Re: Cable break recovery spin entry... as previously discussed

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

<fiveniner2001@xxxxxxxxx> wrote in message
news:1120082069.938323.228360@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
> 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/2005/ausw_fluginfo.php?ref3=197828&ueb=N&olc=olc-usa&spr=en&dclp=c9701de37223903b6f823e438ec30ed8
>
> The test run began at 1454 ET (UTC-4) and ended at 1503 ET.
>


.

Loading