Bell H-13 Sioux

In 1947, the United States Army Air Forces (later the United States Air Force) ordered the improved Bell Model 47A. Most were designated YR-13 and three winterized versions were designated YR-13A. The United States Army first ordered Bell 47s in 1948 under the designation H-13. These would later receive the name Sioux. Initially, the United States Navy procured several Bell 47s, designated HTL-1, between 1947 and 1958. The United States Coast Guard evaluated this model and procured two HTL-1s for multi-mission support in the New York Harbor. The most common U.S. Navy version of the 47 was designated the HTL-4, and dispensed with the fabric covering on the tail boom. The U.S. Coast Guard procured three HTL-5s in 1952 (similar to the HTL-4 but powered by a Franklin O-335-5 engine) and used these until 1960. The Coast Guard procured two of Bell's Model 47G and designated them HUL-1G in 1959. the first contract was for 200 helicopters. The first 50 helicopters of the contract were built by Agusta at Gallarate in Italy followed by 150 built by Westland at Yeovil. The first Westland Sioux made its maiden flight on 9 March 1965. ==Design==

The Sioux is a single-engine, single-rotor, three-seat observation and basic training helicopter. In 1953, the Bell 47G design was introduced. It can be recognized by the full "soap bubble" canopy (as its designer Arthur M. Young termed it), exposed welded-tube tail boom, saddle fuel tanks and skid landing gear. In its UH-13J version, based on the Bell 47J, it had a metal-clad tail boom and fuselage and an enclosed cockpit and cabin. The H-13 and its military variants were often equipped with medical evacuation panniers, one to each skid, with an acrylic glass shield to protect the patient from wind. The development of the Sioux was helped greatly by Bell's implementation of a short weighted gyro-stabilizer bar beneath and perpendicular to the main rotor. It had streamlined counterweights at both tips and was linked so it determined which plane the rotor was in and kept it horizontal. The stabilizer, which was connected to the cyclic pitch control, acted as a hinged flywheel using gyroscopic inertia to keep the rotor blades in plane and independent of fuselage movement due to wind. It ensured that the system had enough inertia due to flight as well, so autorotation would function in case of engine failure. A single 260 hp Lycoming VO-435 piston engine was fitted to the 47G variant. Fuel was fed from two high-mounted external tanks. A single two-bladed rotor with short inertial stabilizing minor blades was used on the Sioux. ==Variants==

Military