Process and Evolution of a "Delta" Wing Aircraft"
by Dr. Reimar Horten
(as translated by: Fernando Walter Siarez, Buenos Aires, Argentina)
(The original article was titled "Desarrollo de aviones rapidos
sin cola", by Dr. Reimar Horten, published in Revista Nacional de Aeronautica
(*) " September 1952, Number 126, pages 20-21, Buenos Aires, Argentina.
(*) Today: "Aeroespacio, Revista Nacional Aeronautica y Espacial."
We thank them for allowing the translation and publication here for all
to share. The article is being provided in both English and Spanish.)
|The author, who has
been incorporated to the staff at the Cordoba Aerotechnic Institute for
several years, has devoted himself, accompanied by his brother Engineer
Walter Horten, to the design and study of tailless airplanes of the "delta
wing" or "flying wing" type. Specialized in this branch of aeronautic
construction, Doctor Horten has designed in our country some prototypes
of tailless gliders, as well as another prototypes to be powered by jet
engines. In this writing, the author overviews the work done in collaboration
with Engineer Walter Horten, between 1935 and 1945, in the conception and
improvement of fast tailless airplanes.
After the determination of aerodynamic drag coefficients, and flight performance of the Ho-II model, good results for a fast "flying wing" airplane project could be foretold. The problems that appeared during its process and development were very complex, and would go beyond the shortness of this article, but in general, it has been confirmed that suitable shapes for fast airplanes are unsuitable for low speed ones.
We started then, to work on gliders and small-motorized airplanes to which we gave the fast aircraft shape. The goal of these tasks were to study the lift relations, specially in low speed flight. Also, good flight and maneuverability qualities for these "flying models" designed as fast airplanes had to be found, and the problem was, then, to establish by the means of flight tests, the influence of many variants that cannot be calculated. For fast airplanes, it was of interest to find out the qualities of tailless airplanes, with small aspect ratio and big sweep angle, the aspect ratio being reduced because of Statics' considerations. Its aerodynamic influence in flight performance is reduced, because in fast flight the induced drag component is small. The “Delta” wing of today is thus obtained.
At that time, the acknowledgment of the advantages of the swept wing for high-speed airplanes, was only a consequence of the institution and just today, science has checked its validness. The development of this theory started in the Ho-V and VII, that had an aspect ratio of 5 and the wing sweep of 42 degrees, with the making of an analysis of all the problems that appeared, that is, twist and airfoil shape variation, rudder shapes, reductions and landing gear. The qualities in flight were, partially, better than those of classic airplanes with fuselage.
Based on such results, we presented in 1942 to the German Aeronautics Ministry the project of a jet engine airplane, which had a moderated both sweep and taper, so as to avoid the risk arising from such an innovation. The project was built as H-IX, and in a somewhat modified way, so as to better respond to the exigencies such imposed -see 'revista Nacional de Aeronautica', May 1950-. After the model was passed to the "Gotha-Waggen" firm for series construction, we started new experiences in the field of supersonic speed.
In order to investigate the qualities of low speed flight and the maximum lift coefficient of a 60 degrees swept wing airplane a fuselage was applied, after some aerodynamic problems with flying models, to the wings of a H-III with an adequate sweep angle. The fuselage was mounted as a blimp gondola in the center section of the wing, under the trailing edge. The flight characteristics of this aircraft, H-III, [must be H-XIII -Trans.] as it was called, were satisfactory. With this aircraft we wanted to measure, in a practical way, in flight, lift distribution in several parts of the wing and along it. Being everything ready for making it, the experience could not be done until after the war. This model was followed by another flying wing project with a 70 degrees sweep. This one had symmetrical laminar airfoils and the pilot had to be laid horizontal. Because of sweep increase, aspect ratio is diminished from 4.0 to 1.5 and in this way, the "Delta" wing was obtained. This new project was in construction phase, when it came to an end of all works and its destruction.
In parallel to these investigations with highly swept wings, other tests for high-speed flights were done. As the "Delta" wing approached the speed of sound, the wing root experimented an increase in aerodynamic drag, before the wing itself and, besides, with the increase in sweep angle caused a decrease in maximum lift, being then logical to think that the solution of static problems consisted in increasing the sweep angle at the wing root. So, for example, with a wing of 35 degrees sweep combined with a root of more than 60 degrees, appears an increase in aerodynamic drag, in first place, at the root, as the craft approaches the speed of sound. To investigate the flight qualities of these kind of airplane, we modified a Ho-II, in which the root sweep was modified, mounting jet engine intakes also. The results from these tests served as a starting point for near war end projects, from which the single jet engine fighter of the photograph is an example.
Flight tests of swept wing airplanes, made by means of gliders or flying models were and are, until today, necessary, due to the little possibilities of making calculations. Neither it is possible to expect a help from science, in the near future, for the flight technology in this field, because the shape of the fluid stream around swept wings, is more dependent on the boundary layer and the layers near the wing, than in straight wings and, besides, these problems present themselves as three-dimensional. This is why the project has to be based on experiments starting with flying models, wind tunnel tests, models, and finally, an experimental aircraft.
Studies made in Great Britain and United States, with flying wings and "Delta" wing aircraft for high speed, indicate that the advantages of this kind of construction is being recognized there. So, the investigations made in Germany, from the point of view of aeronautic science, show that they were not in vain.
(1) "H-XIII glider,
with 60 degrees swept wing."
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Desarrollo de aviones rapidos sin cola -
El autor, que desde hace
algunos años, esta incorporado al personal del Instituto Aerotecnico
de Cordoba, se ha dedicado juntamente con su hermano el ingeniero Walter
Horten, al diseño y estudio de los aviones sin cola, del tipo "ala
delta" o "ala volante. Especializado en esta rama de la construccion
aeronautica, el doctor Horten ha diseñado en nuestro pais algunos
prototipos de veleros sin cola, como asi tambien ha proyectado otros prototipos
para ser impulsados con motores a reaccion. En el presente trabajo, el
autor reseña la labor realizada en colaboracion con el ingeniero
Walter Horten, entre los años 1935 y 1945, para la concepcion y
perfeccionamiento de aviones rapidos sin cola.
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