Nimbus 4DT accident 31 July 2000 in Spain.

On Wed, 22 Jun 2005 12:54:44 UTC, wrote:

I wonder at the thread though. Everyone discussing recognition of a
fully developed spin versus spiral dive.

Isn't it generally more useful to recognize the difference between a
just-developing spin and a just-developing spiral dive?

Which reminds me of Johnston's Test Question for BGA Instructors
Number Three:

"The offical recovery from a stall with wing drop is different from
the official recovery from a spin. At what point do you, personally,
transition from one to the other?"

Ian

--

"Ian Johnston" wrote in message
news:dzZo7CxomoOm-pn2-39ddFD9pBSKp@localhost...
On Wed, 22 Jun 2005 12:54:44 UTC, wrote:

I wonder at the thread though. Everyone discussing recognition of a
fully developed spin versus spiral dive.

Isn't it generally more useful to recognize the difference between a
just-developing spin and a just-developing spiral dive?

Which reminds me of Johnston's Test Question for BGA Instructors
Number Three:

"The offical recovery from a stall with wing drop is different from
the official recovery from a spin. At what point do you, personally,
transition from one to the other?"

Ian


As often happens, the BGA comes through with some useful wisdom. Thanks,
Ian.

As for the difference in sensations between an incipient spin and incipient
spiral, the former seems to me to be like an uncommanded yaw and the later
like an uncommanded roll. To me, at least, they clearly say that if the
situation is allowed to continue without intervention, the uncommanded yaw
will become a spin and the uncommanded roll will become a spiral.

I wish I could capture the sensations and record them. They would be very
useful in training.

As for a spinable trainer with similar characteristics, the venerable IS28b2
would do a creditable job of either spin or spiral and build up speed like
crazy in the ensuing dive. It had the requisite large inertia about all
axes. I found it taught me a lot about how to fly a Nimbus.

Bill Daniels

Bill Daniels writes
"The offical recovery from a stall with wing drop is different from
the official recovery from a spin. At what point do you, personally,
transition from one to the other?"

I'm curious. Although in practical terms I'm quite confident (through
practice) that I can tell one from the other and react and recover
accordingly, but how would you phrase the answer to that?

--
Bill Gribble
http://www.scapegoatsanon.demon.co.uk
- Learn from the mistakes of others.
- You won't live long enough to make all of them yourself.

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.

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?