Cost to Metalize

[8349]

New to the group.

Is it still possible to metallize the wings on a 120 or 140? If any one has done so in the recent past, what is the cost?

I am hoping to buy something end of next year/start of 2020 hopefully. Would love a 120, 140, or older 150 (the square tailed ones). However, will not likely have a hangar (hard to get here in CT and quite expensive), so it will be tied down outside. Seems the metal wings would be the better way to go there, due to exposure to UV rays, snow, rain, etc.

Thanks for whatever help anyone can give.

[6643]

Most people ask how to "un-metalize". If you really want metal wings, I'd suggest you look for a 140a, a 150 taildragger or a 140 that's already metalized.

I don't know if there are currently any active STCs to metalize the wings. You could try contacting Met-Co-Aire. They hold one and are still in business.

[6896]

My C140 project came with metalized wings done under Skycraft DWG 50-1111, revised 11-24-54 and approved 12-10-54. Apparently at the time, this metallization approach was not an STC. During the process of rebuilding my project, I removed all of the old wing skins and repaired cracked ribs and other internal issues that I would have never seen otherwise. I even removed a rusty chisel left inside of one of the wings apparently since June 1957 when the metalization was done. I heard something clunky around, so I am glad I found the chisel. I wasn't pleased with the workmanship done by whomever did the metalization as there were rivet shop heads that looked rather amateurish.

Then to ensure I did everything right, in 2010, I purchased for $150 a copy of the Skycraft wing metalization STC SA1-259, drawings, and one-time use permission letter from John Nicols of
Woodstock Aircraft Services
PO Box 2
White Lake NY 12786
(845) 583-5830
www.woodstockair.com
info@woodstockair.com

My understanding in talking to John Nichols was that the widow of the Skycraft, Inc. estate transferred the various STCs to him, which he took over.

The drawings pretty much matched how my wings were originally metalized, but I was happy to have the detail and parts lists.

Now, there are several idiosyncrasies in the paperwork for this STC SA1-259, which no one has been able to explain to me, and I expect that no explanation will be found as anyone who worked at Skycraft has likely passed on. First, the copy of the STC SA1-259 posted at http://rgl.faa.gov is not current. The online version is unsigned and still under Skycraft Corporation with a reissue date of August 7, 2007. However, the current version that I received is dated September 5, 2007 and is signed with ownership transferred to Woodstock Aircraft Services, which is where I purchased the STC from. I don't think the FAA is obligated to post an STC if the owner does not want it to be posted, which may explain this peculiarity. Next, the title of STC is "Conversion of aileron covering from fabric to alclad panels. Reference Skycraft Design drawing #50-10000." However, the drawings that I received with the STC are numbered 5C-10000 and 5CA-10000. I surmised that there was a typo that caused "5C-" to become "50-" in the STC. Further, one drawing (the 5C- drawing) specifies 0.020-thick skins; the other (the 5CA- drawing) specifies 0.016-thick skins. Also, the 5CA-drawing specifies removal of the compression ribs, rib gussets, and drag wires/hardware. The 5C- drawing is silent on the drag wires, but the presumption is that they are left intact, which is peculiar in that the thinner skin drawing removes them. The 5CA- drawing specifies three spanwise skin angle stiffeners between rib bays, whereas the 5C- drawing requires only two stiffeners.

The quality of the drawings and parts lists on both the 5C- and 5CA- versions is typical of the time-era, but sufficient documentation to do a good job. It was helpful that I had a physical pattern to go by though, and I was able to match drill all of my new skins from the original ones. I bought my 2024T3 Alclad, 0.020 aluminum coiled from Airparts, Inc. I checked back on my orders, and I purchased first a 25-ft long coil in 2010; then a 50-ft long coil in 2012 for 75 feet total. Total cost at the time 2010 - 2012 was $1,043, including freight. I have a fair amount of aluminum left over, so you may not need 75 feet.

I cleaned all of the wing superstructure with dishwashing detergent, then Alumiprep 33, then I Alodined using the safer Henkel Bonderite RTU 5900, which is a Trivalent chromic acid solution vs. the Hexavalent chromic acid solution in Alodine 1201. The 5900 RTU is on the Government's QPL just like the Alodine 1201. After cleaning and repairing, I primed everything, including the wing superstructure and the new skins, with Polyfiber EP-420/430 epoxy. Cleaning, prepping for priming, and priming took a very long time because the parts are large and priming needs to be done rather quickly after Alodining to avoid oxidation buildup an primer adhesion issues.

Riveting took a long time too. Once we started, it was a couple of year project spanning two winters. I was able to bring the wing panels into our basement workshop and set them up on jigs to do one side at a time, starting with the top skin. I had also removed the leading edge, which is metal in the factory build to clean, repair, Alodine, and prime it as well.

The key to reassembling is to keep the wing straight without twist. Our simple jigs captured the spars at the root and tip. I used a 4-ft long level fitted with a digital inclinometer to ensure no twist throughout the process. having the skins match drilled in advance helped a lot, but you still have to be careful.

Parting note. My IA (also a PHD in aerostructures) and I were able to petition my local FSDO to accept as a minor deviation to the STC removing the drag wires when I used the 0.020-thick skins drawing, which as I mentioned did not specify removing the drag wires even though the 0.016-in skin drawings did. Common sense would suggest that this is OK, but the build must match the approved STC design to be legal. I processed the form 337 for this along with a engineering description as to why the deviation was minor. This took some time too. My IA consulted with the small airplane directorate in Wichita, KS to ensure we were on the right track, which they said we were. Having these points of contact helped. For quite some time I was concerned that I was not going to be successful, but in the end, it all came together. I am not the first person to have gone through this minor deviation petition. Another fellow in the C120/140 club on the west coast did the same a couple of years prior to me with his FSDO and ACO, and was approved to remove the drag wires, which serve no useful purpose once the sheet metal is applied to the wing. This removed if I recall about 8 lbs of weight, albeit the skins are heavier than the fabric. I cited the form 337 from the fellow on the west coast as precedent for my form 337 petition and minor deviation.

I like you wanted an all metal airplane for durability, albeit at the expense of slightly heavier weight. I am sure you will find differing opinions on this forum on this topic as many other topics, but for me, this was the right thing to do. It is a big job though, so you if you attempt this, be mindful of your time investment beyond the $1050 cost of the aluminum. I have hundreds of photos along the way showing the step by step process. Applying the skins is tricky in that you have to roll the skin spanwise and rivet a little at a time to not get boxed out where you can't use a bucking bar. We did well in this regard and had to use very few NAS1398AD4 or Cherrymax rivets. Most of the rivets are AN470AD3 type, but you may need a collection of oversized rivets too if your project is like mine with sloppy holes that were redrilled. I spent a fair amount of time sourcing oversized rivets in both the Cherrymax and solid varieties. You'll also need to grind some custom bucking bars to rivet the skins to the spars to work around the bulbed angles. My father and I became pretty good at riveting since there were so many rivets to form.

It's a great experience to do this, but be patient and careful if you attempt it and hopefully you have a good helper.

Tony

[6896]

Here are some photos of my wing re-metallization project on my C140.

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More photos.

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[6896]

Some more, but I have many, many more.

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