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#21
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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. -- Change "netto" to "net" to email me directly Eric Greenwell Washington State USA |
#22
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trailers: fiberglass vs. metal
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 |
#23
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trailers: fiberglass vs. metal
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 |
#24
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trailers: fiberglass vs. metal
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 |
#25
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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) |
#26
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trailers: fiberglass vs. metal
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 |
#27
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trailers: fiberglass vs. metal
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 |
#28
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trailers: fiberglass vs. metal
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 |
#29
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trailers: fiberglass vs. metal
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 |
#30
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trailers: fiberglass vs. metal
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 |
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