|Bell Model 214ST|
In its Isfahan plant, Iran intended to produce a larger and more powerful variant of the Model 214A capable of carrying up to 16 people. A Model 214A was modified by Bell with the installation of two 2,250shp General Electric T700/T1C turbo-shafts and tested in Iran in February 1977. The definitive Model, known as Model 214ST (ST stood for 'Stretched Twin', but this was later modified to 'Super Transport'), had its fuselage stretched by 2.44m. Bell assembled three prototypes (two for commercial certification and one of the military variant, c/n 18401/ 18403). Under the agreement, Iran would have paid up to 50% of the launching programme cost, but with the withdrawal of the United States from Iran, Bell decided to fund the Model 214ST programme alone and initiated the production of a first batch of 100 aircraft in November 1979. The first prototype (c/n 18401, N214BH) flew on 21 July, 1979. The production examples were powered by 2,930shp Avco Lycoming LTC4B-8Ds driving a large five-blade rotor with Noda-Matic head. In 1982, the Model 214ST received FAA and CAA type certification for VFR and IFR operations. A version with wheel undercarriage was certificated in March 1983.
Production began in 1981, deliveries started in 1982 and by the beginning of 1984, some twenty machines were in service and seventy-eight had been delivered by early 1988. Among the first operators were British Caledonian Helicopters (c/n 28109/28110; G-BKFN and G-BKFP) which operated offshore in the North Sea and People's Republic of China. At the time of writing, some two hundred Model 214STs have been sold. The bulk of the Model 214ST production has found its way on to the civil market and only a few have been delivered to military customers: Brunei (one), Peru (eleven), Thailand (nine) and Venezuela (four) and Sultan of Oman's Air Force which operated eight Model 214B/STs from Salalah during the war against Iraq in January/February 1991.
A.J.Pelletier "Bell Aircraft since 1935", 1992
The 214ST was originally designed specifically for production in Iran with development funded by the Imperial government. An interim prototype was built by Bell in 1977, introducing two 1.625 shp General Electric CT7 engines and incorporating a stretched and widened fuselage. Construction of three de-finitive ST prototypes began in 1978 but the fall of the Shah in 1979 forced Bell to rethink the original miltary transport plan, and to re-launch the aircraft with their own funding as a 7.938kg gross weight commercial helicopter produced at Fort Worth.
Initial orders included several for offshore oil support and utility transport roles, in which configura-tion the aircraft seats 18 passengers plus two crew. The twin engines drive a one-hour run-dry transmis-sion with fiberglass rotor blades and elastomeric bearings in the rotorhead. The 214ST is cleared for two-pilot IFR operation, and is the first large Bell helicopter to offer an optional wheeled undercarriage in-stead of skids.
G.Apostolo "The Illustrated Encyclopedia of Helicopters", 1984
Powered by twin General Electric CT7 turboshafts developing 1625shp, the Bell 214ST has a top speed of 296kph and a range of 830km. First flown in July 1979, this was a private venture by Bell Helicopters to develop a fast utility transport helicopter. Using newly designed composite rotors, the 214ST was originally destined for the Iranian Armed Forces but this was cancelled and the 214ST was developed in both a civil and military variant. Capable of carrying two pilots and eighteen passengers, the 214ST is fully IFR certified and has a computer-controlled fly-by-wire automatic elevator trim system, plus a stability and augmentation control system and main rotor blade in-flight tracking system.
P.Allen "The Helicopter", 1996
In late 1970 Bell Helicopters completed the construction of a prototype aircraft to which the identification Bell Model 214 Huey Plus was allocated. It was, in effect, an improved version of the well tried and proven UH-1H Iroquois, using the same airframe, but provided with increased power, some advanced features, and structural strengthening for operation at higher gross weights. From this helicopter was developed the Bell Model 214A 16-seat utility version with a 2185kW Avco Lycoming LTC4B-8D turboshaft engine and, following its demonstration in Iran, the company received an order for 287 of these aircraft, to be acquired by Iran through the US government. Soon after this the government of Iran began negotiations with European and US helicopter manufacturers, with the intention of establishing an indigenous aircraft industry, and concluded an agreement with Bell Helicopters in 1975. This envisaged that the Iranian government and Bell would jointly create facilities in Iran for this purpose, with the Bell 214A as its initial project, to be followed by a new Bell Model 214ST developed especially for operation in Iran. The revolution of early 1979, and subsequent changed national policies in Iran, brought to an end these plans, but Bell decided to continue with independent development of the Model 214ST as a commercial transport with multi-mission capability.
A prototype of the Model 214ST was first flown in February 1977, and was followed by the construction of three pre-production aircraft, beginning in 1978, the first of these flying in the summer of that year. These aircraft were all used in the development programme, with FAA certification for two-pilot IFR operation gained in 1982. By early 1989 a total of 96 had been delivered, the largest order being 45 to the Iraqi Air Force.
Features of the Model 214ST airframe include the large-capacity all-metal fuselage, which includes in its structure a rollover protection ring, providing accommodation for a pilot and co-pilot, plus 16 or 17 passengers according to customer specification. The rotor system includes an advanced technology two-blade main rotor fabricated from glassfibre, its leading edges protected by a titanium abrasion strip and the blade tips each having a replaceable stainless steel cap. The rotor hub incorporates elastomeric bearings which require no lubrication, and the rotor system is mounted on a Bell-developed nodal suspension beam from which the fuselage is suspended. This latter feature is based on the fact that a beam subjected to vertical vibrations will flex in wave form, with nodal points of no relative motion equidistant from the centre of the induced wave form. Bell suspends the helicopter fuselage from the nodal points of such a beam, resulting in a reduction of more than 70% in rotor-induced vibration.
The other major change, by comparison with the Model 214A, is the replacement of the single Lycoming turboshaft by two General Electric turboshafts which, driving the rotor through a combining gearbox, give true single-engine flight capability. Multi-mission roles are catered for by the provision of easily-removable passenger seating to offer 8.95m3 cargo capacity, full IFR avionics and instrumentation, emergency flotation gear, an external cargo suspension system, and an internal rescue hoist.
D.Donald "The Complete Encyclopedia of World Aircraft", 1997
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The prototype 214ST flew for the first time in February 1977, and construction of three preproduction examples began in 1978. The decision to manufacture an initial series of 100 production 214STs was announced in November 1979. FAA and CAA certification for two-pilot IFR operation was obtained in 1982, and deliveries started soon afterwards. The Model 214ST was certified under transport category airworthiness requirements in Canada, Japan, the UK and USA. The CAA approved it for flight into icing conditions with added icing kit.
ROTOR SYSTEM: Two-blade advanced technology main rotor. Each blade has a unidirectionally laid glass fibre spar, with a ±45° wound torque casing of glass fibre cloth. The trailing-edge is also of unidirectional glass fibre, and the space between spar and trailing-edge is filled by a Nomex honeycomb core. The entire blade is then bonded together by glass fibre wrapping, with the leading-edge protected by a titanium abrasion strip and the tip by a replaceable stainless steel cap. Two-blade tail rotor; interchangeable blades, each with a stainless steel leading-edge spar and covering, aluminium honeycomb core and glass fibre trailing-edge strip. Main rotor head incorporates elastomeric bearings. Second-generation Noda-Matic nodal suspension system. Nodal beam requires no lubrication. Main rotor brake standard.
ROTOR DRIVE: Main transmission has a maximum rating of 1,752kW, maximum continuous rating of 1,454kW, and single-engine rating of 1,286kW. Combining, intermediate and tail rotor gearboxes, each with 1 hour run-dry capability.
FUSELAGE: Conventional all-metal semi-monocoque structure, incorporating rollover protection ring.
TAIL SURFACE: Electronically controlled elevator, which minimises trim changes with alterations of power and CG, and improves longitudinal stability.
LANDING GEAR: Choice of energy absorbing non-retractable tubular skid-type or tricycle-type wheeled landing gear.
POWER PLANT: Two 1,212kW General Electric CT7-2A turboshafts, connected to a combining gearbox. In the event of an engine failure, the remaining engine is capable of developing 1,286kW to provide continued flight capability. Standard fuel capacity 1,647 litres, contained in seven interconnected rupture-resistant cells, arranged to provide two independent fuel systems as required by FAR Pt 29. Single-point refuelling. Auxiliary fuel system optional, consisting of two tanks in rear of cabin, each of 329 litres capacity; 95 litre underseat auxiliary fuel tanks also available. Engine anti-icing and inlet screens standard.
ACCOMMODATION: Standard seating for pilot, co-pilot and up to 18 passengers. Dual controls standard. Crew seats adjustable. Passenger seats in three rows across cabin plus a two-place bench seat on each side of rotor mast. Standard configuration offers utility or de luxe interiors with contemporary or energy attenuating seats. Jettisonable crew door each side. Large cabin door on each side for passengers or easy loading of cargo. Glass windscreens, with standard anti-icing system. Two emergency exits on each side. Baggage space aft of cabin, capacity 1.84m3. Passenger seating removable to provide 9.23m3 of cargo capacity. Cabin heated and ventilated.
SYSTEMS: Dual engine-driven hydraulic pumps for fully redundant hydraulic power for flight control system; pressure 207 bars, maximum flow rate 25.4 litres/min for primary control system; 19 litres/min for utility system. Closed bootstrap pressurised reservoirs. Third system operates oil cooler blower for transmission and combiner gearbox. Redundant electrical system with dual engine-driven generators. Stability and Control Augmentation System (SCAS). Main rotor blade in-flight tracking system. Attitude Altitude Retention System (AARS). Computer-controlled fly-by-wire automatic elevator trim system.
AVIONICS AND EQUIPMENT: Standard avionics include dual com, dual nav, R Nav, ADF, transponder DME, air data computer and standby attitude indicator to provide IFR capability. Avionics options include radar, nav coupling and VLF nav system. Optional equipment includes anti-icing kit, emergency flotation gear, external cargo suspension system, internal rescue hoist, and two pneumatically ejected 10- or 12-person liferafts inside engine cowl fairing forward of rotor mast.
Jane's Helicopter Markets and Systems
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Technical data for Bell Model 214ST
Engine: 2 x General Electric CT7-2 turboshaft, rated at 1212kW, main rotor diameter: 15.85m, length with rotors turning: 18.95m, height: 4.84m, take-off weight: 7802kg, cruising speed: 250km/h, hovering ceiling, IGE: 3170m, range: 780km