Yaw String in a Spin

At 18:31 17 January 2005, Greg Arnold wrote:
I am convinced. Keeping the rule as simple as possible:
'Do the same
thing to straighten the yaw string in a spin as you
would do at any
other time.'


Greg,

Getting close to an agreement here but the fullness
of the rudder - not just to straighten the string -
needs to be emphasised. How about:

'Full yaw corrective rudder (in the usual sense as
commanded by the yaw string)' ?

The rudder affects the yaw aspect of a spin and not
(except by secondary effect ) the rolliing/autorotating
aspect so for us to have, all these years, decided
on which sense to move the yaw control by looking at
the roll axis direction has been workable but illogical.

John Galloway

There have been many comments about using the yaw string to determine the
direction of a spin. Most of us will admit that we do not look at the yaw
string while in a spin. One honest pilot even admitted it in print.

Several U.S. pilots have seen the video of the U S Air Force flight tests of
the spin charecteristics of an ASK-21. During a fully developed spins the
yaw string could be seen moving left then right then up and even forward.
The real conclusion to this discussion should be that the yaw string is not
*always* a reliable indication of spin direction.

What is most important is "situational awarness". A pilot must learn to
know where he is and how he got there.

Duane

John Galloway wrote:
At 18:31 17 January 2005, Greg Arnold wrote:

I am convinced. Keeping the rule as simple as possible:
'Do the same
thing to straighten the yaw string in a spin as you
would do at any
other time.'



Greg,

Getting close to an agreement here but the fullness
of the rudder - not just to straighten the string -
needs to be emphasised. How about:

'Full yaw corrective rudder (in the usual sense as
commanded by the yaw string)' ?


Sounds good to me.


The rudder affects the yaw aspect of a spin and not
(except by secondary effect ) the rolliing/autorotating
aspect so for us to have, all these years, decided
on which sense to move the yaw control by looking at
the roll axis direction has been workable but illogical.

John Galloway

At 01:25 18 January 2005, Duane Eisenbeiss wrote:
Several U.S. pilots have seen the video of the U S
Air Force flight tests of
the spin charecteristics of an ASK-21. During a fully
developed spins the
yaw string could be seen moving left then right then
up and even forward.

Well they must have had the balls for it then......

Duane Eisenbeiss wrote:
There have been many comments about using the yaw string to determine the
direction of a spin. Most of us will admit that we do not look at the yaw
string while in a spin. One honest pilot even admitted it in print.

Several U.S. pilots have seen the video of the U S Air Force flight tests of
the spin charecteristics of an ASK-21. During a fully developed spins the
yaw string could be seen moving left then right then up and even forward.
The real conclusion to this discussion should be that the yaw string is not
*always* a reliable indication of spin direction.

The yaw string position is always (*) a reliable indication of the relative direction
of the air flow and the glider at the level of the cockpit. Except in case
there is such turbulence that the air flow has a completely different
direction at the cockpit level and the wings level, this implies that to
unstall the glider you want to align the airflow and the glider, and reduce
angle of attack. Hence you have to center the yaw string, whatever
considerations you may introduce about the spin direction.

(*) by definition. I would be curious to hear arguments to the opposite.


--

Michel TALON

Tony,

If the spin is unintentional, you may not have the presence of mind to
recall, at the moment of recognition, which way you were turning. The
brain is very efficient at dumping extraneous information to focus
entirely on the situation at hand. Unfortunately, this isn't always a
good thing. The whole spin training regimen is flawed, since it
presumes that you know you are entering a spin. It teaches you the
muscle memory to enter a spin, and a reflexive response once you've
entered, based almost entirely on the process of entry. As we become
more aware of the necessary steps to recognize and properly react to a
surprise spin, I think we're likely to become more interested in
improving our skill at avoiding them altogether.

Consider panic stops in an automobile as an anology. If you are on a
test track, you know exactly when you must apply the brakes on a
measured course to determine brake efficiency. A stopping distance of
100 to 140 feet from 60 mph is typical. But on the road we don't know
when we'll need to react. Response time must be added. This increases
stopping distance to over 300 feet.

In the glider we need to recognize that something is wrong, establish
what the problem is, then react properly. Intentionally entering the
spin is like taking a test with a textbook at your side, conveniently
opened to the appropriate page. But a surprise departure and
autorotation is going to require some flipping through the pages. And
getting it wrong could be devastating.

"What is most important is "situational awarness". A pilot must learn to
know where he is and how he got there."

The last part of that statemenht may not always be true. I have read
reports from test pilots who intentionally place the aircraft in
out-of-control positions in order to determine a recovery procedure. A
common response is that they ride the aircraft until they are in a position
they recognize and as soon as that happens they can recover. How they got
there was irrelevant.

Although few airplanes use yaw strings (the pilots are still behind the
curve a bit), they are normally used on helicopters. Although the pedals
are used to counteract the torque of the tail rotor, we operate them the
same way - keep the yarn centered.

Colin N12HS


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Agreed. And even better, the pilot should know where he is and how to
avoid going where he doesn't want to be. We need to be trained in how
to recognize a spin and recover, but even more, we need to be able to
discern the preamble to departure and correct it. Remember, there is an
altitude from which a spin is unrecoverable.

Should we change the way we fly at and below that altitude, or practice
that caution as the rule and be aware when we choose to fly differently?

Good thread, John. Thanks for bringing it up.

I think that the test pilots concerned knew exactly
how they got there but it may not have helped them
much. I re-call seeing a very good video of a Jaguar
that had departed and was tumbling end over end with
fuel being forced out of the jet intakes. I think the
pilot took about 20000ft to find a point where he could
break into the sequence and return to controlled flight.
As a result the action to be taken if a Jaguar departs
is seize the handle between your legs and pull hard.

At 14:31 18 January 2005, Colin Lamb wrote:
'What is most important is 'situational awarness'.
A pilot must learn to
know where he is and how he got there.'

The last part of that statemenht may not always be
true. I have read
reports from test pilots who intentionally place the
aircraft in
out-of-control positions in order to determine a recovery
procedure. A
common response is that they ride the aircraft until
they are in a position
they recognize and as soon as that happens they can
recover. How they got
there was irrelevant.

Although few airplanes use yaw strings (the pilots
are still behind the
curve a bit), they are normally used on helicopters.
Although the pedals
are used to counteract the torque of the tail rotor,
we operate them the
same way - keep the yarn centered.

Colin N12HS


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10/25/04