Letters

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Fiberglass/Epoxy Layups

In “Maintenance Matters” [July, 2015] on page 52, a photo shows a fiberglass/epoxy layup being done over wax paper. This is not good technique, as the wax can get into the layup and weaken it. It’s much better to use freezer paper or plastic to lay the cloth on for wetting out. Mixing cups should also be wax-free.

Also, you don’t wet-out the glass or pre-wet the repair area with resin—you do both with mixed epoxy, which is made from resin and hardener. Nit-picking, I suppose, but if a person follows the instructions in the captions, he is likely to have a mess.

–Phil Kriley

Dave Prizio responds: I always appreciate reader comments, even those who have taken exception to something I have written, because it lets me know that my columns are being read and provides feedback that I am being understood.

Phil says that wax paper is not the best surface on which to prepare a wet fiberglass layup. In response, all I can say is that I have used this method many times with good results, and I have seen other people who know much more about fiberglass than I do use it too. I first saw it done in a SportAir workshop, so I do not hesitate to recommend it to others. There may be something to Phil’s concern, but it has not been borne out by my experience.

Airshow coverage sponsor:

His second comment about pre-wetting with resin and hardener (catalyzed resin) rather than using resin without hardener is certainly correct, but my assumption was that everyone already understood this. If that is not the case, then maybe that point needs to be made. In the processes described in the article, the first thing to do with the resin is to add the catalyst or hardener. All resin applications are done after that step.

Black Beauty

Thanks for this excellent article [“Black Beauty,” April, 2015], but it left me with many many questions. On page 40, center left, the caption says they are using epoxy/flox as structural adhesive. My knowledge is very limited, but I’ve never heard of using flox as an adhesive. Another question I have is about the layup of uni on the spar cap. I would like to know more about how this schedule is designed. Maybe a reference or two?

–Roger Laubhan

Eric Stewart responds: I’m glad you enjoyed the article. Regarding the use of flox, we typically add flox for gap filling/thixotropicity reasons. I did not engineer the spar cap schedule, but it is a basic tapering schedule as would be discussed in any intro structures or composites textbook. I highly recommend Composite Basics by Andrew Marshall, which goes over this topic in detail. Build on!

Beachball

I have no clue if this is right, but since you asked [Letters, July, 2015]—I was told that frequency 123.45 was used by banner towing planes up and down the beaches to alert other airborne traffic in the area. Since most banners were colorful, and you’re near the beach, it became known as “Beachball.”

–Eric E (Rick) Abell

Thanks, Eric. That explanation certainly makes as much sense as anything else we’ve heard. —Ed.


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