On Tuesday, May 21, 2019 at 2:18:43 PM UTC-7, Darryl Ramm wrote:
On Tuesday, May 21, 2019 at 11:16:45 AM UTC-7, Charlie M. (UH & 002 owner/pilot) wrote:
My thoughts are.......UV degradation of the fibers is the prime reason for the white coating (to reduce UV getting to fibers).
Ever see synthetic ropes out in UV? Most are white, but the UV destroyes them, thus strength goes to poop. Same for a lot of plastic woven tarps.
Not saying I am correct, just some observations.....

It's not the fibers, well not with fiberglass and carbon per-se, it's the epoxy resin that is the issue, including how failing epoxy causes the reinforcing fibers to break/degrade. Epoxy is highly prone to UV dammage, it sucks.

And yes the white is also needed to keep the temperature down.

Hard to say there is a "prime reason" when addressing both UV exposure of the epoxy and high reflectivity to keep temperature low are both necessary..

Yes, Darryl is right that the epoxy is what's prone to UV radiation, not the fibers. But at the end of the day the fibers don't do anything unless properly bonded.

Refer to another interesting paper on the effect of UV (and humidity) on composites: http://me.eng.sunysb.edu/~compmech/downloads/N29.pdf
29% decrease in transverse strength over 1000hrs of repeated UV and condensation. Luckily, only a small decrease in longitudinal strength was observed (most of the load bearing is longitudinal). Obviously the gel coat (or polyurethane) will reduce this effect, but dang!

Thomas