Neal Pfeiffer wrote in message om...


Moving of weights within a fuselage (or other part of the aircraft) is
not a viable solution. Response needs to be quick and reliable, even
for unusual attitudes.
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Moveable weights for pitch control aren't as responsive in the
negative pitch airfoils used in conventional gliders because
increasing speed increases the downward pitching moment which the wing
produces. Moving the weight forward to drop the nose and increase
speed leads to the requirement for back stick to increase downward
pressure on the horizontal stab and keep the nose from continuing to
drop. If you tried to do this only with weight shift, you would need
to move the weights forward to increase speed and then progressively
move the weight backward as the speed builds up just to maintain
stability. Computerized fuel shifting on airlines does this but they
still use all-flying-tails for the fine corrections.

Weight shifting for pitch control is very workable in flying-wing type
gliders as they are very responsive to changes in cg; and the inherent
stability of the reflex wing keeps the glider very close to the weight
shifted pitch.(and speed) Several Genesis owners use rudimentary forms
of weight shift on a regular basis. One has mentioned putting ankle
weights on the rudder pedals and moving them back and forth, someone
else has stated in the GenesisFlyers Yahoo Groups site that inflating
the lumbar support adds 4 knots to the trimmed speed. There have been
discussions about using nose and tail water tanks and shifting from
one to the other to trim for best thermalling or high speed. This is
a very workable improvement for Genesis 2 and Marske Pioneer type
gliders. Weight shifting on the Pioneer may work even better as it
may be possible to fly with a very aft cg which keeps the nose high
and then use forward stick to deflect the elevators down increasing
the lift coeffecient of the wing. Moving the weight forward would then
allow it to fly fast with the elevators slightly raised the way
flapped gliders fly with negative flaps.(reflex)

Based on the vast majority of the gliders in existance, however, using a
correctly-sized tail is not a bad way to go. Remember, if you don't
truly enjoy what you're flying, you probably won't fly it long. Tailed
aircraft are probably easier to make fly good.
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It's hard to argue against correctly-sized tails, although I suspect
that what you call "correctly-sized" is what I spitefully and
maliciously call a boomsnapper. Boomsnappers interfere with low
energy landings as your pitch at flair is limited by your willingness
to slam down tail first and damage the boom. Some boomsnappers (G
102) are speed limited because, oops!, the elevator isn't as strong as
we thought and it is prone to flutter. The G103 Acro is acro no more
because that big heavy extremely strong tail boom isn't as strong as
it should be. Need to slap on a few more layers of carbon so's it
don't come off.
So, how strong and durable are those tiny, light weight tail booms on
newer high performance gliders? Are they at least as strong as the
wing spars on Shemp-Hirth gliders? How strong will they be when they
are as old as Grobs?
Got to keep that tape on tight, too, cause lifting of the front edge
of tape near the elevator causes an almost total loss of elevator
authority.
Genesis 2 and Pioneer owners all seem to really like the handling
characteristics of their flying-wing gliders and as a group they don't
seem to miss or wish they had longer tail booms.

Long tailed aircraft are certainly easier to make and they satisfy an
esthetic which sees ships, trains and trucks as boxes or tubes which
carry cargo, so an aircraft should be a box or tube with wings. The
more it looks like a truck the safer it "feels".