Lift Strut Fairings

[HighWing]

Thanks for the explanation. Your comments prompted me to dig out the sample I had made and check it once again. I suspect the two experiences might be akin to the old apples and oranges idea. In my application the use of the foam was primarily as an adhesive with some to added structural stiffness. The foam would have been encapsulated in fiberglass, microballoon filler, primer and top coat. My current set-up omits the fiberglass and replaces it with aluminum sheet with the primer and top coat. The whole object being an aerodynamic reshaping of the round lift strut.

I did a little research on the sprayed on roofing. UV is a big issue as the foam is very susceptible to UV damage and the top coating is critical to protect the foam. It is sprayed on and has to be able to adapt to the daily movement of the foam as it cycles from the heat of full sun to the cool of the night. Then the object is as a weather resistant roof with a thermal barrier added in. The typical lift strut is typically in the shade of the wing and those cyclic temperature swings shouldn't be as critical an issue.

The final thought, though is the advice that I got that it was the foam that was corrosive. My test piece fully dispels that idea as the area in question has been in full contact with untreated steel for almost 18 years with no hint of corrosion. One thing I did notice this time was that the foam does not stick as an adhesive to the unprimed steel, but does adhere quite strongly to the portion that was primed. I am able to scrape the foam residue from the steel with a fingernail. If the foam roof coating was sprayed onto bare metal without a primer, it could allow it to lift due to the cyclic daily temperature shifts and possibly allow capillary water flow between the steel roof and the foam - really bad.