Ufimtsev's Spheroplans
In 1909 a Russian designer named Anatolii Georgyevich Ufimtsev produced a circular-winged airplane, the Spheroplan, with a 20 hp engine. It did not fly. A second model with a 60 hp engine was also unsuccessful.
Ironically, another Ufimtsev - mathematician Pyotr Ufimtsev - would lay the theoretical groundwork in the 1960s for methods that would later be used by US engineers to design the first radar-scattering "stealth" aircraft, the USAF/Lockheed HAVE BLUE and F-117 Nighthawk.
Spheroplan 1
Spheroplan 2
Spheroplan 2 Drawings