On Sunday, April 21, 2019 at 8:04:21 AM UTC-7, Bob Kuykendall wrote:
On Saturday, April 20, 2019 at 11:07:40 PM UTC-7, 2G wrote:

There is a reason why fiberglass gliders are painted white: they can't withstand high temperatures...

It's a bit more complicated than that. We could have blue or black or red composite gliders if we really wanted. Unsurprisingly it comes down to economics.

There are epoxy resin systems that can be used to achieve a Tg well above those achieved by darkly colored surfaces exposed to direct sunlight. We're using one such system right now on some aircraft parts that for a variety of reasons must be painted black.

However, compared to the MGS285 system that has become the de facto standard for European sailplane manufacture, those high-temperature systems are generally some or all of:

* More expensive
* Harder to mix and use
* More toxic
* More sensitizing

Furthermore, for some such systems, the parts must be subjected to elevated post-cure just to make them tough enough to demold. And then they must get an even hotter post-cure after all the parts are assembled.

All of these reasons that high-temperature systems are a pain to use make them more expensive to use, and for no easily justified reason.

There is a critical temperature called the "glass transition temperature" which is where the plastic starts transitioning from a solid into a liquid. A typical glass transition temp for fiberglass is 100C, well below the temps seen in that hanger fire. The fact that they canopy melted demonstrates that the temp was that high for some period of time.
https://en.wikipedia.org/wiki/Glass_transition

Our tests have shown that exceeding Tg does not necessarily weaken a composite structure; depending on a variety of factors it will quite likely regain all its former strength and stiffness once it cools down. Furthermore, the melting of the canopy is not necessarily an accurate indicator of the temperatures reached by the rest of the structure; clear acrylic plastic absorbs a lot of wavelengths that reflect off of a white painted surface.

--Bob K.

Yes, it is always more complicated than what most people are interested in reading. But in the case of this glider, the manufacturer clearly considered it to be unairworthy, period. Further, without having the glider fully instrumented with thermocouples, no one can say how hot, and for how long, each part of the glider got. Absent such data, the only safe course of action is to declare it unairworthy unless the manufacturer details an inspection and test regimen that can assure the glider's safety and continued airworthiness.

Additionally, changing the serial number is a blatant effort to disguise the damage history of the glider and constitutes fraud, in my opinion.

Tom