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cjpilot710(at)AOL.COM
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 Posted: Mon Oct 06, 2008 3:25 pm Post subject: Corrosion Alert CJ-6 |
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Troops,
At OSH this year, during the multitude of conversations, chit chats, and just plain eavesdropping, I heard the word "corrosion" in the same sentence with "CJ-6". Of course my ears perked up. I've done a little research and looked into several of the stories. Thanks to Doug Sapp's pretty wife Katherine, providing me with some phone numbers, and the miracle of e-mail, I've come up with enough to suggest that we CJ-6 owners, take time, soon, and do a detailed inspection of our wings. So far 4 CJ-6 (2 in the US & 2 in NZ) have had significant spar cap corrosion.
The two here in the US were inter granular corrosion of the lower spar cap. One, the corrosion spots was located in the center section, in the other, the corrosion was in the left wing just out board of the landing light. According to my source in NZ Jay McIntyre, those aircraft there, suffered heavy surface corrosion due to very poor storage for a numbers of years.
I've included Jay's e-mail here.
_________________________________________________________________________________
Hi Jim.
This particular machine #1832041 is a 1966 build.
It was brought into Australia with another 17 machines in the early 90's. Due to shady dealings and the vendors wanting exorbitant prices they did not sell. Eventually the company went bust and after many years they were all sold at auction in the late 90's.
Unfortunately they were stored in their shipping cradles on the ground and long grass grew up around them resulting in the problem we now see. A lot of other damage occurred.
The corrosion is not inter granular, but has resulted from moisture pooling in the lower center section area, particularly the lower spar caps. This was initially ground out (see photos), but was way too deep. Many of the wing attach fittings also suffered a similar fate, with the worst one being the item I am trying to source from Jeff (see photo).
One other machine from this batch suffered similar problems and I believe that it has had the spar caps changed. Using the tensile test that the Aussie's had carried out and our own testing it was determined that the material was almost identical to 7075-T 6.
A suitable extrusion was procured but required machining (as the original is not quite a right angle) to achieve the 87 degree angle of the cap. It also required a small amount of wheeling to induce the slight anhedral of the center section.
After having it anodized and primed we have just finished installing it.
The center section belly skins were also very corroded and have been replaced.
Hope this is of help... I will forward another e-mail with some pictures.
Cheers, Jay
_________________________________________________________
Here is a picture of what Jeff Boulware sent me of the damage he found in his aircraft.
Again this damage on this particular aircraft is located in the bay just out board of the landing light. The corrosion is on the lower spar cap. The yellow object behind the lighting holes in the spar web, is the left main fuel tank. The tube in the picture carries wring going to the wing tip and flux gate compass. Because of this and other damage (see below) he replaced the wing.
Below is the corrosion located on the lower spar cap in the center section of Sean Carroll's aircraft.
This next picture is again from Jay Boulware's aircraft. Though not related to the corrosion, it does show what other damage could be found during a really good inspection.
I am not a metallurgist but I've been told that inter granular corrosion is caused by improper quenching of the metal as it comes from the extrusion machine. We found this a few times on some of the propellers from China. It is not unusual to find it on US aircraft also. I just got though replacing the spar caps on an Aerocoup with the same problem. No amount of "Corrosion X," anodization, or zinc chromate will stop it. It is a manufacturing defect.
I think it behooves us CJ-6 owners to do some detail inspections at this time. We need to find the extent of the problem and work up the fixes where needed. If this was an STC'd aircraft, the feds would be rushing out AD notes. We have to be getting at this on our own. We do not need wings coming off our aircraft.
My inspection starts before my next flight in N21710.
Jim "Pappy" Goolsby
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ChangDriver
Joined: 15 Sep 2007
Posts: 266
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| Posted: Tue Oct 07, 2008 7:10 am Post subject: Re: Corrosion Alert CJ-6 |
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Pappy:
The pictures are telling. The last one shows corrosion that would not be detected unless the skin is peeled back. I know many are lulled into the belief that corrosion cannot be a problem on these planes as they are built mostly of anodized aluminum. It may be time to start thinking about very detailed inspections and application of Corrosion-X in the wings.
Craig
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dougsappllc(at)gmail.com
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| Posted: Tue Oct 07, 2008 4:07 pm Post subject: Corrosion Alert CJ-6 |
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