Initial prototype for the R-4 series. Referred to in some references by the designation XR-4A. This aircraft (there was only 1 built) was later converted to the XR-4C prototype.
VTOL type: Helicopter
Lift configuration: Single main rotor
Dedicated control device: Tail rotor
Crew required: 0
Crew seating: Side-by-side
Landing gear: Wheels (non-retractable)