Delivered to United in July 1953 as N37568 "Mainliner Des Moines", it served until October 1968 when it had flown 32,296 hours. In December 1971 it was acquired by the Fairbanks-based Aero Retardant Inc. who converted it as a fire bomber, becoming Tanker 52 / D2. The following year it was transferred to the sister company Pacific Alaska Airlines, and operated until 1980 when it was sold to B&D Aircraft Inc. for parting out. After lingering at on at Chino for many years it was finally broken up c.1990, the nose section being noted at The Aviation Warehouse at El Mirage, CA. in October 1992.

D-5670 was registered in Jul-1999. With the wings starting to flex, it is seen here on an aerotow take-off.

D-5670 was registered in Jul-1999. It is waiting here for its turn to be launched by aerotow for a compeition flight in the contest.