A little consideration before I go try this in the air. First, it is
possible to stall a glider while coordinated. No epiphany there. If you
stall in a bank, you are likely to have the low wing drop, for the
reasons Chris gave. This, however, should not result in a spin.
UNLESS... given the variables Chris has introduced, we have a glider
that is potentially flying well below its 1G stall speed. This means
that the force available to the vertical stabilizer to dampen a yawing
motion is significantly diminished. So then is the power of the rudder.
Adverse yaw of the ailerons is increased at the stall. Harmonization
(ie, required pilot control inputs to maintain coordinated flight)
changes as the horizontal stab is now operating at less than design
speeds. Interesting. There would seem to be a crossover in this regime,
where even if the contols are harmonized (given the relative torques
available to VS and ailerons), there simply may not be enough
weathervaning potential in the VS to prevent autorotation if a stall
develops at the wingtip.

Is it safe to say that winch launching is an aerobatic maneuver, and
therefore requires very specific training techniques since the glider
is likely to be flown outside its design limits? Also, it seems the key
to avoiding this situation is to avoid the stall, which means no sudden
snatching back of the stick (even to neutral) once a "normal" attitude
is achieved. Since this situation is likely to occur near the ground,
where the horizon is not a particularly useful airspeed indicator, do
you teach close monitoring of airspeed throughout the recovery? And a
complicating factor... if there is already a bank during the recovery,
how do you address it? You've noted that AOA differential is enough to
snap the glider into a spin. Attempting to level the wings would seem
to only aggrevate any impending tip stall.

I'm not unfamiliar with this regime. Though I typically don't turn at
the top of a hard pull into a thermal (I generally start the turn
during the pull, if I'm going to turn at all), I do on occasion decide
that I've misjudged the thermal's size and its worth a turn. However,
the glider's roll is typically so slow, I find myself moving the stick
well forward (and sometimes dumping flaps) to increase the roll rate...
a normal reaction to sluggish controls near the stall. So again, I'm
wondering that the pilot isn't introducing an aggrevating factor
(misuse of the elevator), though admittedly, I hadn't considered this
narrow flight band when addressing the first, best recovery to an
unaticipated loss of control.




Chris Reed wrote:
I think it's misleading to say that modern aircraft "must be 'helped'
into the spin". There are some circumstances when a spin entry can be
made without any "odd" control inputs at all.

One of my favourite exercises for my annual checkouts as a UK Basic
Instructor is the spin off a simulated winch launch (only try this at
height with an appropriate instructor with you!). Simulate a winch
launch by diving to 90 kt and then pulling up at 45 degrees. As the
speed drops to about 60 kt cry "BANG - cable break", and push over into
the normal flying attitude. The moment normal attitude is reached, begin
a co-ordinated turn.

All will be fine for a second or so, as you are flying at reduced G.
However, once the G comes back on many gliders will roll smoothly (no
buffeting) into a spin so fast that there is little you can do about it
(though the purpose of the exercise is to show the spin entry and then a
recovery, so I've not tried reducing back pressure as the wing drops).
The Puchacz is excellent for this.

My understanding is that although everything looks fine, in fact you are
flying below 1G stall speed (possible because of the reduced G resulting
from the pushover, which is why BGA training requires you to push over
beyond the normal attitude after a cable break, monitor the airspeed and
not turn until a safe speed is regained). When 1G is restored the wings
stall, but because you're already in a turn the down wing stalls earlier
and autorotation ensues.

If you think about it, an aggressive pull up into a thermal coupled with
turning a little later than normal might produce similar effects.

I believe there are a number of other modes of spin entry without
unusual control movements, though you would need a far more experienced
pilot than me to explain them.

This is not to say that a glider in normal flight will depart into a
spin without abuse of the controls, but I think it important to
recognise that co-ordinated flight is not an *absolute* protection and
to understand when extra precautions are required (and what those
precautions are).

wrote:
Most important is recognition of prestall and initial departure. Since
the spin is a product of yaw moment at departure, you can prevent a
spin with coordinated controls alone. IE, modern aircraft must be
"helped" into the spin. (Put another way, the vertical stabilizer
creates enough yaw dampening to prevent autorotaion at stall so long no
pro spin control imputs are made. Since there are two yaw controls,
that would mean pro rudder or anti stick.) Thus, any prestall or
initial departure that is met with a release of back pressure and use
of coordinated controls to level the wings will produce the desired
effect before a spin or spiral dive can develop. Even if you choose not
to release back pressure, you shouldn't spin. Instead, you might find
yourself in a secondary stall. The longer it takes to apply these
simple actions, the less likely that it will produce an immediate
remedy, as the aircraft will continue into either a spin or spiral dive.