last single-row radial was the R-1300 Cyclone 7, essentially
one row of a R-2600. Designed in
1942, the earliest flight I can find is in 1949 powering the XT-28A.
Production was licensed first to Kaiser-Frazer,
then to Lycoming.
|7 cylinder, air-cooled, radial engine|
|displacement: 1,302 cubic inches (21.3 liters)|
|bore x stroke: 6.125 x 6.3125 inches|