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Hang-gliders

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.

The delta wing

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.

How does it work?

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.

Meet Patrick Monro – passionate about hang-gliders

Many people enjoy the thrill of flying a hang-glider – Patrick Monro, director of Aqua Air Adventure, is no exception. Patrick has always been interested in flight and was intrigued when hang-gliding first started. He said it looked like fun and just had to do it. Patrick has flown hang-gliders both in New Zealand and in other countries, including flying alongside condors in the Andes mountain ranges of South America. He now trains others to fly hang-gliders and takes people for flights in tandem. He is the hang-gliding safety officer for the Auckland Hang Gliding and Paragliding Club.

It’s fun, sometimes scary…

Patrick has had some interesting experiences hang-gliding. Once, he was flying off Beachy Head (300 m white chalk cliffs) in England on a very light wind day and he had some amazing lift that allowed him to fly into Eastbourne and soar over tall apartment buildings. Some ladies spilled their tea when they looked out of their penthouse apartment to see Patrick swooping past only a few metres from their balcony.

A little later, he managed to get into thermal winds off the sea, which is very rare. This allowed him to fly out to sea and fly well out over the English Channel. He was just able to see the coast of France and was thinking he would get to France when he heard a vague rumble in the distance. Suddenly, three jets from the Red Arrows, the British formation flying team, flew past. One was 30 metres above, another 30 metres below and one off to the side. The noise was enormous! Once Patrick realised he was still in one piece, he suddenly recognised the danger he was in from their turbulence, so he made a high-speed retreat back to England!

…and sometimes exhilarating!

Some of Patrick’s experiences are exhilarating –  like the time he was flying at great speed during a competition called speed slalom. It’s like ski slalom, except you are hang-gliding at speed down a mountain slope, manoeuvring between tall thin poles that are 5 metres high. You can get up to speeds of 120 km/h and are sometimes only a few metres above the ground!

Nature of science

The exploration of science can develop in ways it is otherwise intended for. Francis Rogallo, a NASA engineer, researched kites and parachutes in the 1960s and developed the delta or Rogallo wing as a method of returning spacecraft to Earth. The ‘parachute’ was lightweight, durable and highly manoeuvrable and was developed into hang-gliders for sport.

Useful links

Patrick Monro’s organisation Aqua Air can come to your school with all the equipment needed and offer a range of unique, entertaining and educational sessions about the science and history of flight.
www.gethigh.co.nz/pages/schoolprog.htm external link

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