Читать книгу The Rise of the Flying Machine - Hugo Byttebier - Страница 35

Lilienthal’s Flights

Lilienthal started to fly in July 1890. He was able to finance his experiments with the proceeds from a workshop that he owned, so that he was never short of funds and did not have to appeal to third parties for financial assistance and suffer the inconveniences that sometimes result from this.

His first glider consisted simply of a pair of wings with a surface of 107 sq ft. On his first attempt to glide, he started from a slight rise in a field, in a fairly strong wind of 18 mph but the craft overturned and crashed.

A new glider was then built, in which the wing area was reduced to 86 sq ft and, in a first endeavour to stabilize the flightpath, a fixed vertical tail was added to the rear. With this glider, Otto Lilienthal achieved a few successful glides starting from Windmühlenberg at Dernitz, not far from Berlin. In 1891 he was able to cover distances in the air of up to 100 ft but the wing proved too small for successful lifting in the moderate winds which were then a prerequisite for safety.

In 1892 he built a new glider, doubling the wing surface to 172 sq ft, so that flights with little wind became possible. His apparatus was first tested in Steglitz from the roof of a shed, which was built on a slight rise.

This shed limited flights to only a few directions so Lilienthal then decided to build his own artificial hill in the form of a cone 50 ft high near Heimersdorf, not far from his home in Lichterfelde. The top of this hill was crowned with a shed in which Lilienthal housed his aircraft. He was now able to glide downhill in whatever direction the wind blew, whilst the wind was forced upward along the slope of the hill, so that take-off became possible after running a few feet.

From this hill Lilienthal was able to make many impressive glides, and because of this the place became a favourite spot for a family excursion for many Berliners.

Meanwhile, through trial and error, Lilienthal discovered the concept of the stable aeroplane and, possibly without being aware of Pénaud’s designs, he adopted a horizontal and vertical fixed tail at the rear of his gliders and with this his flights improved immeasurably. At Steglitz he made several glides of 80 m (285 ft) in the air and from his artificial hill he did even better.

But the Heimersdorf hill still had a defect in that the wind was apt to be deflected laterally. Lilienthal continued with his search for a better jumping-off point and, later in 1892, he found the “Rhinower Mountains” which were about 35 miles west of Berlin. They consisted of a series of elevations which rose about 200 ft above the surrounding terrain of flat fields covered with grass and heather.

Lilienthal continued his gliding experiments in the Rhinower Mountains over the following years and became so proficient in flying against ever stronger winds that he was eventually able to cover distances of over 1,100 ft in the air.

Commenting in his annual report on his flights during 1892, Lilienthal stated: “Each apparatus had a vertical and horizontal tail without which it is impracticable to practice in the wind.” In order to control and steer, Lilienthal applied the principle of displacement of the centre of gravity by moving his body. This was the simplest way to steer a stable light gliding craft and is still used in today’s hang-gliders.

It is interesting to note that the tail surfaces mentioned by Lilienthal were fixed, so that they were meant for inherent longitudinal and directional stability, whilst the movement of the body was used for control and only incidentally for aid in balancing the aircraft.

In his report about his flights in 1893 Lilienthal wrote: “A slight change in the centre of gravity to one side produces at once a small inclination to the carrying surface so that the supporting air pressure also moves to this side and changes the direction of flight. There is nothing simpler than steering flying machines.”

It may be said that during 1893, Lilienthal acquired the art of sailing or gliding flight to perfection. From then on he began to consider the possibility of carrying out his original aim, which was to build a machine using powered flapping wings for true bird-like flight. Although his experiments had convinced him of the importance of the inherently stable aeroplane, he still wanted to use flapping wings for propulsion.

Towards the end of 1893 he began to make calculations for an aircraft using a 2 hp engine which, by acting on the wings, would propel the plane forward and, he hoped, would thereby convert a downward glide into a horizontal flight.

He thereupon built a steam engine of 2 hp weighed only 20 kg (44 lbs) but later (in 1895) he replaced it by a motor using carbonic acid that also was able to produce 2 hp and was even lighter, giving Lilienthal the opportunity to build a new glider with oscillating wingtips as proposed in his book of 1889. But he was never able to flight-test a powered glider and was thus spared the disappointment of realizing that it would not be possible to achieve horizontal flight with only 2 hp.

During 1894 Lilienthal became world famous. The January issue of L’Aéronaute carried an article which stated that “the whole French Press is agog. The papers are full of articles claiming that the great problem of aerial navigation has at last been solved”. “But L’Aéronaute” commented wryly that “Mr Lilienthal’s apparatus is a dirigible parachute and the parachute is an old device”. Perhaps a touch of envy may be detected here, although it is also true that Lilienthal had followed the proposal of the “dirigible parachute” made by de La Landelle in 1884.

That same year, a French doctor, Emile Veyrin who was an air enthusiast and who possibly understood German, received a letter from Lilienthal advising him and his compatriots to start researching flight according to his teachings, but nobody in France was willing to become a pupil of Lilienthal’s, and it was not until much later that his teachings were to have any effect in France. In February 1895 Veyrin published an article about the “Flying Man”, in which he deduced that Lilienthal must have been a scientist, a craftsman and a gymnast and in this he was very near the truth.

In order to soar better, more wing surface was needed, so Lilienthal built two biplane gliders (during 1895) one of 194 sq ft and a second of 269 sq ft because he had found that monoplanes with greater wing area were difficult to control by the shifting of body weight alone. In an article published in James Means’ Aeronautical Annual of 1896, Lilienthal referred to these biplanes as having “twice the bearing capacity but on account of its small dimensions this apparatus obeys much better the changes in the centre of gravity”.

But Lilienthal did not fully try out these biplanes, which were probably the first flying biplanes in aviation history, because he was beginning to consider other means of controlling his aircraft.

In the article published in the Aeronautical Annual for 1896, already referred to, Lilienthal wrote: “I came to the conviction that an increase in the size of the wings or the utilising of still stronger winds, which would lengthen the journey in the air, would necessitate something being done to perfect the steering and to facilitate the management of the apparatus.” Lilienthal was wrong in this because to perfect the steering would not necessarily facilitate the management of a flying machine.

On 17 April 1896 he wrote to James Means: “I am now engaged in constructing an apparatus in which the position of the wings can be changed during flight in such a way that the balancing is not effected by changing the position of the centre of gravity of the body... It will increase the safety.” In fact the system by which the position of the wings could be changed during flight was developed to its ultimate perfection by the Wright brothers six years later, but it did not lead to an increase in safety.

Lilienthal was about to start a new phase in his progress towards human flight. But the course he was entering upon would have led to a series of struggles, frustrations and difficulties, from which he was fortunately spared by his death at a fateful moment in his career. On 9 August 1896, Lilienthal was again in the Rhinower Mountains to carry out some more practice in sailing flight. According to Paul Beylich, his ever-present trusted assistant, it was a day of gusty winds, but Lilienthal possessed the confidence that comes from long experience. During his fourth gliding flight that day, when he was sailing about 50 ft above the ground, the craft suddenly seemed to stand still in the air. Becoming aware of the danger of a stall, Lilienthal moved his legs so as to give the plane an inclination downwards and to allow it to regain flying speed but it was too late and instead of inclining gently, the plane suddenly dived almost vertically and crashed, breaking Lilienthal’s back. His last words before he died the following day are said to have been “Sacrifices must be made” (Opfer müssen gebracht werden), though there is no mention of this prior to 1930. He was the first martyr of that period in the history of the conquest of the air.

Several sources have recorded that the glider in which Lilienthal crashed was an experimental one in which the fixed horizontal tail had been replaced by a movable one actuated by the pilot through a string attached to his head. Lilienthal would thus have transformed his glider from one that was inherently stable to one of controlled balance and this may have caused the accident.

Percy Pilcher, an Englishman who was Lilienthal’s most brilliant disciple, wrote in 1897: “Herr Lilienthal came to grief through deserting his old method of balancing.”