When you see light, puffy cumulus clouds silhouetted against a blue sky, you’re seeing the effect of a ‘thermal’. Warm air rises until it reaches an altitude and temperature where the moisture in the air condenses into visible vapour. Most thermals rise fast enough to give a glider the lift it needs to overcome its natural descent rate – that’s how a pilot stays aloft. It’s not uncommon for glider pilots to be airborne for upwards of five hours, sometimes reaching heights over 10,000 feet. Gliders have a wide, aerodynamically designed wingspan that gives them much more lift and a better gliding ratio than powered aircraft.
The first records of man-lifting kites come from China. The (636) Book of Sui records that the tyrant Gao Yang, Emperor Wenxuan of Northern Qi (r. 550-559), executed prisoners by making them fly with bird-shaped kite wings
The first towline glider is credited to Jean Marie Le Bris in the 1850s. The French sea captain designed the glider like an albatross with wings controlled with levers. He had it pulled by a horse-drawn carriage in the hope that this would lift his invention into the air. Amazingly it worked. Unfortunately the horse took a dislike to the contraption and bolted causing the tow rope to break.
The first man-carrying gliders have been attributed to an Englishman by the name of Sir George Cayley. Starting with smaller models he progressed to large machines. In 1853, at the age of 80, he talked his coachman into being his human passenger. When the craft crashed in the valley his employee was said to have resigned.
Probably the first controlled flight was done by John Montgomery, circa 1883. Working near the Mexican border, he claimed to have made 600-foot flights there. Later, he was briefly in the limelight when he launched his gliders from balloons at 4,000 feet.
In the 1890s, Octave Chanute wrote a book called ‘Progress in Flying Machines’. With pilot A.M. Herring, he experimented with the principles of stability and developed the ‘standard biplane’. Altogether they made about 7,000 flights.
Otto Lilienthal, the German aviation writer and inventor, built and flew a number of hang gliders. The hang gliders of today are based on his plans. Lilienthal studied how birds fly and designed his gliders in a similar fashion, using body movement to guide the craft through the air. Percy Pilcher and other pioneers built similar types of gliders, but because they were also controlled by the pilot shifting his body weight, their success was limited. Both Pilcher and Lilienthal died as a result of crashing their gliders.
The Wright Brothers were influenced by Lilienthal’s experiments, and later Chanute, whom they contacted for advice. Wilbur kept meticulous notes on hawks in flight, writing: “no bird soars in calm; birds cannot soar to leeward of a descending slope unless high in the air; a damp day is unfavourable for soaring unless there is a high wind…”
The Wrights carefully studied gliding, developing a method of twisting the wings (wing-warping) thus providing roll axis control. From 1900 to 1902 they built three machines. The 1902 model, with its single movable rudder, finally allowed effective control of banked turns and leveling of the wings.
They used gliders to study the principles of flight and once they had learned this, they went on to find a suitable engine and in 1903, produced a powered machine.
The First World War brought a near close to soaring. In the 1920s and 30s German pilots and enthusiasts saw gliding as a way of flying that had not been prohibited by the Versailles Treaty.
The development of high-performance sailplanes took place during this period. Modification of the machines resulted in reduced drag and an improvement in the lift. During this time it was discovered that the glider pilot could take advantage of cumulus clouds to improve the lift.
This knowledge allowed the flier to become independent of hill sites and climb to greater heights for a longer period of time. Variometers were developed to help find the best areas of lift, making flights of over a hundred miles commonplace.
A competition to produce a 15-metre span glider for the Olympic Games resulted in many excellent designs. The winning glider, called the Meise (or Olympia), was developed by Hans Jacob.
THE GLIDER AT WAR
The outbreak of World War II prevented the Games from taking place, but many of Jacob’s machines were produced worldwide. Glider flying became part of the German high school curriculum.
The Luftwaffe was able to put these years of development and training to quietly land assault teams behind enemy lines both day and night. Towed with the Junkers Ju52 3m aircraft to within 20 miles of their destination, gliders were used to successfully attack Eben Emael, a huge – and until then impregnable – fort in Belgium.
In 1941, gliders were used in Crete when 1,300 glider infantry and paratroopers were landed. This was the final largescale use of gliders by the Germans, as over 5,000 casualties were suffered during the 8-day Crete battle.
Meanwhile, the United States started to realize the importance of gliders as trainers. Changes were made to further reduce the drag, such as improvements to fuselage shape, moving the wheel ahead of the center of gravity, seating the pilot in a less upright position and sealing the cockpit better.
American, British and Canadian troops also made extensive use of WACO CG-4A and Airspeed Horsa combat gliders in the battles for Sicily (Operation Husky), Normandy (Operation Overlord), Holland (Operation Market-Garden) and others. Glider use contributed significantly to the D-Day invasion, when they carried troops, nurses and equipment onto enemy fields. Operation Varsity (the Rhine River Crossing), on March 24, 1945, was very high in casualties to both man and his gliding machines, but their use is credited in assisting in the surrender of Nazi Germany to the Allies.
IN RECENT YEARS
Gliders have received further development since the war years and continue to be used as an inexpensive means of providing pilot training, recreation and competitive sport. Ultralights such as hang gliders (where the pilot is usually flying in a prone position) and paragliders (where the pilot is in a sitting position) provide other alternatives to the joy of ‘soaring like a bird’.