Thermals
When
the sun heats an area of ground the air above is then heated and
becomes buoyant to the point where it breaks loose from the
surface building in strength and volume as it rises towards
the clouds. The moisture contained within this thermal mass
of rising air then condenses out to form a cumulous cloud.
Glider pilots learn to read these cumulous clouds then by traveling
from one thermal to the next, can cover great distances.
This is the extra dimension found in no other form of
flight.
Ridge Lift
In
a way similar to wave but without the extreme heights. As the
wind blowing roughly square across a low mountain range or
ridge is forced up and over the obstacle the next layer
above must do the same. On the down-wind side the air
descends rapidly and can curl over dangerously back and down toward
the hill. A glider can fly safely out in front or the up
wind side of this ridge in rising air and thus travel the full
length of the ridge or turn and make several passes
climbing with each pass until sufficient height is
gained to allow the pilot to head off on track again.
Very often as this air is forced up an Orographic cloud
is formed which will sometimes hide the crest of the
range.
The Glider
A
glider is a very high efficiency aircraft designed with an
exceptionally flat glide angle and no mechanical means of
propulsion. At the upper end of sailplane design this glide
angle, expressed as a ratio, can exceed 60:1. In other
words, in still air at say 5200' (1 mile) above ground this
glider will travel 60 miles before touching down. Apply the
same situation to a light aircraft with its engine switched off,
that pilot may just reach 10 miles. These days the average
club single seat glider could have a glide ratio between 33:1 and
44:1. World records for distance flown by a glider in a
single flight have exceeded 3000 kilometers. Local club
cross-country pilots regularly exceed 300 kilometers with flights
700 to 1000 kilometers not uncommon. In most cases
returning to their home fields. Although landing out is
routine and regularly practiced.
The Controls
A
sailplane has all the same directional controls as a powered
aircraft. Speed is controlled by the attitude of the
glider. As with a bicycle with no chain the
only way it can move is to roll down a hill. A gentle
slope results in a gentle speed and a steep slope, high
speed. By lowering the nose the glider increases in
speed and as the nose is lifted it slows down. If the glider
continues to slow it will reach a point where it can no longer fly
and is said to be 'stalled'. This situation is simply
corrected by again lowering the nose and accelerating back to
flying speed. The pilot has total control in all directions
of flight. In most cases, gliders are capable of
performing a wide range of aerobatic manoeuvres. In effect,
the glider is always in descent, the skill being to find air
currents rising faster than the descent rate of the
glider.
Engines
However
much the purist glider pilot rails against the hideousness of an
engine he cannot get off the ground without one. The most
common method of launching a sailplane is by aero-towing
behind a light aircraft powered by an engine
anywhere between about 150 hp and 300 hp. Many
retired top-dressing aircraft find useful employment each weekend
towing gliders aloft. The second most common method is to use
a winch, usually powered by a V8 car engine and set-up way
down the far end of the airfield. Using either a steel wire
or a synthetic rope the glider is winched into the air.
Gliders can be launched behind motor vehicles or catapulted off a
ridge using long bungee cords although these last two methods are
largely out dated. There are several designs of motorised glider
from self launching gliders to motor gliders capable only of
maintaining height but not able to take off under their own
power. These lower powered units are called Sustainers
or more recently, Turbos.
Safety
Gliders are designed and constructed to very high standards of strength, reliability and safety. In service, the glider must conform to rigorous safety standards and regular inspections as specified by the relevant Aviation Authorities. In many cases gliders are able to perform manoeuvres. that powered aircraft could not withstand without damage. This coupled with the sailplane's ability to land safely in virtually any farm paddock from the size of a rugby field up and the slower approach speed further increases the safety margins. Many pilots will tell you they feel safer at altitude in their sailplanes than they do driving home from the air field. However, as with any technically demanding activity there is a certain risk which is minimised by thorough training and regular practice. In New Zealand, all gliding operations must take place under the direct supervision of a Duty Instructor, further enhancing safety.