by Chappy » Sat Jun 26, 2004 11:42 pm
Ray,
Mylar's life is limited by exposure to ultraviolet light, and to a lesser degree exposure to certain chemicals. The worst chemical is ammonia. Unfortunately, some people have used Windex as a spot cleaner on Mylar covered wings, and the ammonia in it will attack the Mylar and shorten its life. I have seen Mylar that didn't make it through a single summer here in Virginia when left outside. I have also had Mylar covering that was well protected from light last well over ten years, perhaps fifteen. If Mylar is always protected except for flight hours, the tapes will probably be the limiting factor in the life of a cover job. I think that generally holds true for Tedlar. I know many people cover Lazairs with fabric and paints, but I don't like that for lots of reasons:
Fabric/paint is HEAVY. It WILL affect the performance of your Lazair.
Fabric/paint is more work to install. It's messy. It is much harder to repair. It makes inspection and minor repairs of the wing structure/ribs/controls much more difficult.
Fabric/paint is expensive.
Owner's are prone to leave their planes tied down outside because they aren't concerned about UV damage, where they are easily damaged by strong storm winds, acid rain, snow loads and vandals.
And, most of all, it just doesn't look like a real Lazair to me without the clear/translucent coverings of Mylar/Tedlar!
I think the reason no one likes Mylar is because there are very few Lazair builders still around to share their experiences with Mylar. It's the cheapest covering traditionally used on a Lazair, so having to recover isn't as bad as with the other materials. Once you have done a cover job of two, you'll be amazed at how fast you can do it. I've covered planes without any assistance (and with a lot less fingerprints on the inside of the wings too). The worst part by far of recovering a Lazair is getting all the old adhesive crap off the wings.
Mylar is much prettier than Tedlar (crystal clear Vs frosted). It's much cheaper. It's available commercially; Tedlar is only available in large amounts, it seems. I think it's easier to stress relieve (shrink) than Tedlar. Mylar/rubber adhesive tapes are cheaper and easier to find. The rubber adhesive is much more resistant to slipping/creaping, unlike the acrylic adhesive used on the 2 inch Tedlar tapes that were custom made for Ultraflight and varied all over the place in quality. The 2 inch Mylar tape was/is made by 3M, with real quality control. Tedlar holds paint much better than Mylar, I have been told. Paint also adds weight.
Mylar was supplied in the same dimensions as Tedlar. Both were 2 mil (.002 inch) thick, 100 foot long by 50 inch wide (IIRC) roll. The 2 inch tapes were also both 2 mil thick.
Obviously, if you can't find a way to keep the sun off your Lazair when not flying it, do not use Mylar.
The next cover job I do I will probably use Mylar again. If I do, I'll post my material costs.
Chappy
Lazair #25, covered in Mylar except for Tedlar covered elevudders