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The last high-performance glider in a biplane configuration was probably the design by Bonnet from Toulouse, which first appeared at the 1937 French national gliding competition on the Banne d'Ordanche. This single-seater with a high-aspect-ratio, pointed wing (23) featured a cantilevered upper wing with a wingspan of 13.20 meters on a slender dome above the fuselage, while the equally cantilevered and only slightly smaller wingspan lower wings were attached to the fuselage in a low-wing configuration. Unfortunately, no performance data has survived for this elegant glider with its highly staggered wings totaling 14.65 square meters and its low empty weight of 125 kg. They would have been interesting, as they might have provided practical evidence that biplanes, with an advantageous arrangement of the wings relative to each other, can be superior in performance to monoplanes of the same class due to their ever-increasing aspect ratio.
Dr. Max Munk, whom Professor Prandtl had already brought to the Model Testing Institute for Aerodynamics in Göttingen in 1915, had conducted fundamental investigations into the biplane and discovered that the total lift and total drag of a biplane system are not equal to the sum of the corresponding values of the individual wings, because each wing generates a downward airflow on the other, which leads to an additionally increased induced drag (edge drag) as well as reduced lift.
However, this was of less interest to the pioneers at first. They accepted the lower lifting capacity and the inevitably high harmful drag in favor of a stable, robust construction. The structural strength of a multiplane, achievable with relatively little weight through struts and wire bracing, could not be surpassed, and speed performance was irrelevant at that time.
In the early days of glider development - when the advantage of the large flight path was Before the concept of gliding was fully recognized and wingspans were generally moderate, there were many multi-planes. A good example of this are the ingeniously simple, lightweight, and stable hang gliders of the Nuremberg-based Willy Pelzner, which, with their sensible static design, sold well for learning to glide. A successful biplane seat glider was the Stehaufchen of the Dresden Akaflieger, with whom they moved to the Rhön region in 1921. (He is described in detail in the brochure "Historical German Aircraft up to 1945", Volume 1, published by our publishing house!)
Munk's theorem on mutual induction or influence in biplane configurations, however, was based on the assumption of two wings of finite span at a certain distance from each other with matching leading edges and the same angles of attack – i.e., without stagger or twist. However, it could be calculated that with an optimal efficiency (the value of the ratio of the wingspan of the lower wing to the wingspan of the upper wing to the ratio of the wing spacing to the maximum wingspan) – possibly supported by staggered wings with a precisely matched washout – very good biplane performance could be achieved.
When Ksoll designed his cantilever high-performance biplane Breslau in 1924, he designed his aircraft so that it was only a few percentage points away from the optimal efficiency.
Joseph Ksoll (1897-1967) from Breslau, who ran a dairy in Schön Ellguth, Trebnitz, was one of the Silesian pioneers of gliding. His appointment as an aircraft designer led him in 1923 to establish a hangar and workshop on the Steinberg hill in Nieder Ellguth in the Katzengebirge mountains, about 25 kilometers from Breslau, to build aircraft.
From 1924 onwards, it was made available for shared use by the "Marcho Silesia" flying club, founded that same year, a student corporation that remained active and successful until its forced integration by the National Socialists. Ksoll also built aircraft for them.
But the design that made Ksoll famous beyond the borders of Silesia as a glider manufacturer was a cantilever monoplane developed in 1923 with a one-piece rectangular/trapezoidal wing with a wingspan of 14 meters. It was particularly appealing due to its dolphin-like, rounded fuselage constructed using a shell design. The wooden aircraft attracted attention at the Rhön airfield in 1923 because many structural details, such as the wing attachment, the seat, the controls, and especially the central skid bearing, were made of steel tubing. It was the first performance glider to fly at the later famous airfield in Grunau and was named "Galgenvogel" (Gallows Bird) after the Galgenberg hill, which served as its launch site. All subsequent Ksoll designs had significantly simpler constructions.
Rectangular fuselages. These included the Galgenvogel II, a shoulder-wing monoplane with an auxiliary engine, which also flew in 1924, and the cantilevered, high-wing light aircraft KE V, built in 1927/1928, with a 36 hp (26.5 kW) British Bristol Cherub III engine, which received official registration as D-1227.
With his Breslau, a high-performance two-seater intended primarily as a research aircraft and intended to participate in the 1924 Rhön competition, Ksoll had the goal of controlled slow flight in mind.
For this purpose, the biplane design seemed particularly suitable to him because he could make one wing (he chose the lower one) movable "...mainly to achieve a damping speed." Ksoll accepted the necessary, robust strut frame in pursuit of this objective. Nevertheless, he aimed for high aerodynamic performance. The wings were given an unusual wingspan-to-chord ratio for the time. And as a wing cross-section, Ksoll chose a strongly cambered profile of only moderate thickness, very similar to the Göttingen Gö 441. At the 1924 Rhön competition, the Breslau was piloted by Richard Tracinsky, an experienced pilot who, in extreme weather conditions, crashed on July 24, 1926, during a scheduled Lufthansa cross-country flight with a Junkers F13 on the island of Juist, killing himself and his four passengers. On the Wasserkuppe, Tracinsky flew on August 11, 1924.
As the conclusion of the aircraft inspection by the TEKO (Technical Commission; an approval committee of the competition management) which had taken place the day before, the Breslau completed its certification flight. The glider remained airborne for one minute and 52 seconds and achieved a distance of 1,070 meters. A subsequent bonus flight even yielded over two minutes of flight time and a distance of 1,250 meters. However, outstanding flight performances could not be achieved with the aircraft in the Rhön region, as it only flew on three further days due to the bad weather. This 5th competition went down in history as the "rainy Rhön," as there was precipitation or fog on 25 out of 28 competition days. Because many flights were cancelled, some advertised competition prizes could not be awarded, including the second prize in the two-seater category, where Breslau won against strong competitors such as the Margarete of the Darmstadt Akaflieger or the "Deutschen Aar", the Baden-Baden world-class glider, had to compete – all mono planes.
But the two-seater Ksoll biplane still got its headlines. For a camera flight, intended to showcase the beauty of gliding, the photojournalist and his equipment were stowed in the front seat – normally the pilot's seat – for better visibility. Tracinsky piloted the aircraft. from the rear seat, located at the center of gravity – otherwise reserved for the passenger or, during training, for the flight instructor. The aircraft got airborne perfectly during the bungee launch, but then the heavy launch rope failed to detach from the tail. Despite the dangling load, the pilot completed a flawless flight. Although the aircraft bounced on its back during landing due to the trailing launch aid and was damaged, Tracinsky received 100 Mark as a bonus for "special achievements of a flying nature." 200 marks for design achievements were awarded to Ksoll.
The fate of the Breslau is unfortunately unknown. It is quite conceivable that the high-performance two-seater served for years on some Silesian slope for training purposes. But wherever it may have appeared, its unusual biplane design would have been admired as an original contribution to the history of gliding.
Its creator, Joseph Ksoll, increasingly developed into a specialist for gliding from the late 1920s onward. High-lift devices on the wing. His inventions,
with many types of slits and the various mounting surfaces, were protected by a number of patents over the following decade and a half.

Type	Werk.Nr	Registration	History

Type	Single seat biplane glider
Dimensions	Length 7,00 m , height 2,75 m , span upper 18,00 m, lower 12,00 m , wing area 28,0 m2 ,
Weights	Empty 250 kg , loaded 390 kg , max. take off weight
Performance	Max.. speed , cruising speed , range , endurance , service ceiling , climb