Page 9 - July 2013

JULY 2013 - SEXY X2 MAGAZINE - 9
opposite directions and the glider begins its
unpowered flight. The tow plane is then
free to return to the airport and set up for
another tow.
Another popular launching method
is winch launching. An engine
powers a large winch on the ground
and a long cable connects the winch
to another release mechanism lo-
cated on the underside of the glider.
When the winch is activated, the glider
is pulled along the ground toward the
winch and takes off, climbing rapidly. As the
glider rises, the pilot can release the winch line
as in an aero-tow and continue his flight.
Staying in the Air
The wings on a glider have to produce enough lift to
balance the weight of the glider. The faster the glider
goes the more lift the wings make. If the glider flies, fast
enough the wings will produce enough lift to keep
it in the air. However, the wings and the body of
the glider also produce drag, and they produce
more drag the faster the glider flies. Since there is no
engine on a glider to produce thrust, the glider has to
generate speed in some other way. Angling the glider
downward, trading altitude for speed, allows the glider
to fly fast enough to generate the lift needed to
support its weight.
The way you measure the perfor- mance
of a glider is by its glide ratio. This ratio
tells you how much horizontal distance a
glider can travel compared to the alti-
tude it has to drop. Modern gliders can
have glide ratios better than 60:1. This means
they can glide for 60 miles if they start at an altitude of
one mile. For comparison, a commercial jetliner might have
glide ratios somewhere around 17:1.
If the glide ratio were the only factor involved, gliders would
not be able to stay in the air nearly as long as they do. So
how do they do it?
The key to staying in the air for longer periods of time is to
get some help from Mother Nature whenever possible. While
a glider will slowly descend with respect to the air around
it, what if the air around it was moving upward
faster than the glider was descending?
It is kind of like try- ing to paddle a kayak
upstream; even though you may be cut-
ting through the water at
a respect-
able
pace,
you
are not really making any progress with respect to the river-
bank. The same thing works with gliders. If you are descend-
ing at one meter per second, but the air around the plane is
rising at two meters per second, you are actually gaining
altitude.
There are three main types of rising air used by glider
pilots to increase flight times:
Ther- mals
Ridge lift
Wave lift
Thermals
Thermals are columns of rising air created by the
heating of the Earth’s surface. As the air near the
ground is heated by the sun, it expands and rises.
Pilots keep an eye out for terrain that absorbs the
morning sun more rapidly than surrounding
areas. These areas, such as asphalt park-
ing lots, dark plowed fields and rocky
terrain, are a great way to find
thermal columns. Pilots also
keep a look out for newly form-
ing cumulus clouds, or even large
birds soaring without flapping
their wings, which can also be
signs of thermal activity.
Once a thermal is located, pilots
will turn back and circle with- in
the column until they reach their desired
altitude at which time they will exit and resume
their flight. To prevent confusion, gliders all circle in
the same direction within thermals. The first glider in the
thermal gets to decide the direction -- all the other gliders that
join the thermal must circle in that direction.
Ridge Lift
Ridge lift is created by winds blowing against mountains, hills
or other ridges. As the air reaches the mountain, it is redirected
upward and forms a band of lift along the windward side of
the slope. Ridge lift typically reaches no higher than a few hun-
dred feet higher than the terrain that creates it. What ridge lift
lacks in height however, it makes up for in length; gliders have
been known to fly for a thousand miles along mountain chains
using mostly ridge lift and wave lift.
Wave Lift
Wave lift is similar to ridge lift in that it is created when wind
meets a mountain. Wave lift, however, is created on the
leeward side of the peak by winds passing over the moun-
tain instead of up one side. Wave lift can be identified by
the unique cloud formations produced. Wave lift can reach
thousands of feet high and gliders can reach altitudes of more
than 35,000 feet.
Detecting Lift
Columns and bands of rising air obviously benefit any glider
pilot, but how can you tell if you are flying in one? The answer
is the variometer, a device that measures the rate of climb or
descent. The variometer uses static pressure to detect changes
in altitude. If the glider is rising, then the static pressure drops
(because air pressure decreases the higher you go). If the
glider is sinking, then the static pressure rises. The needle on
the variometer indicates the rate of change in altitude based