Nagler-Rolz NR 55
The Nagler-Rolz Flugzeugbau built a helicopter similar in configuration to the RI and RII. This ship had an empty weight of 700 pounds and though it was flown in hover, it could not be lifted out of ground effect. With the coming of World War II, the company received contacts from the German Government for the development of small single-seat helicopters.
In 1940 the first machine from the new company appeared as the NR 55, which had a single-blade rotor. This rotor blade was counterbalanced by a 40hp engine which applied to it a torqueless drive by means of two small airscrews which pulled it round at about 135rpm. Because of gyroscopic forces at the engine location, the carburetor was mounted on the centerline of the rotor hub and fuel-air mixture was piped out to the engine cylinders. The rotor diameter was 10.5m, and the machine weighed about 338kg loaded, but, although a cruising speed of 97km/h was thought feasible, only hovering and lift test were undertaken because the machine was built purely for testing the rotor system.
Development of the NR 55 concept continued in 1941 with the generally similar NR 54 V1.