Mark Smith wrote:
guynoir wrote:

All dope and fabric systems use aluminum powder mixed with the finish to
block UV, which causes all fabric and dope to deteriorate. Dacron
"sails" as used on ultralights don't have UV protection, so they must be
changed every few years. The advantage of undoped dacron sails is
simplicity and weight savings.

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Dacron will last for twenty years or so if the plane is hangared when
not flying.

Outside, two years would be expected for sure.

There are also protectants that slow the effects of the sun on the
fibers.


Interesting because balloon envelopes are typically guaranteed for only
500 hrs. Sun and heat cause them to become porous and a yearly annual
inspection will eventually declare your envelope unfit. It's been a few
years but there was not way to renew an envelope although several things
were tried. BTW: that's one of the things that make ballooning soooooo
expensive. Figure $30K for 500 hrs -- that's $60/hr right there!