brainfart

Use the search engine with the search words "cabin heat" and similar. There are several threads covering this, including diagrams, descriptions and links to individuals web sites.

I've seen many gliders and also regular motorized planes with gelcoats that weren't terribly cracked, since plane surfaces usually don't have many sharp bends and corners and attached clamps.

When I took fuselage repair classes we worked on damaged wings of crashed certificated planes (dunno which type) which had gelcoats. We intentionally made holes into the wings, damaged the trailing edge etc. and then repaired that damage, including the application of gelcoat and sanding and buffing as the last step. I might even have some pictures somewhere to prove it.

Here for example is the maintainance handbook for a motorized glider, unfortunately it is in German:

http://www.stemme.de/man/s10v/whb/a4010120_13a.pdf

You don't need to understand German though, just do a search for gelcoat in that document and you'll find the phrase "UP Gelcoat" mentioned several times. UP gelcoat of course means unsaturated polyester gelcoat.

Here is a thread about repairing or painting older gelcoated gliders:

http://www.gliderforum.com/thread-view.asp?posts=18&threadid=319

I'm not insisting on gelcoat being a better or the perfect surface for an airplane, but it is indeed being used on many planes.

A gelcoat sprayed into a mold isn't any heavier than all that epoxy coating/micro stuff, I'm tempted to say the opposite is true. Most gliders from the past and many today use gelcoat, and cracking and durability aren't any concerns. Neither is excessive weight. Using gelcoat is also a big timesaver when laminating in a mould, compared to all the endless sanding, microing etc. required when working without a mould.

> Is a gelcoat UV proof?

Yes of course.

> Can gelcoat be had in an epoxy formulation (I don't know)?

Yes, epoxy gelcoats are available.

> Gel coat will never give you as good looking a finish as paint.

Sorry, but that's just not true.

> Just to say that, with how well the present epoxy finishing works, there is no

> need to, and reason to, use the weight of a gelcoat finish.

Tell that to the glider crowd. Most of them use white gel coat.

I don't know about US autofuel, but here in Europe there are plans to add increasing amounts of alcohols to the gasoline in the next few years. Alcohols will affect many epoxies.

> Why would the tg. of the different epoxies freak you out.

Because the mechanical properties of epoxies and other polymers change drastically above Tg. The polymer turns from a hard solid into a rubbery, soft consistency.

West for example has a Tg of 120-140F. Even a completely white plane will heat up above that temperature in summer.

> These planes are well designed they are not falling out of the air because of

> week epoxy.

That no canard plane has crashed yet as far as we know doesn't mean that someone, someday might crash due to material fatigue caused by above-Tg flying, or that there haven't been any incidents with normal planes.

I don't know anything about the materials used for velocity construction, but every time I see someone using epoxies like West System for aircraft construction this creeps me out. Look it up, the Tg and heat distortion temperatures for West System are below 50°C (you do the conversion ). In other words, that epoxy gets pretty soft even when the aircraft is painted white. It's not just West System, some of the other "approved" epoxies aren't much better. Then again without proper heat treatment (which doesn't seem to be high on most builders' to-do list either) even MGS L285 will not reach its final Tg of 90-105°C.

Thanks, I have an (equally old) interglas sample folder containing all these different glass types, that table is a welcome addition.

As the datasheets show, they are not equivalent. There are differences in fabric weight and yarn size. That would have been too easy. Oh well.

http://www.hexcel.com/NR/rdonlyres/EAA824B6-3AE3-4D5C-8EF2-BC548E2F8358/0/7725.pdf

http://www.hexcel.com/NR/rdonlyres/C459571A-2AAE-493B-A608-C6F531D68D8D/0/7715.pdf

> FFE280T1000 (Interglas 92125BID or RA5277)

> FFE220P1000 (Interglas 92145UND or RA5177)

Is this confirmed?

If it is, then this is great news. Every foreign builder needs to be made aware of this information.

Over here in Europe those Interglas numbers are used extensively to describe glass cloth. This also means that Europeans can get the glass for cheap locally without having to order it from the US, 92125 and 92145 are easily available from every fiberglass supplier.

92125: 280g/m², twill weave, finish FKK/FRP144, dry thickness 0.35mm, thread count 7x6.5, yarn type warp/weft EC9-68x3tO x EC9-204Z (filament dia. 9µm), available colours: black, options: available with non-fraying treatment

92145: 220g/m², plain/UD weave, finish FKK/FRP144, dry thickness 0.25mm, thread count 6x7, yarn type warp/weft EC9-68x5tO x EC7-22Z (filament dia. 9µm, 7µm)

What kind of finish does the Hexcel glass use? The available Interglas FKK/FRP144 is rated for aviation use, so I assume this is truely equivalent?