Controlling Your
Approach Path
Drop flaps or
slip the ship
At any point in the approach,
the airplane has three kinds of energy available to
it: kinetic energy, which is that given it by speed;
potential energy that comes from its height above the
ground; and the controlled energy, which can be given
it by the throttle. The key to a successful approach,
whether it is totally power off from downwind or flown
onto final with power, is to first make sure the airplane
has enough energy of all kinds--especially height and
speed--that you're guaranteed to make the runway no
matter what happens. Then, once we're on final, we can
use the tools at our disposal to gradually get rid of
excess energy so that we land on our chosen touchdown
point.
If we're above the optimum
speed when the nose comes up to flare, the airplane
will skate along in ground effect and float--which not
only makes it more difficult to hit a given spot, but
also gives any crosswind more time to work on us. If
we're slow, the airplane will have less than the normal
amount of hang time during flare and, if slow enough,
can deposit us on the runway in a spectacularly abrupt
manner.
Extending the landing gear
on a retractable-gear aircraft greatly increases drag
and steepens the glidepath. This should be the first
configuration change made while still on downwind, to
avoid forgetting it and help to stabilize the approach.
The only time gear extension would be delayed until
final approach would be on an emergency landing where
we don't want to commit to the permanent drag of the
landing gear until we're positive we're going to make
the field.
Flaps represent a way to
increase the approach angle because the lift generated
by flaps is accompanied by an increase in drag. Although
it varies with the exact type of flap (Fowler, slotted,
unslotted, simple hinged), it is generally assumed that
as flaps are extended past 15 degrees, they begin generating
more drag than lift. As the wing's lift increases, so
does the drag, and the nose must go down to maintain
speed--which increases the glidepath angle. The increase
in lift from 15 degrees to 40 degrees of flap extension
is small, but the drag skyrockets. Those favoring power-on
approaches generally extend their flaps by varying amounts
on the different legs, so that when they turn final,
they extend the last notch.
And then there is the slip.
Before training airplanes were equipped with flaps,
the forward slip was a major part of a student's training.
Knowing how to use a forward slip gives a pilot almost
total control over where his airplane will contact the
runway. A slip is nothing more than holding an airplane
in a bank with aileron and keeping it from turning with
opposite rudder. The resulting cross-controlled, wing-down,
nose-out-of-line attitude dramatically increases drag,
although the maximum amount depends very much on the
make and model of airplane. Some aircraft carry either
prohibitions or cautions about slipping the airplane
with the flaps fully extended; check your POH.
As the airplane approaches
ground effect, the controls are released and the airplane
physically aligned with the runway--unless a crosswind
requires that you transition into a sideslip. For recovery,
rather than suddenly neutralizing the controls at once,
we're going to slowly release the inputs and exit the
slip gradually, which gives us more opportunity to accurately
judge the wind. At the same time, it lets us do a much
better job of getting into ground effect at the altitude
we want, rather than just accepting whatever we get
if we pop out of the slip.
The beauty of coming out of the slip slowly is that,
if we see that we're higher than we want to be, we just
hang on to a bit of the slip a little longer and lose
those last few feet of unwanted altitude.
Controlling the glidepath requires understanding the
techniques available and the dynamics of the airplane,
as well as the effects of the air through which it is
moving. Still, number one on the list of skills we need
to develop is the ability to visually fix on our reference
point on the runway and understand what its movement
is telling us. After all, we can’t correct what
we can't see.
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Gathering
of Mustange & Legends 2007
By Larry Wilcox
Click to view Slideshow Presentation
