MODEL OF A HARGRAVE KITE of the type that Lawrence Hargrave used in his man-lifting experiments in 1894. The area of the kite was ninety square feet. Hargrave used a string of kites in cascade; to the lowest one, which was similar to that shown in this photograph, he attached a seat. Hargrave succeeded in lifting himself in this way; he controlled his height by means of ground tackle.
ALTHOUGH Lawrence Hargrave is chiefly known as the inventor of the box-kite, he made invaluable researches into almost every aspect of heavier-than-air flight.
Lawrence Hargrave was born at Greenwich, near London, in 1850. When he was seventeen years old he went to Australia, where be was trained as an engineer. Private means, however, enabled him to devote his time to aeronautical experiments and he made a close study of bird flight. The results of this study he used in his early work, which was mainly concerned with the study of the flapping motion of wings as a possible means of propulsion in mechanical flight (see the chapter “Experiments with Ornithopters”).
Having made numerous experiments with models, most of which had either rubber bands or clockwork for motive power, and one of which flew 120 feet, Hargrave built a full-sized ornithopter; this was designed to test manual power as applied to the flapping-wing machine. He then experimented with several model-engine types, but his greatest achievement with these particular experiments was the invention of the rotary engine, which was to become one of the most widely used aero engine types (see the chapter “Evolution of the Aero Engine”). The most famous example was the Gnome. Hargrave fitted his rotary engine to his compressed-air-driven ornithopter. It drove a pair of flapping wings by a motion which was invented by Hargrave and which was designed to reproduce the “figure of eight” movement of bird flight. The motion was obtained by coupling the main ends of the wing spars by connecting rods to throws on the crankshaft, whereby the wing spar axes were made to oscillate in addition to their flapping motion.
The engine was of the trunk piston type and had three single-acting cylinders, set radially at 120 degrees apart. A rotary valve on the crankshaft supplied the engine with compressed air at a pressure of 120-150 lb. per square inch. Hargrave then began experimenting with existing forms of kites, and in 1893 he built several cellular kites (or box-kites). His method of construction was the forerunner of cellular construction which was later generally used for aeroplane construction. To obtain data for his experiments Hargrave flew a string of kites, and with one of these, the lowest, which had a seat, he lifted himself with the aid of ground tackle. This kite had an area of 90 square feet.
Having designed and experimented with several types of box-kites, he evolved one model which represented his final contribution to box-kite research, and it is this model which can be described as the first box-kite. Its horizontal surfaces were curved so that the front half of each was slightly convex and the rear half concave. This model had greater stability, more lift and less drag than any of his other models ; it was fitted with an adjustable tail. His experiments with it proved that a comparatively small surface arranged in kite form was enough to lift the weight of a man from the ground.
Lawrence Hargrave, who died in 1915, had a profound effect on early aeroplane design. His box-kites were inherently stable, and many of the early machines, such as the Voisin and the Santos-Dumont, owed their existence directly to Hargrave’s box-kites. The first aeroplane to be built by the British and Colonial Aeroplane Company (now the Bristol Aeroplane Company) was known as the Bristol Box-Kite.