"Evan Carew" wrote in message
t...
BobR wrote:


From wha I have read in the past, the major reason for lack of weight
reduction in composite structures results from differences in the
design standards. The design standard for metal wings is based on a
1.5 times specification. Thus, a wing rated for 3g's is designed for
4.5 g's. The standard used for composite wings has been set at 2
times specification. The composite wing rated for 3g's is designed
for 6g's and as a result any weight savings is lost to the extra
strength. The difference in the standards was ment to compensate for
perceived quality variations in composite contstruction techniques.


The main reason for the 2x standard has to do with the fiber alignment
(or rather misalignment) of the laminations in the spar. Since this is
the single heaviest, and most important component of the wing, its
construction is critical. Unfortunately, with traditional wet layup
techniques, perfect alignment of the fibers in the spar is not possible,
thus decreasing its strength. The obvious solution recommended in the
books is to increase the design over design to compensate.

Not too long ago, I saw that someone had solved this problem by using
small diameter, precured carbon-fiber rods as the core material for the
spar. This solves the disadvantages of the traditional techniques.

Jim Marske has been involved in sailplane construction for many years. I
believe he was one of the first to use carbon rods in the spar caps. Check
out his website for more information: http://marskeaircraft.com/

Aluminum wings can be "profiled" with performance results close to a
composite wing. (http://tinyurl.com/2r8b7d) The time involved is such a
project is normally 400+ hours.

Wayne
HP-14 N990 with profiled aluminum wings
http://www.soaridaho.com/Schreder/N990_Near_Arco.jpg