LF7250 KELLET XR-8

The XR-8 kellet is a prototype American helicopter with main rotors in a counter-rotating twin-rotor system from the Second World War. The machine made its maiden flight in 1944, but never entered mass production. The hull of the helicopter was 6.88 meters long, with a height of 3.35 meters. The main rotors had a diameter of 10.97 meters. The drive was provided by a single Franklin O-405 engine with 245 hp. The maximum speed was up to 160 km / h. The XR-8 helicopter was developed by the US Kellet Autogiro Corporation for the US Air Force. The machine was created in order to test the capabilities of a helicopter with rotors in a counter-rotating twin-rotor system. Such an arrangement theoretically offers the advantages of eliminating the tail rotor and making the structure more compact. However, in the case of the XR-8, it also generated significant problems: first of all, it caused strong vibrations of the entire structure, problems with vertical and horizontal flight stability, as well as was difficult to pilot. Finally, the project was abandoned after testing 2 copies in the period 1944-1946.