|Bell Model 47 "Sioux"|
The Bell Model 47 was ordered for the US Army and Navy towards the end of World War II and first flew in 1945. The pre-production model had a 178hp Franklin engine and a car-type body. Only ten were built, but some were airborne as early as 1943. However, the Model 47 has the distinction of being the first helicopter to receive a CAA (Civil Aviation Administration) approval certificate, which was granted on March 8, 1946. The A and B models used the enclosed body. The 47B-3, a utility and agricultural model, had an open sports-car style body and it was from this design that the now familiar goldfish bowl moulded canopy was derived. The FAA (Federal Aviation Administration) certified the 47D with its new canopy in February 1948. A year later Bell produced the 47D-1 with an openwork tail boom.
The three-seat configuration, later combined with a 200hp Franklin engine, produced the 47G which was granted an FAA certificate in 1953. This became one of the most successful versions remaining in production in improved forms into the 1970s. It was adopted by a wide range of civil and government operators for survey work, traffic control, coastguard work, crop-spraying (using the AgMaster chemical application system) and as an executive transport.
Not content with this success Bell have developed further models and in 1955 they installed a new powerplant. The 200hp Lycoming VO-435 allowed the helicopter to operate at greater weights but without a fall-off in performance.
In 1952 Agusta SpA of Italy was granted a licence to build the Bell 47 and produced its first 47G in 1954. Since then Agusta has built over 1000 G and J marks. Kawasaki in Japan received a licence a year later and like Agusta developed its own versions of the Bell originals.
The Bell 47H with a fully enclosed car-type cabin and 200hp engine was not a commercial success, but in the early 1960s the J series sold well. Seating four in an enclosed cabin, it was powered by a 220hp Lycoming VO-435 engine. With power controls and metal rotor blades in the Model 47J-2 in 1960 it became popular as an executive transport. Agusta produced a three-seat version as the EMA 124 and though Bell have stopped production the G and J series are still being built in Italy and Japan.
Bill Gunston "The Illustrated Encyclopedia of Commercial Aircraft", 1980
On 8 December 1945, Bell flew the prototype of a classic helicopter design, the Bell Model 47. On 8 March 1946 this was awarded the first Approved Type Certificate issued for a civil helicopter anywhere in the world. The type remained in continuous production by Bell into 1973, and was also built under licence by Agusta in Italy from 1954 to 1976. The Model 47 has been used on a large scale by armed forces all over the world, its simplicity and low cost more than outweighing its limited capabilities.
In 1947 the USAF (then USAAF) procured 28 of the improved Model 47A, powered by 117kW Franklin O-335-1 piston engines, for service evaluation: 15 were designated YR-13, three YR-13As were winterised for cold-weather trials in Alaska, and the balance of 10 went to the US Navy for evaluation as HTL-1 trainers. Little time was lost by either service in deciding that the Model 47 was an excellent machine, and the orders began to flow in.
The US Army's first order was issued in 1948, 65 being accepted under the designation H-13B; all US Army versions were later named Sioux. Fifteen of these were converted in 1952 to carry external stretchers, with the designation H-13C. Two-seat H-13Ds with skid landing gear, stretcher carriers, and Franklin O-335-5 engines followed, and generally similar three-seat dual control H-13Es. The H-13G differed by introducing a small elevator, and the H-13H introduced the 186kW Lycoming VO-435 engine. Some of the H-13Hs were used also by the USAF, as were two H-13Js with 179kW Lycoming VO-435s acquired for the use of the US President. Two H-13Hs converted for trial purposes, with an increased-diameter rotor and 168kW Franklin 6VS-335 engine, were designated H-13K. In 1962 US Army H-13E, -G, -H and -K aircraft were redesignated with the prefix letter O, for observation. US Air Force H-13Hs and H-13Js were given the U prefix as utility helicopters. Later acquisitions were the three-seat OH-13S to supersede the OH-13H, and the TH-13T two-seat instrument trainer.
US Navy procurement began with 12 HTL-2s and nine HTL-3s, but the first major version was the HTL-4, followed by the HTL-5 with an O-335-5 engine. HTL-6 trainers incorporated the small movable elevator. The HUL-1 was acquired for service on board ice-breaking ships, and the final HTL-7 version for the US Navy was a two-seat dual-control instrument trainer with all-weather instrumentation. In 1962 the HTL-4, HTL-6, HTL-7 and HUL-1 were redesignated respectively TH-13L, TH-13M, TH-13N and UH-13P
The Model 47 has been built under licence by Agusta in Italy, Kawasaki in Japan, and Westland in the UK (the 47G-2 for the British Army, with the name Sioux), and in various roles Model 47s have served with more, than 30 armed services.
Experimental versions have been numerous. Perhaps the two most important were the Bell Model 201 (service designation XH-13F) and the Bell Model 207 Sioux Scout. The Model 201 was powered by a Continental XT51-T-3 (licence-built Turbomeca Artouste) turboshaft. The Model 207 was the first true armed helicopter: powered by the 194kW turbocharged Avco Lycoming TVO-435-A1A piston engine, the Sioux Scout featured a revised cabin seating two in tandem, small stub wings containing additional fuel and helping to offload the main rotor in forward flight, and a remotely controlled chin barbette, containing two 7.62mm M60 machine-guns, and movable 200° in azimuth, with elevation from -45° to +15°.
In parallel with production of military aircraft, by both Bell and its licencees, there were civil versions for a wide variety of purposes. These have included the Model 47B (equivalent to the military YR-13/HTL-1), and the agricultural/utility Model 47B-3 with open crew positions. The following Model 47D was the first to appear with a moulded 'goldfish bowl' canopy, and the Model 47D-1 of 1949 introduced an openwork tailboom as on the H-13C.
A first important change came with introduction of the Model 47G, which combined the three-seat capacity of the Model 47D-1 with a 149kW Franklin engine. Substitution of the similarly powered Avco Lycoming VO-435 resulted in the Model 47G-2 (H-13H). A 179kW VO-435 engine brought the changed designation Model 47G-2A, followed in 1963 by the wider cabin Model 47G-2A-1 with improved rotor blades and increased fuel capacity. Other engine installations included a 168kW supercharged Franklin 6VS-335-A (Model 47G-3); 209kW turbocharged Avco Lycoming TVO-435 (47G-3B); and normally aspirated Avco Lycoming VO-540 and VO-435 engines in the three-seat utility Model 47G-4 and Model 47G-5 re spectively. A two-seat agricultural version of the latter was known as the Ag-5, and a civil version of the USAF's H-13J VIP transport was marketed as the VO-435 engines in the three-seat utility Model 47G-4 and Model 47G-5 respectively. A two-seat agricultural version of the latter was known as the Ag-5, and a civil version of the USAF's H-13J VIP transport was marketed as the Model 47J Ranger. Bell's production of Model 47s eventually came to an end in late 1973, versions of the Model 47G-5 being the last to be built.
Agusta in Italy, and Kawasaki in Japan, both produced helicopters comparable to some of Bell's civil Model 47s, and added variants of their own. In addition there have been specialised conversions by at least two American companies, including a high-performance Carson Super C-4, and a number of El Tomcat agricultural aircraft developed by Continental Copters Inc. Turboshaft conversions of several models have been produced by Soloy in the USA.
D.Donald "The Complete Encyclopedia of World Aircraft", 1997