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

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

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

"Gary Boggs" wrote in message ...
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
Hood River, Oregon, USA


You're welcome, Gary! BTW, I'll be giving a seminar on Stalls & Spins
at the NW Aviation Conference in Puyallup, WA on Feb. 21 (4:00 PM) if
anyone's interested...

Rich
http://www.richstowell.com

At 19:00 31 January 2004, Arnold Pieper wrote:
I see Dave.

I'm courious now :
When you're teaching Stalls and a wing is low just
before the stall, you
don't pick it up until AFTER the stall ?

This is not the way it's done in both countries where
I fly.


Arnold

Effectively Yes, and it works.

Rather than me try to explain my thoughts and experience
the manual explains the logic quite neatly (18.6)

'Whilst use of the rudder to prevent yaw in the direction
of the down-going wing is a counsel of perfection,
it must be realised that the pilot caused the inadvertent
stall in the first place by inappropriate use of the
controls. He is unlikely to start making skilful or
precise movements now. Do not attempt to use the secondary
effect of the rudder to restore the wings to the level
position. This would introduce yaw which could result
in the glider spinning. The priority must be to unstall
the glider by moving the stick forward.'

There are further spinning exercises including a demonstration
of the changing effect of the rudder at the stall to
emphases this point.

Dave

In article , Dave Martin
writes

snip

it must be realised that the pilot caused the inadvertent
stall in the first place by inappropriate use of the
controls. He is unlikely to start making skilful or
precise movements now. Do not attempt to use the secondary
effect of the rudder to restore the wings to the level
position. This would introduce yaw which could result
in the glider spinning. The priority must be to unstall
the glider by moving the stick forward.'

I agree 100% with the above and some years ago had a short article
published in the BGA magazine Sailplane and Gliding on this precise
subject. I repeat this article at the end as it is still relevant.
Timeless, even.

Question: What is the use of lots of rudder near the stall likely to
induce?

No prize for the answer!

The answer is the same whether the use of rudder was well-intentioned or
not.

In the 1950s I was taught to "pick a wing up near the stall by using
rudder", but this often led to a low speed situation being converted
into the first stages of a spin, and sometimes a fully-developed spin
with a tragic conclusion if near the ground.

By the time I became an instructor in the UK Royal Air Force (1965),
instruction had changed to "in an inadvertent slow speed situation,
first reduce angle of attack using forward stick. When at a normal
flying speed, level the wings by gentle use of aileron". Incidentally,
at this time in the RAF, spinning was no covered pre-solo, only stalling
and recovery from inadvertent slow-speed situations. Fully-developed
spinning was covered at about the 30-hour stage as part of training for
aerobatics. Food for thought in the gliding world? There have been
quite a few glider spinning accidents during spinning training. I used
to be a Canberra (US B-57) flying instructor and we killed more people
in training for engine failures than were killed by engine failures
themselves. There is training and there is training, and when the
training itself becomes lethal we need to analyse carefully what we are
doing it for.

Anyway, here is the old S&G article, a bit long but it has many
significant points:

-------------------------------------------------------------------------
-------------

From Sailplane and Gliding, October 1989 edition, page 221

SPINNING TRAINING - A CAUTIONARY NOTE

My basic point is very simple - The automatic application of large
amounts of opposite rudder in slow-speed "wing-drop" situations will,
for most gliders and powered aircraft, make the situation worse. This is
particularly important near the ground, where rudder applied
unnecessarily at slow speed can actually cause a crash.

I know of several accidents where this occurred, in each case the
machine being written off and the pilots badly injured.

1. In one case a stall was being deliberately practised and a
mild wing-drop occurred. Full rudder was applied and the machine quickly
entered a spin from which the pilot was unable to recover before the
ground intervened.

2. A similar case was where an inadvertent wing-drop at low
speed was turned into a full spin by coarse use of rudder, the machine
also crashing into the ground.

3. Another case that I witnessed happened at the launch point
and was even more ironic; a wing-drop occurred at about 200ft on the
approach which the pilot diagnosed as due to a stall but almost
certainly was simply due to turbulence. He had been taught to apply
opposite rudder in this situation, he duly did and the glider crashed
into the ground with its wings almost vertical.

The instinctive reaction to detecting an inadvertent low speed situation
should be to move the stick rapidly forward by an amount proportional to
the severity of the situation and then away from the dropped wing (if
there is a wing-drop). But please be very careful with the rudder until
a fully developed spin is diagnosed. It is a powerful control at the
stall and must not be abused.

I well recall gliders with horrendous stalling characteristics where a
stall was virtually an incipient spin. They would not nowadays be
granted a C of A by the National Regulatory Bodies (CAA/BGA in the UK,
FAA in the USA, LBA in Germany). I vividly remember stalling the Kite 2
(most were spun in) and Geoffrey Stephenson's Gull 1 (also eventually
spun in). A large wing-drop was usually implicit even in an attempted
"straight stall. Fortunately, stalling characteristics have improved
considerably since those days and automatic application of large amounts
of rudder to correct a wing-drop is no longer necessary, if indeed it
ever was.

Having also flown over 50 types of powered aircraft I can assure you
that, at the wing-drop stage, using forward stick for recovery followed
by normal control actions to level the wings, works equally well in a
Harvard (the 1930s piston version, not the Harvard 2 turboprop of
today), Hawk, Hunter, Canberra, Nimrod, Provost/Jet Provost, Vampire and
indeed all aircraft and gliders I have stalled except perhaps the said
Kite 2 and Gull 1 which, unfortunately, are not now available for
experiment.

As an example, the piston Harvard usually has a nasty wing-drop at the
stall, and a "classic" full spin, losing about 60Oft per turn. Many have
been "spun in", with fatal results at low level. In this context I quote
the current Boscombe Down Pilots' Notes (Boscombe Down is the UK
equivalent of Edwards and Eglin AFB in the USA, and used the Harvard for
slow speed photo-chase): "At the stall, the nose and either wing may
drop. With flaps up, the wing drops more rapidly than with flaps down.
If the stick is held back, the aircraft will spin. To recover from the
stall with minimum loss of height, apply power and simultaneously move
the control column sufficiently far forward to unstall the aircraft.
Ailerons then become effective and wing-drop should be corrected with
lateral stick. Ease out of the dive into a gentle climb ..."

Note the absence of any instruction to use rudder (that comes later in
the recovery drill for a fully developed spin), and the emphasis on
smooth handling with no automatic use of coarse or full control
deflections - "Sufficiently far forward", "Ease out", "Gentle climb".

In gliding, what we need is instruction which clearly distinguishes
between a fully developed spin, which should now be very rare except for
deliberate training at a safe height, and the earlier stages such as
wing-drop at a stall which are better recovered by quickly reducing the
angle of attack and then levelling the wings in the normal way, and not
by inducing autorotation the other way by unfeeling boots of rudder.

Stalling and spinning characteristics also vary with the C of G
position. At forward C of G all aircraft tend to be very stable in pitch
and some may not spin at all, just exhibiting a sideslipping spiral dive
in response to full pro-spin control. But as C of G moves aft, pitch
stability reduces and the tendency for a wing-drop at the stall, and to
enter a full spin, increases.

Light pilots, beware!

The Janus is an example, which I had to test for the UK Military (the
Air Cadets, anyway). It will only exhibit a true spin at fully aft C of
G, at all other C of Gs it enters a rather horrendous sideslip in
response to boots of rudder. It has very low directional stability and
is unstable in sideslip below about 55kt. Perhaps this has something to
do with some other Janus accidents (see S&G 1998 page 97). It is also
extremely twitchy in pitch control at fully aft C of G, which shows up
particularly on an aerotow in turbulent conditions and indeed sets the
aft C of G limit. These considerations should be borne in mind when, for
instance, stalling or spinning two-seaters when solo, where C of G will
generally be further aft than when dual.

Instructors have their uses, even if only as ballast!

Wind Gradient.

Stalling and spinning training is carried out at a safe height, whereas
the "worst case" inadvertent slow speed situation is probably the final
turn in a field landing in conditions of turbulence and wind gradient.
Airfields are generally flat (there are some notable exceptions) whereas
the topography around fields may not be, and wind gradient will
therefore be more severe. A slow speed situation could easily get
out-of-control (due to the lower wing being in a lower wind speed, and a
glider with benign characteristics when practising stalls at height
might bite you if you are less than careful near the ground.

There are two rather pessimistic "old adages" which may, on field
landings, be relevant -

1. "If you are going to crash, crash with your wings level".
Particularly relevant in the case of asymmetric thrust on aircraft such
as Camberra/B57, Boeing 707 etc. But also applicable to a glider on an
awkward approach to a field.

and

2. "Always hit the far hedge rather than the near hedge".

Think about it!

I am sorry this article is so long, but my overall conclusion is that we
want more practice in slow-speed situations which we may meet
inadvertently, such as a slow, badly flown turn with thermalling or
landing flap, rather than over-concentration on the deep stall or the
full spin.

And we should practise a recovery technique which is both
straightforward and that will not get us into more trouble.

Lots of us do not have either the regular flying practice of the
professional pilot, or the intuitive handling ability of a Chuck Yeager,
Neil Armstrong, John Farley or Brian Trubshaw (the latter two are
distinguished Brit test pilots, on Harrier and Concorde respectively,
Brian departing to the great test flying "cloud in the sky" a couple of
years ago).

Glider stalling characteristics will, of course, vary with type, flap
position, C of G an even wing condition (bugs, rain etc). Practise
recoveries regularly at a safe height to optimise your technique. But
generally, short of a fully developed spin, the best technique will be
to rapidly move the stick centrally forward to unstall the wings (just
enough to do this, not mechanically fully forward), and then recover
from the ensuing attitude by normal use of controls. Beware the
unnecessary use of coarse control, particularly rudder and particularly
near the ground!

IAN STRACHAN
Lasham Gliding Society

Ian is a qualified Service test pilot and an A1 category RAF flying
instructor as well as being a glider and motor glider instructor. It is
understood that Bill Scull, BGA director of operations, and Bernie
Morris, chairman of the BGA Instructors' Committee, are in agreement
with the main points of this letter.

------- end of quote from S&G ---------

--
Ian Strachan
Lasham, UK

Bentworth Hall West
Tel: +44 1420 564 195 Bentworth, Alton
Fax: +44 1420 563 140 Hampshire GU34 5LA, ENGLAND

"Ian Strachan" wrote in message

There are two rather pessimistic "old adages" which may, on field
landings, be relevant -

1. "If you are going to crash, crash with your wings level".

OK

2. "Always hit the far hedge rather than the near hedge". Think about
it!

This one has me stumped. Does it refer to a circumstance when one is too
high on final and an overshoot is unavoidable, in which case you want to
burn up the most energy before the inevitable?

If someone is low and they try to stretch the glide, it seems like this is
an invitation to stall prematurely and really do some damage and/or cause
injury.

What's the context for this advice?

Pete Brown

Bang on! If it isn't stalled it can't spin!

Allan

Glider stalling characteristics will, of course, vary with type, flap
position, C of G an even wing condition (bugs, rain etc). Practise
recoveries regularly at a safe height to optimise your technique. But
generally, short of a fully developed spin, the best technique will be
to rapidly move the stick centrally forward to unstall the wings (just
enough to do this, not mechanically fully forward), and then recover
from the ensuing attitude by normal use of controls. Beware the
unnecessary use of coarse control, particularly rudder and particularly
near the ground!

IAN STRACHAN
Lasham Gliding Society

Beware the
unnecessary use of coarse control, particularly rudder and particularly
near the ground!

IAN STRACHAN
Lasham Gliding Society

I did a few calculations of an imaginary glider with a stall speed
of 32 knots, a min sink speed of 43 knots, and
a wingspan of 87 feet.

In a 50 degree bank at 54 knots (good thermalling speed if you
believe)

www.stolaf.edu/people/hansonr/soaring/spd2fly/

the fuse and ASI says you are at radius 180 ft circling every
7 seconds. The inner wingtip is 3/4 of that distance, and
3/4 of that airspeed, and should be stalled. The outer
wingtip is 5/4 of that distance from center, and 5/4
of that airspeed, and producing excellent lift.

Now throw in a down aileron near the wingtip, increasing the
AOA of the inner wing. Now have the student
not compensating for adverse yaw, and the instructor yelling
"get that string centered right now!"

Now have the student jam in lots of rudder, and watch the
difference in airspeed and AOA during this coarse
movement.

This is probably why coarse rudder is often used to
coarsely demonstrate a spin entry...

This is also why I fly a glider with a short wingspan and
a weak rudder... (getting a worse L/D design was faster
than getting better skill)

Mark James Boyd wrote:
...
I did a few calculations of an imaginary glider with a stall speed
of 32 knots, a min sink speed of and
a wingspan of 87 feet.

In a 50 degree bank at 54 knots (good thermalling speed if you
believe)

www.stolaf.edu/people/hansonr/soaring/spd2fly/

the fuse and ASI says you are at radius 180 ft circling every
7 seconds. The inner wingtip is 3/4 of that distance, and
3/4 of that airspeed, and should be stalled. The outer
wingtip is 5/4 of that distance from center, and 5/4
of that airspeed, and producing excellent lift.
...

I don't completely agree with your computations. I agree with
the 54 knots, i.e. 43 knots multiplied by the square root of
the load factor at 50 degree bank. However the radius I find
for this speed and bank is 66 m (sorry, I prefer to do my
calculations in metric, because I know the formulas for metric
data), i.e 216.5 ft. A wingspan of 87 feet translate into 26.5 m,
the inner wingtip is inside the circle by an amount which is
the half wingspan multiplied by the cosine of 50 degree, this is
8.5 m or 27.8 ft. The ratio of the two radii is .87 rather than
..75 and the speed at the inner wing tip is 37.4 kt.

Anyway even with your values tis doesn't implies the inner wing tip
is stalled, because stall depends on AOA rather than speed. Of course
you need an increase of AOA in order to compensate for the
lower speed in order to keep an equal lift on both wings. 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. The complement is provided
by aileron deflection, which change not only the AOA but the whole
airfoil shape, so that the action is an increased Cl due to both changes
in AOA and shape. The stall case would be if the needed Cl would be higher
than the maximum achievable Cl, but this can't be decided just from the
value of the speed at wing tip.

Dave Martin wrote:

it must be realised that the pilot caused the inadvertent
stall in the first place by inappropriate use of the
controls. He is unlikely to start making skilful or
precise movements now.

LOL. Back to the "don't stall either wing in the first place"
technique.