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Using rising currents of air to keep the
sailplane airborne, the experienced glider pilot is able to soar like a bird,
silently exploring the skies and often covering many miles before returning home
several hours later. Modern gliders, or sailplanes as they are frequently
called, are built of fibre glass, they have wingspans of between 15 and 25
metres and their advanced design enables them to glide long distances - up to 30
miles from 5,000'.
Gliders
Gliders are essentially light aircraft without
engines. With the same basic controls as any other aeroplane, they are
highly manoeverable and extremely controllable. Unlike most powered
aircraft, however, modern gliders have long slim wings which are capable of
generating large amounts of lift and their overall design is highly streamlined
to reduce drag. For many years most gliders were made from wood and
fabric, however the development of modern materials such as glass fibre, carbon fibre and kevlar
has revolutionised glider design resulting in today's high performance
sailplanes.
Getting Airborne
There are several methods of launching
gliders, but the most common are by a static winch or a tow behind a light
aeroplane (aerotow).
 | Winch:
The winch is positioned at the upwind end of the airfield, the glider launch
point at the other end. When the pilot is ready to launch a steel
cable is attached to the glider and then wound onto the drum at the winch,
this pulls the glider forward and the wing generates lift enabling the pilot
to climb, very much like launching a kite. The height achieved on a
winch launch varies and is dependent on a number of factors - the length of
the field and therefore how much cable can be pulled out, the power of the
winch and on a daily basis how strong the wind is. At Cross Hayes we
average around 1,300' to 1,600' although on some stronger wind days 2,000'
is possible. |
| Aerotow:
The glider is towed into the air behind a light aircraft (tug). During
the tow, the pilot of the glider flies in formation behind the tug and is
able to choose the point at which he releases the tow rope. |
Staying Airborne
Following its launch, the glider embarks on a gradual
descent path through the surrounding air. Fortunately, however, the air is
never perfectly still - in places it will be rising, in others it will be
descending. By flying in air which is rising faster than the glider is
descending the pilot can gain height. The principle is the same as that of
a person trying to walk down an escalator that is traveling in the opposite
direction - if the escalator is moving upwards fast enough, the person will be
carried to the top despite their efforts to go down. There are three main
sources of rising air, or lift as it is more commonly referred to:
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Thermal:
This is the most common form of lift used by pilots flying from Cross
Hayes. Differential heating of the ground causes some surfaces to heat
the air above them more quickly than surrounding areas. Eventually
this warm air will start to rise, producing a column of rising air, known as
a thermal. On a summers day these ‘thermals’ are often marked by small cumulus
clouds. Having found a thermal, the glider pilot will circle in the rising
air, often turning quite tightly, as the rising air carries the glider
upwards. By staying within the area of rising air the glider pilot will be
able to gain height, often reaching the bottom of the clouds above, and, by moving from one area of lift to the next, can cover
many miles in a single flight. |
| Hill Lift:
When the wind blows against an obstruction such as a hill or ridge of higher
ground, the air is forced upwards as it follows the contours. This creates a band of lift
parallel to the ridge and the glider pilot can fly back and forth in this lift,
maintaining or gaining height, for as long as the wind carries on blowing. |
| Wave:
Most commonly found in mountainous
regions, wave occurs when the air blowing over a mountain or hill sets up an
oscillatory motion, similar to that achieved by rapidly jerking a long rope
up and down. These oscillations often go to great heights - far in
excess of the height of the original obstruction - and cover large
areas. By flying in the up going part of the system the glider pilot
can often make extremely high altitude climbs as well as being able to
travel great distances along the system. |
Gliding Records
There are national and international records
for gliding covering overall distance, time taken to complete closed circuits of
set distance and for absolute altitude and gains of height. In July 1995 the UK distance record for Gliding was
broken when the first 1,000 km (620 miles) flight to be made in the UK was
completed. Flying in a two seater glider the pilots landed back at their
launch site after a 12 hour flight. The fastest recorded cross country to be
flown in the UK was a 100 kilometre flight which was completed at an average
speed of 173 kph (107 mph). The UK height record currently stands at
11,570 metres (37,700 feet), which was achieved in wave over Scotland during
1995.
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