In article 17byb.356395$HS4.2988006@attbi_s01,
"Paul Hastings" wrote:

One has to also consider the quality of workmanship, composite designs are
generally overdesigned because the designer is trying to cover differances
in workmanship from builder to builder. With aluminum, the same thickness
aluminum will yield the same strength part, but with composites differences
in technique and preparation can yield widely different results with the
same materials and number of layups. Designers compensate for this in the
beginning, IMHO this is the main reason why a composite will weigh more than
an equivilant aluminum structure. This is just a generalization that applies
mainly to amatuer built wet layups, in more controlled conditions(prepreg
carbon, vacuum bagged parts) the composite part can be lighter and stronger
than a similar aluminum part. However most homebuilders do not have access
to low cost supplies, tooling, and an oven large enough to do a complete
fuse, wing, etc... YMMV



It will depend too on the configuration of the aircraft. Fer instance,
modern open class sailplanes that have wingspans in the 24 to 30 meter
(or more) range just could not be built out of aluminum. These things
have fantastically narrow wing chords with wing thicknesses less than
15% of chord. I'm not sure an aluminum wing like that could be made at
all at any weight. You should see the flexing of those big glider's
wings!