A new direction for an old thread: Crosswind landings

My opinion exactly. How many pilots use slipping to
correct for wind
while flying cross country?

Landing and flying cross country are comparing apples
and orange...at altitude you don't have to worry about
damaging gear from landing in a crab, so don't consider
your analogy accurate.



My wild guess is: none. We all crab without
even talking about it. So what is the reason they don't
do so during the
landing?

Uhh...here in the colonies, we don't have a lot of
grass to land on...and grass is much more forgiving
for a crabbed touchdown. Try landing less then straight
on asphalt a few times. Likewise asphalt does not
grab wingtips like grass.

I can think of only two reasons: They've never learnt
to master the
rudder or they've never learnt to recognize and hold
the runway axis
unless it's right ahead of their nose.

Hmmm....no comment. You seem to be assuming a lot
though
Both reasons claim for more
training, not a change of method.

Seems like we do what works best for us....suggest
the same for you

Stefan

Agreed. A pilot should be the master of both. And I believe the first
step in that direction is to divorce these two maneuvers, slips and
skids, from any discussion of "compensating" for a crosswind. These are
alignment maneuvers only, each having its relative merits.
Don Johnstone wrote:
First , sorry for the kick off the drift, you are absolutely
right.
I have used both methods and in a high wing glider
with the tips well clear of the ground wings level
I would agree the wing down (slipping) method is OK.
Even in a 15 metre glass glider I would accept that
it is a matter of choice. Big wings, especially where
the wing is already low is a different matter. I would
rather make an untidy arrival than catch a wingtip.
The lesser of two evils and I KNOW which is lesser
in that case. Remember the force required at the wingtip
to induce a ground loop reduces in proportion to the
increase in span. With full flap deployed the roll
rate is not exactly sparkling either.

Both should be taught, it then becomes a matter of
choice for the pilot, what he is most comfortable with.
I am not saying my way is better but it works for me.


At 17:30 21 February 2005, J.A.M. wrote:
Excuse me... I slip for crosswind correction on final,
rather than crab
(wich I assume is to correct the wind with heading;
sorry, english is not my
native language).
I find it more effective as the fuselage is already
aligned with the runway,
and a more elegant manouevre as well.
I live in Spain. Does it count as Europe?
A lot of people does it here. I teach both methods,
being crab easier to
grasp at the beggining, slipping more effective and
elegant when the student
becomes proficient, IMHO.

Jose M. Alvarez.
ASW-24 'BR'

At 12:30 21 February 2005, Bert Willing wrote:
Additionally, if you don't crab to stay centered during
final, you stalling
speed will be higher. I never saw anybody slipping
for wind correction in a
glider in Europe...

--
Bert Willing

ASW20 'TW'

I fly a lot at a mountain site where the winds can be strong, gusty and
turbulent; 20 to 60 degrees (or more) off the runway heading, and constantly
changing. The pattern there can be wicked at times. I am flying 18 and 20
meter gliders off a runway that is 75 feet (22.9 meters) wide with lights,
sagebrush, and rocks past the edges.

On days like that and at places like that there is no time for asking myself
whether I should slip or crab. I just want to get the damn sailplane down
in one piece. For flying like this you need to have your spurs on (be
proactive and decisive). The only rules a Don't ground loop. Don't
cartwheel. Don't hurt the pilot or glider.

I would bet that if you debriefed me just after I stopped and got out of the
glider, I would not be able to tell you very well what I had just done. One
just does what is necessary to get down safely. When you get it slowed down
somewhere near the ground in the middle of the runway and pointed pretty
much down the runway, you had better plant it right then. Better safe than
pretty.

I do know that I have used a combination slip and crab many times, just so I
don't run out of control travel before I get the desired response. Is that
additive? You just lift the upwind wing before it hits the runway and use
rudder as needed to establish/maintain heading. The upwind wing stays
slightly down throughout the flare and rollout.

At a sea level site with a steady wind and no upwind obstructions one can
(yawn) take the time to worry about style points for slipping or crabbing
approaches. :-)

Teaching pilots to fly is, of course, a very different proposition.
-Bob Korves

wrote in message
oups.com...
Bruce,

An even better way to think of this is simply to let the dihedral
effect roll the wings level. An intent to "roll" the glider level will
produce aileron drag with a yaw in the wrong direction. Since we're
holding stick into the slip, the process only requires a relaxation of
this force. And not even to neutral.

That said, the majority of competent crosswind landings I've seen in
open class ships usually involve flying the glider (wing low) onto the
runway. The big gliders clearly require greater competence and a more
flexible, not necessarily ideal approach to dealing with such problems.

Also, I note that Don used the words "Kick off the drift." This is
inaccurate. Since the crab is used to track down the runway, there is
no longer a "drift." He is, in fact, kicking to align the gear with the
runway. I point this out because sloppiness with terminology percolates
up to our understanding of the model. And then back down to the control
inputs we make.

As for concerns of yawing while increasing angle of attack, remember
you are near the ground. The real disadvantage of the wings level skid
to align the gear is that you are introducing an unbalanced force. If
your touch down is delayed, or you bounce, you will begin to turn
downwind. It is an interesting dilemma. On the one hand, the alignment
slip requires greater skill and understanding. On the other, the
alignment skid requires a "touch" on both the rudder and the stick. I
suspect the wings level approach is safer of low time pilots since they
have greater controlability in the event of turbulence. But the wing
low landing is easier since control movements are intuitive.

There is a great big HOWEVER. A wing low landing into crops is
completely unacceptable (as is flying the glider on). Each method has
its role. We should be competent at both. But to be competent we need
to clearly understand not just the obvious differences, but the
similarities as well.


Those of you who would prefer not to make the "additive" argument in
public, please back channel. I am genuinely interested in understanding
why this concept works... or perhaps, doesn't.

OC


Bruce Hoult wrote:
In article ,
Don Johnstone wrote:

Can't speak for 25 metres but I can for 20 metres and
it's crabbing. I fly an ASW 17 and the tips are not
that far from the ground, even when the wings are level,
and sideslipping (using bank) near the ground has never
appealed to me. My aim is to keep the wings level near
the ground and kick off the drift at the point of flare
but I have often wondered if it is a really good idea
to apply yaw at the same time as increasing the angle
of attack of the wing. Of course to conteract the further
effect of rudder opposite aileron may have to be applied
to keep the wings level but can be avoided by not being
too heavy footed with the rudder.

If you want, you can side slip and when close to the ground use the
ailerons to level the wings. You are then in precisely the same
situation as if you crabbed and then kicked in rudder, except that
levelling the wings is probably easier and less critical than
precisely
timing and judging a bootfull of rudder.

--
Bruce | 41.1670S | \ spoken | -+-
Hoult | 174.8263E | /\ here. | ----------O----------

I don't agree that they aren't additive.

Say you are side slipping, but are still drifting off centerline. So
you turn into the wind (crab) and hold the same amount of slip. It
seems to me that you are combining, i.e. "adding", the crab component
to the slip component. Works with vector arithmetic, should work in the
air, too.

Tom

As often happens, the discussion is digressing into the particulars of
landing in a crosswind, and I couldn't be happier. Watching pilots
wrangle through the explanation of why they do what they do is
fascinating, especially since the inference chain gets all kinds of
twisted as they work their way back up to the model.

The trick, I'm convinced, is to completely divorce the slip/skid
alignment maneuvers from the maneuver required to establish a track
down the runway. Once we've determined that there is a crosswind, the
only way to establish a proper track is to change our direction through
the airmass. The problem arises when pilots confuse the alignment
maneuver with the turn. We've discovered this slick maneuver where we
can turn base to final and initiate the slip all in one motion. Which
leads to a false perception that we only turned 90 degrees, then used
the wing to compensate for crosswind. But we have in fact changed our
direction by more than 90 degrees and inserted our alignment slip early
on final. But whether your turn is coordinated throughout, or slipped,
the means by which we change direction is exactly the same. Remove the
slip, and you'll point upwind, put the slip back in and you'll point
down the runway. The forces produced by the glider remain balanced
throughout.

Maybe it is easier to conceptualize this if you simply ignore the
direction the nose is pointing and think of it in terms of the glider's
path through the air. Because in a side slip the nose is pointing down
the runway, there is an illusion that the lowered wing is dragging the
glider sideways, compensating for the "force" of the wind. But in a
side slip (as in a foward slip), the horizontal component of lift is
exactly balanced by the force created by sideways motion of the
fuselage. There is no extra force to compensate for an external force.
Which is a good thing since there is no external force from the wind.

That said, an unbalanced force is required to establish a new direction
through the air that will produce a desired ground track. And this is
only accomplished by turning. Whether the turn is slipped or skidded or
coordinated is a matter of pilot choice. It is nonetheless a turn since
the direction of the glider changes. When the new direction is
achieved, the turn ceases. Whether this is accomplished by rolling the
wings level or increasing beta to balance the wing turning force is a
matter of pilot choice.

On 22 Feb 2005 05:51:33 -0800, wrote:


Maybe it is easier to conceptualize this if you simply ignore the
direction the nose is pointing and think of it in terms of the glider's
path through the air.

Why not simply fly according to the feeling in your pants?
I've seen a lot of bad landings - but I never saw a landing where the
pilot had difficulties with crosswind. Therefore I think the whole
discusion is not really ... necessary.

Why make things more difficult than they are in real life?





Bye
Andreas

I am getting a little lost here. If you are trying
to say that an aircraft when flying moves relative
to the airmass it happens to be in you are right. The
direction in which the airmass is moving is unimportant
as far as the aircraft is concerned, as long as it
remains flyng. The concept of what happens when a pilot
has to change the movement of his glider from relative
to the air to releative to the ground because it is
about to become a wheeled vehicle with wings is not
that important. What is vital is that pilots are trained
how to change from being a vehicle moving relative
to the airmass to one moving relative to the ground.
As pilots, unlike the aircraft, we are more concerned
with our movement relative to the ground.
Do we really seek to change our direction through the
airmass? What we seek to achieve is changing our direction
relative to the ground, to align track and heading,
we don't really care a jot that our movement relative
to the airmass has changed (or not) until we try to
operate outside the limits of the aircraft, then we
care a lot. I suppose what I am trying to say is that
the procedure is a very human thing, a skill that requires
teaching, and not one which deep scientific analysis
will help as there are so many variables.

At 14:00 22 February 2005,
wrote:
As often happens, the discussion is digressing into
the particulars of
landing in a crosswind, and I couldn't be happier.
Watching pilots
wrangle through the explanation of why they do what
they do is
fascinating, especially since the inference chain gets
all kinds of
twisted as they work their way back up to the model.

The trick, I'm convinced, is to completely divorce
the slip/skid
alignment maneuvers from the maneuver required to establish
a track
down the runway. Once we've determined that there is
a crosswind, the
only way to establish a proper track is to change our
direction through
the airmass. The problem arises when pilots confuse
the alignment
maneuver with the turn. We've discovered this slick
maneuver where we
can turn base to final and initiate the slip all in
one motion. Which
leads to a false perception that we only turned 90
degrees, then used
the wing to compensate for crosswind. But we have in
fact changed our
direction by more than 90 degrees and inserted our
alignment slip early
on final. But whether your turn is coordinated throughout,
or slipped,
the means by which we change direction is exactly the
same. Remove the
slip, and you'll point upwind, put the slip back in
and you'll point
down the runway. The forces produced by the glider
remain balanced
throughout.

Maybe it is easier to conceptualize this if you simply
ignore the
direction the nose is pointing and think of it in terms
of the glider's
path through the air. Because in a side slip the nose
is pointing down
the runway, there is an illusion that the lowered wing
is dragging the
glider sideways, compensating for the 'force' of the
wind. But in a
side slip (as in a foward slip), the horizontal component
of lift is
exactly balanced by the force created by sideways motion
of the
fuselage. There is no extra force to compensate for
an external force.
Which is a good thing since there is no external force
from the wind.

That said, an unbalanced force is required to establish
a new direction
through the air that will produce a desired ground
track. And this is
only accomplished by turning. Whether the turn is slipped
or skidded or
coordinated is a matter of pilot choice. It is nonetheless
a turn since
the direction of the glider changes. When the new direction
is
achieved, the turn ceases. Whether this is accomplished
by rolling the
wings level or increasing beta to balance the wing
turning force is a
matter of pilot choice.

While I agree with the majority of Todd's post, it
would be beneficial to have some clarification on point
5.

T O D D P A T T I S T wrote:
5) If you slip while flying straight for very long,
you need
to lower the opposite wing or you will begin a skidding
turn. Modern gliders have a low fuselage side area
and take
a while to begin this type of skidding turn.

I know this may sound petty but considering how
this thread has evolved, it's appropriate.
Exactly what is your definition of 'flying straight'
and 'turn'? Remember what Clinton taught us about
something we thought was as simple as the word 'is'.


Apparently the consensus seems to be that there are
three types of crosswind landing techniqes used. Crab
or side slip or some combination of both. Would it
be commonly accepted to say that while using the same
spoiler setting for both a crab and a side slip crosswind
landing, that the glider side slipping will have a
higher rate of descent?

M Eiler

A fun intellectual exercise, but you have to fly the airplane. You also have to
make the transition to ground transport in such a way as to avoid unpleasant
noises and disorienting motion...

Most pilots I have observed use a combination of slip and crab depending on a
number of factors. Not always voluntary.

My experience is that you have to be very careful in a vintage wood and fabric
job. When the crab angle is extreme, and you have all the penetration of a well
thrown wet tissue, and there is a strong wind gradient it is doubtful whether
you would want to use a slip to increase your drag.

Lower drag means more options, so a 'higher performance' airplane can do both,
and may need to do both if you have carried extra height for whatever reason.

Not a bad idea to think it through on the ground - at least you can change your
mind without damage, in the circuit might not be a good place to be
philosophizing about it all.

Don Johnstone wrote:
I am getting a little lost here. If you are trying
to say that an aircraft when flying moves relative
to the airmass it happens to be in you are right. The
direction in which the airmass is moving is unimportant
as far as the aircraft is concerned, as long as it
remains flyng. The concept of what happens when a pilot
has to change the movement of his glider from relative
to the air to releative to the ground because it is
about to become a wheeled vehicle with wings is not
that important. What is vital is that pilots are trained
how to change from being a vehicle moving relative
to the airmass to one moving relative to the ground.
As pilots, unlike the aircraft, we are more concerned
with our movement relative to the ground.
Do we really seek to change our direction through the
airmass? What we seek to achieve is changing our direction
relative to the ground, to align track and heading,
we don't really care a jot that our movement relative
to the airmass has changed (or not) until we try to
operate outside the limits of the aircraft, then we
care a lot. I suppose what I am trying to say is that
the procedure is a very human thing, a skill that requires
teaching, and not one which deep scientific analysis
will help as there are so many variables.

At 14:00 22 February 2005,
wrote:

As often happens, the discussion is digressing into
the particulars of
landing in a crosswind, and I couldn't be happier.
Watching pilots
wrangle through the explanation of why they do what
they do is
fascinating, especially since the inference chain gets
all kinds of
twisted as they work their way back up to the model.

The trick, I'm convinced, is to completely divorce
the slip/skid
alignment maneuvers from the maneuver required to establish
a track
down the runway. Once we've determined that there is
a crosswind, the
only way to establish a proper track is to change our
direction through
the airmass. The problem arises when pilots confuse
the alignment
maneuver with the turn. We've discovered this slick
maneuver where we
can turn base to final and initiate the slip all in
one motion. Which
leads to a false perception that we only turned 90
degrees, then used
the wing to compensate for crosswind. But we have in
fact changed our
direction by more than 90 degrees and inserted our
alignment slip early
on final. But whether your turn is coordinated throughout,
or slipped,
the means by which we change direction is exactly the
same. Remove the
slip, and you'll point upwind, put the slip back in
and you'll point
down the runway. The forces produced by the glider
remain balanced
throughout.

Maybe it is easier to conceptualize this if you simply
ignore the
direction the nose is pointing and think of it in terms
of the glider's
path through the air. Because in a side slip the nose
is pointing down
the runway, there is an illusion that the lowered wing
is dragging the
glider sideways, compensating for the 'force' of the
wind. But in a
side slip (as in a foward slip), the horizontal component
of lift is
exactly balanced by the force created by sideways motion
of the
fuselage. There is no extra force to compensate for
an external force.
Which is a good thing since there is no external force

from the wind.

That said, an unbalanced force is required to establish
a new direction
through the air that will produce a desired ground
track. And this is
only accomplished by turning. Whether the turn is slipped
or skidded or
coordinated is a matter of pilot choice. It is nonetheless
a turn since
the direction of the glider changes. When the new direction
is
achieved, the turn ceases. Whether this is accomplished
by rolling the
wings level or increasing beta to balance the wing
turning force is a
matter of pilot choice.

While I agree with the majority of Todd's post, it
would be beneficial to have some clarification on point
5.

T O D D P A T T I S T wrote:
5) If you slip while flying straight for very long,
you need
to lower the opposite wing or you will begin a skidding
turn. Modern gliders have a low fuselage side area
and take
a while to begin this type of skidding turn.

I know this may sound petty but considering how
this thread has evolved, it's appropriate.
Exactly what is your definition of 'flying straight'
and 'turn'? Remember what Clinton taught us about
something we thought was as simple as the word 'is'.


Apparently the consensus seems to be that there are
three types of crosswind landing techniqes used. Crab
or side slip or some combination of both. Would it
be commonly accepted to say that while using the same
spoiler setting for both a crab and a side slip crosswind
landing, that the glider side slipping will have a
higher rate of descent?

M Eiler