Rick Durden wrote:

snip

Because of the FAA's extremely conservative certification procedures
for composites, the structures are far, far stronger than metal
airplanes, which is why they also weigh as much. The FAA
certification procedures took away the weight advantage of composites,
but what it did was give us airplanes that are evern more overbuilt
than the Grumman Ironworks figthers of WWII.

Generalising quite a bit there a few other issues apart from the
conservative safety factor in strength requirements which tend to increase
weight in composites.

The stiffness issue which often requires extra material (most composites
have 1% strain at yield)

Low work of fracture compared to metals.

Difficulty in inspection for defects especially after minor impact damage
considering that damage can be at some distance from the impact point.


regards

jc