In "Helicopters Of The Third Reich" by Steve Coates a German designer and constructor of helicopters is mentioned,
who, contrary to Anton Flettner, Gerd Achgelis or Henrich Focke remained widely unknown : Walter Rieseler, born in
1890. He started to build his first helicopter in 1936 after securing an order by the RLM. The aircraft with an open steel
tube fuelage and contra rotating rotor was powered by a 90 hp engine was designated R I. Apart from cooling problems
it suffered from figt control problems, nevertheless it was demonstrated to RLM officials, including Ernst Udet. This demonstration
ended with a crash, commented by Udet laconically "I'm not impressed ! I'm quite capable of producing a crash myself!"
The R I was repaired later and handed ove to the DVL (Deutsche Versuchsanstalt für Luftfahrt= German aviation test institute)
and Rieseler started the construction of a improved design in 1937, the R II, powered by two Siemens Sh14 engines. Flight
tests again ended with a crash (Not directly related to the design) and work on a third prototype ended with the death of Walter
Rieseler in May 1937.