>Brian Whatcott Altus OK
>
>At 21:39 6/3/98 -0400, you wrote:
>>....It's time for the dumb question. Why are there more layers
>>on the top rather than the bottom of the canard and wing. It seems most
>>airplanes are built with the lower spar cap being the beefyest. Can
>>someone explain?
Composites are stronger in tension than compression. The top of the wing
is under compression and if it buckles, the fibers misalign and the
structure is no longer able to resist the force. The lower side is under
tension which tends to keep the fibers aligned for maximum strength.
However, the difference in strength, ~35/~45 kpsi (compression/tensile
strength), is not the only reason for the asymetry.
The Dragonfly is designed to fly with more positive Gs than negitive.
Also, the wings are designed to absorb landing loads, another high
positive G event. These higher loads require more layers although the
ratio should be fairly constant. On the other hand, if the Dragonfly were
designed to fly inverted at the same Gs and land upside down, the wing
spar layups would be symetrical and so too could the airfoil.
<humor>
This design approach would provide a fail-safe procedure for fuel-pump
failures and aleviate concerns about canopy escape systems. Combined with
operational features, like landing gears on both sides of the canard,
top-of-rudder mounted landing wheel/skid, fully inverted oil and fuel
vents, would reduce the useful load but then again, a passenger might not
appreciate these fail-safe features. However, fully inverted landings
would squelch any unfair criticisms.
</humor>
Bob Wilson
-----------------------------------------------------------------------------
dragonlist is hosted courtesy of Interstice Inc., a provider of reasonably
priced virtual domain hosting for the world, and dedicated circuit and
dialup for Silicon Valley. http://www.interstice.com (408) 369-4490
