On Oct 30, 6:58*am, Paul Tribe wrote:
At 05:54 30 October 2011, Bruce Hoult wrote:On Oct 29, 12:22=A0pm, Martin Gregorie
wrote:
Both show what we are exhaustively trained against:

assuming that you're









OK once you've pushed over to a normal gliding attitude.
You're not of
course, because you'll be too slow and, unless you reacted
IMMEDIATELY
and got the stick far enough forward for a zero G push-over
you'll be
below stall speed, from where any turn will spin
immediately.

The rule of thumb[*] is to push over until your dive attitude
is as steep
as you were going up and then hold the attitude without
attempting to
turn until you've reached the landing approach speed you'd
chosen for the
day. Then, and only then you decide whether you've space
to land ahead or
whether you need to turn.

Yes, I agree with this, except there's no need to push. Simply
keeping
the stick roughly in the middle will allow the nose to fall
through as
the speed drops, without any danger of stalling, and with the
wing
operating at an efficient (low drag) angle of attack.

That is incorrect and sounds positively dangerous - the speed
will drop off to well below the stall speed before the nose comes
down sufficiently for the airspeed to increase due to gravity. You
are, in effect, doing a steep stall, which is means that the
aircraft goes through a phase of not being positively controlled!





Easing the stick forward enough to get zero G is OK too, but
unnecessary. Negative G is likely to be counterproductive and
actually
cause more drag and therefore bleed off more energy than a
small
amount of positive G.

While there may be slightly less drag with neutral control rather
than with the elevator pointing down, this is a moot point. you
may save a little potential energy, but this will be at the expense
of airspeed and it will take longer to regain it than if you push
the stick over. The idea is to rectify the "unusual" undesirable
attitude before it becomes an issue. Near the ground, airspeed is
everything.













[*] unless, of course, its a low break where you'd become a
lawn dart if
you used the above technique. Off a winch you'll always
have plenty of
specs ahead, so a shallower recovery attitude is OK once
you're
comfortable above stall speed and anyway you won't need
to turn.

I don't agree.

Assuming you maintain a low drag angle of attack, you'll arrive
back
at the release height with the same speed you had on the way
up. We
know you made the pull up into the climb from just above
ground level,
with an adequate safely margin from stalling, and with lower
speed
than you had in the climb. There's no reason at all that you
can't
safely pull out of the dive, starting from the cable break height,
even if the cable broke just as you were entering full climb.

Again, I'd rather have the positive control that pushing the stick
forwards (obviously without being a lawn-dart) gives than
wallowing about at less that 100' agl.
I'm totally with Martin and the BGA (and all of the winch qualified
instructors!) on this. If I demonstrated this laissez-faire attitude
to winch launch failures (in the UK at least), I would not be
allowed to fly solo!

This explains it in much more detail (and with greater authority)
than I can hehttp://www.gliding.co.uk/bgainfo/saf...ts/safewinchbr
ochure-0210.pdf

Addressing the two previous posts which are somewhat misguided.

The minimum height loss in a winch launch failure is determined by the
airspeed at the top of the ballistic trajectory. The proper action is
that which maintains as much airspeed as possible. The airspeed over
the top is greatest if the recovery is flown at slightly negative G
but zero G is 99% as good and is readily teachable without a G-
Meter.

Why zero G? The glider has no induced drag and is therefore losing
airspeed at the minimum rate. It is also impossible to stall a glider
whose wings are not producing lift regardless how low the airspeed
goes - stall is determined by AoA, not airspeed.

If the pilot is very skilled, or uses an AOA indicator, the wing may
be gently reloaded to an angle of attack corresponding to best L/D
starting at the top of the trajectory for even less height loss.
Otherwise, it's better to go for greater stall margin by diving to
about 1.5 x Vs before starting to level out.

Pushing the nose down to a dive angle equal to the climb angle at the
rope break is easy to teach and provides a large stall margin but
burns up height. If the landing is to be made ahead, this is fine -
especially on large airfields where the maximum height at which a
landing ahead is possible is large. On smaller airfields, max land-
ahead height will be much lower so retaining enough height for a
circle to land maneuver has to be considered.

Now commenting on the BGA Condor derived video.

Fully developed 4-turn spins to impact are rare - especially with
modern, spin-resistant gliders. Far more common is a 180 degree
rolling dive into terrain starting with a stall and wing drop. These
unfortunate pilots could have simply stopped the roll with ailerons
then recovered from the dive. Check the ASI. If airspeed is swiftly
increasing, you're not in a spin.

Modern gliders require full-aft stick to spin. If the entry is with
less than full-back stick - likely in inadvertent situations - the
resulting incipient spin will instantly transition into a spiral dive
which, to a less than spin-current pilot, will look and feel like a
spin. If the pilot delays spiral dive recovery - or worse, applies
spin recovery controls - the result is the all too familiar
unsurvivable dive into terrain.