cal (BD5ER) wrote in message ...
A 1500-lb aircraft pulling six g's puts a 9,000 lb
load on the spar whether the wingspan is 25 feet or 50 ft. Unless
I've forgotten something fundamental, you'd have 2250 lbs of tension

Either I'm mis-reading or you have forgotten something fundanental. The length
of the wing does have a very real effect on the spar attachment points.

A quick example. Pick up an 8 lb sledge hammer by the head at arms length. snip
The same thing happens to spar attach fittings. My little 600 lb 16 ft span
canard has over 100,000 lbs on its little spar caps at the fuselage at 6 G's.
3 is about all it will ever see unless I bounce it real bad.



I haven't forgotten the bending moment. It's just that I don't think
it comes into play. For a given weight of airplane, the tensile force
on the bottom spar cap is the same for any length wing, because the
downward force creating the tension is acting through the airplane's
center of gravity. The moment arm from the cg to the hinge doesn't
change with span - only with the spanwise location of the hinge.

Yes, the balancing upward force acts through the wing's center of
lift, but remember - the lift force is actually a distributed load,
not a point load. If the span is longer, then the lift-per-unit-span
is smaller for a given weight. It cancels out. I'm willing to admit
that I'm in error - my aero structures and statics classes were a long
time ago. But I think I'm figuring things correctly.

I hadn't considered laid-up carbon fittings.

Forget hand laid carbon. The end result is generaly no better than E glass.
Graphite takes considerable process control to take advantage of it's full
potential.

Makes sense to me. Thanks for the advice. I'm strongly leaning
towards aluminum or steel - assuming I do this crazy thing at all,
mind you!