At 11:24 14 March 2009, The Real Doctor wrote:
Summary: in a steady climb or glide, the lift needed from a
glider's wing is as equal to the weight as makes no
difference ...

Hmmm. In a glider with C of G in the correct place the tail plane will be
producing a down thrust, hence the wing will need to generate lift greater
than the weight of the glider when in more or less level flight. The more
back stick, the more down thrust and the harder the wing will need to work
to maintain level flight.

Now my Discus turbo stalls in free flight in the low 40s (kts). With the
engine out and the thrust line well above the fuselage, thus pushing the
nose down, the best climb speed in the POH is given as 49 to 54 kts
depending on weight. If I let if fall to about 45 kts it is still
perfectly controllable - just less efficient. However aerotowing on the
nose hook at that speed would not be a happy experience. I have never
done a slow tow on a belly hook so don't know if the symptoms are the
same.

What I have observed on slow tows, and has been reported by others in this
thread, is that the ailerons are ineffective, the glider tends to wallow,
the stick is a long way back and the nose high - even though the speed is
above the normal 1G stalling speed. These seem to be symptoms of an
accelerated stall or incipient spin - but the rope pulling ahead seems to
stop the glider rotating into a spin with the associated wing drop.

I wish I knew the answer, but if I have the symtoms of an accelerated
stall in more or less straight level flight above the 1g stall speed that
sugests that the wing is generating more lift than the weight of the
glider for some reason; if the stick is near the back-stop at 50 kts there
is more elevator downforce so the wing will have to compenstate for that.
The pull from the rope may be slightly down if I'm in high tow,
especially with a long heavy rope with a slight bow in it, but to raise
the stall speed from say 42 to 50 kts (* 1.2) is equivalent to an increase
in load on the wing from 1g to about 1.4g. At a take-off weight of say 475
kg this is equivalent to an additional 190kg or another 418 lb. Where
could this come from??? The downthrust from the elevator fighting the tow
rope?