trailers: fiberglass vs. metal

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

Eric Greenwell wrote:
Marc Ramsey wrote:

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.

True, but it a trailer which admits no visible light is also likely
blocking UV, a trailer that admits visible light may (or may not) be
also passing UV.

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.

Except one could also make out the shadows of the wing saddles, etc.,
which is why we concluded it was UV damage.


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.

I wasn't offered that option with the last trailer I bought, but it
sounds like a good one...

Marc

Marc Ramsey wrote:

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.


Except one could also make out the shadows of the wing saddles, etc.,
which is why we concluded it was UV damage.

What glider was this? Discoloration from two years exposure indicates a
really poor quality gel coat. The exposure during flying must have
caused considerable yellowing, too.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

Eric Greenwell wrote:
Marc Ramsey wrote:
Except one could also make out the shadows of the wing saddles, etc.,
which is why we concluded it was UV damage.


What glider was this? Discoloration from two years exposure indicates a
really poor quality gel coat. The exposure during flying must have
caused considerable yellowing, too.

A DG-101 (now owned by a friend). Actually, the gel coat has stood up
remarkably well, with no obvious crazing 20 years after it was built,
but the different shades of yellowing were visible under shop lights...

Marc

Comparing modern Cobra trailers the glass top is less expensive and
(subjective) looks better than the metal top. I would also expect the
glass top to be easier to repair in the event of minor damage. I have
no concern about UV penetration of the glass top. It is double
skinned.

The downside of the glass top is that the the finish does not seem to
last no matter how often it is polished and waxed. The dealer that
sold me my ship suggested it would be cheaper to repaint the top in 5
years that to have paid for the metal top. We'll see.

If buying a used trailer you should look for a problem common to both
types of top. The base of the top is a special aluminium (there I
said it) extrusion that carries the retainers for the wing spar
fittings. If the top is closed with the wing fittings not fully
forward the retainer hits the fittings and the side rail extrusions can
be badly damaged. I have seen several trailers with this problem,
including one that was delivered that way from the (sailplane) factory.

Andy (GY)

UV transmission, through the laminate of a fiberglass trailer top, is
not an issue in regard to degrading the finish of a glider stored
inside. The titanium dioxide pigment in the exterior white gel coat of
the trailer top absorbs most of the energetic UV bandwith. The
remaining longer wavelength radiation is dispersed within the laminate
matrix.

The affects of the UV bandwith a

UV-A
- Wavelength - 400 - 315 nm
- Has a slight affect on polymers.
- Transmits through window glass
- Does not transmit through white gel coat (TiO2)

UV-B
- Wavelength - 315 - 280 nm
- Highly energetic - degrades polymers
- Filtered out by window glass

UV-C
- Wavelength - 280 nm
- The most energetic band
- Filtered out by atmosphere

So don't lose any sleep over this speculative issue. However, keeping
the trailer cool and well ventilated is worth the effort.

Bob




Marc Ramsey wrote:
Eric Greenwell wrote:
Marc Ramsey wrote:
Except one could also make out the shadows of the wing saddles, etc.,
which is why we concluded it was UV damage.


What glider was this? Discoloration from two years exposure indicates a
really poor quality gel coat. The exposure during flying must have
caused considerable yellowing, too.

A DG-101 (now owned by a friend). Actually, the gel coat has stood up
remarkably well, with no obvious crazing 20 years after it was built,
but the different shades of yellowing were visible under shop lights...

Marc

Seems like the answer might depend on the particulars
of the trailer. My 3-year-old Cobra has a glass top
that is black on the inside and zero visible light
gets through.

I bought it because I though it was more attractive.
I also was paranoid about leaks opening up on the
seams as it accumulated open/close cycles and road
miles - not that I have any evidence of that actually
happening.

9B

Andy Blackburn wrote:
Seems like the answer might depend on the particulars
of the trailer. My 3-year-old Cobra has a glass top
that is black on the inside and zero visible light
gets through.

I bought it because I though it was more attractive.
I also was paranoid about leaks opening up on the
seams as it accumulated open/close cycles and road
miles - not that I have any evidence of that actually
happening.

After a 100,000 miles on my Cobra trailer, including a trip to Alaska,
and thousands of open/close cycles, the seams are still in perfect
condition. The newer trailers have about one-half the amount of seam
that my 10 year old trailer does, because they redesigned the front end
in a lovely way a few years ago, and now (in my opinion) it looks just
as nice as the fiberglass top.

--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

What is the conventional wisdom on fiberglass top trailers?

Thanks for all the responses. Some of the thoughts mentioned here did not
occur to me before. -- Y

My all glass trailer (LAK T-5) is in it's 5th year of Arizona and
California sunshine with the only obvious degradation being the
fenders, which are faded and show a significant amount of deep surface
chaulking and the vinyl stick-ons which are starting to peel. The
inside is painted and the top doesn't seem to transmit visible light.
I gave it the WX treatment a few years ago, but haven't repeated it.
The tires showed sidewall checking after 3 years sufficient that they
had to be replaced.

Looking at the row of trailers where I fly, I'd have to say that the
older aluminum ones seem to age better than the glass, though. My
semitrailer was reskinned with aluminum with a baked-on finish which
has lasted 12 years with no apparent flaws other than dents and
scratches.

Ray Warshaw