A new direction for an old thread: Crosswind landings

The last few threads I initiated were preambles to a discussion I don't
think we've sufficiently explored. Those of you who keep track will
recall that I've asked first, whether we are sufficiently well-trained
(Dear Burt), and second, if some of the models we use to understand
flight couldn't stand improvement.

Let me preface this thread with an analogy. I think we can agree the
that the majority of drivers have little understanding of how their
vehicles work. They have learned that certain control movements result
in changes of direction and speed, but if asked to work their way
intellectually though the process, most would fall short of the level
of knowledge demanded of a pilot about his/her aircraft. And yet, the
vast majority of drivers manage to operate their vehicles successfully
(and safely).

My point is, just because we ask pilots to acquire more knowledge than
drivers, it isn't necessarily required to effectively pilot an
aircraft. And by extension, just because the pilot can control the
aircraft, doesn't necessarily mean that the intellectual models he uses
are accurate.

My object was to get us on a path where we could look more closely at
these models to discern where they might stand improvement.

Obviously, I have a very high opinion of the RAS!

That said, let's talk crosswind landings again. And to start the
discussion, one area of false intuition may result from the differing
nature of wind for an aircraft on the ground and one in the air. While
on the ground, the wind exerts a force on the aircraft. In the air, it
does not. This dichotomy becomes very important during a crosswind
landing, when we transition from being a part of the airmass to
becoming an object on the ground.

I've found that pilots can speak very clearly about the role of wind on
navigation when they are in cruising flight. But the closer they get to
the ground, I start to see control usage more appropriate for taxiing
than flying. Has our understanding of the effect of wind as viewed from
the ground infected our understanding of its effect on flight? And do
these become more obvious as we get approach the transition from flight
to taxiing? And perhaps, thus, much of the confusion pilots suffer over
side slips?

Asking pilots to describe the crosswind approach leads to a variety of
inaccurate language. Digging deeper will lead, almost inevitably, to
the conclusion that the wind is exerting a force on the glider, and
that the wing must be tilted in order to counteract that force (and the
rudder applied against the bank to keep the glider from turning). This
works, and even makes some sense. But the notion that the tilted lift
vector is compensating for wind drift is flawed. Useful, but flawed.

The Soaring Flight Manual (1999) says the following on the subject of
Crosswind Landings (page 14-15):

"The traffic pattern for crosswind landings is the same up to the final
approach using crab to maintain pattern alignment. In light to moderate
crosswinds, a wing-low sideslip or crab may be used on final to
maintain runway alignment. A strong crosswind usually REQUIRES a
COMBINATION of the two."
[the emphasis is mine]

This is an interesting mix of useful yet incorrect information. What
concerns me most is the implication that crabbig and side slipping are
additive. They are not. But if you deconstruct the implicit logic, you
are led to the conclusion that side slips counteract the force of the
wind. Otherwise, how can the effects be additive?

I suspect there is a visual/pschological effect that has crept its way
into the way we rationalize control use during the crosswind approach.
Consider it from another point of view. You adjust your path across the
ground by changing your direction. The most efficient way to do this is
by executing a coordinated turn. Once on the appropriate heading to
achieve a desired ground track, you fly wings level. If there is a
crosswind and your heading differs from your ground track, you are
crabbing. Just that simple. Whether you are 10 feet, 100 feet, or 1,000
feet above the ground.

The role of the side slip, then, since it is aerodynamically the same
as a forward slip, is solely to change the heading (but not the
direction) of the aircraft. The effect on flight path is exactly the
same as applying some spoiler. The advantage gained is that it brings
the landing gear more closely aligned to the aircraft's direction over
the ground, and thus reduces any sideloadings at touchdown. This is one
of two reasons to perform a slip during a crosswind landing: aligning
the gear with the direction of travel. The other, to steepen the glide.

So why might a pilot think that the side slip adds "additional force"
against the crosswind? Perhaps we are put ill at ease by a large crab
angle. Pointing the fuselage more directly down the runway makes the
approach look better (closer to "normal") and perhaps gives the
impression of additional control. But it doesn't add any force, and, in
fact, reduces the freedom of control.

I know one direction this thread will follow... a perfectly reasonable
one, but let me color it a little: is it appropriate that we should ask
fledgling pilots to handle the controls differently in the riskiest
flight environments? We are taught, rehearsed, and tested on our
abilities to maintain coordinated flight. Then, under the most trying
conditions, we are asked to apply counter intuitive control movements
at low altitudes, many of them based on a false impression of the
forces acting on the aircraft and the effects control usage has on
balancing those "external" forces. It should be mantra with us all,
that when things are going bad, the first thing we should do is return
to and/or maintain coordinated flight. Understanding the foundations of
crosswind navigation are critical to helping all pilots fly more
safely. If you are confused about what keeps the aircraft tracking down
the runway, you may find yourself making control inputs against upsets
that increase your risk of loss of control.

Shouldn't every pilot know that when things are going bad on final, you
should return to a wings level, coordinated crab, where your ASI is
accurate, you have full control available, and you are exercising those
skills which your training has made most instinctive. Once you've
sorted out the upset, then you can return to your "runway alignment"
slip.

Lately I've been testing an exercise, one I tried years ago with
several students (with good results) but never formalized: I would have
pilots establish their final leg with a crab. Then I would have them
enter and recover from a slip, descibing is utility in aligning the
gear with the runway, noting its increased drag. This reinforced the
role of the slip, the role of the crab angle, and the necessity to exit
the slip if you needed to extend your glide. Two distinctly different
maneuvers meant to achieve different ends, applied together to ease the
tranistion from flight to taxi.

You might want to run through the Building Models thread where I've
tried to address the false dichotomy of side and foward slips. Viewing
a side slip as two distinct maneuvers... a turn and a slip, migh help
to put my last paragraph in context.

I'm hoping you'll poke holes, and not take too much offense when I
return your efforts in kind. That's the point of this thread.