Flight, February 12, 1915.
THE EVOLUTION OF THE ETRICH "TAUBE."
THE evolution of the Etrich "Taube" monoplane, a type upon which so many different makes of German machines are based, is not only of special interest just now on account of the prominence of the "Taube" in the daily events of the present war, but is in itself a particularly interesting subject from the historical point of view. "Taube," as, no doubt, most readers know, is simply the German for dove, and, as will be seen later, the different types of Etrich machines are designated by the names of various birds, owing to the fact that the planes are wing-shaped. As a matter of fact, this design does not derive its origin from the bird, but from the seed-leaf of the Zanonia palm, which possesses remarkable gliding properties when dried. From the sketch of this leaf (a), Fig. 1, it will be seen that the seed-pod has been provided by Nature with a perfect gliding mechanism in the shape of a crescent-shaped leaf. When the leaf dries the extremities curl both laterally and longitudinally, with the result that when the seed is ripe and falls from the tree, it makes a long stable glide to the ground. This fact was noted in a brochure written by Prof. Ahlborn, and it was this which first attracted the attention of Herr Igo Etrich, an Austrian, whose father, Herr Iganz Etrich, had started in 1898 to carry on the work of Otto Lilienthal, having bought the original gliders of that pioneer. A thorough study of the Zanonia leaf proved to be no easy matter owing to the difficulty first of obtaining specimens and then of observing the curves assumed by the leaf when gliding. However, a number of paper models were made, and the results obtained convinced Herr Etrich that in a machine constructed on these lines would be found the solution of the problem of making a flying machine automatically stable.
In conjunction with Franz Wels, he set to work, and a large glider, 12 m. span and weighing 20 kg., was built in 1904, the framework being bamboo. With a load of 25 kg., several hundred very successful glides were made, the apparatus showing a marked degree of stability. The success of these experiments induced Etrich and Wels to go astep further and endeavour to obtain prolonged horizontal flights. To this end they constructed another model, to which they fitted a 3 1/2 h.p. Laurin and Klement motor cycle engine. This machine had two ski-like skids, and was tested over snow, but the experiments met with little success, the machine never leaving the ground, owing, no doubt, to insufficient power and the incorrect location of line of thrust. The next move was to construct the large man-carrying glider (b) Fig. 1, and this was completed in 1906. It had an area of 35 sq. m., with a span of about 12m., and weighed, light, 164 kg. It was built up in three sections, the central section being supported on a skid under-carriage. In the centre, near the leading edge, an opening was cut in the plane for the pilot, who stood upright and held on to the cross beam in front of him. By swaying his body he could, to a certain extent, correct any rolling or pitching of the glider, caused by wind gusts, &c, but there was no other means of control. With 70 kg. sand ballast numerous successful glides were made, some about 300 m. in length, whilst equally encouraging glides were effected with Wels on board. On the 2nd of October, 1906, three flights of 150, 180 and 225 m. in length respectively were accomplished, the average height being about 10 m. Four more glides were made on October 8th. All these glides were started by running the glider on a small truck down an incline of 28 per cent., the glider "taking the air" when a certain speed was reached. When gliding the speed attained was from 13 to 15 m. per second, whilst the gliding angle was 7° or 8°.