Hang-gliders are unpowered aircraft. They maintain flight by employing a flying surface (wing) called an aerofoil. While powered aircraft use their own power source (motor and propeller or jet turbine) to stay up, hang-gliders require air movement to stay aloft.
Hang-gliders are triangle-shaped aerofoils, called delta wings. They have evolved from modified parachutes (Rogallo wings) to the sleek aerofoil shapes we see today. Modern hang-gliders have stiff aluminium struts inside the fabric to give them shape.
Since a hang-glider is unpowered, it can’t take off from low ground. It has to be launched from somewhere high like a hill or mountain. Gravity is the main force on a hang-glider. This is the weight of the pilot and the wing. The weight produces the thrust that keeps the aerofoil moving through the air. The aerofoil shape of the wing stops the hang-glider from dropping like a stone. It produces lift. The aerofoil forces the air flowing over the top of the wing to travel faster, thereby ‘stretching’ it to produce a low-pressure area. Meanwhile, the downward and forward motion of the wing compresses the air flowing under the wing. The aerofoil is then drawn up into the area of low pressure, producing lift.
If the air is still, it will slowly descend. A hang-glider descends at the rate of about 1 metre per second (a slow walking pace of about 3.6 km/h). In order to not lose height, a hang-glider must find air going up as fast as the glider is descending. For example, if a glider is flying over a vertical coastal cliff and there is a light breeze blowing in directly from the sea and the air is being forced vertically upwards by the cliff at 3.6 km/h, the hang-glider can fly along the cliff without losing height. If there is a stronger breeze, the glider will start gaining altitude.
Some hang-glider pilots attach small motors and propellers to their hang-gliders. This turns them into microlights and means they can take off and climb from flat ground just like a normal aircraft.
While any form of aviation carries an element of risk, gliding is relatively safe. Gliders are very strongly built, and there is no engine to fail. In the unlikely event of an accident occuring, there is no fuel to burn. Gliding is a weather dependent sport. In the absence of thermals, which gliders use to stay in the air, an average flight to 3000ft will last approximately 20 minutes. When learning to fly, you will be taught how to find & stay in thermals, and a thermalling flight is much longer.
Gliders can stay aloft by a number of means. By far the most common is called thermalling. When the ground is heated by the sun, periodically a parcel of heated air ascends, often to many thousands of feet, as the temperature of the air close to the ground becomes higher that its surroundings. If a glider is flown to stay in that column of rising air, by circling, the glider will also be swept aloft. After the pilot reaches the top of the thermal, they fly off, gradually losing height, until they reach the next one.
When the thermals stop working, the glider will gradually descend. A glider can fly about 10 km for each 1000 feet of height, so there is a good chance that an airfield will be within reach. In the event of no airfield being within reach, the glider will land in a paddock. Paddock landings are part of the training of every glider pilot once they are ready to fly cross country. The glider can be retrieved by a tug, or, of this is not possible, the glider is disassembled and returned to the airfield in its container.
