Kellett did not give their model numbers to XR-2 or XR-3. These were the only two "non helicopters" to get XR designations by the military. The XR-l was the Platt-LePage helicopter and the XR-4 was a Sikorsky helicopter. Earlier the autogiro had "O" designations for the Navy as XOP-l and XOP-2. "P" was for Pitcairn. The Army Air Corps had no such manufacturer designators. YG-l (A&B) were Kellett Autogiros. The YG-2 was the Army Air Corps version of Pitcairn's Navy XOP-2. Later the Army Air Corps designated all observation craft, either fixed or rotorwing as "O" of "XO." "XO" indicated Experimental Observation. "YO" indicated a service test model. When the model was accepted, the "Y" was dropped. The autogiro never made it to this level because the helicopter took its place with the military. YO-60 was Kellett's machine, while the XO-61 was Pitcairn's.
The XR-2 was modified YG-1B with a jump takeoff system the same as the XO-60 and with 330hp Jacobs engine installed. It used a single beam landing gear instead of the outriggers. A Hamilton-Standard constant-speed propeller replaced the Curtiss-Reed.
The XR-2 never flew. It was totally destroyed in a ground runup accident.
G.Townson "Autogiro. The Story of the Windmill Plane", 1985