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. 

Wave

Lee waves occur when a wind blows over a mountain. Provided that there is a steady increase in wind strength with altitude without a significant change in direction, standing waves may be created. These waves reach heights much greater than the original obstruction and so can permit gliders to climb to the stratosphere. This lift is often marked by long, stationary lenticular (lens-shaped) clouds lying perpendicular to the wind. A mountain wave was used to set the record for highest altitude by a glider when Steve Fossett and Einar Enevoldson, wearing pressure suits, soared to an altitude of 50,699 feet (15,453 m) on August 29, 2006. The current world distance record of 3,008 km (1,869 statute miles) was also flown using mountain waves in South America

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.