hang gliding- history & science
Many thanks to John Barratt of South Downs Hang Gliding for the information in the following article on The History of Hang gliding and How a Hang Glider works.
Hang gliding is an air sport in which a pilot flies a light and non-motorized foot-launch aircraft called a hang glider. Most modern hang gliders are made of an aluminium or carbon fibre frame covered with synthetic sailcloth to form a wing. The pilot is enclosed in a harness suspended from the airframe, and exercises control by shifting body weight in opposition to a control frame. Other devices, including modern aircraft flight control systems, may be used.
In the sport's early days, pilots were restricted to gliding down small hills on low-performance hang gliders. However, modern technology gives pilots the ability to soar for hours, gain thousands of metres of altitude in thermal updrafts, perform aerobatics, and glide cross-country for hundreds of kilometres.
The British Hang gliding and paragliding Association, Fédération Aéronautique Internationale and National Airspace governing organizations now control the regulatory aspects of hang gliding. As a result safety standards are rigorous and training schools are highly regulated.
Early Gliders:
Most early glider designs did not ensure safe flight; the problem was that early flight pioneers did not sufficiently understand the underlying principles that made a bird’s wing work. Starting in the 1880s technical and scientific advancements were made that led to the first truly practical gliders. Otto Lilienthal built controllable gliders in the 1890s, with which he could ridge soar. His rigorously documented work influenced later designers, making Lilienthal one of the most influential early aviation pioneers. His aircraft was controlled by weight shift and is similar to a modern hang glider.
Hang gliding saw a stiffened flexible wing hang glider in 1904, when Jan Lavezzari flew a double lateen sail hang glider off Berck Beach, France. In 1910 in Breslau, the triangle control frame with hang glider pilot hung behind the triangle in a hang glider, was evident in a gliding club’s activity. The biplane hang glider was very widely publicized in public magazines with plans for building; such biplane hang gliders were constructed and flown in several nations since Octave Chanute and his tailed biplane hang gliders were demonstrated. In April 1909, a how-to article by Carl S. Bates proved to be a seminal hang glider article that seemingly affected builders even of contemporary times, as several builders would have their first hang glider made by following the plan in his article.
On November 23, 1948, Francis Rogallo and Gertrude Rogallo applied for a kite patent for a fully flexible kited wing with approved claims for its stiffenings and gliding uses; the flexible wing or Rogallo wing, which in 1957 the American space agency NASA began testing in various flexible and semi-rigid configurations in order to use it as a recovery system for the Gemini space capsules. The various stiffening formats and the wing’s simplicity of design and ease of construction, along with its capability of slow flight and its gentle landing characteristics, did not go unnoticed by hang glider enthusiasts. In 1960-1962 Barry Hill Palmer adapted the flexible wing concept to make foot-launched hang gliders with four different control arrangements. In 1963 Mike Burns adapted the flexible wing to build a towable kite-hang glider he called Skiplane. In 1963, John W. Dickenson adapted the flexible wing airfoil concept to make another water-ski kite glider; for this, the Fédération Aéronautique Internationale vested Dickenson with the Hang Gliding Diploma (2006) for the invention of the “modern” hang glider. Since then, the Rogallo wing has been the most used airfoil of hang gliders.
Modern Glider Construction
Due to the poor safety record of early hang gliding pioneers, the sport had traditionally been considered unsafe. Advances in pilot training and glider construction have led to a much improved safety record. Modern hang gliders are very sturdy when constructed to HGMA, BHPA, DHV, or other certified standards using modern materials. All modern gliders have built-in dive recovery mechanisms such as luff lines in kingposted gliders, or “sprogs” in topless gliders.
Fabrics Used
There are basically two types of sail materials used in hang glider sails: Woven Polyester Fabrics, and Composite Laminated Fabrics made of some combination of polyester film and polyester fibers.
Woven polyester sailcloth is a very tight weave of small diameter polyester fibers that has been stabilized by the hot-press impregnation of a polyester resin. The resin impregnation is required to provide resistance to distortion and stretch. This resistance is important in maintaining the aerodynamic shape of the sail. Woven polyester provides the best combination of light weight and durability in a sail with the best overall handling qualities.
Laminated sail materials using polyester film achieve superior performance by using a lower stretch material that is better at maintaining sail shape but is still relatively light in weight. The disadvantages of polyester film fabrics is that the reduced elasticity under load generally results in stiffer and less responsive handling, and polyester laminated fabrics are generally not as durable or long lasting as the woven fabrics.
Triangular control frame
In most hang gliders, the control is and has been achieved using a horizontal bar held by the pilot, also known as ‘triangle control frame’ (TCF), ‘control bar’ or ‘base bar’. This bar is usually pulled to allow for greater speed. Either end of the control bar is attached to an upright, where both extend and are connected to the main body of the glider. This creates the shape of a triangle or A-Frame. In many of these configurations additional wheels or other equipment can be suspended from the bottom bar or rod ends.
The Harness
Pilots fly in a harness which supports their body. Several different types of harnesses exist. Pod harnesses are put on like a jacket and the leg portion is behind the pilot during launch. Once in the air the feet are tucked into the bottom of the harness. They are zipped up in the air with a rope and unzipped before landing with a separate rope. A cocoon harness is slipped over the head and lies in front of the legs during launch. After getting into the air the feet are tucked into it and the back is left open. A knee hanger harness is also slipped over the head but the knee part is wrapped around the knees before launch and just pick up the pilots leg automatically after launch. A supine or suprone harness is a seated harness. The shoulder straps are put on before launch and after take off the pilot slides back into the seat and flies in a seated position.
Safety Features
Pilots carry a parachute enclosed in the harness. In case of serious problems the parachute is manually deployed and carries both pilot and glider down to earth. Pilots also wear helmets and generally carry other safety items such as knives (for cutting their parachute bridle after impact or cutting their harness lines and straps in case of a tree or water landing), light ropes (for lowering from trees to haul up tools or climbing ropes), radios (for communication with other pilots or ground crew), and first-aid equipment.
Pilot Skills
The accident rate from hang glider flying has been dramatically decreased by pilot training, this includes a deep understanding of meteorology and the weather. Early hang glider pilots learned their sport through trial and error (and gliders were sometimes home-built). Training programs have been developed for today’s pilot with emphasis on flight within safe limits, as well as the discipline to cease flying when weather conditions are unfavourable, for example: excess wind or risk of cloud suck.
Launch techniques
Launch techniques include foot-launching from a hill, tow-launching from a ground-based tow system, aerotowing (behind a powered aircraft), powered harnesses, and being towed up by a boat. Modern winch tows typically utilize hydraulic systems designed to regulate line tension, this reduces scenarios for lock out as strong winds result in additional length of rope spooling out rather than direct tension on the tow line. Other more exotic launch techniques have also been used successfully, such as hot air balloon drops from very high altitude.
Understanding Meteorology & Weather
Top to bottom
When weather conditions are unsuitable to sustain a soaring flight, this results in a top to bottom fight and is referred to as a “sled run”.
Longer flights
For soaring flight and cross-country flying you need good gliding weather. Well formed cumulus clouds with darker bases suggest active thermals and light winds. A glider in flight is generally continuously descending. To achieve an extended flight, the pilot must seek air currents rising faster than the sink rate of the glider. Selecting the sources of rising air currents is the skill that has to be mastered if the pilot wants to achieve flying long distances, known as flying cross-country (XC). Rising air masses derive from the following sources:
Thermals
The most commonly used source of lift is created by the sun’s energy heating the ground which in turn heats the air above it. This warm air rises in columns known as thermals. Soaring pilots quickly become aware of land features which can generate thermals and their trigger points downwind, because thermals have a surface tension with the ground and roll until hitting a trigger point. When the thermal lifts, the first indicators are the swooping birds feeding on the insects being carried aloft, or dust devils or a change in wind direction as the air is pulled in below the thermal. As the thermal climbs, bigger soaring birds indicate the thermal. The thermal rises until it either forms into a cumulus cloud or hits an inversion layer, which is where the surrounding air is becoming warmer with height, and stops the thermal developing into a cloud. Also, nearly every glider contains an instrument known as a variometer (a very sensitive vertical speed indicator) which shows visually (and often audibly) the presence of lift and sink. Having located a thermal, a glider pilot will circle within the area of rising air to gain height. In the case of a cloud street, thermals can line up with the wind, creating rows of thermals and sinking air. A pilot can use a cloud street to fly long straight-line distances by remaining in the row of rising air.
Ridge lift
Ridge lift occurs when the wind encounters a mountain, cliff or hill. The air is pushed up the windward face of the mountain, creating lift. The area of lift extending from the ridge is called the lift band. Providing the air is rising faster than the gliders sink rate, gliders can soar and climb in the rising air by flying within the lift band and at right angle to the ridge. Ridge soaring is also known as slope soaring.
Mountain waves
The third main type of lift used by glider pilots is the lee waves that occur near mountains. The obstruction to the airflow can generate standing waves with alternating areas of lift and sink. The top of each wave peak is often marked by lenticular cloud formations.
Convergence
Another form of lift results from the convergence of air masses, as with a sea-breeze front. More exotic forms of lift are the polar vortices which the Perlan Project hopes to use to soar to great altitudes. A rare phenomenon known as Morning Glory has also been used by glider pilots in Australia.
Use of Instruments
To maximize a pilot’s understanding of how the hang glider is flying, most pilots carry instruments. The most basic being a variometer and altimeter—often combined. Some more advanced pilots also carry airspeed indicators and radios. When flying in competition or cross country, pilots often also carry maps and/or GPS units. Hang gliders do not have instrument panels as such, so all the instruments are mounted to the control frame of the glider or occasionally strapped to the pilot’s forearm.
Vario-altimeter
Gliding pilots are able to sense the acceleration forces when they first hit a thermal, but have difficulty gauging constant motion. Thus it is difficult to detect the difference between constantly rising air and constantly sinking air. A variometer is a very sensitive vertical speed indicator. The variometer indicates climb rate or sink rate with audio signals (beeps) and/or a visual display. These units are generally electronic, vary in sophistication, and often include an altimeter and an airspeed indicator. More advanced units often incorporate a barograph for recording flight data and/or a built-in GPS. The main purpose of a variometer is in helping a pilot find and stay in the ‘core’ of a thermal to maximize height gain, and conversely indicating when he or she is in sinking air and needs to find rising air.
Radio
Aircraft radio. Pilots use 2-way radio for training purposes, for communicating with other pilots in the air, and with their ground crew when traveling on cross-country flights. One type of radios used are PTT (push-to-talk) handheld transceivers, operating in VHF FM. Usually a microphone is incorporated in the helmet, and the PTT switch is either fixed to the outside of the helmet, or strapped to a finger.
GPs
GPS (global positioning system) can be interesting to view a GPS track of a flight when back on the ground, to analyze flying technique, and to assist flight performance in competitions and cross country flying, where restricted Airspace needs to be considered.
Competition
Competitions started with “flying as long as possible” and spot landings. With increasing performance, cross-country flying replaced them. Usually two to four waypoints have to be passed with a landing at a goal. In the late 1990s low-power GPS units were introduced and have completely replaced photographs of the goal. Every two years there is a world championship. Hang gliding is also one of the competition categories in World Air Games organized by FAI
Aerobatics
Hang gliders are not certified for aerobatic flight so pilots perform these at their own risk. There are many varied manoeuvres, including loops, climbovers, spins and rollovers.
The skills of flying hang gliders are what you learn with us in a systematic and simple manner when you start training. You will be taken through each step and shown clearly how the weather, the techniques and the equipment all play their part in getting you up in the air in a safe and fun way. Our instructors have years of experience and hours of flying and instructing under their belts. You won't ever need to be that first person, jumping off a cliff in their own untested hand made glider!!!
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