Spinning the SZD 50-3

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

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

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/l...ogue_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?

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/l...ogue_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.

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 om...
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 OCallaghan) wrote in message . com...
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 om...
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.

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

Depending on the cockpit load, the spin is not possible, or it stops =
rotating itself. Maybe this third, slow turn was because it wanted to =
get out, and You were forcing it to stay in the spin?

Regards,


--=20
Janusz Kesik

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

Heh, in Poland, there is a short story of two bored pilots who wanted to =
have some fun in Puchacz when returnig from a wave flight. They spun the =
Puchacz from the 7000m, and kept it spinning till 2000m. When they =
started the recovery, there was.... nothing, the Puchacz still spinned!
Finally, they stopped after the 6'th or 7'th turn since the recovery =
procedure has begun.

Remember about inertia guys!!!


--=20
Janusz Kesik

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

Also it seems strange for me, especially considering that Junior has the =
most effective airbrake I have ever seen.
If one adds a deep sideslip to this, it's sink rate can be compared with =
a stone only.

Regards,


--=20
Janusz Kesik

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

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.