Marc Ramsey wrote:

Lew Hartswick wrote:

Shawn wrote:

Some claim UV light can penetrate a fiberglass top and that the
accumulated irradiation of the glider will cause damage to the ship.
Shawn


Have any of "some" ever done a transmission spectra of the material?
Fat chance. Even window glass cuts of about 400 nm.
...lew...


I suspect some UV gets through fiberglass cloth, it is a woven material,
after all. Not all fiberglass trailer tops are created equally. Some
are a few layers of glass supported by a steel tube frame, some are free
standing glass/foam/glass sandwiches. Some have gelcoat on the outside,
some are painted with polyurethane or acrylic. Some have dark opaque
paint on the inside, some are just left bare.

I had a trailer with a sandwich top, polyurethane on the outside, pretty
grey spackle paint on the inside. I could read a book by the light that
came through the top when I was closed up inside (the glider was also
painted with polyurethane, however, no gelcoat to damage).

This is also true of your canopy, but it still stops almost all the UV.
The amount of visible light that penetrates is not a good indication of
the UV shielding. I believe the resins used in composite construction do
a good job of filtering, but I don't have any data for them.

I had
another trailer with a sandwich top, gelcoat outside, thick dark gray
paint inside, it was totally dark inside. I had yet another trailer
with glass on steel frame, the gelcoat deteriorated, so I had it sanded
and repainted in white automotive acrylic. Within a year or two it was
obvious which parts of the glider were facing upwards in the trailer, as
those parts were distinctly yellower. I've seen a glider which had
badly crazed gelcoat just in those areas that face upward in its
fiberglass top trailer.

This discoloration and crazing might also be caused the heat and
dampness in the trailer. The upper foot or so inside a trailer can be
very hot in the summer sun, much hotter than the outside air temperature.

An aluminum top protects the glider from UV, even without paint. If I
were to roll the trailer with the glider inside, I'd rather have an
aluminum top. If I lived in a damp warm area, I'd rather have a
fiberglass sandwich top with dark paint on the inside, as there would
likely be a lot less condensation inside the trailer...

Also my sentiments, though I would also consider an aluminum top that I
insulated.

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Eric Greenwell
Washington State
USA