First flight of the Bölkow Bö 103, 1 blade main rotor helicopter
Thursday, September 14, 1961 - Neubiberg, Germany
The Bo 103 Ein Mann- Ein Blatt (One Man - One Blade) had a single main rotor blade and a single tail rotor blade (more details of the aircraft can be found in the following reference - "MBB's Helicopter History - Based on a Solid Heritage", Christina Gotzhein, VERTIFLITE May/June 1984, Page 95).
Only one aircraft was built. It can be seen in the German Helicopter Museum in Bückeburg.
Source: AHS Calendar September 2015 for more details.