YR-13/H-13/OH-13 Series Sioux
light observation helicopter

h-13_oh-13.jpg (54711 bytes)

(1946) The Bell (model 47) H-13 Sioux, with a crew of three, was one of the most popular light utility helicopters ever built. The Bell model 47 was produced continuously from 1946 to 1973, and in other countries through 1976. Produced in 20 different configurations, with model numbers ranging from A to T, the Bell model 47 was used in 40 countries. The combined total of commercial and military versions of this series was 5,000. The U.S. Army Air Force procured it's first YR-13 (model 47B) in December 1946. The OH-13 had a cruising speed of 70 mph (60 knots).

An important Bell innovation during the early development of the helicopter was the use of short weighted gyro-stabilizer bar at 90° to, and beneath, the main rotor. The gyro-stabilizer bar, with streamlined counterweights at both tips, was linked to the rotor in such a way that it determined the plane of the rotor, and maintained it generally in the horizontal, regardless of the angle of the mast. The stabilizer bar, connected to the cyclic pitch control, acted as a hinged flywheel utilizing gyroscopic inertia to keep the teetering rotor blades in-plane and independent of fuselage movement due to gusts of wind, providing stability during flight. Arthur Young, Bell's designer, ensured the system had high enough inertia so sufficient energy would be stored in the rotor to permit safe autorotation in event of engine failure, an important safety consideration.

The H-13 was used for observation, reconnaissance and in the MedEvac role as a litter carrier in Korea, following initial fielding in 1951. In the MedEvac role a cocoon-like stretcher pod could be mounted on each skid. A distinctive feature of the Bell (model 47D) H-13D/H13E was the now familiar "Goldfish bowl" Plexiglas canopy, featured in the TV-series MASH (Mobile Army Surgical Hospital). The H-13 earned the nickname "Angel of Mercy" for evacuating some 18,000 United Nation's casualties during the war. The OH-13 Sioux also saw service during the early days of the Vietnam war before the fielding of the OH-6A Cayuse in early 1968. The Sioux had a single two-bladed main rotor and a metal two-bladed tail rotor. The H-13 had a speed of 106 mph (92 knots). The Sioux could be armed with twin M37C .30 Cal. machine guns on the XM1 armament subsystem or twin M60C 7.62mm machine guns on the M2 armament subsystem.

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