Puchaz Spinning thread that might be of interest in light of the recent accident.

On Tue, 03 Feb 2004 14:41:20 -0500, Tony Verhulst
wrote:


....in a stable descending turn the inside wing is always undergoing a
downward motion relative to the outer wing. This is one cause for the
inside wing to be at a higher AOA than the outer wing, and one reason
for the resulting earlier stall than the outer wing.

Understood! What I don't unerstand is how much washout plays into this
equation. I would suspect that it would reduce this efffect but how much?

Tony V.

Really good question! I don't know. Since washout is, in a sense, a
relative term -- that is washout produces a lower AOA at the wing tips
compared to the AOA at the wing roots -- my guess is that in all cases
where AOA is critical the wing tip washout delays the effects we might
expect from what we see of the nose attitude of the aircraft. But
then, this is really not saying anything new!

Hi All,

A couple of important points regarding this discussion:


(Mark James Boyd) wrote in message news:401eb7ea$1@darkstar...
A spin means both wings have too high AOA and
one wing has more AOA than the other.

If you can change the AOA of both wings so they are unstalled,
using elevator only, and the stress from the now entered spiral
doesn't make the aircraft wings twist and shatter during recovery dive,
then fine, do that.

Attempting an elevator-only recovery (similar to a straight stall
recovery) from a spin, particularly a developed spin, will only serve
to accelerate the rotation; hence, the term "Accelerated Spin."

Doing this in some airplanes will cause them to spin fast enough for
the airframe to vibrate; others may spin fast enough to cause the nose
of the airplane to pop up into an unrecoverable flat spin mode, even
though forward elevator has been applied. If you're strong enough, you
can apply full forward elevator; yet the airlane continues to spin
really, really fast!

Accelerating the rotation aside, applying elevator PRIOR TO the
opposite rudder in airplanes with conventional tail configurations
also serves to blanket additional surface area of the rudder that may
be necessary to upset the dynamics of the spin.

Once the line from "stall" has been crossed to "spin," the order of
recovery inputs becomes critical. The sequence of Rudder--full
opposite FOLLOWED BY Elevator--forward (upright spins) is essential to
maximize the probability of spin recovery in light, general aviation
airplanes (single engine). Reversing that order can seriously alter
spin behavior for the worse and can transform an otherwise recoverable
spin into an unrecoverable spin.


snip

I suspect this is the reasoning behind
the PARE mnemonic, where rudder is used before elevator.

See above.


Power off (for them motorglider thingies)
Aileron Neutral
Rudder Opposite
Elevator forward enough to break stall

Of course, even this mnemonic doesn't work all the
time (sometimes extra power to make the tail surfaces
more effective is better, etc.).

The PARE acronym points to the same tried-and-true (optimized) spin
recovery actions discovered through spin research first in the UK in
1918, later confirmed by NACA in the 1930's, then re-affirmed by NASA
in the 1970-80's. The more things change, the more they stay the
same... And the volumes of reports on spin behavior in light,
single-engine airplanes repeatedly point to these actions.

As for the comment about power -- this is a persistent aviation myth
as it relates to light, single-engine airplanes (which make up more
than 75% of the general aviation fleet, with gliders making up 1%).
The correlation between power and the rate of spin rotation is simple:
less power = slower spinning; more power = spinning faster.

In fact, a small addition of power during a normal spin can increase
the rate of rotation by more than a factor of 2! In some airplanes,
adding power not only speeds up the rotation, but also flattens the
spin. And with all other things being equal, flatter spin attitudes
are more difficult to recover from (take longer, etc.) than steeper
spin attitudes.

To eliminate the aggravating effects associated with power, reduce it
to idle right away as part of the spin recovery process.

Hope this clarifies things a bit,

Rich
http://www.richstowell.com

Robert,

If you look at the actual Schleicher Tech Note to the K21 No. 23 (Jan. '91),
you will find that it gives information as to why the change in the Flight
Manual was made (London Sailplanes should have a copy).

I do not have a copy myself, but from memory the alteration was made after
test flying in the USA by the military. As I recall it was used at the US
Navy Test Pilots School at Pautuxtent River (their equivalent to Boscombe
Down), and they flew it ballasted to an extended aft C. of G.

How this ties in with Cindy's information about a USAF accident and
Evaluation I don't know, perhaps my memory is at fault.

Bill.

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


"Robert John" wrote in
message ...

Cindy,

Thanks for that. I fly K21s very often (though I've never been able to
spin one). I'll look at the latest POH.

Any idea why the pause is recommended? Can't be the 'shadowing' effect.

Incidentally, the Duo Discus flight manual has the usual order of actions
(Ailerons neutral, Opposite rudder, Stick forward until rotation ceases
and airflow restored, Centralise rudder and pull out) but no mention of a
pause. I haven't experimented with it.

Rob


Then I hope you will read the revision to the AS-K 21 POH, which
updated/changed the spin recovery protocol to include the 'pause' based
on flight testing, after a spinning fatality in the K-21.

No pause, slower recovery.
Pause, more prompt recovery.
K-21 is a T-tail.

Beware broad judgments.
Please know your POH and its recommended procedures.
If you teach/deliberately enter spins, have a predetermined exit
altitude for non-responsive behaviour, or don't bother wearing the
chutes.

If there was on line access for the USAF Spin Eval report for the K-21,
I would make it available... but I have no electronic source.

Cindy B
www.caracolesoaring.com

The paper that Rich wrote on spin training that is posted on his web site is
a must read!

Thank you very much Rich.

--
Gary Boggs
3650 Airport Dr.
Hood River, Oregon, USA
97031-9613
"Rich Stowell" wrote in message
m...
Hi All,

A couple of important points regarding this discussion:


(Mark James Boyd) wrote in message
news:401eb7ea$1@darkstar...
A spin means both wings have too high AOA and
one wing has more AOA than the other.

If you can change the AOA of both wings so they are unstalled,
using elevator only, and the stress from the now entered spiral
doesn't make the aircraft wings twist and shatter during recovery dive,
then fine, do that.

Attempting an elevator-only recovery (similar to a straight stall
recovery) from a spin, particularly a developed spin, will only serve
to accelerate the rotation; hence, the term "Accelerated Spin."

Doing this in some airplanes will cause them to spin fast enough for
the airframe to vibrate; others may spin fast enough to cause the nose
of the airplane to pop up into an unrecoverable flat spin mode, even
though forward elevator has been applied. If you're strong enough, you
can apply full forward elevator; yet the airlane continues to spin
really, really fast!

Accelerating the rotation aside, applying elevator PRIOR TO the
opposite rudder in airplanes with conventional tail configurations
also serves to blanket additional surface area of the rudder that may
be necessary to upset the dynamics of the spin.

Once the line from "stall" has been crossed to "spin," the order of
recovery inputs becomes critical. The sequence of Rudder--full
opposite FOLLOWED BY Elevator--forward (upright spins) is essential to
maximize the probability of spin recovery in light, general aviation
airplanes (single engine). Reversing that order can seriously alter
spin behavior for the worse and can transform an otherwise recoverable
spin into an unrecoverable spin.


snip

I suspect this is the reasoning behind
the PARE mnemonic, where rudder is used before elevator.

See above.


Power off (for them motorglider thingies)
Aileron Neutral
Rudder Opposite
Elevator forward enough to break stall

Of course, even this mnemonic doesn't work all the
time (sometimes extra power to make the tail surfaces
more effective is better, etc.).

The PARE acronym points to the same tried-and-true (optimized) spin
recovery actions discovered through spin research first in the UK in
1918, later confirmed by NACA in the 1930's, then re-affirmed by NASA
in the 1970-80's. The more things change, the more they stay the
same... And the volumes of reports on spin behavior in light,
single-engine airplanes repeatedly point to these actions.

As for the comment about power -- this is a persistent aviation myth
as it relates to light, single-engine airplanes (which make up more
than 75% of the general aviation fleet, with gliders making up 1%).
The correlation between power and the rate of spin rotation is simple:
less power = slower spinning; more power = spinning faster.

In fact, a small addition of power during a normal spin can increase
the rate of rotation by more than a factor of 2! In some airplanes,
adding power not only speeds up the rotation, but also flattens the
spin. And with all other things being equal, flatter spin attitudes
are more difficult to recover from (take longer, etc.) than steeper
spin attitudes.

To eliminate the aggravating effects associated with power, reduce it
to idle right away as part of the spin recovery process.

Hope this clarifies things a bit,

Rich
http://www.richstowell.com

....in a stable descending turn the inside wing is always undergoing a
downward motion relative to the outer wing. This is one cause for the
inside wing to be at a higher AOA than the outer wing, and one reason
for the resulting earlier stall than the outer wing.

Understood! What I don't unerstand is how much washout plays into this
equation. I would suspect that it would reduce this efffect but how much?

Really good question! I don't know. Since washout is, in a sense, a
relative term -- that is washout produces a lower AOA at the wing tips
compared to the AOA at the wing roots

After thinking about this for a while, I suspect that it (washout)
doesn't matter. After all, both wings tips have an equal amount of
washout and so the net effect cancels out. The lower wing tip will still
have a higher angle of attack than the upper and will still stall first.
In this case, the effect of washout is a (wait for it :-) ) wash.

Tony V.

On Wed, 04 Feb 2004 11:14:33 -0500, Tony Verhulst
wrote:


....in a stable descending turn the inside wing is always undergoing a
downward motion relative to the outer wing. This is one cause for the
inside wing to be at a higher AOA than the outer wing, and one reason
for the resulting earlier stall than the outer wing.

Understood! What I don't unerstand is how much washout plays into this
equation. I would suspect that it would reduce this efffect but how much?

Really good question! I don't know. Since washout is, in a sense, a
relative term -- that is washout produces a lower AOA at the wing tips
compared to the AOA at the wing roots

After thinking about this for a while, I suspect that it (washout)
doesn't matter. After all, both wings tips have an equal amount of
washout and so the net effect cancels out. The lower wing tip will still
have a higher angle of attack than the upper and will still stall first.
In this case, the effect of washout is a (wait for it :-) ) wash.

Tony V.

Makes sense to me! Thanks.

Jim

Jim wrote:
...
In a descending turn, which is what gliders do in turns, it is not the
case that both wings have the same vertical component of velocity. In
a stable descending turn the inside wing is always undergoing a
downward motion relative to the outer wing. This is one cause for the
inside wing to be at a higher AOA than the outer wing, and one reason
for the resulting earlier stall than the outer wing. In an ascending
turn, power airplanes I guess, it is the outer wing that is always
undergoing a downward moovement relative to the inner wing.

I found this difficult to visualize at first, but if you try "flying"
a stable descending "turn" with your hand you will experience it
clearly.


Can't understand that. If both wingtips have a different vertical component
of velocity, the vertical distance between them should change,
increasing the bank angle if the inner wing sinks faster than the outer
one. This difference must anyway stop at 90 degrees bank. But as long
as the bank angle remains constant, both wings should have the same
vertical component of velocity.

Robert Ehrlich wrote:
Jim wrote:

...
In a descending turn, which is what gliders do in turns, it is not the
case that both wings have the same vertical component of velocity. In
a stable descending turn the inside wing is always undergoing a
downward motion relative to the outer wing. This is one cause for the
inside wing to be at a higher AOA than the outer wing, and one reason
for the resulting earlier stall than the outer wing. In an ascending
turn, power airplanes I guess, it is the outer wing that is always
undergoing a downward moovement relative to the inner wing.

I found this difficult to visualize at first, but if you try "flying"
a stable descending "turn" with your hand you will experience it
clearly.



Can't understand that. If both wingtips have a different vertical component
of velocity, the vertical distance between them should change,
increasing the bank angle if the inner wing sinks faster than the outer
one. This difference must anyway stop at 90 degrees bank. But as long
as the bank angle remains constant, both wings should have the same
vertical component of velocity.
Relative to what? - is the point.

You are correct that their vertical component of velocity must be the
same because of geometry, if the bank angle remains constant. However,
because the inner wing is describing a smaller diameter spiral the
relative wind will present at a higher angle of attack on the inner wing
tip - relative to the outer wingtip. Velocity relative to the ground is
not entirely sufficient to understand what is happening in three dimensions.

In the same time the inner tip travels a smaller distance, but descends
the same vertical distance, hence the greater angle of descent, not
rate. People seem to continuously confuse rates and angles? Airflow
behavior is very dependent on angles and chord wise component of airflow
velocity...

On Wed, 04 Feb 2004 16:06:08 -0500, Todd Pattist
wrote:

Bruce Greeff wrote:

You are correct that their vertical component of velocity must be the
same because of geometry, if the bank angle remains constant. However,
because the inner wing is describing a smaller diameter spiral the
relative wind will present at a higher angle of attack on the inner wing
tip - relative to the outer wingtip.

This is quite true, but it's the difference in the
horizontal velocity that causes the difference in the angle
of attack, and IIRC, that's what Robert said in his earlier
post in this thread when he wrote:

"Some difference in AOA between both wings is already
provided by the simple fact that the glider is sinking, i.e.
both wings have the same vertical component of velocity but
different horizontal ones. "

In the same time the inner tip travels a smaller distance, but descends
the same vertical distance, hence the greater angle of descent, not
rate.

True, but Jim was disagreeing with Robert when he
(incorrectly) wrote:

"In a descending turn, which is what gliders do in turns, it
is not the case that both wings have the same vertical
component of velocity."

People seem to continuously confuse rates and angles?

Too true :-)

Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

Thank you for pointing this out! I guess my fingers on the keyboard
out ran my brains. I should not have gone farther than just the
observation that the inside wing in a stable descending turn is
going down while the outside wing is going up ( and the opposite
situation in an ascending turn). I guess I really don't understand
the notion of differing horizontal vs vertical "components".
In other words, the aircraft is actively rolling about its
longitudinal axis during the turns. From this I incorrectly deduced
that one wing was moving downward more than was the other wing.

I also wish I could remember where I first read this description.
It was in a book about stalling and spinning by the fellow who
I believe flew with Tony DeVere and originally set up the
emergency maneuver training at Santa Paula. Oh well, this
is hardly the only memory that has vaporized from my ageing
brain!

On Wed, 04 Feb 2004 14:07:52 -0800, Jim wrote:

On Wed, 04 Feb 2004 16:06:08 -0500, Todd Pattist
wrote:

Bruce Greeff wrote:

You are correct that their vertical component of velocity must be the
same because of geometry, if the bank angle remains constant. However,
because the inner wing is describing a smaller diameter spiral the
relative wind will present at a higher angle of attack on the inner wing
tip - relative to the outer wingtip.

This is quite true, but it's the difference in the
horizontal velocity that causes the difference in the angle
of attack, and IIRC, that's what Robert said in his earlier
post in this thread when he wrote:

"Some difference in AOA between both wings is already
provided by the simple fact that the glider is sinking, i.e.
both wings have the same vertical component of velocity but
different horizontal ones. "

In the same time the inner tip travels a smaller distance, but descends
the same vertical distance, hence the greater angle of descent, not
rate.

True, but Jim was disagreeing with Robert when he
(incorrectly) wrote:

"In a descending turn, which is what gliders do in turns, it
is not the case that both wings have the same vertical
component of velocity."

People seem to continuously confuse rates and angles?

Too true :-)

Todd Pattist - "WH" Ventus C
(Remove DONTSPAMME from address to email reply.)

Thank you for pointing this out! I guess my fingers on the keyboard
out ran my brains. I should not have gone farther than just the
observation that the inside wing in a stable descending turn is
going down while the outside wing is going up ( and the opposite
situation in an ascending turn). I guess I really don't understand
the notion of differing horizontal vs vertical "components".
In other words, the aircraft is actively rolling about its
longitudinal axis during the turns. From this I incorrectly deduced
that one wing was moving downward more than was the other wing.

I also wish I could remember where I first read this description.
It was in a book about stalling and spinning by the fellow who
I believe flew with Tony DeVere and originally set up the
emergency maneuver training at Santa Paula. Oh well, this
is hardly the only memory that has vaporized from my ageing
brain!


Now I remember! The book is "Stalling, spinning and safety"
by Sammy Mason. It's a good read.