Double Covering Super Cub Wings and Tail Airtech

I’m considering double covering my wings and tail feathers on my Experimental Super Cub PA18 using Airtech has anyone got suggestions comments ideas pro,s and con,s on this subject all input appreciated.

What problem would this solve?

Only time I ever saw this done was when Delmar Bengerman recreated the GeeBee R2 racer. Ribs were only 3 or 4 inches apart making putting tapes on difficult so they just doubled covered the wings and stitched them.
But, I don't think your going over 300mph?

Glenn

It is a popular covering method among the aerobatic. We also use it as the Bee Gee did where there are a lot of stringers spaced closely.

I have seen it don't on Staggerwings and a certain Pearl Pacer. See no reason on a Cub and thinning all that glue and seems like a lot of extra work and a way to create a huge fubar to me.

Mike Patey is doing it on his "Scrappy" build. Because of the IO-780 engine. I guess you would have a good reason to add the weight and extra work?

Down side is weight. On something like a Cub where speed isn’t an issue, the big question is Why?

I did double cover on the belly of my Howard. Only reason was one of the wheel cylinders had leaked (for years before I owned the airplane) and saturated the fabric on the belly, and all the dope peeled off. Cleaned it as good as possible and peeled dope off until I had about 6” of clean white fabric to glue to. Put a second layer of fabric over the hydraulic fluid contaminated fabric, and finished it as usual. Lasted as long as I owned the airplane.

I’ve heard of ag operators that do it on the lower surfaces of elevator and stabilizers to give a little better protection from rocks and gravel.


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Can one of you walk through the process of how you do a double layer on a new fabric job? How do you shrink, coat, etc so two layers are bonded? I've never heard of it before.

no need on a cub... just adds weight...

Its just a neat look if on an experimental . Almost all the model 12 pitts have it to get a certain look. It can be an issue if your r a beginner, would not recommend. As for weight it a small amount. With Airtech by using the thinned glue to attach, you are basisically using it like a polybrush method. ALL the reducer evaps away and 65 percent of glue solvent evap away. Only few oz per wing. But with the glue base you can go one less coat of primer fill because you filled with glue . So that starts to offset the weight of 1.8 oz per 9 sq ft of fabric overlay. I have actual test weight. 1sq foot of standard fabric with primer and one piece of 2 inch tape glued on( remember to be fair there is a lot of tapes on a plane that you rae doing awaywith on double cover) —verses 1sq foot of standard fabric with 1.8 oz overlay and one less coat of primer. 4.3grams difference . 4.3 x 700ish sq ft on supercub is around 6 lbs with the advantage of being tough like heavy fabric and having a neat look . Like i said , not for everybody.

Don’t do it. You don’t need the added weight.


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Stewart’s system has a video or two on doing it. It makes the claim that it saves quite a bit of time vs. taping, looks better and is tougher. I’m not to the point in my project of doing any fabric work so have zero experience with it.

If you want a stronger and/or smoother wing surface, why don’t you just metallize the wings?

...not that I recommend doing that.

Or maybe buy a Cessna?

Thanks for the great and honest reply’s gentlemen I really appreciate all your input. Ideas and suggestions.

While we are on the topic, why don’t we see more experimental builders metallize their Cub wings?

I wonder what the weight difference would be

Paul Heinrich said:

While we are on the topic, why don’t we see more experimental builders metallize their Cub wings?

Click to expand...

Why would you ever want to? One of the worst things that can be done to an originally fabric covered airplane, in my opinion; heavier, harder to repair, usually damages the underlying structure, and most I have seen look terrible. I want to weep every time I see a Stinson someone has scabbed metal onto...

It's much stronger! Time savings is pretty substantial. Weight penalty is 0 or just a tiny bit, and less than going to heavy weight fabric. I haven't done it with Robbie's system yet, but I have with Stewarts (I did the video and went down and demo'd it to Mike Patey) and it's awesome. On an experimental, I'd personally go with 2 layers of light fabric and it'd be way stronger than any medium fabric.
John

Here is a double cover on a Super Cub with AirTech...

https://www.youtube.com/watch?v=r63f8tniN-4&t=4s

I am curious about the extra time it takes to do the compound areas at the tips and if it is prone to getting bubbles under the second layer?

once we put the first layer on and shrink and stitch, the second is added the same way with the exception of not doubling up on back in cove areas etc. I just terminate it at railing edge like a tape or maybe slightly wrap. we double wrap the leading edge on the first layer so no need for any extra on LE, i just terminate 1 inch on to leading edge sheet. if you do like me, you glue the perimeter then shrink the second , the activate it through, but when on bottom flat side beware it can stretch across and bridge. i pre tack through on the ribs and on the insp rings, to avoid this and the bubbles you mentioned . i have never did it the way the guy did in the Stewarts video. I like the second layer shrunk also, but his way makes perfect sense as to work it out as you go from center out. i may have to try that. But like i said before its not for everyone and not actually recommended. I like REAL numbers when I speak on anything so I did my Javron super cub and timed every thing like compare a conventional way on an PA18 elevator up to point of primer , vs. the double cover up to primer. (with the exception I covered the tail the Maule way), the time savings on mine was enough that I am embarrassed to post, to the point I could be called a liar . but some of the savings was the Maule way. BTW, when I'm done i want to come play on the river!!