trailers: fiberglass vs. metal

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)

Y,

I own two Cobra trailers -- one fiberglass topped, the other aluminum.
The fiberglass trailer is only 5 years old but is already dull and
oxydized (it spent two years in Colorado and two in Arizona). It needs
a day or two of work with a polisher and buffing compound. The aluminum
trailer is 2 years younger but still looks brand new after three years
in Arizona. Given a choice between the two, if I was ordering new, it
would be the aluminum.

-ted/2NO

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...

Yuliy Gerchikov wrote:
What is the conventional wisdom on fiberglass top trailers? I've never had
any experience with one. Should I keep it this way and stay away from it by
all means? Or is it OK, really, and not much worse than Al top? How long do
they last and how much maintenance require? What are the pros and cons of
each? I'd think that metal is more durable and virtually maintenance free,
while glass may be a bit lighter. Anything else? Thanks! -- Y



No UV is going to be able to penetrate the fiberglass top. This is a
myth. One plus for the fiberglass is that there are no seams and I do
know of one aluminum topped trailer which developed a leak when it
rained. Probably a bad data point, but if you have a seam, it is a
place that can leak later in life...

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)

Yuliy Gerchikov 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. I
used to fly at Boulder, CO where all of the trailers are parked oriented
nearly east-west exposing a long southern face to the Colorado sunshine.
Trailers occupy the same spot for years on end, and, not that I've taken a
poll, but I've never heard of any ships with damage to the top of one wing
and the bottom of the other, or one side of the fuse or fin due to a
fiberglass top.


Could it be because sun in Colorado in summer shines straight DOWN?

Nah, just feels that way when you haven't used enough sunscreen.
Boulder straddles the 40th parallel, the highest the sun gets at the
summer solstice, is 73.5 deg above the southern horizon, and that's the
cloudy season. All those fair weather cu's :-)

Seriously though, can fiberglass top be painted with aluminum silver (inside
or outside) for added UV protection?

Don't see why not, but what for?

Shawn

Having had two makes of lift top trailer - one with
a seamed aluminium top and one GRP - if I were going
to get another then it would have a one-piece metal
top with optional factory insulation - like Cobra offer.




At 18:54 08 January 2006, Gary Emerson wrote:
Yuliy Gerchikov wrote:
What is the conventional wisdom on fiberglass top
trailers? I've never had
any experience with one. Should I keep it this way
and stay away from it by
all means? Or is it OK, really, and not much worse
than Al top? How long do
they last and how much maintenance require? What are
the pros and cons of
each? I'd think that metal is more durable and virtually
maintenance free,
while glass may be a bit lighter. Anything else? Thanks!
-- Y



No UV is going to be able to penetrate the fiberglass
top. This is a
myth. One plus for the fiberglass is that there are
no seams and I do
know of one aluminum topped trailer which developed
a leak when it
rained. Probably a bad data point, but if you have
a seam, it is a
place that can leak later in life...

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.

Not that I've heard. UV measurement inside trailers has been discussed
here before too.
Why bother if after nearly forty years of glass ships in glass trailers
hasn't shown obvious damage. Lots of crazed finishes in old gliders in
metal trailers too.

Shawn

Marc Ramsey wrote:
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

Now you've done it. Ruined a perfectly good discussion with data. ;-)

Good to know, thanks.

Shawn

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). 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.

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...

Marc