Yaw String in a Spin

At 12:00 16 January 2005, John Galloway wrote:
In another thread Ian Strachan wrote:

'The standard recovery procedure once a full spin has
developed that
works for most aircraft is,

1. Full rudder opposite to the spin direction (make
sure it really is
opposite to the rotation, I for one have applied the
wrong rudder in a
spinning jet when I was caught by a surprise departure).'
=======================================

I have long surmised that application of the wrong
rudder in a panic situation might be a cause of failure
to recover from a spin. If it can happen to a military
test pilot of Ian's calibre then it can certainly happen
to me.

The yaw string *always* points to the inside of a spin
(according the Reichmann and others) and modifying
the teaching to 'apply full rudder opposite to the
direction of the yaw string' would be a more certain
way of choosing the life rudder pedal rather than the
death one at low altitude

Slip balls do not, apparently, invariably point to
the outside of spins so they are not as certain a guide.

'Every saiplane should have a yaw string' - said Helmut
Reichmann for this reason.

John Galloway



Good post, but I must point out a trap. I learned
from a student that it is easy to misunderstand which
end of the string is doing the pointing.

I always taught students to 'step on the head of the
snake.' One student could never get it right (never
been around snakes) and he was stepping on the tail
-- the aft, unattached end. I found that other students
had figured out their own way of bringing the string
into line and just ignored my comments.

We should have a conversation with students specifically
about which end of the yaw string is the pointer/tail/indicator,
etc. and which foot does what to that end of the string
under discussion.

On the other hand, perhaps my analogies are just weird.

"Nyal Williams" wrote in message
...

We should have a conversation with students specifically
about which end of the yaw string is the pointer/tail/indicator,
etc. and which foot does what to that end of the string
under discussion.

View the string as a pointer. The forward end (the point) points at the
required rudder pedal.

Duane

"Duane Eisenbeiss" wrote in message
...

"Nyal Williams" wrote in
message
...

We should have a conversation with students specifically
about which end of the yaw string is the pointer/tail/indicator,
etc. and which foot does what to that end of the string
under discussion.

The above post was incomplete. Over sensitive Send button.

View the string as a pointer. The forward end (the point) points at the
required rudder pedal to continue the turn or stop yaw. Therefore opposite
rudder in a spin would be the other rudder pedal or the top of the string.

Duane

Duane Eisenbeiss wrote:

The above post was incomplete. Over sensitive Send button.

View the string as a pointer. The forward end (the point) points at the
required rudder pedal to continue the turn or stop yaw.

It is impossible for the forward end to "point" at anything,
since it is fixed in place by tape. The string pivots
around its stationary forward end.

Any "pointing" is of course done by the free aft end
of the string, away from the pivotal point.

Same thing as the hands of a clock. The minute hand
points "right", not left, at five past twelve.

If you give left rudder you will slip to the right
and the string will point left.

Cheers CV

CV wrote:
Duane Eisenbeiss wrote:


The above post was incomplete. Over sensitive Send button.

View the string as a pointer. The forward end (the point) points at the
required rudder pedal to continue the turn or stop yaw.


It is impossible for the forward end to "point" at anything,
since it is fixed in place by tape. The string pivots
around its stationary forward end.

Any "pointing" is of course done by the free aft end
of the string, away from the pivotal point.

Same thing as the hands of a clock. The minute hand
points "right", not left, at five past twelve.

If you give left rudder you will slip to the right
and the string will point left.

So do you tell students that the wind sock points to where the wind is
going?
Impossible or not, by using my *imagination* early in my flying career,
I was able to simply and quickly make sense of what the yaw string was
indicating without having to think about where the relative wind was
coming from, or which pedal to push.
Jeez.

Shawn

"Apply full rudder opposite to the direction of the yaw string" -- what
does that mean? What is the direction of the yaw string? If the loose
end of the yaw string is on the right side of the canopy, is the
direction of the yaw string to the right, or is it to the left?

I think you mean that if the loose end of the yaw string is on the right
side of canopy, you apply right rudder? Or the opposite of the normal rule?




The yaw string *always* points to the inside of a spin
(according the Reichmann and others) and modifying
the teaching to 'apply full rudder opposite to the
direction of the yaw string' would be a more certain
way of choosing the life rudder pedal rather than the
death one at low altitude

At 18:30 16 January 2005, Nyal Williams wrote:
Good post, but I must point out a trap. I learned
from a student that it is easy to misunderstand which
end of the string is doing the pointing.

I always taught students to 'step on the head of the
snake.' One student could never get it right (never
been around snakes) and he was stepping on the tail
-- the aft, unattached end. I found that other students
had figured out their own way of bringing the string
into line and just ignored my comments.

We should have a conversation with students specifically
about which end of the yaw string is the pointer/tail/indicator,
etc. and which foot does what to that end of the string
under discussion.

On the other hand, perhaps my analogies are just weird.


I don't think they are weird, mine were 'kick the ball'
and 'draw the string'. Of course these days I never
have to use them that is why I remember them so well.
Isn't stepping on snakes a bit dangerous? :-)

At 19:00 16 January 2005, Greg Arnold wrote:
'Apply full rudder opposite to the direction of the
yaw string' -- what
does that mean? What is the direction of the yaw string?
If the loose
end of the yaw string is on the right side of the canopy,
is the
direction of the yaw string to the right, or is it
to the left?

Seems like there is some potentially confusing terminology
being used here that I've never heard before. I've
always been taught that the the 'direction' of the
yaw string is the side of the glider it leans to, and
so you correct by pressing the rudder on the opposite
side.

Here I think people are saying that if the yaw string
is displaced to the right side of the glider it is
'pointing' left. While I can understand how you might
naturally want the front end to be the tip of the 'pointer',
I think it's confusing to refer to 'pointing' at all
because of this left/right confusion. I prefer to
say the yaw string is 'to the left' or 'to the right'
as position is less ambiguous that the 'pointing' direction.

To be honest, I've never looked at the yaw string in
a spin as it has never been ambiguous to me which way
the world was turning - if the world is going round
and round counter-clockwise how can this not be spinning
to the right? I guess I presumed that for a spin to
persist the glider would have to stay skidding, but
in a fully established spin you might wonder, if the
yaw string was far enough forward (say in a two-seater),
whether the rotation overcomes the skid in terms of
the local flow across the canopy - apparently not given
the comments here. Boy I'd hate for that to be wrong
though.

Years ago when I was flying a Ventus A 16.6 (easy to
spin unintentionally in my experience) I taught myself
that if the inside wing in a turn ever dropped, to
push the stick forward and into the turn and to hit
top rudder. You try to make it as instinctive as possibe,
but it takes practice. The top rudder is the easiest
part - the stick movement is against most people's
instincts.

9B

Andy,

Remember my spin entry tests in the V2b a year and a half ago. One of
the departures was so violent, I lost reference, and even though I knew
which way I entered, I can see how a surprise stall with the same sort
of departure could cause disorientation and application of pro spin
rudder. At low altitudes (during a save, for instance), the delay in
recovery could be very bad news.

As for spin dynamics, it might be interesting to look at airfoil tufts
throughout to see what's going on. Anyone have a link? I think most of
us envision a spin as a straight line down, the aircraft rotating about
this axis. That seems too simple. At any rate, the yaw string should
always be displaced into the direction of spin (or average there if
oscillating). Staying in the spin requires that the inside wing be
producing higher drag (as a result of AOA), and thus the pro-rotation
displacement.

I won't be able to fly until April, but maybe one of you southwestern
types could provide some video of the yaw string through 2 or three
full rotations. We can discuss this ad nauseum, but a few pictures
would make the discussion much more interesting and possibly fruitfull.
Andy, you up for it?

At 17:00 19 January 2005, wrote:
Andy,

Remember my spin entry tests in the V2b a year and
a half ago. One of
the departures was so violent, I lost reference, and
even though I knew
which way I entered, I can see how a surprise stall
with the same sort
of departure could cause disorientation and application
of pro spin
rudder. At low altitudes (during a save, for instance),
the delay in
recovery could be very bad news.

As for spin dynamics, it might be interesting to look
at airfoil tufts
throughout to see what's going on. Anyone have a link?
I think most of
us envision a spin as a straight line down, the aircraft
rotating about
this axis.

This vision was the basis for my remarks about not
recognizing a spin on turn to final. We need to re-think
the teaching of spin recognition to include a better
vision of what the aircraft movement really is -- a
circular skid path, to point that out and impress it
on students and ourselves. Successive spins at lower
and lower altitudes will demonstrate that the lower
one is the more obvious the sidewise motion will be.
But no demonstrations in the pattern, please!




That seems too simple. At any rate, the yaw string
should
always be displaced into the direction of spin (or
average there if
oscillating). Staying in the spin requires that the
inside wing be
producing higher drag (as a result of AOA), and thus
the pro-rotation
displacement.

I won't be able to fly until April, but maybe one of
you southwestern
types could provide some video of the yaw string through
2 or three
full rotations. We can discuss this ad nauseum, but
a few pictures
would make the discussion much more interesting and
possibly fruitfull.
Andy, you up for it?