Spinning the SZD 50-3 [Archive]

Tim Shea

January 28th 04, 12:56 AM

I love to spin. It's exciting. I took aerobatic training with Wayne
Handley and was taught spin recoveries by him.

I have direct experience spinning the Puchacz at Minden. This is what
I remember from my experience. Your mileage may vary.
With friends (usually lighter than me) in the front, I spun it while
sitting in the back seat more than a dozen times. The CG was within
the published range and I didn't have any trouble with simple
recovery- stick centered and forward and rudder away from the
direction of rotation. Worked great.
I should mention that I used to be 50 lbs heavier than I am now, but
still in the published range for the plane.
During the training towards my instructors rating, I spun the Puch
twice with my instructor. The first 2 or so rotation spin I was able
to recover normally, no sweat. The second manuver was quite different.
I was asked to let the spin develop a little deeper for the second.
After 4 or so rotations, the nose seemed to float up and the rotation
*seemed* to slow considerably. I remember thinking that this is cool!
Kind of like floating. When it was time for the recovery I applied the
control inputs I'd been taught (as specified above) and much to my
surprise, nothing different happened.....for a long time. I estimate
that we completed another 5+ rotations nose high before it broke,
rolled over and recovered. I had the stick centered and against the
front stop with the rudder also pegged away from the rotation. We
recovered with several (4 or 5) thousand feet under us (we'd been
playing at cloudbase at about 15K).
Once on the ground, we discussed this incident in the grumpy bar for
at least an hour. I (and he) decided to never spin the Puch again. I
didn't. I doubt he did either.
I had heard of this happening before. I assumed that it was from
operation outside of the design envelope. Apparently I was wrong.
John Shelton probably said it best: "On my own as a test pilot, I will
certainly get killed". I felt like a dumb-ass for quite a while (more
than usual) after that.

Shawn Curry

January 28th 04, 01:13 AM

Tim Shea wrote:
> I love to spin. It's exciting. I took aerobatic training with Wayne
> Handley and was taught spin recoveries by him.
>
> I have direct experience spinning the Puchacz at Minden. This is what
> I remember from my experience. Your mileage may vary.
> With friends (usually lighter than me) in the front, I spun it while
> sitting in the back seat more than a dozen times. The CG was within
> the published range and I didn't have any trouble with simple
> recovery- stick centered and forward and rudder away from the
> direction of rotation. Worked great.
> I should mention that I used to be 50 lbs heavier than I am now, but
> still in the published range for the plane.
> During the training towards my instructors rating, I spun the Puch
> twice with my instructor. The first 2 or so rotation spin I was able
> to recover normally, no sweat. The second manuver was quite different.
> I was asked to let the spin develop a little deeper for the second.
> After 4 or so rotations, the nose seemed to float up and the rotation
> *seemed* to slow considerably. I remember thinking that this is cool!
> Kind of like floating. When it was time for the recovery I applied the
> control inputs I'd been taught (as specified above) and much to my
> surprise, nothing different happened.....for a long time. I estimate
> that we completed another 5+ rotations nose high before it broke,
> rolled over and recovered. I had the stick centered and against the
> front stop with the rudder also pegged away from the rotation. We
> recovered with several (4 or 5) thousand feet under us (we'd been
> playing at cloudbase at about 15K).
> Once on the ground, we discussed this incident in the grumpy bar for
> at least an hour. I (and he) decided to never spin the Puch again. I
> didn't. I doubt he did either.
> I had heard of this happening before. I assumed that it was from
> operation outside of the design envelope. Apparently I was wrong.
> John Shelton probably said it best: "On my own as a test pilot, I will
> certainly get killed". I felt like a dumb-ass for quite a while (more
> than usual) after that.

Anyone else spin the Puch for more than three turns? What happened
(obviously you survived)? I've heard that some other aircraft also have
a flatter spin mode that after several turns that is hard to recover
from. Any knowledge of why this happens? (Now where's my copy of Stick
and Rudder?)

Shawn

Geir Raudsandmoen

January 28th 04, 01:34 AM

If you were within the permitted CoG range, and used
the standard recovery method, the spin behaviour you
described is definitely non-compliant with JAR 22 certification
rules. JAR22.221 states that a sailplane certificated
for intentional spinning must be able to recover from
a fully developed spin (5 turns) within 1 turn after
recovery action is done. This has to be demonstrated
in several loading and control conditions.

Additionally, this paragraph states that it must be
impossible to obtain uncontrollable spins with any
use of the controls.

The Puchacz may not have been certificated to JAR 22,
but possibly to the older OSTIV rules. However, I very
much doubt that this type of behaviour would have been
acceptable under older certification rules, although
the verification/testing requirements might have been
less strict in earlier days.

Geir

At 01:00 28 January 2004, Tim Shea wrote:
>I love to spin. It's exciting. I took aerobatic training
>with Wayne
>Handley and was taught spin recoveries by him.
>
>I have direct experience spinning the Puchacz at Minden.
>This is what
>I remember from my experience. Your mileage may vary.
>With friends (usually lighter than me) in the front,
>I spun it while
>sitting in the back seat more than a dozen times. The
>CG was within
>the published range and I didn't have any trouble with
>simple
>recovery- stick centered and forward and rudder away
>from the
>direction of rotation. Worked great.
>I should mention that I used to be 50 lbs heavier than
>I am now, but
>still in the published range for the plane.
>During the training towards my instructors rating,
>I spun the Puch
>twice with my instructor. The first 2 or so rotation
>spin I was able
>to recover normally, no sweat. The second manuver was
>quite different.
>I was asked to let the spin develop a little deeper
>for the second.
>After 4 or so rotations, the nose seemed to float up
>and the rotation
>*seemed* to slow considerably. I remember thinking
>that this is cool!
>Kind of like floating. When it was time for the recovery
>I applied the
>control inputs I'd been taught (as specified above)
>and much to my
>surprise, nothing different happened.....for a long
>time. I estimate
>that we completed another 5+ rotations nose high before
>it broke,
>rolled over and recovered. I had the stick centered
>and against the
>front stop with the rudder also pegged away from the
>rotation. We
>recovered with several (4 or 5) thousand feet under
>us (we'd been
>playing at cloudbase at about 15K).
>Once on the ground, we discussed this incident in the
>grumpy bar for
>at least an hour. I (and he) decided to never spin
>the Puch again. I
>didn't. I doubt he did either.
>I had heard of this happening before. I assumed that
>it was from
>operation outside of the design envelope. Apparently
>I was wrong.
>John Shelton probably said it best: 'On my own as a
>test pilot, I will
>certainly get killed'. I felt like a dumb-ass for quite
>a while (more
>than usual) after that.
>

Bill Daniels

January 28th 04, 01:43 AM

"Shawn Curry" > wrote in message
link.net...
> Tim Shea wrote:
> > I love to spin. It's exciting. I took aerobatic training with Wayne
> > Handley and was taught spin recoveries by him.
> >
> > I have direct experience spinning the Puchacz at Minden. This is what
> > I remember from my experience. Your mileage may vary.
> > With friends (usually lighter than me) in the front, I spun it while
> > sitting in the back seat more than a dozen times. The CG was within
> > the published range and I didn't have any trouble with simple
> > recovery- stick centered and forward and rudder away from the
> > direction of rotation. Worked great.
> > I should mention that I used to be 50 lbs heavier than I am now, but
> > still in the published range for the plane.
> > During the training towards my instructors rating, I spun the Puch
> > twice with my instructor. The first 2 or so rotation spin I was able
> > to recover normally, no sweat. The second manuver was quite different.
> > I was asked to let the spin develop a little deeper for the second.
> > After 4 or so rotations, the nose seemed to float up and the rotation
> > *seemed* to slow considerably. I remember thinking that this is cool!
> > Kind of like floating. When it was time for the recovery I applied the
> > control inputs I'd been taught (as specified above) and much to my
> > surprise, nothing different happened.....for a long time. I estimate
> > that we completed another 5+ rotations nose high before it broke,
> > rolled over and recovered. I had the stick centered and against the
> > front stop with the rudder also pegged away from the rotation. We
> > recovered with several (4 or 5) thousand feet under us (we'd been
> > playing at cloudbase at about 15K).
> > Once on the ground, we discussed this incident in the grumpy bar for
> > at least an hour. I (and he) decided to never spin the Puch again. I
> > didn't. I doubt he did either.
> > I had heard of this happening before. I assumed that it was from
> > operation outside of the design envelope. Apparently I was wrong.
> > John Shelton probably said it best: "On my own as a test pilot, I will
> > certainly get killed". I felt like a dumb-ass for quite a while (more
> > than usual) after that.
>
> Anyone else spin the Puch for more than three turns? What happened
> (obviously you survived)? I've heard that some other aircraft also have
> a flatter spin mode that after several turns that is hard to recover
> from. Any knowledge of why this happens? (Now where's my copy of Stick
> and Rudder?)
>
> Shawn

OK, this is speculation.

Remember the old spin-the-hammer trick from freshman physics? It seems
solid objects don't like to spin around their long axis - they prefer to
spin about their shortest. Imagine a glider with the CG in the middle of
the allowed range but the mass distributed far away from the CG in heavy
wings and long fuselage with a heavy load in the cockpit balanced with a
weight in the tail. Might it tend to flatten and spin about the vertical
axis?

BTW, any time I feel a glider hesitate to recover from a spin, I'm going to
throw full aileron into the spin. (As per the POH of most Eastern European
gliders.)

Bill Daniels

Bill Daniels

Arnold Pieper

January 28th 04, 01:44 AM

You shouldn't spin more than 3 turns unless you're practicing for aerobatic
flight.

In a case as you describe, application of full PRO-SPIN controls for a few
seconds should have been performed prior to a second attempt at recovery.
And recovery should be rudder and stick at the same time (as recomended by
Dick Johnson after his testing) or with the Rudder leading the recovery by 1
second or so (as recomended by the Puchacz's POH).
Commencing recovery with the Stick first is not recomended, and it may in
fact retard recovery significantly.

Also, chances are that you didn't have the stick and/or rudder against the
stops, for simple reasons such as Trim not being Neutral (as recommended by
the manual), or the Ailerons might not have been Neutral (as they should),
or the CG may have been slightly off-limits.
The same things would cause similar behaviour in any other modern training
glider.

In a regular spin, with 3 or less rotations, some of these things are less
of an issue, but they have to be observed anyway.

Recovery however has to be the same way in a fully developed spin :
-Anti-spin rudder to the stop
-After 1 second or less, release back pressure on the stick or even move it
forward, all-the-way if you have to.
Rotation should stop.
If it doesn't, apply full pro-spin controls, verify the ailerons in neutral
(stick not in any of the sides) and trim in neutral, then repeat recovery.

"Tim Shea" > wrote in message
m...
> I love to spin. It's exciting. I took aerobatic training with Wayne
> Handley and was taught spin recoveries by him.
>
> I have direct experience spinning the Puchacz at Minden. This is what
> I remember from my experience. Your mileage may vary.
> With friends (usually lighter than me) in the front, I spun it while
> sitting in the back seat more than a dozen times. The CG was within
> the published range and I didn't have any trouble with simple
> recovery- stick centered and forward and rudder away from the
> direction of rotation. Worked great.
> I should mention that I used to be 50 lbs heavier than I am now, but
> still in the published range for the plane.
> During the training towards my instructors rating, I spun the Puch
> twice with my instructor. The first 2 or so rotation spin I was able
> to recover normally, no sweat. The second manuver was quite different.
> I was asked to let the spin develop a little deeper for the second.
> After 4 or so rotations, the nose seemed to float up and the rotation
> *seemed* to slow considerably. I remember thinking that this is cool!
> Kind of like floating. When it was time for the recovery I applied the
> control inputs I'd been taught (as specified above) and much to my
> surprise, nothing different happened.....for a long time. I estimate
> that we completed another 5+ rotations nose high before it broke,
> rolled over and recovered. I had the stick centered and against the
> front stop with the rudder also pegged away from the rotation. We
> recovered with several (4 or 5) thousand feet under us (we'd been
> playing at cloudbase at about 15K).
> Once on the ground, we discussed this incident in the grumpy bar for
> at least an hour. I (and he) decided to never spin the Puch again. I
> didn't. I doubt he did either.
> I had heard of this happening before. I assumed that it was from
> operation outside of the design envelope. Apparently I was wrong.
> John Shelton probably said it best: "On my own as a test pilot, I will
> certainly get killed". I felt like a dumb-ass for quite a while (more
> than usual) after that.

Bruce Hoult

January 28th 04, 03:28 AM

In article >,
Geir Raudsandmoen
m> wrote:

> If you were within the permitted CoG range, and used
> the standard recovery method, the spin behaviour you
> described is definitely non-compliant with JAR 22 certification
> rules. JAR22.221 states that a sailplane certificated
> for intentional spinning must be able to recover from
> a fully developed spin (5 turns) within 1 turn after
> recovery action is done. This has to be demonstrated
> in several loading and control conditions.

Fine.

> Additionally, this paragraph states that it must be
> impossible to obtain uncontrollable spins with any
> use of the controls.

But how on earth can that be demonstrated? No matter *what* you do, you
can't get into an uncontrollable spin? But there are an infinite number
of possible things you *might* do with the controls. They can't ALL be
tested.

-- Bruce

Buck Wild

January 28th 04, 07:02 AM

Shawn Curry > wrote in message . net>...
> Tim Shea wrote:
> > I love to spin. > Anyone else spin the Puch for more than three turns?

What happened
> (obviously you survived)? I've heard that some other aircraft also have
> a flatter spin mode that after several turns that is hard to recover
> from. Any knowledge of why this happens? (Now where's my copy of Stick
> and Rudder?)
>
> Shawn

The Puke will usually recover quickly within the first 3 or so turns,
but it does go int a more stable, nose higher-type rotation after
maybe 4 or 5.
I've spun both the 55 and the 59 out of wave, maybe 15 turns or so,
and experianced what Tandem Tim described. I also got into this mode
in the 103 once, believe it or not, spinning it up over 17K. I believe
it has most to do with the gyroscopic inertia that builds after a few
turns.
SInce I was plenty high, ( in each case) my first thought was to
loosen the belts & lean forward, but I wanted to try control input
first. I held full opposite rudder, and centered & full forward stick.
In each case, they dropped through & recovered, but you had to sit
through a few rev's just holding those inputs and Believe that it will
eventually work. I was ready to try other options & inputs, but I
wanted to see if the hold-it & wait method would work.
It was a bit unnerving, the 103 went on for maybe 3 turns, the Puch
maybe 4, and the 59 maybe 5 or 6. (I don't remember if I had the tips
on) and I would never enter that mode again without 2 miles between me
and the nearest planet, and a rented plane.
If you instruct to fully developed rotation, start recovery in the
Puch as soon as it falls through, or within 1 turn, and don't stick
yer toes under the back seat pedals.
I fully agree with putting the emphasis on incipiant recovery, tho I
think there's value in training a pilot to remain calm & methodical in
an unexpected emergancy event, when the world is spinning way faster
than it should.
For those up to it, it does a nice snap at 55~60, nose up a little, &
full rudder, elevator & aileron. If you hold it all the way through,
it comes around a second time with the nose real high. (Flame suite on
for the safety nazis)

Remember to live live at your own risk,
Choose your level of involvement to be just under your ability, and
remember...
You've gotta be tough...
If you're gonna be stupid.
-Dan

Chris Rollings

January 28th 04, 08:52 AM

The Puchacz WAS certified to JAR 22. When it was first
imported into the UK I repeated the tests, prior to
the BGA granting it certification. The testing included
five turns spins with the C of G at the manufacturers
aft limit; recovery was normal in well under one turn.

Having said that:

1. I once had a similar experience to the one described,
when flight testing the Grob Twin II for BGA certification.
Earlier spins at mid-range C of G had been typically
Grob - self recovery after less than a turn. I expected
that it would be just possible to hold it in at aft
C of G. In fact the spin started to flatten after
about two turns. I initiated recovery immediately,
it took three turns to recover (I was considering abandoning
the aircraft at that point).

After lots of phone calls to the manufacturer (who
said it had never happened in their testing), we resumed
testing (Cautiously) and approached the aft C of G
in small increments. Eventually we got to the C of
G position at which I had had the problem - the spin
was perfectly normal! So far I was aware, I had used
exactly the same spin entry technique in both cases.
Clearly there must have been some small difference
(ailerons not quite central, or some such) that made
an important difference. Whatever the cause, I couldn't
get it to repeat, all subsequent spins were unremarkable.

Rogue spins can happen, IN ANY TYPE.

2. The Puchacz described may have had some repair,
or equipment change, that moved the C of G further
aft, and this failed to get into the aircraft's records
(appalling, I know, but it has happened).

3. The elevator deflections may have become mis-set,
allowing greater upward deflection, and less downward.
This can happen unintentionally, I don't know how,
but it would very likely produce the result described.

At 01:36 28 January 2004, Geir Raudsandmoen wrote:
>If you were within the permitted CoG range, and used
>the standard recovery method, the spin behaviour you
>described is definitely non-compliant with JAR 22 certification
>rules. JAR22.221 states that a sailplane certificated
>for intentional spinning must be able to recover from
>a fully developed spin (5 turns) within 1 turn after
>recovery action is done. This has to be demonstrated
>in several loading and control conditions.
>
>Additionally, this paragraph states that it must be
>impossible to obtain uncontrollable spins with any
>use of the controls.
>
>The Puchacz may not have been certificated to JAR 22,
>but possibly to the older OSTIV rules. However, I very
>much doubt that this type of behaviour would have been
>acceptable under older certification rules, although
>the verification/testing requirements might have been
>less strict in earlier days.
>
>Geir
>
>At 01:00 28 January 2004, Tim Shea wrote:
>>I love to spin. It's exciting. I took aerobatic training
>>with Wayne
>>Handley and was taught spin recoveries by him.
>>
>>I have direct experience spinning the Puchacz at Minden.
>>This is what
>>I remember from my experience. Your mileage may vary.
>>With friends (usually lighter than me) in the front,
>>I spun it while
>>sitting in the back seat more than a dozen times. The
>>CG was within
>>the published range and I didn't have any trouble with
>>simple
>>recovery- stick centered and forward and rudder away
>>from the
>>direction of rotation. Worked great.
>>I should mention that I used to be 50 lbs heavier than
>>I am now, but
>>still in the published range for the plane.
>>During the training towards my instructors rating,
>>I spun the Puch
>>twice with my instructor. The first 2 or so rotation
>>spin I was able
>>to recover normally, no sweat. The second manuver was
>>quite different.
>>I was asked to let the spin develop a little deeper
>>for the second.
>>After 4 or so rotations, the nose seemed to float up
>>and the rotation
>>*seemed* to slow considerably. I remember thinking
>>that this is cool!
>>Kind of like floating. When it was time for the recovery
>>I applied the
>>control inputs I'd been taught (as specified above)
>>and much to my
>>surprise, nothing different happened.....for a long
>>time. I estimate
>>that we completed another 5+ rotations nose high before
>>it broke,
>>rolled over and recovered. I had the stick centered
>>and against the
>>front stop with the rudder also pegged away from the
>>rotation. We
>>recovered with several (4 or 5) thousand feet under
>>us (we'd been
>>playing at cloudbase at about 15K).
>>Once on the ground, we discussed this incident in the
>>grumpy bar for
>>at least an hour. I (and he) decided to never spin
>>the Puch again. I
>>didn't. I doubt he did either.
>>I had heard of this happening before. I assumed that
>>it was from
>>operation outside of the design envelope. Apparently
>>I was wrong.
>>John Shelton probably said it best: 'On my own as a
>>test pilot, I will
>>certainly get killed'. I felt like a dumb-ass for quite
>>a while (more
>>than usual) after that.
>>
>
>
>
>

Chris Nicholas

January 28th 04, 09:48 AM

Reading of these brave souls who have been testing the Puchaz spinning
characteristics with multi-turn spins at high altitudes reminds me of an
anecdotal rumour which reached me about at least one other glider type,
and I think also some power aircraft, which similarly misbehaved until
many turns/it got lower. It made me wonder a few things:

At the heights people here have been writing about - 10 to 17 thousand
feet - what is the true airspeed at which it enters the spin on command
and how does that differ from the lower altitude airspeed used for
certification tests? Bear in mind also one poster's comments that a
glider does not instantly cease forward motion and go instead into
vertical motion with a rotational component - in the absence of infinite
forces, the first is subject to some deceleration taking time and space,
and the second some vertical acceleration taking time and height.

Similarly, what is the true vertical velocity at onset and when stable
in the spin?

What is the ratio of those two velocities compared with the ratio at
test air densities?

Does the rotation rate remain identical, whether at height (lower air
densities) or at lower altitude (higher density)?

Does all that have an effect on true angle of attack?

Could such things account for high altitude spins when fully developed
requiring more turns to recover?

I wonder if the people who conduct these high altitude tests were in a
regime not tested by the maker or the certification test pilots such as
Chris Rollings?

Chris N.

Ian Johnston

January 28th 04, 11:17 AM

On Wed, 28 Jan 2004 00:56:12 UTC, (Tim Shea)
wrote:

: After 4 or so rotations, the nose seemed to float up and the rotation
: *seemed* to slow considerably. I remember thinking that this is cool!
: Kind of like floating. When it was time for the recovery I applied the
: control inputs I'd been taught (as specified above) and much to my
: surprise, nothing different happened.....for a long time. I estimate
: that we completed another 5+ rotations nose high before it broke,
: rolled over and recovered.

I am told that a Junior oscillates nose up and down while spinning,
and that recovery is much much snappier nose down.

Ian

Ian Johnston

January 28th 04, 11:20 AM

On Wed, 28 Jan 2004 01:43:36 UTC, "Bill Daniels" >
wrote:

: Remember the old spin-the-hammer trick from freshman physics? It seems
: solid objects don't like to spin around their long axis - they prefer to
: spin about their shortest.

Actually, the physics says that objects are stable when rotating
around the axes corresponding to the greatest and least moments of
inertia. For a glider I'd expect yaw to be the highest moment of
inertia and pitch to be the lowest. Howver, that ignores aerodynamic
effects, which I'd expect to be much more significant.

Ian
--

Martin Gregorie

January 28th 04, 12:52 PM

On 28 Jan 2004 11:17:41 GMT, "Ian Johnston" >
wrote:

>On Wed, 28 Jan 2004 00:56:12 UTC, (Tim Shea)
>wrote:
>
>: After 4 or so rotations, the nose seemed to float up and the rotation
>: *seemed* to slow considerably. I remember thinking that this is cool!
>: Kind of like floating. When it was time for the recovery I applied the
>: control inputs I'd been taught (as specified above) and much to my
>: surprise, nothing different happened.....for a long time. I estimate
>: that we completed another 5+ rotations nose high before it broke,
>: rolled over and recovered.
>
>I am told that a Junior oscillates nose up and down while spinning,
>and that recovery is much much snappier nose down.
>

That's all in the POH. A Junior has three different spin behaviours
depending on cockpit load. IIRC the oscillation occurs with a light
pilot.

I'm in the middle group (180 with a chute) and it recovers
automatically after just over 2 rotations, even with the controls
still fully crossed. The last half rotation gets really slow. I was a
bit annoyed. Having just done Silver height and wanting down in a
hurry, I was after 3 turns and was intending to come most of the way
down in a 3-turn - recover - spin the other way sequence. Still, I
repeated the experiment in the other direction and with recovery by
merely centreing the controls and got consistent recovery after just
over 2 rotations.

Be sure to read the POH before attempting more than one rotation.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Pete Zeugma

January 28th 04, 01:42 PM

>I'm in the middle group (180 with a chute) and it recovers
>automatically after just over 2 rotations, even with
>the controls
>still fully crossed. The last half rotation gets really
>slow. I was a
>bit annoyed. Having just done Silver height and wanting
>down in a
>hurry, I was after 3 turns and was intending to come
>most of the way
>down in a 3-turn - recover - spin the other way sequence.
>Still, I
>repeated the experiment in the other direction and
>with recovery by
>merely centreing the controls and got consistent recovery
>after just
>over 2 rotations.
>

I quite frankly find this a quite scary post! I do
hope you allowed suficient height above the start of
your 1000m gain. I take it you are also one of the
'glider pilot hero' types? Still, i'm sure you impressed
everyone at the bar afterwards..........

So, what was wrong with a more conventional 'rapid
decent', you know, the one that uses full airbrake
circling in sink, or sideslipping with full airbrake.

W.J. \(Bill\) Dean \(U.K.\).

January 28th 04, 02:12 PM

I have been told two things:

1. That the Reynolds number applicable to a glider changes with altitude,

2. That the Reynolds number affects the stall/spin behaviour and recovery.

I can remember an anecdote (I am vague as to who or when) about a K21 at
Aboyne. The glider was at about 20,000 ft., and the crew wanted to get
down for the next pupil. They put it into a spin (which it entered without
difficulty), and then held the spin without moving the controls. It span
down to about 7,000 ft. and then self-recovered without any
change in control position. Heights are QNH.

I don't understand Reynolds numbers, but I know it matters; and it would
seem not only to designers. It might well be that some gliders more easily
spin and are harder to recover at height. I would expect this to apply at
altitudes above about 7,000 ft. QNH, above which height they are almost
certainly not test flown.

W.J. (Bill) Dean (U.K.).
Remove "ic" to reply.

>
> "Chris Nicholas" > wrote in message
> ...
>
> Reading of these brave souls who have been testing the Puchacz spinning
> characteristics with multi-turn spins at high altitudes reminds me of an
> anecdotal rumour which reached me about at least one other glider type,
> and I think also some power aircraft, which similarly misbehaved until
> many turns/it got lower. It made me wonder a few things:
>
> At the heights people here have been writing about - 10 to 17 thousand
> feet - what is the true airspeed at which it enters the spin on command
> and how does that differ from the lower altitude airspeed used for
> certification tests? Bear in mind also one poster's comments that a
> glider does not instantly cease forward motion and go instead into
> vertical motion with a rotational component - in the absence of infinite
> forces, the first is subject to some deceleration taking time and space,
> and the second some vertical acceleration taking time and height.
>
> Similarly, what is the true vertical velocity at onset and when stable
> in the spin?
>
> What is the ratio of those two velocities compared with the ratio at
> test air densities?
>
> Does the rotation rate remain identical, whether at height (lower air
> densities) or at lower altitude (higher density)?
>
> Does all that have an effect on true angle of attack?
>
> Could such things account for high altitude spins when fully developed
> requiring more turns to recover?
>
> I wonder if the people who conduct these high altitude tests were in a
> regime not tested by the maker or the certification test pilots such as
> Chris Rollings?
>
> Chris N.
>

Martin Gregorie

January 28th 04, 03:51 PM

On 28 Jan 2004 13:42:00 GMT, Pete Zeugma
> wrote:

>>I'm in the middle group (180 with a chute) and it recovers
>>automatically after just over 2 rotations, even with
>>the controls
>>still fully crossed. The last half rotation gets really
>>slow. I was a
>>bit annoyed. Having just done Silver height and wanting
>>down in a
>>hurry, I was after 3 turns and was intending to come
>>most of the way
>>down in a 3-turn - recover - spin the other way sequence.
>>Still, I
>>repeated the experiment in the other direction and
>>with recovery by
>>merely centreing the controls and got consistent recovery
>>after just
>>over 2 rotations.
>>
>
>I quite frankly find this a quite scary post! I do
>hope you allowed suficient height above the start of
>your 1000m gain.
>
I was at 5300 ft when I decided to come down and to practise spinning
on the way, ending the last spin at about 2500 ft. That's quite low
enough for me: I won't deliberately initiate a spin under 3000 ft.

>So, what was wrong with a more conventional 'rapid
>decent', you know, the one that uses full airbrake
>circling in sink, or sideslipping with full airbrake.
>
Not as much fun. Besides I hadn't spun the Junior for a while and
thought I needed the practise.

--
martin@ : Martin Gregorie
gregorie : Harlow, UK
demon :
co : Zappa fan & glider pilot
uk :

Paul Repacholi

January 28th 04, 04:27 PM

Shawn Curry > writes:

> Anyone else spin the Puch for more than three turns? What happened
> (obviously you survived)? I've heard that some other aircraft also
> have a flatter spin mode that after several turns that is hard to
> recover from. Any knowledge of why this happens? (Now where's my
> copy of Stick and Rudder?)

The Pitts S-1S is the one for this. Get it spinnong, then let the
controls train and open the throttle. It will go into a FAST flat
spin, picking the nose up to above the horizon. If you are not carfull
and precise in the recovery you can inadvertantly flick it into a spin
in the other direction, or into an outside spin. Not ever heard that
it is hard to recover from though.

--
Paul Repacholi 1 Crescent Rd.,
+61 (08) 9257-1001 Kalamunda.
West Australia 6076
comp.os.vms,- The Older, Grumpier Slashdot
Raw, Cooked or Well-done, it's all half baked.
EPIC, The Architecture of the future, always has been, always will be.

Shawn Curry

January 28th 04, 04:39 PM

W.J. (Bill) Dean (U.K.). wrote:

> I have been told two things:
>
> 1. That the Reynolds number applicable to a glider changes with altitude,
>
> 2. That the Reynolds number affects the stall/spin behaviour and recovery.
>
> I can remember an anecdote (I am vague as to who or when) about a K21 at
> Aboyne. The glider was at about 20,000 ft., and the crew wanted to get
> down for the next pupil. They put it into a spin (which it entered without
> difficulty), and then held the spin without moving the controls. It span
> down to about 7,000 ft. and then self-recovered without any
> change in control position. Heights are QNH.
>
> I don't understand Reynolds numbers, but I know it matters; and it would
> seem not only to designers. It might well be that some gliders more easily
> spin and are harder to recover at height. I would expect this to apply at
> altitudes above about 7,000 ft. QNH, above which height they are almost
> certainly not test flown.
>
> W.J. (Bill) Dean (U.K.).
> Remove "ic" to reply.

So I'm a test pilot every time I fly from my home field at 7,500 ft MSL?

Ian Johnston

January 28th 04, 05:28 PM

On Wed, 28 Jan 2004 14:12:44 UTC, "W.J. \(Bill\) Dean \(U.K.\)."
> wrote:

: I don't understand Reynolds numbers

They are simply a way of comparing flow patterns round gliders in
different situations. If two gliders have the same Reynolds number
then the flow round them will look the same - the stream lines are the
same shape - regardless of the velocity. It's given by density *
velocity * characteristic length / viscosity. So if you go to a high
altitude (-> low density) you need a higher speed for the same flow
pattern [1]. Or if you make a 50% scale model (-> smaller length) you
also need a higher speed.

But beware - Reynolds numbers can be used to compare smaller parts of
aerodyamics as well. For example, separation of a boundary layer
typically occurs at a particular Reynolds number based on distance
from the leading edge of the wing, frontal drag from the fuselage will
depend on the Reynolds number based on the mean diameter of the
fuselage and so on. This is one of the main reasons people find
Reynolds numbers confusing ...

Ian, with his Fluid Dynamics Lecturer's hat on.

[1] Yes, I know viscosity must change with pressure and density, but I
can't offhand remember how!
--

Ian Johnston

January 28th 04, 05:29 PM

On Wed, 28 Jan 2004 15:51:28 UTC, Martin Gregorie
> wrote:

: On 28 Jan 2004 13:42:00 GMT, Pete Zeugma
: > wrote:

: >So, what was wrong with a more conventional 'rapid
: >decent', you know, the one that uses full airbrake
: >circling in sink, or sideslipping with full airbrake.
: >
: Not as much fun.

Coo. You've been and gone and said it now. "Fun", eh?

Ian

Chris Nicholas

January 28th 04, 05:38 PM

Shawn Curry wrote "So I'm a test pilot every time I fly from my home
field at 7,500 ft MSL?"

I suspect you may be, if you go in for multi-turns spins at much above
that sort of altitude. That's the point I was asking about. What do
you think?

More conventional high flying is probably within the range of Reynolds
numbers that correspond with tests, provided you don't push the envelope
at the edges. Also the difference in density and RN is not great from
7,000 to 7500 feet.

If you know all this, of course, you can educate me by telling me the
answers.

If you don't - . . . back to your own question, I think, or perhaps an
aerodynamicist could tell us both (and any others who may be
interested).

The higher you go, of course, the more difference it makes. As pointed
out in other threads, if you go high enough, you stall at the same speed
as flutter onset, which leaves no usable envelope at all.

In my earlier post about true velocities/IAS/density/AoA/rotational
speed etc., as I don't know if everyone realises their tie up with
Reynolds numbers, I deliberately didn't refer to RN. Few (certainly not
me) would know off by heart the formulae, even if they have heard of the
things, or how the other factors and RN change with height. I did,
however, presume that all post bronze or equivalent people will have
done some reading on true vs IAS, flight envelopes, etc.. and might
therefore appreciate that the geometry of a spin, effectiveness of
control surfaces, and rotational aspects, high up could be different
from lower down.

Chris N.

Shawn Curry

January 28th 04, 06:11 PM

Chris Nicholas wrote:
> Shawn Curry wrote "So I'm a test pilot every time I fly from my home
> field at 7,500 ft MSL?"
>
> I suspect you may be, if you go in for multi-turns spins at much above
> that sort of altitude. That's the point I was asking about. What do
> you think?
>
> More conventional high flying is probably within the range of Reynolds
> numbers that correspond with tests, provided you don't push the envelope
> at the edges. Also the difference in density and RN is not great from
> 7,000 to 7500 feet.
>
> If you know all this, of course, you can educate me by telling me the
> answers.
>
> If you don't - . . . back to your own question, I think, or perhaps an
> aerodynamicist could tell us both (and any others who may be
> interested).
>
> The higher you go, of course, the more difference it makes. As pointed
> out in other threads, if you go high enough, you stall at the same speed
> as flutter onset, which leaves no usable envelope at all.
>
> In my earlier post about true velocities/IAS/density/AoA/rotational
> speed etc., as I don't know if everyone realises their tie up with
> Reynolds numbers, I deliberately didn't refer to RN. Few (certainly not
> me) would know off by heart the formulae, even if they have heard of the
> things, or how the other factors and RN change with height. I did,
> however, presume that all post bronze or equivalent people will have
> done some reading on true vs IAS, flight envelopes, etc.. and might
> therefore appreciate that the geometry of a spin, effectiveness of
> control surfaces, and rotational aspects, high up could be different
> from lower down.

My education on the subject has been to the extent that TAS increases
for a given altitude vs IAS and the need to decrease Vne to avoid
flutter at altitude. The notion that RN changes significantly from sea
level to 17,999 feet (where I often fly over Colorado) and that this
changes how the aircraft performes WRT spins, or any other performance
factor is news to me. From reading about the PERLAN project in Soaring
a couple years ago, I new this was significant at 100,000 ft MSL. Maybe
someone else can give more insight into real changes up to the bottom of
Class A.

Shawn

Klein

January 28th 04, 07:26 PM

On Wed, 28 Jan 2004 01:44:10 GMT, "Arnold Pieper"
> wrote:

>You shouldn't spin more than 3 turns unless you're practicing for aerobatic
>flight.

If your purpose is International Aerobatic Club competition, you don't
need to do it for that either. According to the FAI catalog of
aerobatic figures, there is no spin allowed to be done with greater
than 2 turns. For unknown flights at the unlimited level, the max is
1.5 turns.

So I would modify what you say above to say, "you shouldn't spin more
than 2 turns unless you are practicing to be a test pilot."

Be safe,
Klein

Bob

January 30th 04, 04:49 AM

> Clearly there must have been some small difference
> (ailerons not quite central, or some such) that made
> an important difference. Whatever the cause, I couldn't
> get it to repeat, all subsequent spins were unremarkable.
>
> Rogue spins can happen, IN ANY TYPE.
>

Could it be that a spinning glider is governed by laws that are
not well described by more traditional linear equations of
aerodynamics (or JAR-22)? I am reminded of some articles related to the
loss of ships at sea to "Rogue Waves" or "Freak Waves".
http://members.shaw.ca/diesel-duck/library/articles/rogue_waves.htm

Ships designed to the standard engineering models of expected maximum
wave heights for the worst predicted conditions were being lost and
those describing witnessing these waves at sea were dismissed as
crackpots until only very recently.

Now, application of a non-linear model i.e. chaos
theory, seems to be describing these freak ocean waves more accurately,
where there very existance was doubted until jut a few years ago. Your
description of a very small variation in the initial conditions,
resulting in a very much different situation describes an outcome that
might be predicted by chaos theory better than some of these other
explanations. The non-linear SchrÖdinger equation was originally
developed in the field of quantum mechanics but is now being applied to
modeling freack ocean waves. Could we be dealing with a "quantum"
phenomenon when dealing with a spinning glider where it behaves nicely
according to our traditional model most of the time, but every once in a
while it produces a "Freak Spin" do to the complex interaction of all
the forces involved?

Robert Ehrlich

January 30th 04, 04:00 PM

Bob wrote:
>
> > Clearly there must have been some small difference
> > (ailerons not quite central, or some such) that made
> > an important difference. Whatever the cause, I couldn't
> > get it to repeat, all subsequent spins were unremarkable.
> >
> > Rogue spins can happen, IN ANY TYPE.
> >
>
> Could it be that a spinning glider is governed by laws that are
> not well described by more traditional linear equations of
> aerodynamics (or JAR-22)? I am reminded of some articles related to the
> loss of ships at sea to "Rogue Waves" or "Freak Waves".
> http://members.shaw.ca/diesel-duck/library/articles/rogue_waves.htm
>
> Ships designed to the standard engineering models of expected maximum
> wave heights for the worst predicted conditions were being lost and
> those describing witnessing these waves at sea were dismissed as
> crackpots until only very recently.
>
> Now, application of a non-linear model i.e. chaos
> theory, seems to be describing these freak ocean waves more accurately,
> where there very existance was doubted until jut a few years ago. Your
> description of a very small variation in the initial conditions,
> resulting in a very much different situation describes an outcome that
> might be predicted by chaos theory better than some of these other
> explanations. The non-linear SchrÖdinger equation was originally
> developed in the field of quantum mechanics but is now being applied to
> modeling freack ocean waves. Could we be dealing with a "quantum"
> phenomenon when dealing with a spinning glider where it behaves nicely
> according to our traditional model most of the time, but every once in a
> while it produces a "Freak Spin" do to the complex interaction of all
> the forces involved?

Maybe you don't need to invoke such complex things like chaos. Things
which are not taken in account by JAR-22 and usual procedure for weight and
balance, as somebody pointed it, are the moments of inertia around the
3 axis of the glider. Of special importance is the moment of inertia around
the pitch axis, a higher inertia around this axis favors flattening the
spin. And 2 gliders may have exactly the same weight and same CG postion
with different such moments.

Chris OCallaghan

January 30th 04, 11:05 PM

Tim,

I've experienced exactly the same scenario (spin flattening) in the
G103. It began with a penulum motion of the logitudinal axis, quickly
progessing to a point where the apex was above the horizon and the
nadir nearly vertical. Then it simply parked the nose a few degrees
below the horizon and continued to spin. It was very slow to recover.
So much so that I started pumping the stick and cycling the spoilers.

Since then I recover at first sign of these oscillations, though I
typically wait for the nose to rise before releasing the stick (a much
more graceful, less nose down recovery that way).

It is very possible that you have found a mode that makes the Puch
unreliable for spin training. At least the Grob gives some warning.
But it only spins to the left with the trim handle full forward and
the cg well aft.

(Tim Shea) wrote in message >...
> I love to spin. It's exciting. I took aerobatic training with Wayne
> Handley and was taught spin recoveries by him.
>
> I have direct experience spinning the Puchacz at Minden. This is what
> I remember from my experience. Your mileage may vary.
> With friends (usually lighter than me) in the front, I spun it while
> sitting in the back seat more than a dozen times. The CG was within
> the published range and I didn't have any trouble with simple
> recovery- stick centered and forward and rudder away from the
> direction of rotation. Worked great.
> I should mention that I used to be 50 lbs heavier than I am now, but
> still in the published range for the plane.
> During the training towards my instructors rating, I spun the Puch
> twice with my instructor. The first 2 or so rotation spin I was able
> to recover normally, no sweat. The second manuver was quite different.
> I was asked to let the spin develop a little deeper for the second.
> After 4 or so rotations, the nose seemed to float up and the rotation
> *seemed* to slow considerably. I remember thinking that this is cool!
> Kind of like floating. When it was time for the recovery I applied the
> control inputs I'd been taught (as specified above) and much to my
> surprise, nothing different happened.....for a long time. I estimate
> that we completed another 5+ rotations nose high before it broke,
> rolled over and recovered. I had the stick centered and against the
> front stop with the rudder also pegged away from the rotation. We
> recovered with several (4 or 5) thousand feet under us (we'd been
> playing at cloudbase at about 15K).
> Once on the ground, we discussed this incident in the grumpy bar for
> at least an hour. I (and he) decided to never spin the Puch again. I
> didn't. I doubt he did either.
> I had heard of this happening before. I assumed that it was from
> operation outside of the design envelope. Apparently I was wrong.
> John Shelton probably said it best: "On my own as a test pilot, I will
> certainly get killed". I felt like a dumb-ass for quite a while (more
> than usual) after that.

Caracole

January 31st 04, 04:34 AM

(Chris OCallaghan) wrote in message >...
SNIP portion
>
> It is very possible that you have found a mode that makes the Puch
> unreliable for spin training. At least the Grob gives some warning.
> But it only spins to the left with the trim handle full forward and
> the cg well aft.

Chris:

There is a very reasonable explanation for why you found the left
rotation to be true. Do you know what it is? Would you tell the
group? (All Grob pilots should know.)

But the answer will not be 'always' true for each serial number of
same models of Grobs. Spins are variable polynomial equations.

Cindy B
Caracole Soaring

>
> (Tim Shea) wrote in message >...
SNIPPED portion
> > John Shelton probably said it best: "On my own as a test pilot, I will
> > certainly get killed". I felt like a dumb-ass for quite a while (more
> > than usual) after that.

Janusz Kesik

January 31st 04, 01:17 PM

Independently of the type of certification which did the Puchacz =
undergo, it has been put through a very extensive in-flight testing =
program. The SZD used to be a state runned company which in this area =
meant that the new glider has to pass a very detailed programme of tests =
almost without counting the costs (remember that it was designed in deep =
communism era where the economy rules we know didn't exist in practice).
It has to be tested thoroughly as it was intended to be full acro =
allowed two seater which was mainly designed to be a primary trainer.

Nowadays *all* Polish clubs use the Puchacz for spin training (the =
Bocians have been prohibited to spin after they reached the age of 25), =
as there are no other trainers than few (maybe 5 all) KR-03 Puchateks =
(known also as Krosno or Peregrine). For ten years I have been flying =
gliders I have never heard of any accident like this one which started =
all the recent threads on Puchacz. There were few spin fatalities =
indeed, even one in aour club, but all of them happened on the final =
leg, or in the moment of the base/final leg turn, most of them caused by =
the licensed (but not used to fly from the instructor's cockpit) pilot =
in the backseat carrying passenger in the front seat.

Regards,

--=20
Janusz Kesik

visit www.leszno.pl - home of the www.css-leszno.it.pl