If you imagine that you are climbing at 55kts no probs
and the cable breaks. The glider starts to decelerate
so the immediate action is to push the stick forward
to pitch the nose down. The glider flies a parabolic
arc and while it's mass remains the same the weight
that the wing has to support is dramatically reduced
at the top of the arc. So the glider can be at 45kts
or less and the wing has not stalled, the AoA is still
below the stalling angle and the airspeed is sufficient
with the reduced G to keep the glider flying. The harder
the push the greater the reduction in G and effective
weight the wing has to support. Because of inertia
the glider will take time to accelerate to sufficient
speed to generate the lift necessary to support the
glider as the G increases to 1. If aileron is applied
to turn before this acceleration takes place the increasing
G can mean that in effect the wing is stalled and application
of aileron could initiate the spin. It is important
to remember that it is the attitude of the glider to
the relative airflow that determines the angle of attack,
not the relationship of the glider to the horizon.
The picture the pilot sees in these circumstances could
well be one where the nose is well below the horizon
(approach attitude) but acceleration has not taken
place and the wing is stalled. Once the glider accelerates
it is then safe to use the ailerons as normal. It is
a reversal of the situation where high G increases
the stalling speed, the further stalling exercise.
I have seen as little as 20 kts at the top of a push
over with no ill effect provided the ailerons remain
central. Try it sometime at a safe height, this will
be a far better way of seeing the problem than my explanation.

At 14:36 30 June 2005, Mike Schumann wrote:
It is not obvious to me, why, in a cable break scenario,
you would be close
to stalling when you push the nose down to a normal
attitude while you
maintain 60 knot airspeed. This sounds like you are
flying significantly
above stall speed. Could you elaborate?

Thanks,
Mike Schumann

wrote in message
roups.com...
Pilots depend on simple, quickly applied remedies
to any loss of
control. Since we are not always afforded the luxury
of examination,
analysis, and consideration of options as a preamble
to action, any
flight condition where these simple rules of recovery
do not work
demands closer examination and appropriate training
to recognize
symptoms and take appropriate actions.

Modern aircraft are designed to meet well-defined
controllability
requirements. For example, in the United States, the
recommended
recovery (generic) for any impending or developed
stall is to move the
control column forward while applying coordinated
aileron and rudder to
halt an un-commanded roll. The Flight Manual for my
S-H Ventus 2bx
states on page 3.4:

--On stalling whilst flying straight ahead or in a
banked turn, normal
flying attitude is regained by firmly easing the control
stick forward
and, if necessary, applying opposite rudder and aileron.--

Page 3.5 (Spin Recovery) continues...

--Note: Spinning may be safely avoided by following
the actions given
in section 3.4 'Stall Recovery'-

During the past several years, I have made it a point
to experiment
with various applications of controls throughout the
stall break (and
in a variety of makes and models). In all cases where
I maintained
coordination, either paying attention to the yaw string
or through
application of equal amounts of aileron and rudder,
the aircraft did
not spin, even if I held the stick firmly against
the rear stop.
Instead, it would transition from stall to spiral
dive.

In a recent RAS thread (Nimbus 4DT accident 31 July
2000 in Spain), I
was introduced to a maneuver practiced by BGA instructors
to
demonstrate that a quick transition from coordinated
flight into a spin
can take place while recovering from a winch launch
cable break. This
was pointed out to refute my comment in that thread
that modern gliders
need to be 'helped' into a spin (by either intentional
or
inadvertent abuse of the controls).

Chris Reed described the following:

--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.--

For me, this raised an immediate alarm. It indicates
that there are
flight regimes (whether experienced during a cable
break recovery,
during an aggressive thermal entry, or as a result
of turbulence) where
normal control movements may result in an immediate
and unannounced
spin entry.
Since such matters are best examined in the air, I
put together an
informal flight test plan to measure just how sudden
the spin entry is
and whether there might be mitigating factors.

To prepare for the test, I set up the following limits:

First, I would at no time during the maneuver bring
the stick back all
the way to the stop. We must assume that all pilots
meet a base level
of competency, and under no circumstance would any
competent pilot
resort to full up elevator to maintain attitude during
a cable break
recovery. I would consider such control usage an abuse
of the controls.

Second, I would remain coordinated (as indicated by
my yaw string)
throughout the maneuver per the instructions of my
flight manual.

Third, at stall break, I would hold the controls firm
and visually
verify their positions, then wait for the sailplane
to assume its new
state (either spin or spiral dive) then clearly identify
that state
before making an appropriate recovery.

I began the test sequence with a series of four dives
and recoveries
just as Chris described, but without introducing a
bank. At 60 knots, I
called out 'Bang - cable break - recover!' I pushed
the stick
firmly forward. Three out of the four, I briefly suspended
loose dirt
in the cockpit. As soon as the nose passed through
the horizon into a
normal flying attitude, I moved the stick quickly
back to its normal
position for that attitude. Of course, this did not
entirely halt the
downward pitch of the nose. However, it was clearly
apparent through
the feel of the controls that the sailplane was either
stalled or on
the edge of a stall as a result of my quick application
of stick from
well forward to neutral. It was very clear that bringing
the stick
straight back to the stop would result in a full stall.

I began the dives in flap position -1, moving the
flaps to position +1
as I slowed through 70 knots, as I might if I were
entering a thermal,
though my recovery (pitch over) was much more aggressive
than any I
would use during cross-country flight. Once I was
comfortable with my
ability to keep myself from making an immediate recovery
from any
stall, I stopped to thermal, then found a clear patch
of sky and warned
off others away, as I fully expected to spin the sailplane.

In order to force an immediate turn, I imagined that
there was an
obstruction preventing a straight ahead landing. As
soon as the nose
came down, I determined that I would have to make
an immediate turn to
the right, which I did, without adverse results. The
sailplane rolled
sluggishly and felt on the edge of stall, but there
was no loss of
control, and certainly no sudden yaw and entry into
a spin. I thought
perhaps I had waited too long to initiate the turn,
so with the next
pull and recovery, I made the decision, before the
nose came fully
over, that I would land to the left in an adjoining
field. I rolled to
about 30 degrees, then as the nose reached normal
flying attitude, I
brought the stick right back to neutral... and braced
myself against
making an immediate recovery.

As before, there was a sense of mushing through the
air, but no
tendency for the glider to yaw itself into a spin.
For the next pull
and recovery, I delayed saying 'Bang - cable break
- recover!'
until 50 knots. Given the additional delay, I was
much more aggressive
with the stick, both moving it forward and returning
it to neutral once
I reach normal flying attitude. And once again, the
sailplane
demonstrated a sluggish, heavy feel as the g force
came back on, but
without any tendency to 'fall' into the direction
of the turn.

It was clear to me that I could have easily induced
a spin during this
maneuver. A little too much rudder or stick against
the turn coupled
with bringing the stick full aft would have tipped
the sailplane right
over. But my intent was to produce an unanticipated
spin, even though I
was, ostensibly, doing everything right.

I repeated this maneuver several more times, making
slight adjustments
to angle of bank, but without adverse effects.

My conclusions:

This is an interesting flight regime. I suspect that
it would prove
useful for producing spins in typically resistant
aircraft, and require
significantly less control abuse among those gliders
that are inclined
to spin. However, for my make and model (which can
be easily coaxed to
incipiency), normal attention to stall warning signs
and application of
coordinated aileron and rudder are adequate. There
does not appear to
be any tendency for the glider to spin suddenly or
unpredictably,
though I would caution that if the stick is used to
catch a dropping
wing without appropriate application of rudder, the
spin entry could be
significantly accelerated.

The greater the span, the more pronounced the effects
of a tip stall
would be, but greater span is usually compensated
for by a longer tail
boom and larger vertical stabilizer. Some designs
may choose to
underpower the vertical stabilizer to increase glide
performance, but
hopefully these would include appropriate warnings
and recovery
procedures in their respective flight manuals.

As far as thermal entry is concerned, I would give
the same warning: if
you delay your pushover on thermal entry to the point
where G and
airspeed are significantly reduced below the norms
(generally not the
most efficient way to enter a thermal), extra attention
should be paid
to coordination. I wouldn't expect the glider to snap
into a spin,
but it is entirely possible that the now underpowered
vertical
stabilizer may not adequately compensate if you have
any tendency
towards sloppiness.

I intend to experiment with this maneuver some more
over the coming
weeks. As I discover anything interesting, I'll add
my comments to
the thread. Also, I uploaded my FR trace to the OLC,
but my sampling
was 4 seconds, hardly adequate for analysis. However,
just in case you
are tempted to make an armchair assay, be my guest!

http://www2.onlinecontest.org/olcphp...info.php?ref3=
197828&ueb=N&olc=olc-usa&spr=en&dclp=c9701de37223903b6f823e438ec30
ed8

The test run began at 1454 ET (UTC-4) and ended at
1503 ET.