Soaring is the act of working to remain aloft, while gliding is the management of a controlled but constant rate of descent.
A sailplane always sinks relative to the air around it. Motorless flight is maintained by periodically flying in updraughts where the air is rising faster than the sailplane’s rate of sink. Efficient use of naturally occurring updraughts can sustain flight for many hours at a time.
Updraughts, or “thermals” as referred to by soaring pilots, are by-products of solar heating. As the sun heats the ground, the ground in turn heats the air immediately above it. Since the warm air rises, the warmer air near the ground form thermals which reach an average altitude of 4,000 to 5,000 feet.
Sailplanes are designed to fly with very little loss of altitude as they pass through the air. Even relatively weak thermals can support soaring flight. The majority of sailplanes have wing spans ranging form 50 to 70 feet with weights ranging from 600 to 1,400 pounds. Modern sailplanes have maximum speeds in excess of 250km/h and “best glide ratios” between 30 and 55 (the glide ratio represents the forward distance achieved per unit of height loss – a glide ratio of 30 means that a sailplane can glide 30 km for every 1 km of height lost).
A sailplane is controlled by the coordinated use of elevator, ailerons and rudder which steer the aircraft in an efficient manner.
The first step to maintaining flight is maintaining adequate airspeed over the wings to produce lift and forward momentum. A horizontal movable surface on the tail helps push the nose of the aircraft down (for increased speed) or up (to reduce speed). It is known as the ‘elevator’ and is controlled by the stick. This motion is known as ‘pitch’. Without airspeed the wing will not produce lift and will ‘stall’.‘
Turning the sailplane is controlled by the use of ‘ailerons’. Ailerons are movable surfaces on the wings that once activated alter the lifting characteristic of each wing respectively. They work in opposition to each other (as one goes up, the other goes down). The pilot controls these by moving the ‘stick’ left and right. The effect will be to raise one wing and lower the other. This is how a turn is initiated and is referred to as ‘roll’.
A side-effect of the roll, particularly noticeable with sailplanes, is that the roll will cause the aircraft to ‘slip’ sideways as one wing moves faster than the other due to its improved efficiency. This is shown by the nose pointing in the opposite direction to the desired turn. This motion is known as ‘adverse yaw’. This slipping must be counteracted or else the aircraft will not be efficient in the air and will sink. A large movable vertical surface on the tail known as the ‘rudder’ is used to counteract this effect. The pilot operates this through pedals in the cockpit.
A pilot will maintain safe and efficient flight when all three, pitch, roll and yaw are ‘coordinated’ in both turning and straight and level flight.
In addition to achieving sustained flight soaring pilots challenge themselves through ‘cross country flying’
Similar to the challenge of open water sailing or back country hiking, a pilot will attempt to fly beyond the minimum safe glide distance from the air field (the distance that can be achieved without the assistance of thermals as dictated by the glide ratio of the aircraft). The pilot will navigate from one region to another while sustaining flight and return to their home airfield at the end of the day. Competitions are regularly held whereby pilots will be set a ‘task’ for the day relating to time and distance to be achieved. This challenge carries with it the specter of the ‘land out’. Sailplanes regularly land in open fields when they can no longer sustain lift.