By Coy G. Jacob,
Contributor Aviation Consumer Magazine and
Senior Editor The Mooney Pilot Magazine
 

Mooney’s former long-time Chief Aeronautical Engineer and airframe guru Rocky Peters was quoted in a national aviation magazine as saying: "If a Mooney airframe gets professional maintenance, no substantial un-addressed abuse, and you protect it from corrosion, it may very well have a useful life of 20,000 hours to as much as double that and maybe upwards of 50,000 hours."   What Rocky was saying, is that it will be excessive insidious airframe corrosion that will kill your airframe, not the stresses induced by normal flying...Surprise, surprise!

While the neophyte or un-enlightened buyer may initially shy away from buying an airframe which has clocked more than say 7-8,000 hours total time in today’s market, upon an intelligent evaluation of the facts, it is clear that when evaluating the condition of any Mooney, it’s what is on the inside and between the laps and under rivets that you should be concerned with (or even fear), not how much time the airframe spent moving through the air.  Often it is how an airframe was maintained, where and/or how it was stored, and if preventative maintenance (fogging) had been done on a regular basis that is far more telling and vital than (for example) the shine of the paint on the outside. 

There is no doubt that the most effective tool any of us have to protect aluminum airframes and the M20's unique 4130 structural tubing is fogging with an anti-corrosion compound such as CorrosionX.  However make no mistake here, not all such products are alike; not by a long shot.  Lab tests indicate that while WD 40 (for example) may be better than nothing around the house on your door hinges, it is largely solvent (over 70%) and doesn't even come close to passing the Navy's Mil Spec requirements for anti-corrosion products. And while several other products (such as BoShield T-9 and ACF-50) have their value, CorrosionX not only has Navy/Mil Spec approval, but it has shown to be superior in both our independent tests where we used salt water sprayed on engine oil and various anti-corrosion soaked steel wool pads, and it also was superior in more formal lab tests.  It is clear it is the anti-corrosion protectant of choice when you consider results vs marketing hype.  

The problem here however for us individual aircraft owners, is that it isn't simply practical or effective to apply any anti-corrosive product like CorrosionX via an aerosol can entire airframes.  While cans work fine for small topical areas such as rod ends, control cables, and battery boxes etc., the product needs to be atomized and applied under more pressure than any aerosol can can provide.   To be effective over large areas such as the innards of the typical GA airframe, it must be fogged inside via a professional spray rig such as found in a CorrosionX Treatment Center, if not at least the belt pac sprayer via long thin wands that can reach inside controls as well as wing/tail fuselage compartments via inspection plates and/or tooling holes etc.  Click Here For Info on Magna Lab's M20 U-Fog-It Back Pac 

Luckily for us, most Mooneys had some internal corrosion protection built-in at the time of production. Except for some early ‘70’s or "Butler vintage" Mooneys, the huge majority of the production runs were internally treated or painted with zinc chromate primer.  Make no mistake however, that doesn’t mean the entire Mooney airframe innards were primed or treated, it means that the areas most likely to attract corrosion and perhaps commonly visible to the owner or A&P were so treated.  The areas typically treated with the yellow/green zinc chromate were around lap joints, the internal fuselage tail cone areas, and select internal components and skins. As we disassemble the average M20 for major airframe repairs, we find huge areas not treated such as the internal wing areas, control surfaces, fuselage skins, and tail group.

As more and more evidence comes in, there is little doubt airframe corrosion is simply your Mooney’s main enemy, not total time spent aloft. What you see accompanying here is a sample of a fuselage skin which was removed due to a minor incident on an aircraft which otherwise looked good. It was not, repeat not exhibiting any signs of significant EXTERNAL corrosion, even around rivets or externally around lap joints, but internally, well it was a different matter..

However, as the center photo shows, the lap joints were significantly involved with corrosion between the seams, as were the internal skin surfaces. This sporadic surface corrosion is sometimes what A&P’s term "popcorn" surface corrosion and if un-checked can eventually deem the component un-airworthy.

We feel so strongly about this problem being THE major threat to most Mooney owners nowadays, that MOA will be doing an on-going series on revealing M20 corrosion and advising how to insure that this insidious enemy isn’t at your doorstep and eating away at your beloved Mooney while you sleep; or fly...

Coy G. Jacob

Note: Coy has probably penned most of the research articles on airframe corrosion and the various corrosion protection products available as published in Aviation Consumer Magazines over the last 15+ years. We look forward to reading more about this insidious problem here in future MOA Pilot Magazine articles. We also encourage you to look through back issues of Aviation Consumer for more information or visit them on their web site at: www.aviationconsumer.com