Unknown

The 'Unknown' was a pioneering single‑seat monoplane built in 1928 by the little‑known German constructor Walter Rieseler. Rieseler, formerly a mechanic at a larger factory, founded his own workshop in Stuttgart to experiment with lightweight airframes and low‑drag wing profiles. The Unknown featured an all‑wooden structure covered with fabric, a 55 hp Oberursel rotary engine, and a cantilever wing with a thin, tapered airfoil that reduced drag by roughly 15 % compared with contemporaries. Its fixed, tail‑wheel undercarriage was simplified to a single axle, saving both weight and maintenance time. Only three prototypes were completed, but the type attracted attention at the 1929 Berlin Aero‑Show, where Rieseler demonstrated a 220‑km cross‑country flight that set a new distance record for aircraft under 150 kg empty weight. Although financial difficulties prevented series production, the Unknown’s aerodynamic concepts influenced later German sport aircraft, notably the Klemm L 25. Today the surviving prototype is preserved in the Deutsches Museum, serving as a testament to Rieseler’s innovative spirit and the experimental zeal that propelled interwar aviation forward. The aircraft’s modest success inspired a small community of amateur builders in the 1930s, who adopted its construction techniques, thereby extending its influence beyond the factory walls.

Walter Rieseler

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