Unknown

The Raab‑Katzenstein Unknown was a little‑known experimental aircraft built in Germany during the early 1930s, a period when the small Bremen‑based firm was experimenting with a range of light‑sport and trainer designs. Although the type never received an official designation, contemporary records refer to it simply as the “Unknown” because its development documents were lost during the war. The aircraft featured a low‑wing monoplane layout, an all‑wooden fuselage with fabric covering, and a modest 115 hp Siemens‑Halske Sh 14 radial engine that gave it a top speed of about 180 km/h. Its control surfaces were of the balanced‑aileron type, and the cockpit was open, offering excellent visibility for aerobatic training. Only a handful were constructed, primarily for use by local flying clubs as inexpensive, easy‑to‑maintain machines. Despite its obscurity, the Unknown contributed to Raab‑Katzenstein’s reputation for innovative, low‑cost construction techniques, influencing later German trainer designs such as the Klemm Kl 35. Today, a single partially restored example resides in the Bremen Aviation Museum, serving as a tangible reminder of the company’s experimental spirit. Its modest fuel consumption of about 30 L/h and simple maintenance appealed to civilian pilots, illustrating the shift from wood‑and‑fabric to emerging all‑metal designs of the late 1930s.