Originally Posted by
cub builder
It used to be acceptable to use any polyurethane paint over polyfibre, but the STC was rewritten to require the use of their paints. It gives them better control of the finishes and limits the blame if you use something other than what was recommended.
I painted my SuperCub Clone with an automotive polyurethane paint over butyrate dope. It worked well enough, and at 7 years old, so far still looks great. Admittedly, it rarely spends a night outside, but it does see plenty of flight time. I needed to touch up some fabric damage on a gear leg and found the original paint had precipitated out a bit in the can and no longer matched, so had some acrylic urethane mixed to match. I also needed to modify an elevator, so when I recovered the elevator, I finished it with Acrylic Urethane over top of butyrate dope. The Acrylic Urethane is easier to shoot and much easier to spray a nice finish as compared to polyurethane, and so far, I am not seeing any issues with the Acrylic Urethane either. I'm thinking if I ever build another Experimental, or live long enough to need to recover the Cub Clone, I'll likely cover with Stewart's and finish it with an Acrylic Urethane. Before someone jumps on the "you can't do that" bandwagon, note that it would be an E-AB aircraft, and would definitely be an experiment; albeit based on my experiments so far, an experiment I predict to be successful.