M.Simons The World's Vintage Sailplanes 1908-45

THE HARTH-MESSERSCHMITT GLIDERS

  Friedrich Harth of Bamberg grew up in his father’s forest ranger’s cottage, where as a child he watched storks nesting, fluttering and soaring. This was the beginning of his passion for motorless flight and dynamic soaring. Early in 1910 he observed a Bleriot monoplane struggling against a gusty headwind and this gave him his great inspiration. Each gust, met head-on by the little aeroplane, caused it to rise higher. The Segelflugzeug 1 or S-1, was a flimsy monoplane and the pilot sat on a light saddle beneath the wing. He took off by running, and after becoming airborne he could raise his feet to place them on a horizontal bar in front. The glider had a fixed tail unit without any rudder or elevator, but the pilot was supposed to warp the wings to give lateral control, in the manner of ailerons, by moving his head. A helmet, attached to wires, was devised for this purpose. The S-1 did not last long.
  The S-2 had orthodox tail controls and two control columns, a feature which Harth retained on all his future designs. The most remarkable feature of the S-2, and of all other Harth gliders, was the variable-incidence wing. Instead of mounting the wing rigidly to the fuselage structure, it was pivoted so that control in pitch could be achieved by moving the whole wing. Harth's idea was to use gust energy for soaring.
  Sitting on the ground, facing into the wind, the pilot would feel a sudden gust and by sharply increasing the wing incidence he would rise a few metres into the air. As the glider’s airspeed fell off. he could return the wing angle to normal and glide forward until another gust came along to enable him to gain a little more height. Small changes of wind speed. Harth was sure, would yield sufficient energy to permit true soaring flights.
  The S-2 did not fly very well but his next design, the S-3, was much better. Many short flights were made over nearly level ground until, early in January 1914, in the S-3, Harth made a flight of more than a minute’s duration and covered 120 metres distance. The S-3 was very simple with a completely open, gate-like fuselage, the wing and tail being fastened on the top rail while the pilot’s saddle and control columns were mounted above the lower rail, at the front. This and all Harth’s subsequent gliders had a simple, central landing skid so that one wingtip would normally rest on the ground when the aircraft was still. The two control sticks, pivoted on the keel at the bottom, came up in a 'V'. Each hand grasped a stick.
  Harth realised the need for a better site and moved his operations to the Heidelstein, only a few kilometres from the Wasserkuppe where the Darmstadt group had already achieved gliding flights. Harth was now joined by an enthusiastic schoolboy, Willy Messerschmitt, who was sixteen years old when Harth gave him his first flight in the new glider, the S-4, in July 1914. Messerschmitt, like the Darmstadt group, had been inspired by a visit to the Frankfurt Airshow in 1909. He had begun to build model aeroplanes after this. When the family moved to Bamberg, he met Harth and his career in aviation began.
  In 1917 Messerschmitt was drafted into the army but managed to get himself transferred to a flying school before the war ended in the following year. After the armistice the pair continued their experiments. By the summer of 1921 they were achieving flights of six and seven minutes over gently sloping terrain.
  Great success, but also disaster, came with the S-8. This was an improved version of the previous machines, the latest in a long line of steady development. The span was eleven metres, the wing being wire braced and pivoted on the fuselage in the usual Harth fashion. The bracing points further out on the wing were in line with the pivot and so did not restrict the movement. The fabric covering of the wing was not doped, to permit the lateral control by warping. Too much stiffness in the covering would be a nuisance. The extreme leading edge was skinned with plywood to provide a better aerodynamic form. The aerofoil was developed from a bird’s wing section. To control the wing a fairly elaborate system of cables and pulleys was used, running to the twin control columns.
  The fuselage was built of steel tubes, through-bolted together in the simplest possible fashion. Although by this time the rubber bungey launch had become generally accepted on the Wasserkuppe, the Harth-Messerschmitt gliders were still taking off unaided with the variable wing. On 13 September 1921, after a six minute flight earlier in the day, Harth took off into a rising wind and, sensing the changing gusts, he soared up to height of 150 metres. Passing back and forth above his starting place, he seemed likely to remain aloft for a long period and Messerschmitt, excited beyond measure, rushed to get his camera. By the time he got it, Harth had lost some of his height and, to the young man’s horror, the S-8 suddenly veered off and came crashing down, apparently as a result of a jammed control cable. Harth was badly injured and was rushed to hospital, the S-8 was wrecked, but the world duration record for gliders was broken. Harth had been soaring for 21 minutes 37 seconds.
  There had been only one witness, and the flight had nearly killed Harth. He had a double fracture of the skull and some brain damage from which he never entirely recovered. Whilst the older man was in hospital, Messerschmitt, impressed by the tailless gliders of Dr Wenk, built the S-9, a 12 metre span flying wing. Aerodynamically the design was unsuccessful and once he was active again, Harth declared it a waste of time. He encouraged Messerschmitt to start work on two new sailplanes to much the same old pattern, the S-10 and S-11. These were like the S-8 but had wingspans of 14 metres and more lifting surface. At last, in 1922 the independent couple turned up at the Wasserkuppe. One of the first to show keen interest was Wolf Hirth, who later described how Harth and Messerschmitt taught him to fly in the S-10, pulling him forward by means of ropes attached to his wingtips and guiding him carefully down the gentler slopes until he had the feel of the extraordinary wing angle control system. Harth’s achievement in soaring was almost totally eclipsed and forgotten when, at the same meeting, Martens and Hentzen demonstrated hill soaring with flights of an hour, then of two and three hours. The S-10 became almost a regular training glider.
  The S-11 encountered problems. With changed proportions in the linkages and a new aerofoil section, it proved sluggish in control. The flexible wing, in gusty weather, tended to twist unexpectedly and the fore and aft pitching action of the pivoted main lifting surface sometimes caused a sharp snatch on the sticks. These problems grew suddenly much worse with the S-12, for which Messerschmitt had held great hopes. The S-12 had an enclosed plywood fuselage instead of the previous open frame structure. It also had yet another new aerofoil, the one which, later, was tested at the Goettingen wind tunnel and became known by its Goettingen number, 535. Wolf Hirth. who had advanced rapidly from pupil status to become an instructor and test pilot for the Messerschmitt School, made the first gentle hop, gliding slowly down the slope until, as he tried to ease back for a smooth landing, the pivoted wing snatched violently as the centre of pressure shifted, and the S-12 dived into the ground. Hirth was rushed to hospital with a nasty throat injury caused by a sharp plywood edge. The glider was wrecked. It was rebuilt and in October Hirth tried again but with a similar result. The S-12 dived to earth and stood on its nose. Hirth was luckier this time and emerged unhurt.
  This failure seems to have been the last straw for Harth. He and Messerschmitt had been at loggerheads since the ‘time-wasting’ S-9. Now, publicly, they separated. Harth reappeared at the Wasserkuppe with his Pilotus, essentially the same design as the old well-tried S-10 which was now clearly out of date. Thus ended the first serious experiments with dynamic soaring. Although Harth demonstrated his techniques at the Wasserkuppe, repeatedly taking off from a standing start and gaining heights of 40 and 50 metres before gliding on, hill soaring flights of much greater duration were now commonplace and spectacular progress was being made with sailplanes designed for this sort of sport. Even those who observed gust soaring being demonstrated before their eyes, saw little point in it when slope winds were so much more predictable and reliable. No-one continued Harth’s work.
  Messerschmitt went on to design the S-13, a 14 metre type. He retained the wing warping system of lateral control, but used a stiffer, steel torque tube system, inherited from the S-9, instead of wires and pulleys. The S-13 should have been very successful but, like the S-12, it nearly killed Wolf Hirth on its first flight. After starting from the south slope of the Wasserkuppe, floating over the small valleys and crossing the spurs only 8 to 10 metres above the ground, suddenly a pushrod broke, causing the wing to rotate to a negative angle of attack. This produced a vertical dive into the ground, fortunately only from a small height. Hirth was badly injured but lived.
  Messerschmitt improved the design and built the S-14 before the end of 1923. He subsequently fitted this aircraft with a 500 cc motor cycle engine driving a propeller. Flugzeugbau Messerschmitt Bamberg was established.

  Technical data:
  S-10: Span 14.00 m. Wing area 10.3 sq m. Aspect ratio 10.3. Empty weight 80 kg. Flying weight 150 kg. Wing loading 7.9 kg/sq m.