A new direction for an old thread: Crosswind landings

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 an "inertia induced
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

Hello everyone!

I have been following ras for a few years now and have finally felt
compelled to add my voice. Other than the threads on V-tails& flaps of
death, this has been the most interesting discussion although for an
entirely differing reason. Usually there is no need for comment as most
important bases on topics generally get equal time. Aside from wading
or suffering through some personal opinions I have enjoyed the comments
and insights.

The opinions that I have been hearing in this thread have all sounded
as if they have come from mostly instructors and or folks who fly
primarily slippery glass.One day I will be there as well, but for the
past 6 years I have been flying an SGS 1-35c model on the East coast w/
a commercial ticket. If any of you do not know them, they have only
flaps or slips for vertical glidepath control. My introduction to
soaring instruction began in 1998 and still is as fresh today as it was
then. On more than one occasion my instructor's voice has come back
when things were not very plesant in the air. And having said that, I
believe how information is passed along to be very important. I
consider all landings as practice for off field landings of which I
have my share, some of which have been done in rotor in and near
Petersburg W.Va. W-99.I am chiming into this thread because I still
have pretty vivid recollection of my training.

As I recall, slips were taught to me after stalls but before spin
entry and exits.At our club, I observe both slipping and crabbing style
allignments. Our strip is wide grass adjacent a hardpaved runway. It is
my opinion that the more experienced pilots choose the slip method and
the less experienced generally opt for the crab. I believe the reason
goes back to their training. With the less experienced being closer to
theirs. When learning the stall warning signs in most any older early
training ship ie; 2-33, Ka-13, Ka7 the pre-stall buffeting is quite
pronounced and makes quite an impression on the student. Therefore I
believe that early pilots transfer the pre-stall noises to a ship
slipping and are therefore uncomfortable doing so, esp closing in on
the grounds proximity! As for myself I agree that I use both and
sometimes together although generally I prefer the slip. I only tend to
use the crab as a combination during high x-wind.

Last fall one of our glass pilots had his canopy come loose on base.
Concentrating on the canopy, he failed to control his decent and
eventually his directional control. Extensive damage to the ship but
no more than an ego bruise to the pilot. During the ensuing discussions
slipping to keep the canopy closed was pretty generally the method we
all agreed we would have chosen. Of those in the discussion I might
have been the only one to have had practice at this during my late
stage training.That due to my instructor's foresight.

After all was said and done, one of my instructors challenged me
again. He asked me what I would do if one day while checking my flaps
upon entering the pattern the lever arm came off in my hands
essentially eliminating their use? Obviously slipping is the answer, so
I began to try this method.To this day I have only witnessed one other
club member attempt it.

Which brings me to my point. I believe having an effective slip in
every pilot's pocket is an essential thing. That pre-solo students
should be able to land their ship without the use of additional
mechanical devices.Taught late in the program to the point of
proficiency. If slips were used more, possibly even the deadly canopy
open on tow might loose some of it's near certainty! I do not see this
@ our club but wish I did.If slipping had been regularly practiced by
the accident pilot,he might have used it rather than his hand to keep
the canopy closed freeing up one for the divebreaks.

I have had the opportunity to to add a full slip to 75 deg. flaps @
90 mph. to extricate myself from a fast closing wave system. You need
to do it once to appreciate the view!

Paul Rehm KW

Graeme Cant wrote:
Eric Greenwell wrote:
snip...
After a while, found I preferred a side-slip to a crab;

So do I. Much more fun. but I do it in Cezznas, not my ASW20.

even so, I still use some crab in a strong crosswind.


I think that makes my point. Very sensible with 18 metres of floppy
Schleicher wing to keep dust-free.

My 18 meter Schleicher (ASH 26 E) doesn't have a floppy wing like my ASW
20 C did. I start using crab when I"m close to full rudder in the
side-slip, which can happen in strong cross winds. The low wing still
seems sufficiently high at that point, but I don't have a measurement
for the angle it makes with the ground.

Regardless, it's very rare that I've had to land where the height of the
grass or bushes was a concern. If I routinely landed where the wing tips
were over 20"-30" high grass, perhaps I'd be using a crab instead.
--
Change "netto" to "net" to email me directly

Eric Greenwell
Washington State
USA

At 06:00 26 February 2005, Eric Greenwell wrote:
I start using crab when I'm close to full rudder in
the
side-slip, which can happen in strong cross winds.
The low wing still seems sufficiently high at that
point,
but I don't have a measurement for the angle it makes
with the ground.

Regardless, it's very rare that I've had to land where
the height of the grass or bushes was a concern.
If I routinely landed where the wing tips were over
20'-30' high grass, perhaps I'd be using a crab instead.

Here's some interesting data. ASK-21's have quite
a bit of dihedral and relatively stiff wings as
compared to most fiberglass single place gliders.
A K-21 pilot landing with the upwind wing leading
edge parallel to the ground has a 3.5 degree bank.
If he was foolhardy enough to touch down with the
main wheel and upwind wing at the same time,
he would be in a 6.5 degree bank. So it might
seem reasonable to expect that a pilot proficient
in side slips would therefore maybe be willing to
touch down with a 5 degree bank.
M Eiler

I was doing side slips and forward slips a few weeks ago with
a well respected SSA Master X-C instructor. He pointed out that
to lose altitude, slipping with the down wing AWAY from the airport
during the base leg makes the glider go further from the
airport and this helps by allowing a longer final.
I taught this technique this weekend in an, ahem, towplane
to lose altitude, and it worked great! Funny I hadn't read
this anywhere...

I prefer to avoid forward slips or crabs on short final
because I like to see a stabilized approach, instead of
a dramatic yaw right at the very end. Forward slips right
down to the last part of final also means not good ASI indications.
I wish I had a braunschweig tube on these gliders!

But a forward slip on base seems to work very, very well.
Although I teach turning slips also, I've found that
maintaining a rectangular pattern is easier to describe, teach,
and judge. You can still do a turning slip base to final, for example,
but I don't generally teach a 180 degree turning slip from downwind
to final.

In article ,
T o d d P a t t i s t wrote:
wrote:

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

I'll take this as directed to me, since it seems to be under
my post, but it would have helped to quote some of the
original post, for context. :-)

Side slipping does not change your direction.

Agreed. In a stable side slip you are flying straight.
Entering the side slip can be done to maintain the original
heading or to turn during the entry. I think we agree on
this.

What you have done is to
define the limits of side slipping as an alignment maneuver.

Agreed.

This doesn't make side slipping and crabbing additive.

Depends on what you mean by "additive." The track over the
ground and through the air mass are not additive. The angle
between the nose and the runway are - although in a negative
sense. You have to deal with both during a landing.

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.

This point has theoretical merit, but in practice, a glider
will fly at an amazing angle with only a small amount of
wing down. We have a rudder large enough to counter
significant adverse yaw and a small fuselage cross section,
so if you truly need more than full rudder as you reach the
lower speed crosswind at touchdown, you are probably in a
world of hurt crabbing or slipping. Conversely, I add
slipping into my approach in a strong crosswind. I want to
minimize the large yaw change required at touchdown, I can
see the runway better, and it seems to be more in control
for me in gusts.

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?

I think you are emphasizing the fact that both approaches
must follow the same path over ground and through moving
airmass. That leads you to believe that both are a crabbed
approach, while slipping is just an optional alignment
issue. That's fair, but alignment is important too and your
position ignores the fact that historically we differentiate
the two approaches based on the fuselage alignment.

There is a reverse logic at work here which
gives the side slip a false role in crosswind management.

The pilot has to manage both the approach and the touchdown.
Slip plays an essential part mostly in the latter, but
putting some in the former may help manage the latter.

Put another way, a side slip is only appropriate for light to moderate
crosswind components and flat landing surfaces.

I disagree. In a strong crosswind, I'm more likely to add
slip to my approach.

The stronger the
crosswind, the rougher the runway, the more critical it is to have
maximum yaw performance at touch down.

I find I use full rudder many times during a typical
thermalling flight, but I can't recall ever needing it as I
touched down.

Side slips and skids are additive,

Huh? They are opposites.

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.

What is the worst of both worlds? I missed something here/

Think of it another way... if I slow down on final, I'll need to change
my direction to maintain a constant ground track.

Agreed. It also changes as wind speed and direction change
with altitude, a common occurrence.

(This is simple trig
that I'll leave to you.) I cannot accomplish this by adding side slip.

Depends on how you use side slip. A slight differential in
the timing of the balanced rudder produces a slipping turn
and the desired new heading.

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.

See above.

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.

As long as you enter it in a balanced way, but the pilot is
not required to do that, and often does not want to.

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

Have a good trip, wherever you're going.



--

------------+
Mark J. Boyd

"T o d d P a t t i s t" escribió en el
mensaje ...
wrote:

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.

Why not just say that in a crosswind landing, on final, you
always have to fly an upwind course through the air to
achieve a ground track aligned with the runway. Always.


Because it is not true...

.... 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.

... etcetera
... etcetera

it is not that complex.
or that subtle
approaching it with the "it is hard to understand" attitude maybe one
reason why
the pilots at your club go all "eyes glaze over" when you offer to run
through the 'subtleties of the slip/crab interaction at point of
flight/landing interface' with them 'just one more time'.

p.s. why not discuss ground erffect again - I *love* that one.

- what I know about ground effect from things pilots have told me:
* the vortex at the tips gets cut in half so the drag is reduced
* list improved relative to the 'thicker' air squashed under the wings

hello & love to all who rig and then de-rig without flying

jonny.

Jonny.

Jonny ;-)

is that Zeb?
jon gogan

"T o d d P a t t i s t" escribió en el
mensaje news
"J.A.M." wrote:

Why not just say that in a crosswind landing, on final, you
always have to fly an upwind course through the air to
achieve a ground track aligned with the runway. Always.


Because it is not true...

More?

No thank you!!!
Obviously I lack the ability to explain myself well enough to be understood.
You see, english is not my craddle language, and I am having some trouble
with it...
And from other posts, as the one you don't see how a slip on base will get
you a longer final, I'm afraid that we have some confusion going here about
the manouever discussed. Maybe we are talking about different manouevers.
I'll try to make a diagram (one image is worth a thousand words...) and post
it somewhere.

Just for this one, I'll fall, though...
Imagine a runway, a left crosswind, for example, and you trying to land. If
your fuselage is aligned with the runway the wind will blow you to the right
of the centerline. You can turn left, into the wind, and then compensate as
you say. Your nose will point left of the runway, and your ground track
(velocity vector) will be aligned with the runway.
Or you can put the left wing down. The glider will try to turn to the left
(uncoordinated), but then you, as a savvy pilot, push the right rudder to
mantain the fuselage aligned with the runway. Ah and pull the nose slightly
up to compensate for the lift loss resulting from moving the lift vector
from the vertical when you banked. Maybe if you are already on the desired
glide slope, you will hide some airbrake to compensate for that lift loss
and not become one with the earth prematurely.
Well, now we are aligned with the runway, wind wing (left) down, right
rudder to mantain alignment... the wind drift now is compensated with the
lateral force produced by the banked wings. So you are not turning upwind as
you suggest, and your ground track is aligned with the runway. Voila!!!
When you are closer to the ground as to concern you, reduce the bank and the
rudder as fit. It'll be for a few seconds anyway.
I've used this technique many times. I have also induced severe slips to
augment my descent rate and make for steeper approaches into short fields
(outlandings) and with obstacles.

Anyway it's sunny outside, I'll be flying again soon! Suggest you to do the
same.
And sorry for the large post!

Jose M. Alvarez.
ASW-24 'BR'

It would appear that there has been confusion over
track and heading, I know you have susssed it Todd
but others may not.

If we consider the relative airflow in the horizontal,
Ignoring the vertical, it is simple. With the wings
level the relative airflow is straight down the fuselage,
the string is in the middle. With a slipping approach
the relative airflow is at an angle from the side of
the lowered wing, the string will be blowing away from
the lowered wing. The aircraft is balanced as you say.

In both cases the track over the ground will, if we
have got it right be lined up with the runway centreline/direction
What puzzles me is that we fly around all day using
the first method to achieve our required track, why
complicate things near the ground.


At 19:30 28 February 2005, T O D D P A T T I S T wrote:
Why not just say that in a crosswind landing, on
final, you
always have to fly an upwind course through the air
to
achieve a ground track aligned with the runway.
Always.

'J.A.M.' wrote:
Because it is not true...

Obviously I lack the ability to explain myself well
enough to be understood.

You are doing fine - better than my Spanish, which
is the
closest I can come to a second language :-)

You see, english is not my craddle language, and I
am having some trouble
with it...
And from other posts, as the one you don't see how
a slip on base will get
you a longer final, I'm afraid that we have some confusion
going here about
the manouever discussed. Maybe we are talking about
different manouevers.

Perhaps

I'll try to make a diagram (one image is worth a thousand
words...) and post
it somewhere.

Just for this one, I'll fall, though...
Imagine a runway, a left crosswind, for example, and
you trying to land. If
your fuselage is aligned with the runway the wind will
blow you to the right
of the centerline.

That's clear.

You can turn left, into the wind, and then compensate
as
you say. Your nose will point left of the runway, and
your ground track
(velocity vector) will be aligned with the runway.

Correct - we agree. At this point, your flight through
the
air is angled to the left of the runway to achieve
the
ground track carrying you straight to the runway, or
as I
originally wrote, you are flying 'an upwind course
through
the air to achieve a ground track aligned with the
runway.'

Or you can put the left wing down. The glider will
try to turn to the left
(uncoordinated), but then you, as a savvy pilot, push
the right rudder to
mantain the fuselage aligned with the runway.

Correct. This is the upwind wing down slipping approach.
The first was the level wings, nose pointed upwind,
crabbing
approach.

Well, now we are aligned with the runway, wind wing
(left) down, right
rudder to mantain alignment...

We are in agreement to here.

the wind drift now is compensated with the
lateral force produced by the banked wings.

But here we disagree. The drift is not stopped by
'lateral
force produced by the banked wings.' It is stopped
because
you are flying a course upwind. You are confused with
exactly the confusion that the original poster felt
was a
problem. Lowering the upwind wing does not oppose
the wind
with a force. The force produced by the wing is countered
by an opposite force produced by the fuselage that
is flying
at an angle to the direction of motion. The direction
of
motion is upwind relative to the air to achieve motion
over
the ground straight towards the runway.

So you are not turning upwind as
you suggest,

Yes, you are. You suffer from the same misunderstanding
that started this thread - a belief that the lowered
upwind
wing produces an unbalanced force. It does not..
You can
see that by considering that you can fly straight towards
the runway in a slip when there is no crosswind, only
by
pointing the fuselage to the side. When slipping the
direction you are going through the air is never aligned
with the fuselage.

and your ground track is aligned with the runway. Voila!!!

Think carefully again.

When you are closer to the ground as to concern you,
reduce the bank and the
rudder as fit. It'll be for a few seconds anyway.
I've used this technique many times.

So have I. It is not the technique that is wrong,
just your
understanding of the aerodynamics.

I have also induced severe slips to
augment my descent rate and make for steeper approaches
into short fields
(outlandings) and with obstacles.

And when you did that, you should have noticed that
your
nose was pointed to the side of the direction you were
actually traveling.

Anyway it's sunny outside, I'll be flying again soon!
Suggest you to do the
same.

It's getting closer to that time - can't wait.