Composite Aircraft in the long term...

In article ,
Jim wrote:
I'm not a boater, but what happens to 15 year old fiberglass boats?

I've got a 25 year old J-24 (sailboat). It was built using good
quality (but conventional) production techniques for the day:
polyester resin with woven glass cloth, balsa core, and gelcoat. The
basic structure appears to be in as good shape as it was the day it
left the factory. From a cosmetic point of view, it's a mess, but the
hull is sound.

I'm not really sure what you can learn from that, however. The kinds
of construction being used for aircraft today are a world apart from
what was used when my boat was built. Epoxy resin instead of
polyester. Cloth today is kevlar or carbon fiber instead of glass. I
assume aircraft are vacuum bagged and/or kiln baked.

All of these are better techniques, but on the other side, the layups
are a lot thinner. Anything built with the layup schedule of my boat
would be so heavy you'd never get it off the ground.

The only structural fiberglass part on my boat which approaches the
aspect ratio of an airplane wing is the rudder (300mm chord, 20mm max
camber, approx 1100mm unsupported span). Out of the factory, many of
the old rudders were thicker than the class rules allow (thick = more
drag) and in the old days, people tried to fair a few mm off the glass
to make the boats faster. The unfortunate side effect of this was a
lot of broken rudders!

The other high-aspect ratio piece of the hull is the keel. It's made
of lead and weighs 900 lbs. There's probably very little you can
learn about airplane construction from that :-)

Composite gliders have been around for over 40 years with an excellent
record for structural integrity. My Glasflugel H301 Libelle glider,
N301BW, will be 40 years old in 2004. Made of plain 'ol E glass and
epoxy. Closing in on 3000 hours of flying time, still looks and performs
great. Very few AD's, all on the metal parts.

I have owned and flown old wood, old metal, and old glass. I have had
more problems with the metal than the wood and glass put together.
Corrosion and fatigue. Probably because people are more likely to take
care of wood and plastic and to neglect metal. Fabric covered aluminum
wings are probably the worst for this. Often left sitting out for years
with moisture collecting in wing, not to mention rodent urine, etc. Seen
aircoupe spars that were little more than aluminum oxide powder.

One thing about old glass: Old fiberglass aircraft were significantly
overbuilt to get some rigidity out of the very flexible fiberglass.
Hence, my glider has a 9.5 g wing just to make the wing stiff enough to
keep both tips from drooping to the ground when it's not flying. Carbon
is stiff enough that you can build a stiff structure that is still
pretty weak.

Composite materials tech and fabricating methods are advancing at a high
rate. Eventually, new metal airplanes are going to get rare (says the
guy who just bought a bunch of steel tubes, rags, and sticks with a late
40's Continental to drag it through the air).