Flight Training - July 2013 - 38

THE PURPOSE OF FLYING GLIDERS IS TO HARNESS
THE EARTH'S ENERGY
AS A MEANS OF STAYING ALOFT.
The purpose of flying gliders is
to harness the Earth’s energy as a
means of staying aloft. Sometimes
that may be for only a few minutes,
and sometimes it’s for many hours,
thousands of miles, and at altitudes
usually reserved for airliners. Given
that atmospheric energy often is
irregular and unpredictable, glider
pilots who excel do so by maximizing altitude gain during periods of
lift and minimizing altitude loss in
sink—areas in which no lift exists.
With more than 50 gliding world
records, and as the first person in
the world to fly a glider more than
1,000 miles, Knauff knows something about the basics of his sport.
In a powered airplane, he says, you
select a throttle setting that results
in a certain speed and fuel burn for
a given altitude. But in soaring, the
pilot picks the airspeed that results
in a certain amount of sink or lift.
“In gliders, if we want to get there,
the speed turns out to be important,” he says. Knauff’s favorite
tool for explaining the relationship
between sink and airspeed is a polar
graph—a two-axis graph that plots
descent rate versus airspeed.
Although the graph is a good way
to illustrate best glide speed, minimum sink, and other speeds to fly,
more than anything else it shows
how wind and weight affect the
speed we pick to make the airplane
glide a certain distance (see “Polar
Graph,” page 39).

Best glide is the airspeed that gets an
airplane the farthest distance through the
air with the least altitude loss. It’s also
known as max L/D (articulated as lift over
drag). Every airplane design results in
an inherent glide ratio—7 to 1 or 9 to 1, or
whatever the number is. An aircraft with a
9-to-1 glide ratio can go nine feet forward
for every foot of altitude lost. Competitionlevel gliders boast a ratio of around 60 to 1,
while in the upper atmosphere the Space
38 /

FLIGHTTRAINING.AOPA.ORG

Shuttle was around 1 to 1—something similar to what you would get throwing a rock
out a window.
Student pilots are taught that if the
engine quits at altitude, the strategy is
to pick a landing site, pitch for best glide
speed, and then try a restart. This is a
logical chain of events, but it ignores many
variables—including altitude, weather, and
location. Understand Knauff’s approach to
soaring and those gaps start to fill in.

REAL WORLD. The polar graph
is a great theoretical tool to help
us conceptually understand the
relationship of sink to airspeed,
but putting it into practice isn’t always
straightforward. We generally practice
engine failures in flight training as if
they are sudden and unexpected events,
but in many cases there is some amount
of warning. When those warnings start
to sound, it’s clearly time to look for a
place to land, whether that’s an airport or the closest farm field. But if the
engine is still running and producing

http://FLIGHTTRAINING.AOPA.ORG

Flight Training - July 2013

Table of Contents for the Digital Edition of Flight Training - July 2013