The HKS-1 was a German 19 span high performance two seat sailplane, designed around 1950 to use recent advances in laminar flow airfoils. To avoid premature transition from laminar flow caused by surface interruptions, the HKS-1 dispensed with hinged ailerons, flaps and spoilers and replaced them with a flexible trailing edge. Two were built, setting several records.
==Design and development== Any aerodynamic approach that decreased wing drag was welcomed by sailplane designers, who reduced lift-induced drag with high aspect ratio wings. Profile drag was reduced by maintaining laminar flow over as much of the wing as possible. The NACA 6-series profiles of the late 1930s suggested that laminar flow might be maintained as far back as 70% chord, though military experience during World War II showed that much less ambitious targets were hard to achieve with riveted surfaces on wings with gaps for control surfaces, armament, service hatches etc. After the war, sailplane designers realised that their wooden surfaces could, with care, be made smoother over long distances than metal ones, that sailplanes had fewer wing surface interruptions than military machines and their lower speeds meant lower Reynolds numbers, encouraging stronger laminar flow. Such aircraft began to appear from 1950 onwards and showed striking improvements in performance.
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