Bell H-12

The Bell R-12, later redesignated H-12 and known inside the company as the Model 48, was an American military utility helicopter of the 1940s built by Bell. It grew out of the larger Model 42 that Bell began developing in 1946, which used a scaled-up version of the Model 47 rotor system but suffered serious rotor problems and mechanical complexity. The United States Air Force ordered a military version as the XR-12, powered by a Pratt and Whitney R-1340 radial engine and seating five, and a production batch of 34 R-12A helicopters was ordered and then cancelled in 1947. A larger XR-12B followed, with seats for eight plus two pilots, then ten pre-series YR-12B machines with a glazed nose. Flight tests showed major rotor problems from blade weaving and poor governor performance, so no production H-12 was built, although the prototypes were used in various test programmes under the nickname Fat Boy.