In a message dated 6/4/01 You wrote:
<< Given: a built-up polyhedral wing, two piece, bolt-on to the fuse.
spruce/CF/shear-web spar at 1/3 chord with a 5/16" steel wing rod at the
spar. This is more or less the conventional wing construction.>>
Bill,
You can save weight and gain the necessary strength by using a 3/8 ID
carbon tube through the ribs the length of the inner panel. A 7075 aluminum
joiner rod can be used to tie the center sections together. The entire
system weighs 4 ounces not including any glue you might use. The
installation is simple. Stack the ribs and drill a .44 inch hole through all
ribs, slide the ribs on the tube, place on your building board and CA in
place. If you want it to look like built up, enclose the spar in balsa to
hide the CF look. As a reference, the Super V 100 used a 3/8 aluminum joiner.
As for stress and failure, most of the failures I have seen were in the
first few inches out from the root. The top skin or spar usually fails in
compression.
In a 100 inch span airplane, a 30 inch carbon fiber tube spar will
distribute the load evenly without breaking. It may flex a bit but will
never break.
However, if you are concerned you could use a 1/2 inch tube and rod which
would add another 2-3 ounces, but give you the strength of an unlimited TD
airplane.
This has been a shameless commercial announcement as the tubes and rods
are sitting in my shop waiting for your order.
Don Richmond
Hilaunch.com
San Diego, CA
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