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Aviation History
1964
1964 - 2034.PDF
'LIGHT International, 9 July 1964 57 Although seemingly complicated, this illustration of the main rotor hub does not include the hydraulic blade-folding system employed in the naval carrier-based version 1 Hydraulic-fluid reservoir 2 Hinge lubrication dashpot 3 Blade root forging 4 Locking device for (3) 5 Cyclic-pitch swashplate 6 Pitch control link 7 Hydraulic damper 8 Coning-angle stop and damper 9 Drag and flapping hinge H) Rotor-head body firewalls isolating the engines, transverse firewalls separating front and rear engines from the rotor gearbox, and zonal engine firewalls. Apart from the restrictions imposed by these fire precautions the whole of the mechanical equipment on top of the fuselage is laid bare for access when eight sturdy hinged doors are opened. The compactness of the Turmo allows ample space around the engines for the ground crew to work without external platforms. At the rear of the cabin is a tapered portion, of simple semi- monocoque construction, which is closed by a robust hinged rear loading ramp. This is the main entrance for bulky loads or equip- ment, and it is jettisonable in emergency. On the starboard side forward there is a 4ft-wide sliding door, and on the port side aft a small hinged emergency door. Tail-boom construction is a conventional semi-monocoque with closely-spaced notched channel-section frames and continuous stringers, without major longitudinal members or longerons. The cranked section carrying the tail rotor and trim plane is more robust, with a solid-web spar and solid or pierced-web frames with shear stiffeners. The juncture of the main boom and cranked section is hinged, so that the folded length of the aircraft is reduced to 58ft. Along the top of the boom the tail-rotor shaft is covered by hinged fairing. The fixed landing gear has twin wheels, with scissor torque links, on each of the three vertical shock-absorber struts. The main units are mounted on triangulated tubular structures, while the nose unit is bracketed to the cockpit bulkhead and passes through a water- tight seal in the planing bottom. The main wheels have hydraulic brakes operated from the pedals, with a parking hand brake, and the nose unit is fully castoring. Rotor System Design and manufacture of both rotors was under- taken by Sikorsky under a contract which includes the supply of initial production units. The system consists of a six-bladed main and five-bladed tail rotor driven from a central gearbox. Close above the latter is the main rotor head, with hydraulically assisted cyclic • and collective pitch controls, drag hinges and flapping-hinge dampers for low speed. The tail rotor is driven by a sectional hollow shaft supported by a series of bearings to the angular gearboxes at the crank of the tail boom and rotor mounting. Tail-rotor pitch is varied by cables and push/pull rods controlling hydraulic jacks at the spider. The all-metal main rotor blades have a hollow extruded D-spar with light-alloy trailing-edge "boxes" heat-bonded to its rear face. The blades have an indefinite life because the spar is pressurized for crack detection, Sikorsky fashion. They are pretracked, and so individually interchangeable in the field. The blades can be folded (manually or by power) and electrically-heated rubber boots for anti-icing are available. The tail-rotor blades are also all-metal and individually interchangeable. Design of the main-rotor, intermediate and tail-rotor gearboxes was shared by Sud-Aviation, Fiat and Sikorsky. A diagram shows how the free-turbine drives, reduced to 5,700 r.p.m. by the engine gearboxes, are coupled into the first horizontal spur reduction gear (3,420 r.p.m.) and then reduced by the initial bevel and two planetary stages of the vertical main reduction gear to 202.448 r.p.m.—an overall ratio of 29 to 1. Spur gears take power from the inter-engine coupling shaft to the tail rotor, which is driven at 952.95 r.p.m. Each engine coupling includes a freewheel, and a brake on the main gearbox stops the system in 40sec. Nominal design capacity of the main gearbox is 3,300 h.p. con- tinuously and 3,650 h.p. for take-off. The production Turmo HI C3 is rated at 1,350 s.h.p. continuously and 1,500 s.h.p. for take-off. The difference between engine total power and gearbox capacity leaves the required margin for tropical and high-altitude operations. The Turmo III C3 has an axial/centrifugal compressor, a two-stage com- Schematic diagram of the Super Frelon gearboxes and transmission systems. The three free power- turbine input shafts are seen driving through their over-running clutches; t/)e two axial fans on the left serve *ne oi/ coolers WfcWMM
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