AOPA Pilot Magazine - April 2020 - 95

Standard glide
Power: Idle
Prop: Low pitch
Flaps : Retracted
No wind

Flaps: Extended
Headwind/downdrafts
Slipping

Power: Increase
Prop: High pitch
Tailwind/updrafts

FOR GLIDES WITH GEAR DOWN, increasing power, placing the propeller in high pitch, tailwinds, and updrafts will extend the glide distance

and decrease the glide angle. Extending the flaps, slipping, headwinds, and downdrafts have the opposite effect.

Approach path angle. Many PAPIs
and VASIs provide a 3-degree approach
path to a point along the runway, and keeping a balance of white and red lights can
maintain this angle-along with obstacle clearance. The trouble is that, upon
engine failure, most airplanes will land
short of the runway (see "Gliding Flight,"
p. 96). Maintaining such an approach path
requires power, and that's fine until the
day that there isn't any. On one approach
to my home airport at which the runway is
surrounded by tall trees, the only reason I
was able to land on the runway following
an engine failure on final was the relatively
steep approach path I maintain when landing there.
Propeller configuration. For an
adjustable-pitch propeller, low pitch (high
rpm) provides significant drag, but it makes
sense to maintain a low pitch in the pattern in case a go-around is necessary. In an
emergent engine-failure situation, though,
consider pulling the propeller back to a
high pitch (low rpm) setting as a way to
extend the glide.
Gear. While the drag penalty for lowered gear is significant, the gear should
be in landing configuration no later than
the downwind leg of the pattern unless an
emergent situation indicates otherwise.
Compensate for the increased approach
angle with gear down by altering the pattern instead.
Pattern dimensions. With a strong
tailwind on the downwind leg, it makes
sense to turn onto the base leg of the

pattern early. A headwind on landing is
great for minimizing stopping distance
but a headwind on final can significantly
increase the approach angle. In my Cessna
152, a 20-knot headwind increases the
glide angle from 5 degrees to 7.5 degrees,
a 50-percent increase. Always remember
where the wind is coming from and adjust
the pattern accordingly.
Power. Approaching and landing with
minimal power is a good habit. Relying
on power to flatten an approach is not
good preparation for the day it won't be
available. In fact, practicing power-off
approaches regularly guarantees you will
always be familiar with the glide characteristics of your own aircraft. An engine
failure situation is the worst time to
acquaint yourself with them.
Flaps. From my experience, many
pilots extend flaps too early and pay the
price with an attendant increase in drag.
In an experiment with my airplane, adding full flaps (30 degrees) increased the
no-wind glide angle by 50 percent, the
same penalty that a 20-knot headwind
exacted (see "Effects of Flaps," this page).
As a rule, I don't land with full flaps so
that I always have an easy way to add drag
if I need to on short final.
Coordination. Slipping offers an efficient means of increasing the glide angle
without gaining unwanted airspeed. With
unsteady wind, a short slip can give a small
adjustment to the approach path without
destabilizing the approach, as adding and
removing flaps would.

EFFECT OF FLAPS
Choosing the right tool for the job
An ideal aircraft is one that
takes us quickly and efficiently
to our destination and doesn't
require a long runway to land.
But aircraft design involves a
sequence of compromises and
results in a model that is optimized for a specific mission. In
particular, a higher wing loading
(weight/wing area) provides for
a higher cruise speed but comes
at the cost of a higher stall
speed and greater landing distances (see "The Perfect Aircraft
[for the Mission]," September
2019 AOPA Pilot).
This is where high-lift devices
like flaps come in. Extending
flaps can lower stall speed,
increase wing area (and thereby
decrease wing loading), and provide more lift at lower airspeeds.
Flaps also increase approach
angles, which can be both good
and bad. For a field with obstructions near the approach end, an
increased approach angle can
help navigate over them.
But the drag that flaps provide curbs glide distance, and
in an engine-out scenario their
effects can be devastating. Slipping can provide a more flexible
way to manage the approach
path angle.
-CC

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AOPA Pilot Magazine - April 2020

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