What is
Gliding ?
The term "glider" is broadly used to refer to all types of unpowered
aircraft - from older low performance gliders that have only a limited
ability to gain altitude to modern high performance gliders capable of
flying thousands of kilometers in a single day. The term is also used
to refer to motorgliders of various types (see below). The term
"sailplane" is of more recent vintage and implies higher performance -
at least sufficient for the glider to climb in rising air. (See the
article on gliding for more complete information about the sport of
soaring.) The term "pure glider" (or equivalently, but less commonly
"pure sailplane") may be used to distinguish an unpowered glider from
a motorglider, without implying any differential in gliding or soaring
performance.
Gliders
are aircraft with no internal powerplant. Model gliders are usually
hand-launched or catapult-launched (using an elastic bungee.) The
newer "discus" style of wingtip hand launching
has largely supplanted the earlier "javelin" type of launch. Other
launch methods include ground based power winches, hand-towing, and
towing aloft using a second powered aircraft. As gliders are unpowered,
flight must be sustained through exploitation of the natural wind in
the environment. A hill or slope will often produce updrafts of air
which will sustain the flight of a glider. This is called slope
soaring, and when piloted skillfully, RC gliders can remain airborne
for as long as the updraft prevails. Another means of attaining height
in a glider is exploitation of thermals, which are bubbles or columns
of warm rising air created by hot spots on the ground. As with a
powered aircraft, lift is obtained by the action of the wings as the
aircraft moves through the air, but in a glider, height can only be
gained by flying through air that is rising faster than the aircraft
is sinking relative to the airflow.
Sailplanes are flown using available thermal lift. As thermals can
only be indirectly observed through the reaction of the aircraft to
the invisible rising air currents, pilots find sailplane flying
challenging yet rewarding.
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