282 



DISCOVERY 



Gliding Flight 



By " Rafex " 



The remarkable performances of certain German 

 gliders starting from the summit of the Wasserkuppe 

 in the Rhone valley during the last two years have 

 aroused popular interest in a subject which is difficult 

 to assess at its true importance. It is, of course, the 

 fact that the progressive gliding experiments of 

 Lilienthal, Pilcher, Chanute, and others led directly 

 to those of the Wright brothers, which in their turn 

 resulted in the invention of the first successful power- 

 driven aeroplane ; and therefore the aeroplane may 

 be said without question to owe its birth to gliding. 

 On the other hand, it is at least debatable whether we 

 have not now got beyond the stage where anything 

 further can be learnt bysuch embryonic flyingmachines, 

 and have not advanced to the point where laboratory 

 experiments, checked by full-scale tests, provide the 

 true scientific road to further development. Be that 

 as it may — and we will return to the subject later — 

 no consideration of the sport, or science, of gliding 

 can hope to be complete without a brief outline of 

 the achievements of the pioneers, which gives a measure 

 ■of the merit of recent advances as well as a glimpse of 

 the foundations upon which all modern progress has 

 been built. 



The " father " of all gliding was Otto Lilienthil, 

 whose first experiments, with flapping-wing models, 

 were made at the early age of thirteen. It is an 

 interesting example of the tortuous path frequently 

 followed by scientific development that his later 

 gliding experiments, which were perhaps the first 

 practical step towards the modern aeroplane, were 

 intended by him as a prelimiirary to the production 

 of an ornithopter. He realised the importance of 

 overcoming the difficulty of maintaining equilibrium 

 in the air, and for this purpose made many glides with 

 fixed wing machines, but he does not appear to have 

 visualised the aeroplane of which they were the pre- 

 cursors. Lilienthal started in 1891 by making jumps 

 from a spring-board in the garden of his house at 

 Lichtefelde, on the outskirts of Berlin. During the next 

 three years he tried several suitable mounds in the 

 neighbourhood and made many short glides over a 

 gravel pit on the edge of which he had built a shed, 

 from the top of which the jumps were made. In 1894 

 he had a small hill 50 feet high specially constructed 

 from a mound of earth, with a shed for housing the 

 gliders sunk in the top. Shortly afterwards he moved 

 to his final experimental ground among the sand-hills 

 at Sollen. 



Lilienthal's gliders were of the simplest possible 

 form with no mechanical means of controlling the 



balance. The earlier t\'pes were of monoplane design 

 with the wing on each side stiffened by wooden ribs, 

 radiating from a point near the operator's shoulders, 

 who occupied an upright position with his weight 

 carried on padded supports under the armpits. Balance" 

 was maintained entirely by moving the legs to alter 

 the position of the centre of gravity. A horizontal 

 fin was fitted at the rear which gave some automatic 

 fore-and-aft control, as it was designed to yield slightly 

 in an upward direction under the influence of wind- 

 gusts. Above this horizontal sm'face was a vertical 

 fin which was not movable. In spite of the crudity 

 of this method of maintaining balance. Otto Lilienthal 

 succeeded in making glides of over 1,100 feet, starting 

 from a point 150 feet above the surrounding plain. 

 In his own account of these glides he says ^ ; "I often 

 reach positions in the air which are much higher than 

 my starting-point," and, "At the climax of such a 

 line of flight I sometimes come to a standstill for some 

 time, so that I am enabled whUe floating to speak 

 with the gentlemen who wish to photograph me." 

 There does not appear to be any record of the actual 

 time he remained in the air on any of his glides, but 

 enough has been said to show that he appears to have 

 had considerable control over the balance of his 

 machine simply by moving his body. The biplane 

 gliders, on which his later experiments were made, 

 were in aU essentials precisely the same in principle 

 as the monoplanes. They had a total wing surface 

 of about 200 square feet, with a span from wing-tip 

 to wing-tip of 18 feet, which enabled him to glide 

 straight off the top of the hill " almost horizontally," 

 without any preliminary jump, in a wind of 20 miles 

 per hour. Lilienthal unfortunately met his death 

 while gliding on Sunday, August 9, 1896, but not 

 before he had shown the way to other practical experi- 

 menters and obtained much laboratory information of 

 inestimable value on aerod\Tiamics. 



The mantle of Lilienthal fell on Percy Pilcher,^ a 

 young English naval architect and marine engineer, 

 who took up gliding in 1895, when he built his first 

 machine. He visited Lilienthal in the same year 

 and made one or two glides on the German's biplane 

 glider. Pilcher, however, preferred the monoplane, 

 and all his own machines were of that type. Fig. i 

 shows him in the air on his most successful glider 

 named the "Hawk," which bears a striking resem- 

 blance in general outline to Lilienthal's monoplane and 

 was undoubtedly influenced by the visit to Germany. 

 It had a supporting surface of 180 square feet with a 

 span of 23 feet 4 inches and chord of 8 feet 4 inches, 

 the overall length being 18 feet 6 inches. It was con- 



' The Aeronautical Annual, No. 2 (1896), p. 16. 

 - The Aeronautical Classics, No. 5: "Gliding," by Percy 

 Pilcher. 



