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----------