Bell H-12

The Bell R-12 (Model 48), re-designated as the Bell H-12, was an American 1940s military utility helicopter built by Bell Helicopter company.

Design and development
During 1946, Bell Helicopter began development of a new utility helicopter, the Model 42, much larger than the Model 47, utilized a scaled-up version of the Model 47's rotor system. Three prototypes were built but serious rotor problems and complexity of mechanical systems precluded production. The initial Model 42 variant was civilian, but the United States Air Force ordered the development of its military variant, the Model 48, of which, two prototypes were ordered as the XR-12, powered by a single 540 hp Pratt & Whitney R-1340-AN-1 radial engine and featuring seating for five. Of very similar construction to the Model 42 the Model 48 had a shorter rotor mast. A production batch of 34 helicopters was ordered, under the designation R-12A, but cancelled in 1947.

Another enlarged prototype (the XR-12B, Model 48A) with seats for eight plus two pilots and a more powerful 600 hp Pratt & Whitney R-1340-55 engine was also ordered, followed by 10 pre-series YR-12B helicopters, with a glazed nose, instead of the car-like nose of the Model 42 and XR-12. Whilst under flight test the helicopter was re-designated the H-12, but the results were not satisfactory, there were major problems with the main rotor due to blade weaving and poor rotor governor performance.

Operational history
No production H-12 aircraft were built but the prototypes and pre-production aircraft were used for various test and development programs.

Variants

 * Model 42
 * Bell's initial foray into the civilian luxury helicopter market, seating five. Three prototypes were built but serious problems precluded production.


 * Model 48
 * Company designation for the military version of the Model 42, given the designation R-12. Two built as XR-12s and a production contract for 34 was cancelled in 1947.


 * Model 48A
 * The more powerful derivative of the Model 48 with a 600 hp engine and 10 seats. One XR-12B/XH-12B prototype was produced and a pre-production batch of 10 were also built as YR-12B/YH-12Bs


 * XR-12
 * Prototype, redesignated XH-12, two built.


 * R-12A
 * Production version, 34 on order cancelled.


 * XR-12B
 * Prototype with more powerful engine and increased seating, re-designated XH-12B, one built.


 * YR-12B
 * As XR-12B but with R-1340-55 engines, re-designated YH-12B, 10 built.


 * XH-12
 * XR-12 re-designated in 1947.


 * XH-12B
 * XR-12B re-designated in 1947.


 * YH-12B
 * YR-12B re-designated in 1947.

Operators

 * United States Air Force
 * United States Air Force