techniques than is common in GA. Frankly, we feel the workmanship typically coming out of Kerrville over the years was second to none in GA. So, typical "field" repairs stick out more if they aren't up to OEM standards. This can be high rivets or dimpling when a rivet is "over-driven" etc. It can also mean a less than perfect shop side of a rivet. When making field repairs, few A&P's recognize the importance of this unless they are "Mooney specific" experience-wise.

The key to examining any Mooney sheet metal repair and workmanship out in the field is that you should NOT be able to detect any repairs were made by a casual observation or walk around inspection. The shop making the repairs should be adroit at milling and driving rivets precisely and no (or very little) evidence of excessive rivet driving be evident. In fact, many use a rivet squeezer (when applicable) rather than to drive the rivets by hand. The shop side of the rivet should be uniform in compression and expansion and never bent over or sloppy.

Fitting of skins properly, especially back to OEM factory standards usually requires tools such as dead hammers and such-tools many shops simply aren't use to using. Picking a good shop to do sheet metal repairs (corrosion or not) can make a significant difference in resale value later on as well as deter from the visual appearance. Again, the better the job the more difficult it should be for anyone (especially an A&P) to detect. When it comes to M20 corrosion, an once of prevention is worth far more than a pound of cure.
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When it comes to 4130 tubular rust (see enclosed pics) or heat treated aluminum 7606-T6 wing spar area corrosion, we advise you inspect and verify this type of damage yourself with your own eyes once discovered if at all possible, prior to beginning any professional repairs. Perhaps the most important determination in dealing with this type of repair/rebuild is making sure the shop that notifies you of this problem is the one best qualified to affect the repairs! Most often they are not, as repairing primary Mooney aluminum structure and especially removing the wing and/or repairing/welding fuselage 4130 tubular primary structure requires a significant level of expertise and innovative procedures. Please keep in mind, most A&Ps are reluctant to admit they aren't "Mooney experts" of sorts, but replacing spar cap material or entire clusters or sections of your fuselage 4130 tubular structure is best done by somebody who has done it before and isn't learning on your Mooney.

Remember in most cases a FAA Ferry Permit can be obtained (even if it means some re-assembly has to be done) so the aircraft can be flown to a Mooney specific shop. If not, it is entirely possible to transport your Mooney de-mated (tailcone or wing removed) for transportation to a Mooney specific shop. We caution you that sloppy repairs in these areas can cost fare more long-term than the cost of transportation. In our opinion, there are only a handful of shops across the country which regularly do this type of work and who are good at it. We especially recommend employing a Mooney specific shop has a current labor force experienced in this type of repair when it comes to welding in new 4130 tubular fuselage sections. Make no mistake, this type of repair will typically be visible once the Royalite is removed and it will be closely examined by virtually every future buyer and their mechanic down the line for years to come.

Suggested PDF Reprints On Corrosion From The MOA PILOT Magazine
Note: Same as when you download our entire magazine, you will be required to have Adobe Acrobat to download these articles. Acrobat Reader software is available FREE from: Adobe on-line

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September, '01 MOA Pilot Magazine: "Corrosion: THE ENEMY FROM WITHIN", By Jim VanGilder. This was Jim's first installment on his column titled "Corrosion Corner". It is very good reading.
July, 01 MOA Pilot Magazine: "Aluminum For Mooniacs" , By Michael J. Matisko, Engineer Alcoa Aluminum Co. This is the first installment on the proper care and feeding of the aluminum structure of your Mooney aircraft.
August '01, The MOA PILOT Magazine: "Aluminum For Mooniacs: Part II" By Michael J. Matisko, Engineer Alcoa Aluminum Co. This is the second installment on the history of the current "high tech" aluminum alclads used on Mooneys.
September '01, The MOA PILOT Magazine: "Aluminum For Mooniacs: Part III" By Michael J. Matisko, Engineer Alcoa Aluminum Co. This is the third installment on the proper care and feeding of the aluminum structure of your Mooney aircraft.
March '01, The MOA PILOT Magazine: "Airframe Corrosion.... Any Disbeliveers Still Out There?", By Coy Jacob. Several illustrated cases on-point show why Mooniacs should be seriously concerned about corrosion and thus adopt effective preventative maintenance procedures.