The Sisu 1A is a competition sailplane built in the United States in the late 1950s and early 1960s. Originally designed by Leonard Niemi as a homebuilt sailplane its first flight in 1958 showed such promise that Niemi decided instead to manufacture it in series production. Niemi formed the Arlington Aircraft Company for this purpose. The Sisu 1A quickly proved itself as the most competitive American sailplane ever developed winning the 1962 1965 and 1967 U.S.
