Yaw String in a Spin

Thanks Z. Couldn't have put it better myself - in
fact I didn't!



It is interesting that I have had various feed back
from pilots who have applied the wrong rudder or found
it difficult to instantly decide which way they were
rotating in a sudden unexpected spin or knew about
someone else who had reported this experience.

To refocus, and taking into consideration the fact
that my use the word 'opposite' has created confusion
that I really didn't expect, my new improved (?) wording
is:

1)The string acts laterally in the same sense in a
spin as at all other times and the rudder correction
for a given direction of yaw string deviation is exactly
the same direction as in level flight.

2)Deciding how to correct yaw by use of a yaw string
is a task that glider pilots do almost continually
during flight but deciding which way the glider is
rotating in a spin is a very occasional task - and
one that is survival critical

3)Use the yaw string as the primary reference to decide
the correct rudder to apply in the event of an unexpected
spin

4)All sailplanes should have yaw strings.

John Galloway

At 06:00 17 January 2005, Z Goudie wrote:
At 04:00 17 January 2005, Greg Arnold wrote:
Are you sure? Imagine a flat spin. If the loose end
is pointing to the
left, doesn't that mean yoiu are spinning to the right?
So don't you
want left rudder?

You better sort that out in your head quick!

Think. Start straight level and slow. Feed in full
left rudder. The glider rotates (yaws) left but continues
initially on the track it was going. The airflow is
now coming more from the right and blows the yaw string
out to the left (the slip ball, which is free to move
in its tube, goes out to the right sharply because
the airflow is decelerating the whole aircraft apart
from it).

The left wing reaches the stall, the wing drops and
the angle of attack increases even further. The increase
in drag on the wing causes the glider to continue rotating
to the left.
The glider is now sinking rapidly with the left wing
more badly stalled than the right due to the rotation.
This means that the glider continues to yaw and roll
left.

Looking from above the glider is now following a circular
anti-clockwise path with the nose pointing into the
circle and the tail out. The airflow is still coming
more from the right (over the whole aircraft and not
just forward of the centre of gravity) and the yaw
string is being blown out to the left whether the nose
pitches down or up into a flat attitude or not. The
slip ball (and you) are trying to continue in a straight
line and feel a force throwing you to the right. This
is a left hand spin!

The anti-spin action at this point is to reduce the
yaw to the left with full right rudder; pull the string,
push the ball or step on the head of the snake (sounds
like a position in the Kama Sutra) as your personal
mantra dictates and then move the stick forward from
its central position (where I hope you placed it as
the spin developed) until the wing unstalls. Now centralise
the rudder before loading the wing up on the pull out
or you'll be off the other way.

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."


John Galloway wrote:
Thanks Z. Couldn't have put it better myself - in
fact I didn't!



It is interesting that I have had various feed back
from pilots who have applied the wrong rudder or found
it difficult to instantly decide which way they were
rotating in a sudden unexpected spin or knew about
someone else who had reported this experience.

To refocus, and taking into consideration the fact
that my use the word 'opposite' has created confusion
that I really didn't expect, my new improved (?) wording
is:

1)The string acts laterally in the same sense in a
spin as at all other times and the rudder correction
for a given direction of yaw string deviation is exactly
the same direction as in level flight.

2)Deciding how to correct yaw by use of a yaw string
is a task that glider pilots do almost continually
during flight but deciding which way the glider is
rotating in a spin is a very occasional task - and
one that is survival critical

3)Use the yaw string as the primary reference to decide
the correct rudder to apply in the event of an unexpected
spin

4)All sailplanes should have yaw strings.

John Galloway

At 06:00 17 January 2005, Z Goudie wrote:

At 04:00 17 January 2005, Greg Arnold wrote:

Are you sure? Imagine a flat spin. If the loose end
is pointing to the
left, doesn't that mean yoiu are spinning to the right?
So don't you
want left rudder?

You better sort that out in your head quick!

Think. Start straight level and slow. Feed in full
left rudder. The glider rotates (yaws) left but continues
initially on the track it was going. The airflow is
now coming more from the right and blows the yaw string
out to the left (the slip ball, which is free to move
in its tube, goes out to the right sharply because
the airflow is decelerating the whole aircraft apart

from it).

The left wing reaches the stall, the wing drops and
the angle of attack increases even further. The increase
in drag on the wing causes the glider to continue rotating
to the left.
The glider is now sinking rapidly with the left wing
more badly stalled than the right due to the rotation.
This means that the glider continues to yaw and roll
left.

Looking from above the glider is now following a circular
anti-clockwise path with the nose pointing into the
circle and the tail out. The airflow is still coming
more from the right (over the whole aircraft and not
just forward of the centre of gravity) and the yaw
string is being blown out to the left whether the nose
pitches down or up into a flat attitude or not. The
slip ball (and you) are trying to continue in a straight
line and feel a force throwing you to the right. This
is a left hand spin!

The anti-spin action at this point is to reduce the
yaw to the left with full right rudder; pull the string,
push the ball or step on the head of the snake (sounds
like a position in the Kama Sutra) as your personal
mantra dictates and then move the stick forward from
its central position (where I hope you placed it as
the spin developed) until the wing unstalls. Now centralise
the rudder before loading the wing up on the pull out
or you'll be off the other way.

Possibly looking through the string and just observing the direction
the world is moving and inputting rudder in the direction counter to
the direction of motion might have merit?

No. Too low tech.

--
Bert Willing

ASW20 "TW"


"Jackal" a écrit dans le message de news:
...
Possibly looking through the string and just observing the direction
the world is moving and inputting rudder in the direction counter to
the direction of motion might have merit?

At 11:30 21 January 2005, Jackal wrote:
Possibly looking through the string and just observing
the direction
the world is moving and inputting rudder in the direction
counter to
the direction of motion might have merit?



Yes - I think there is no choice.

I started the thread because that is apparently not
always as easy to do in an unexpected spin as in a
practice or training spin - and was prompted by the
posting from a professional test pilot that even he
had once used the wrong rudder in a spin recovery in
a jet.

The suggestion about considering using the string was
based on Helmut Reichmann's comment in Cross Country
Soaring (P147 Revised Edition) that 'the string always
points to the inside in a spin'.

Two interesting things have come out of the feedback
within the thread and directly:

1) Confirmation that even experienced pilots and instructors
can get disorientated about rotational direction an
unexpected spin.

2) Reichmann's assertion has been undermined and consequently
the behaviour of the string can't be said to be reliable
enough to advocate as the primary reference for which
rudder to use in a fully developed spin.

John Galloway