Nimbus 4DT accident 31 July 2000 in Spain.

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.

Interesting set of circumstances. I'll try it, before I comment at
length. However, I will not recover to see if it really is a spin. I
suspect I'll see it become a spiral dive based on previous flight
testing in this regime. But experimentation will tell.

By the way, I do this often, though not in quite the order you state or
for the same reason. I enjoy pointing the nose up 60 degrees or so,
then letting it park. The stall and pitch through is typically well
past vertical. Great fun, and completely self recovering after the
stall break. And much, much more exciting than a wing over.



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.

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.

wrote in message
ups.com...

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?

Absolutely not true. Winch launch and the associated maneuvers are well
within the design limits of any modern glider. Winch launch is not an
aerobatic maneuver.



Chris Reed wrote:
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.

One of my favorites too but it needs to be understood that, in Chris Reed's
example, the glider is at a very high AOA and deeply stalled, or will be as
soon as 1G is re-established. The ASI will only be indicating 10 - 15
knots. Initiating a turn while in a deep stall will cause a wing drop and a
spin entry - no surprise here. This 'feels' normal only because of the
normal glide attitude. It is a variant of an accelerated stall.

This maneuver is for instructors so they can anticipate the results if a
student botches a wire break recovery. I've sometimes used it with student
to demonstrate WHY the nose needs to be well down and the airspeed seen to
be above best L/D and increasing before initiating a turn. In all cases,
this practice maneuver is done at a safe altitude.

To further explain, if a wire break occurs during the nose high part of a
winch launch, it's very likely that the best landing option is straight
ahead. When the glider is high enough that a turn is needed, the nose
attitude will be lower and the height AGL will be much greater.

Bill Daniels

Chris Reed wrote:

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.


I've recently been doing this as a student and personally I found it a very
valuable lesson as (a) it required no "forcing" from the instructor to initiate
the spin and (b) it makes you realise how quickly you can transition from an
apparently normal flying attitude into a serious situation.

Chris Gadsby

Bill,

In fact, at least according to US regs, a winch launch IS an aerobatic
manuever. But that wasn't my point. If normal recovery from a normal
operation places the pilot on the ragged edge of a deep stall, then I
think it best to characterize the operation as "ab"normal., requiring
reactions unique to that environment. And thus my toying with the term
aerobatic.

There remains a problem with this argument, however. Maybe the subject
of a different thread.

BTW, have you demonstrated this maneuver without revocery? IE, have you
left the controls in place to let the spin fully develop?

wrote in message
ps.com...
Bill,

In fact, at least according to US regs, a winch launch IS an aerobatic
manuever.

I believe you are referring to the +-30 degrees pitch and +-45 degrees bank
definition of aerobatics. I believe there is an exclusion for aircraft for
which these are normal maneuvers. Gliders routinely exceed these values
thus they are not considered aerobatic for gliders.

But that wasn't my point. If normal recovery from a normal
operation places the pilot on the ragged edge of a deep stall, then I
think it best to characterize the operation as "ab"normal., requiring
reactions unique to that environment. And thus my toying with the term
aerobatic.

Normal winch operation does not place the glider on the ragged edge of a
stall. A normal launch places the max AOA very near that for best L/D. A
wire break handled properly with a prompt pushover is flown at a still lower
AOA with the airspeed not dropping below 1.3 x Vs or so. The margin is even
greater when you consider that the pushover is at less than one G so the
stall airspeed is lower.

The wire break training maneuver described by Chris is to show an instructor
candidate what can happen if the student is allowed to mis-handle the wire
break and is WAY outside normal operation.

The whole point is to drum into the instructors who will then insist that
his students learn that the nose must be promptly lowered well below normal
glide and the airspeed seen to be at a safe value and increasing before any
thought is given to a turn. This is to establish and maintain a large
safety margin. In many cases no turn is necessary and the glider lands on
the remaining runway.


BTW, have you demonstrated this maneuver without recovery? IE, have you
left the controls in place to let the spin fully develop?

Yes, It is a normal spin with a normal recovery at least with the trainers
in common use.

The wire break recovery being discussed here is safer and less dramatic than
the equivalent airtow maneuver consisting of a 200 foot AGL release on
departure and a turn back to the runway.

Bill Daniels

Silly me, playing too loosely with terms.

What interests me is that recovery from a cable break, if misapplied,
appears to place the pilot in a very unusual situation. This flight
condition was presented to put into question the abolutism of some
simple control movements that should keep pilots out of danger of loss
of control. So my question becomes one of instructional emphasis. Since
some problems evolve so quickly that thoughtful consideration isn't
always a best first course, some absolutes are needed. But if you are
flying outside normal flight conditions (IE, aerobatics or cable break
recoveries), those absolutes might not apply. Yanking the stick back to
neutral to fix the horizon on the canopy at the top of a cable break
recovery qualifies as departing from normal flight conditions. But I
certainly see the problem you face. We train pilots to take note of a
stick well aft as one sign of an imminent stall. They might not so
quickly recognize that the glider can be stalled with the stick at
neutral under these conditions. Nor might they realize that
coordination of ailerons and rudder has changed at extremely low
airpseed. Thus the opportunity to enter a wing low stall with your
hands and feet in a position that should normally signal safe flight.

All that said, I spent about 15 minutes on Sunday afternoon
experimenting with this maneuver. The results weren't as previously
published, so I'll need to take some time to write up the results. I'll
start this as a new thread.

Bill Daniels wrote:
wrote in message
ps.com...
Bill,

In fact, at least according to US regs, a winch launch IS an aerobatic
manuever.

I believe you are referring to the +-30 degrees pitch and +-45 degrees bank
definition of aerobatics. I believe there is an exclusion for aircraft for
which these are normal maneuvers. Gliders routinely exceed these values
thus they are not considered aerobatic for gliders.

But that wasn't my point. If normal recovery from a normal
operation places the pilot on the ragged edge of a deep stall, then I
think it best to characterize the operation as "ab"normal., requiring
reactions unique to that environment. And thus my toying with the term
aerobatic.

Normal winch operation does not place the glider on the ragged edge of a
stall. A normal launch places the max AOA very near that for best L/D. A
wire break handled properly with a prompt pushover is flown at a still lower
AOA with the airspeed not dropping below 1.3 x Vs or so. The margin is even
greater when you consider that the pushover is at less than one G so the
stall airspeed is lower.

The wire break training maneuver described by Chris is to show an instructor
candidate what can happen if the student is allowed to mis-handle the wire
break and is WAY outside normal operation.

The whole point is to drum into the instructors who will then insist that
his students learn that the nose must be promptly lowered well below normal
glide and the airspeed seen to be at a safe value and increasing before any
thought is given to a turn. This is to establish and maintain a large
safety margin. In many cases no turn is necessary and the glider lands on
the remaining runway.


BTW, have you demonstrated this maneuver without recovery? IE, have you
left the controls in place to let the spin fully develop?

Yes, It is a normal spin with a normal recovery at least with the trainers
in common use.

The wire break recovery being discussed here is safer and less dramatic than
the equivalent airtow maneuver consisting of a 200 foot AGL release on
departure and a turn back to the runway.

Bill Daniels

wrote:

But if you are
flying outside normal flight conditions (IE, aerobatics or cable break
recoveries),

A cable brake during a winch launch is a perfectly normal flight
condition, and as such, is regulariliy trained. Maybe I'm wrong, but it
seems you didn't do many winch launches, did you?

Stefan

wrote in message
oups.com...
Yanking the stick back to
neutral to fix the horizon on the canopy at the top of a cable break
recovery qualifies as departing from normal flight conditions.

We agree. This is the reason for the training scenario which teaches
avoidance of this situation.

But I certainly see the problem you face. We train pilots to take note of
a
stick well aft as one sign of an imminent stall. They might not so
quickly recognize that the glider can be stalled with the stick at
neutral under these conditions.

To stop the nose at the normal gliding attitude after a wire break requires
a powerful elevator and full back stick. This is definitely a pilot induced
stall resulting from a mis-use of the elevator. However, accident records
show that this has occasionally been the cause of a spin accident so the
training scenario was added. To repeat what I wrote earlier, this is merely
a slight variant of an accelerated stall. If the stick were held neutral,
the nose would fall through to a steep nose down attitude. This is not the
best technique but it wouldn't result in a deep stall.

Bill Daniels