A new direction for an old thread: Crosswind landings

Martin, you are entirely wrong. I'm not obsessed. Really. No, I mean
it. ;-)

I use slips as a matter of course because I understand their USE and
RISKS and I am competent. What I am obsessed with is finding the
language that will let me explain clearly, succinctly, that crabbing
and slipping are not means to the same end. Perhaps I should refocus
attention on the word crabbing... which give the impression that it is
a maneuver as opposed to being normal wings level flight. Maybe the
better way to discuss this is to talk about approaches being
coordinated or uncoordinated.

We all agree that in order to transition to the ground in a crosswind
situation, we must move from coordinated to uncoordinated flight. You
have a choice when to apply controls to establish uncoordinated flight.
You can do it just before touch down (in which case the turn that
accompanies a skid is manageable), or you may do it earlier on final.
What I want to knock down is this notion of either a crab or a slip as
it infects our understanding of the purpose of the slip.

In order to establish a new ground track, you must turn. A side slip is
not a turn. All forces are balanced. As I've already described, many
pilots are confused about this difference. They explain that the side
slip works because the tilted left vector points into the crosswind,
dragging the glider sideways and compensating for wind drift. This
works in practice, but is wrong in fact because the tilted lift vector
is exactly matched by fuselage drag. If there were an unbalance force,
the glider's direction would continue to change... that is, circle. The
point is to find a better way of saying this. The place I'm trying to
get to is that when we compensate for crosswind on final, what we are
really doing when we initiate the side slip is a turn... what is in the
first instant a coordinated turn (remember which way the nose goes if
we don't use coordinating rudder while we roll into the bank), which
becomes a slipped turn as we reverse the progressively rudder against
the turn to keep heading aligned with runway, until we reach a beta
where the wing turning force is exactly compensated by the fuselage
force.

A better way to teach this and practice it is to keep the turn
coordinated until the desired ground track is achieved. This
demonstrates clearly the only way to establish a new ground track... by
turning to what we typcially call a crabbed approach. Then, at the
pilot's option, he may enter a slip, which will align the gliders
heading with its ground track. This crearly demonstrates that the
slip's only purpuse is alignment, just as the only purpose for the
rudder kick before touchdown is alignment (the only purpose of which is
to reduce side loading on the gear). The advantage of the slip is that,
unlike the rudder kick, all foreces are balanced. If the touch down is
delayed, you are much less likely to have to make large corrections in
direction.

In your experience, how many pilots stick with this sport. I've heard
commercial operators say it's about 1 in 5. Twenty percent get it.
Eighty percent don't. And of the 20% that get, how many really get it?

I already know how to do it. Now I'm trying to "get it" in a way that I
can easily explain, and maybe help that other 80% figure things out.

Martin Eiler wrote:
The following is a snip from one of Fiveniner's
early posts regarding the use of side slips for
dealing with wind drift while on final.

At 00:00 20 February 2005,
wrote:
But the notion that the tilted lift vector is compensating
for
wind drift is flawed. Useful, but flawed.

Having read all of his posts in this thread, it is
apparent that he has supplied no real data
capable of substantiating his position that side
slips cannot compensate for wind drift. Yes,
there is a portion of the soaring community
that are die-hard crab pilots. That does not
mean that their choice automatically validates
his opinion that side slips can't compensate for
cross wind. Those pilots who are experienced
with side slips seem to agree with the SSA's
Soaring Manual, in that a side slip does have
some limitations, and consequently at some point,
some amount of crab may be needed to be added
to the side slip to achieve the desired result.

Interestingly, after rereading his other posts, it
becomes quite obvious that he is obsessed with
the opinion that pilots should only be allowed to
fly coordinated while at or below pattern altitude.
Although he is entitled to his opinion, few other
pilots would support the concept that a pilot who
intentionally flies uncoordinated on final is operating
dangerously.

Generally speaking having lofty ideals is admirable,
however it is more warmly accepted when an
individual signs his post with his real name.

M Eiler

Sorry Marty. I type at warp speed and don't always leave a name at the
end. For 17 years my contest ID was 59, thus the yahoo address. And
perhaps as a frequent contributor to the group, I've let my ego swell
to the point that I figure others will recognize me by content or
style.

Chris O'Callaghan
Ventus 2bx -- Oscar Charlie
Frederick, Maryland
Member of the Mid-Atlantic Soaring Association

OK. I think this thread has served its purpose, at least for me. It
looks like the key may be centered on "coordination."

Might I suggest to active instructors that you try my exercise and
report back: coordinated turn to a heading that establishes ground
track as you would at altitude, the entry and recovery from a slip to
demonstrate gear alignment and return to wings level coordinated
flight. You might preface this with a forward slip demonstration in
light winds and comment on the misalignment of the gear with the runway
and the need to align before touch down. When might this misalignment
be useful? Let the student mull that over... then start talking about
crosswind navigation and see if he makes the connection.

I'm checking out for the next week. If someone has an epiphany, please
copy me back channel.

Cheers,

Chris O'Callaghan

Still, Martin's point stands - you don't sign with your name.

And the whole thing somehow looks pretty much like intellectual
masturbation. Getting a ship onto a runway in a crosswind isn't the most
diffult thing in flying glider, and if a student doesn' get it, he wouldn't
get a number of things anyway.

--
Bert Willing

ASW20 "TW"


a écrit dans le message de news:
...
Martin, you are entirely wrong. I'm not obsessed. Really. No, I mean
it. ;-)

I use slips as a matter of course because I understand their USE and
RISKS and I am competent. What I am obsessed with is finding the
language that will let me explain clearly, succinctly, that crabbing
and slipping are not means to the same end. Perhaps I should refocus
attention on the word crabbing... which give the impression that it is
a maneuver as opposed to being normal wings level flight. Maybe the
better way to discuss this is to talk about approaches being
coordinated or uncoordinated.

We all agree that in order to transition to the ground in a crosswind
situation, we must move from coordinated to uncoordinated flight. You
have a choice when to apply controls to establish uncoordinated flight.
You can do it just before touch down (in which case the turn that
accompanies a skid is manageable), or you may do it earlier on final.
What I want to knock down is this notion of either a crab or a slip as
it infects our understanding of the purpose of the slip.

In order to establish a new ground track, you must turn. A side slip is
not a turn. All forces are balanced. As I've already described, many
pilots are confused about this difference. They explain that the side
slip works because the tilted left vector points into the crosswind,
dragging the glider sideways and compensating for wind drift. This
works in practice, but is wrong in fact because the tilted lift vector
is exactly matched by fuselage drag. If there were an unbalance force,
the glider's direction would continue to change... that is, circle. The
point is to find a better way of saying this. The place I'm trying to
get to is that when we compensate for crosswind on final, what we are
really doing when we initiate the side slip is a turn... what is in the
first instant a coordinated turn (remember which way the nose goes if
we don't use coordinating rudder while we roll into the bank), which
becomes a slipped turn as we reverse the progressively rudder against
the turn to keep heading aligned with runway, until we reach a beta
where the wing turning force is exactly compensated by the fuselage
force.

A better way to teach this and practice it is to keep the turn
coordinated until the desired ground track is achieved. This
demonstrates clearly the only way to establish a new ground track... by
turning to what we typcially call a crabbed approach. Then, at the
pilot's option, he may enter a slip, which will align the gliders
heading with its ground track. This crearly demonstrates that the
slip's only purpuse is alignment, just as the only purpose for the
rudder kick before touchdown is alignment (the only purpose of which is
to reduce side loading on the gear). The advantage of the slip is that,
unlike the rudder kick, all foreces are balanced. If the touch down is
delayed, you are much less likely to have to make large corrections in
direction.

In your experience, how many pilots stick with this sport. I've heard
commercial operators say it's about 1 in 5. Twenty percent get it.
Eighty percent don't. And of the 20% that get, how many really get it?

I already know how to do it. Now I'm trying to "get it" in a way that I
can easily explain, and maybe help that other 80% figure things out.

Martin Eiler wrote:
The following is a snip from one of Fiveniner's
early posts regarding the use of side slips for
dealing with wind drift while on final.

At 00:00 20 February 2005,
wrote:
But the notion that the tilted lift vector is compensating
for
wind drift is flawed. Useful, but flawed.

Having read all of his posts in this thread, it is
apparent that he has supplied no real data
capable of substantiating his position that side
slips cannot compensate for wind drift. Yes,
there is a portion of the soaring community
that are die-hard crab pilots. That does not
mean that their choice automatically validates
his opinion that side slips can't compensate for
cross wind. Those pilots who are experienced
with side slips seem to agree with the SSA's
Soaring Manual, in that a side slip does have
some limitations, and consequently at some point,
some amount of crab may be needed to be added
to the side slip to achieve the desired result.

Interestingly, after rereading his other posts, it
becomes quite obvious that he is obsessed with
the opinion that pilots should only be allowed to
fly coordinated while at or below pattern altitude.
Although he is entitled to his opinion, few other
pilots would support the concept that a pilot who
intentionally flies uncoordinated on final is operating
dangerously.

Generally speaking having lofty ideals is admirable,
however it is more warmly accepted when an
individual signs his post with his real name.

M Eiler

Oups - I take back my first remark.

--
Bert Willing

ASW20 "TW"


a écrit dans le message de news:
...
Sorry Marty. I type at warp speed and don't always leave a name at the
end. For 17 years my contest ID was 59, thus the yahoo address. And
perhaps as a frequent contributor to the group, I've let my ego swell
to the point that I figure others will recognize me by content or
style.

Chris O'Callaghan
Ventus 2bx -- Oscar Charlie
Frederick, Maryland
Member of the Mid-Atlantic Soaring Association

Yes, well said. But still wrong, in this sense:

Side slipping does not change your direction. What you have done is to
define the limits of side slipping as an alignment maneuver. This
doesn't make side slipping and crabbing additive. It simply says that
you've been taught or you prefer to uncoordinate the aircraft early on
final to align the gear with the runway. However, the rudder will only
allow a finite maximum angle of yaw, which limits the amount of bank
you can use before the wing turning force exceeds the fuselage force
and you start turning. So put another way, a side slip is only useful
for gear alignment up to some fixed crosswind component speed. Above
that speed, you will need to add a skid before touch down... but
wait... your rudder is already full over. How will you align the gear?
Well, if you had both the full authority of the rudder and the adverse
yaw or you ailerons, you might be able to manage it. But that would
require a crabbed (coordinated) approach. Which just happens to be the
same path you were moving through the air while side slipping "plus"
crabbing. Do you see why I just can't stomach the notion of side slips
and crabs being additive? There is a reverse logic at work here which
gives the side slip a false role in crosswind management.

Put another way, a side slip is only appropriate for light to moderate
crosswind components and flat landing surfaces. The stronger the
crosswind, the rougher the runway, the more critical it is to have
maximum yaw performance at touch down. Side slips and skids are
additive, but only to the degree that you have any rudder left to yaw
the glider. Since everyone seems to have a preference, I would guess
this is the worst of both worlds.

Think of it another way... if I slow down on final, I'll need to change
my direction to maintain a constant ground track. (This is simple trig
that I'll leave to you.) I cannot accomplish this by adding side slip.
A side slip changes heading only, not track. I must turn in order to
maintain track. This isn't even apples and oranges. This trying to add
fruits and vegetables.

So here I am on final in calm conditions... I slip to the right. I
recover. I slip to the left. I recover. Net force always equals zero.
My flight path remains the same. Track, the same. Heading swings 20
degrees either side of the runway center line. Same thing in a cross
wind. I establish a ground track. I point down the runway. I recover
form the side slip. For amusement I slip in the other direction - with
the downwind wing low (is this a side slip or a forward slip???!!!). I
recover. Net force always equals zero. My track remains exactly the
same while my heading swings through 40 total degrees, centered on my
path through the air.

I'll see if I can't find a new direction to come at this. Redefining
the approach in terms of coordination may be the way. But I really do
need to check out. Be back in a week or two.

OC aka 59 aka Chris O'Callaghan

It obviously has been a long winter in your part of the country. You
badly need to go flying!


wrote:
Yes, well said. But still wrong, in this sense:

Side slipping does not change your direction. What you have done is to
define the limits of side slipping as an alignment maneuver. This
doesn't make side slipping and crabbing additive. It simply says that
you've been taught or you prefer to uncoordinate the aircraft early on
final to align the gear with the runway. However, the rudder will only
allow a finite maximum angle of yaw, which limits the amount of bank
you can use before the wing turning force exceeds the fuselage force
and you start turning. So put another way, a side slip is only useful
for gear alignment up to some fixed crosswind component speed. Above
that speed, you will need to add a skid before touch down... but
wait... your rudder is already full over. How will you align the gear?
Well, if you had both the full authority of the rudder and the adverse
yaw or you ailerons, you might be able to manage it. But that would
require a crabbed (coordinated) approach. Which just happens to be the
same path you were moving through the air while side slipping "plus"
crabbing. Do you see why I just can't stomach the notion of side slips
and crabs being additive? There is a reverse logic at work here which
gives the side slip a false role in crosswind management.

Put another way, a side slip is only appropriate for light to moderate
crosswind components and flat landing surfaces. The stronger the
crosswind, the rougher the runway, the more critical it is to have
maximum yaw performance at touch down. Side slips and skids are
additive, but only to the degree that you have any rudder left to yaw
the glider. Since everyone seems to have a preference, I would guess
this is the worst of both worlds.

Think of it another way... if I slow down on final, I'll need to change
my direction to maintain a constant ground track. (This is simple trig
that I'll leave to you.) I cannot accomplish this by adding side slip.
A side slip changes heading only, not track. I must turn in order to
maintain track. This isn't even apples and oranges. This trying to add
fruits and vegetables.

So here I am on final in calm conditions... I slip to the right. I
recover. I slip to the left. I recover. Net force always equals zero.
My flight path remains the same. Track, the same. Heading swings 20
degrees either side of the runway center line. Same thing in a cross
wind. I establish a ground track. I point down the runway. I recover
form the side slip. For amusement I slip in the other direction - with
the downwind wing low (is this a side slip or a forward slip???!!!). I
recover. Net force always equals zero. My track remains exactly the
same while my heading swings through 40 total degrees, centered on my
path through the air.

I'll see if I can't find a new direction to come at this. Redefining
the approach in terms of coordination may be the way. But I really do
need to check out. Be back in a week or two.

OC aka 59 aka Chris O'Callaghan

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.

At 18:30 25 February 2005,
wrote:
Yes, well said. But still wrong, in this sense:

Most of us mere mortals are very broad minded about
this; why don't you just fly the bleedin' picture as
it changes!

T o d d P a t t i s t wrote:

However, your yaw string will NOT be straight when you apply
rudder to line up and you will NOT be in coordinated
flight.

Got me. But then, who looks at the yaw string during the flare anyway?

BTW: I know that in the US, you make a difference about "forward" and
"side" slip. How would this one be called? Maybe a "wing level straight
forward slip"? :-)

I'd like to emphasize that I usually land in a crosswind
pretty much as you are describing, I fly coordinated until

Thank you, Todd. Makes me sleep better. :-)

Stefan