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Aviation History
1958
1958 - 0108.PDF
110 FLIGHT Fiat's New Helicopter Notes on the 7002 and its Powerplant NOW under construction at Turin, the Fiat 7002 medium-size, general-purpose helicopter promises to give a ratio ofempty weight to useful load of 1:1.33. The main rotor is driven by compressed-air jets at the blade tips, supplied from aspecially developed turbo-generator. This type of "cold jet" propulsion was chosen by Fiat on thegrounds of lightness, constructional simplicity, low initial cost, high reliability, long overhaul life, and low maintenance andoperating costs. The compressed air is supplied by a Fiat 4700 turbo-generator in which the turbine-driven air compressor isoperated by a primary hot-gas generator based on the Fiat 4002 turbojet. The air compressor and the primary engine are mechanicallyindependent, resulting in free-turbine advantages and permitting the optimum compression ratio for the best pneumatic transmis-sion efficiency to be selected. The absence of reaction torque would have allowed the abolition of the tail rotor, since directionalcontrol could be obtained by means of a rudder. In order to ensure complete manoeuvrability at low forward speeds and in verticalautorotation, however, a small ducted tail rotor, mechanically driven by the main rotor, is employed. In general construction as well as in structure, the machine isbased on the concept of flexibility for a number of military and civil applications. The two main-rotor blades have leading edgesand spars made from stainless steel welded sheets and incorporat- ing air ducts to the tips. The rotor hub is of the tilting type, theblades being connected by steel strips which bear centrifugal loads and permit blade-pitch variations. Constructed from light-alloy sheet, the fuselage consists of threemain sections which house respectively the cockpit, the main cabin, and the vertically mounted powerplant. A short tail beamcarries the ducted tail rotor and a tailplane. The upper portion of the fuselage centre-section embodies the attachments of the mainrotor hub, and the fuel tanks. The landing gear is of the skid type. Normal loads envisaged for the 7002 are (1) one pilot and sixpassengers, (2) one pilot, one assistant and two stretchers (two additional stretcher litters can be mounted externally), and (3) onepilot and 90 cu ft of freight. Adaptation for other specialized purposes such as rescue or agricultural work is possible, and fulldual control is fitted. Specially developed for use in a cold-jet drive helicopter, the4700 compressed-air generator is of the free-turbine type, having a prime mover consisting of compressor, combustor and turbinewhich generates gas to be fed to a further power turbine. This The Fiat 7002 helicopter is illustrated in model form in the heading pic- ture; and in the g.a. drawing (right). Left, the Fiat 4700 com- pressed-air turbo-genera- tor, the prime - mover section of which is simi- lar to the 4002 turbojet. latter turbine drives the power air compressor. Vertical mountingof the engine reduces the length of the compressed-air duct to the rotor. In the primary engine, air suction is of the updraft type throughan air-intake casting made of magnesium-zirconium light alloy. The rotating unit, supported at the lower end upstream of thecompressor by a ball thrust bearing and at the upper end by a roller bearing, is pneumatically balanced in order to reduce theaxial thrusts on the bearings. The mixed-flow combustion chamber has a high specific capa-city, with reduced overall area and weight. High-altitude operat- ing characteristics are good, and the simplicity of design and smallnumber of parts have resulted in high efficiency and simple accessibility.An axial-flow, alloy steel turbine is employed, with high-nickel alloy turbine blades. The rear bearing and the turbine are cooledby air bled from the compressor. The free-turbine compressor is a self-contained unit connectedto the primary engine through a flange and sheet-metal structure. Provision is made in the connection of the two units for thermaldistortions without any adverse effect on their operation. Primary engine and compressor do not need to be accurately lined upduring assembly, with consequent speed and simplicity of strip- ping and reassembly in maintenance and servicing. The axial-flow, single-stage turbine is made of alloy steel, withfabricated high-nickel blades. The compressor is fitted with a magnesium alloy fabricated impeller. Compressor-diffuser frameand air manifold consist of a single magnesium-zirconium casting. The rotor main bearings are accommodated in an internal housingattached to the compressor-diffuser frame. Air for the power compressor is downdrafted through an airintake, and the power air supply is fed through a scroll on the upper end of the unit. The exhaust manifold is annular anddeflects the exhaust gas through 90 deg, so that it flows parallel to the longitudinal axis of the helicopter. The remaining thrust isthus available for forward movement. FIAT 7002 HELICOPTER (FIAT 4700 TURBO-GENERATOR) Dimensions and Performance Data Rotor diameter, 39.4ft; blade chord, 1.4ft; fuselage length, 20.1ft; fuselagewidth, 4.6ft; fuselage height, 6.2ft; maximum height, 9.4ft; fuel capacity, 125.5 Imp. gal.; normal gross weight, 3,085 Ib; empty weight, 1,320 Ib; useful load, 1,765 Ib.Estimated performance: maximum speed, 106 m.p.h.; cruising speed, 84 m.p.h.; service ceiling, 11,160ft; operating range, 190 miles.Powerplanc data: total weight, 265 Ib; equivalent power, 530 g-h.p. (take-off), 500 a.h.p. (max. contin.); compressed air flow, 7.5 Ib/sec (take-off), 7.36 Ib/sec.(max. contin.); compression ratio, 3 (take-off), 2.8 (max. contin.).
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