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.



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Mark J. Boyd