Cable break recovery spin entry... as previously discussed

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...823e438ec30ed8

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