The XR-3 was used as a flying test bed for rotor blades and components to be used on Kellett's XR-8 helicopter that was being designed.
In general it had the same dimensions as the YG-1B using the fuselage, tail and landing gear with no changes. The only change to the powerplant was the use of the YO-60 power takeoff. As in the YO-60, the intermediate gear box was eliminated driving from the back of the engine to a modified YO-60 rotor head.
The head was locked so that it did not tilt. Control, instead, was done by feathering the blades cyclically as is done now in a helicopter. Jump takeoff was provided by manually operated "collective" pitch control of the blade pitch angle for takeoff and a quicker descent. The normal blade for the XR-3 was tapered in thickness and plan form. Plywood ribs were spot welded through their metal collars to the heat-treated 4130 steel spar tube. Plywood covered the leading edge of the blade then the blade was fabric covered and doped. Because of the extra weight of the hub controls and blade controls, blade-to-blade dampers had to be added.
The rotor pylon was mounted on rubber at the fuselage to eliminate vibration. This was later blocked out and extra struts were added to the pylon to brace it.
A movie camera was mounted on the top of the rotor head, rotating with the blade that could take pictures of one blade that was going to be used on the XR-8 helicopter. The blades were flown, photographed and studied while the autogiro was flown in various modes of flight. When pilots saw the pictures of the wild gyrations the blades went through – bending, flapping and twisting - they almost quit flying the autogiro.
Pilots who flew the XR-3 like it very much. One takeoff was made with the autogiro buried in a snowdrift higher than its wheels. The autogiro jumped straight up without any forward motion.
At the end of its tests, it was sold surplus to Westinghouse who had an aerodynamic research center in Schenectady, New York.
G.Townson "Autogiro. The Story of the Windmill Plane", 1985
Technical data for Kellett XR-3
Gross weight: 1200kg, max speed: 170km/h