10/31/2007. Remarks by Johan Visschedijk
: "The Model 47G-2 registered N6723D and nicknamed "Wing Ding" was converted under the leadership of Jan Drees and flown by Floyd Carlson and Lou Hartwig in 1963. The purpose of the Wing Ding program was to develop an aircraft which would lift very large payloads in excess of its hover capability, taking advantage of running take-offs and landings. In addition to the wing the rotor's mast angle could be varied in flight."