04/30/2019. Remarks by Johan Visschedijk: "August Kupper (1905–1938) was a physicist and aerodynamicist. His career began at the Akaflieg at the Technical University in Munich, Germany, where he was involved in the development of the Akaflieg Munich Mü.3 glider, which Kupper designated Ku.1 in his own designation system. Kupper continued to work with the Akaflieg students, but also designed his own gliders.

Kupper's best known design was the extraordinary Ku.4 Austria, which he designed for the famous glider pilot Robert Kronfeld. The sole example was constructed in 1930 by the Kegel-Flugzeugbau in Kassel, hence the aircraft is also referred to as the Kassel Austria.

Of wooden construction, the single-seat glider was designed with the goal of low sinking speed and high glide angle. The cantilever wing was tapered, the 18 ft 2.5 in (5.5 m) long outer parts had slightly negative V-position. The 30 ft 6.15 in (9.3 m) long inner surfaces were trapezoidal. Six fabric covered flaps over the entire span of the wing served the warping of the wing and the transverse control. The cockpit was in a 1 ft 9.65 in (55 cm) wide fuselage, which merged upward into a streamlined structure that supported the center wing. At the end of the tubular tail boom was a damped horizontal stabilizer with end side elevators. Both rudders could be knocked out by pressing both rudder pedals to act as an air brake. The landing gear was an air-sprung ash wooden skid under the fuselage, laterally held by elastics.

After a number of test flights, Robert Kronfeld made a six-hour 25.5 mls (41 km) long flight from the famous Wasserkuppe gliding field near Fulda on July 19, 1932. On the next flight on July 22, 1932, participating in the Rhön gliding competition from the Wasserkuppe, Kronfeld entered cumulus clouds and one wing broke off. Kronfeld parachuted to safety, the Austrian was destroyed. It was by far the largest glider built at that time, and it was not until 2000 that a glider barely larger was built, the Kickert eta ƞ of 98 ft 5.1 in (30.90 m) span.

August Kupper died in 1938 in a crash with the Ku.7 of his own design.

Span: 98 ft 5.1 in (30.00 m)
Length: 29 ft 6.3 in (9.00 m)
Height: 8 ft 10.3 in (2.70 m)
Wing area: 376.41 sq.ft (34.97 sq.m)
Wing aspect ratio: 25.7
Ailerons area (total) : 202.36 sq.ft (18.80 sq.m)
Fin area: 13.24 sq.ft (1.23 sq.m)
Rudder area: 9.56 sq.ft (0.89 sq.m)
Tail plane area: 21.85 sq.ft (2.03 sq.m)
Elevators area: 13.89 sq.ft (1.29 sq.m)
Empty weight: 887.14 lb (402.40 kg)
Loaded weight: 1,063.51 lb (482.40 kg)
Wing loading: 2.83 lb/sq.ft (13.80 kg/sq.m)
No performance data available.

---

The character ƞ in the designation is the Greek letter eta, which, in the world of technology, stands for the degree of efficiency, i.e. a gauge for the efficiency of energy utilization. For gliders, a high degree of efficiency is particularly important in order to use weak thermals for gaining height and maintaining achieved heights on long runs."