On Thu, 29 Apr 2004 16:35:41 -0400, Todd Pattist
wrote:

"John C" wrote:

The author asserts that:
" The ratio of empty to gross weight is one of the most telling measures of
structural efficiency.
He goes on to use this determination of strength/weight (or, structural
efficiency) to determine that composites do not offer a greater
strength/weight ration in airframe construction applications.

But then I read about the new 7E7, which is a largely composite aircraft,
thus lighter, thus more efficient.

How do I reconcile these conflicting pieces of information

They don't conflict. The author acknowledges that lighter
weight is possible with a composite if you use advanced
composite techniques. The 7E7 uses such techniques, but
they are expensive. Modern racing gliders and small
composite aircraft are not built using those techniques, and
they don't use composites to get weight reduction. They use
composites to get smooth curves, low drag and high speed for
about the same weight.

The author's "structural efficiency" formula ignores drag,
and that's the main concern for those using composites.
Todd Pattist

I agree with Todd; further, the ratio comparison likely is significant
only within similar types of aircraft. I suspect the advantages of
one construction technique over another change rather significantly
from ultralight to glider to SEL to MEL to heavy.

Have we any experts around to comment?