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Aviation History
1958
1958 - 0358.PDF
374 FLIGHT, 21 March 1958 Lett and below, Westland Wessex. Helicopters of the World ... a 14.85 speed reduction for the main rotorand a 2.25 reduction for the tail rotor. A freewheel unit overrides in the event ofengine failure, enabling the rotor to con- tinue turning. The gearbox takes the mainlifting load of the helicopter. The main rotor head incorporates flapping and draghinges. A cyclic-pitch control column and rudder pedals are installed in the conven-tional manner together with a collective pitch lever adjacent to the left side of theseat and incorporating a twist-grip throttle. Spring-loaded trimming gives "feel" to thecyclic pitch stick and a positive central position. The trim can be adjusted foreand aft by a handwheel on the control pedestal and laterally by an electric switchoperating an actuator. Cyclic and collec- tive pitch systems are servo-assisted. Thehydraulic pump is driven from the tail rotor shaft, maintaining servo control inthe event of engine failure. Manual rever- sion is possible in the event of hydraulicfailure. When the Widgeon is used as an ambu-lance the triple rear seats are removed and the port side front seat is transferred toa position behind the pilot, for use by a medical attendant. Accommodation is pro-vided for two stretchers, one above the other positioned lengthways in the cabin. # Rotor diam., 49ft 2in; fuselage length, 41ft 3in; empty weight (passenger role), 4,322 lb; gross weight, 5,900 lb; max. per- missible speed, 109 m.p.h.; economical cruis- ing speed, 80 m.p.h.; hovering ceiling (10ft wheel clearance) at 5,900 lb, 7,500ft; best rate of climb at s.l., 600ft/min; max. range, 310 miles. Whirlwind The Whirlwind continues in production for civil and military applica- tions, and offers a particularly attractive performance with the Alvis Leonides Major engine, although the Pratt and Whitney R-1340 and Wright R-1300 arealternatives. The latest Service variant is the HAS.7 anti-submarine helicopter, nowstandard equipment in the Royal Navy. This version is equipped with "dippingAsdic" detection apparatus and can be armed with a homing torpedo. The fuselage of the Whirlwind com-prises two main assemblies of magnesium alloy semi-monocoque construction. Fueltanks are under the cabin floor and a fire- wall isolates the engine from the cabin.The soundproofed cabin can have eight seats—five facing aft and three forward.The standard Whirlwind has two windows on each side of the cabin, but additionalwindows, increasing the viewing area by approximately 60 per cent, can be fittedif required. The cockpit is raised and has sliding side windows. The pilot's seat is tostarboard and fixed fittings are provided to take a co-pilot's seat and dual control.A cyclic-pitch control column and rudder pedals are installed in conventional man-ner together with a collective pitch lever adjacent to the left side of the seat andincorporating a twist-grip throttle. Cyclic and collective systems are servo assisted.The servo units are operated by the main hydraulic system with both an emergencylateral servo unit and the ability to revert to manual control. A diagonal shaft trans-mits power through a clutch to a main gearbox centrally mounted above thecabin, carrying the main lifting loads and providing gear reduction for the main andtail rotor and accessory drives. As an added safeguard in the event of enginefailure a freewheel unit over-rides and enables the main and tail rotor to continueturning in autorotation. The four-wheel undercarriage has oleopneumatic legs and fully castering nose- wheels. A Dunlop brake system acts onthe main wheels and is operated by toe controls on the pilot's rudder pedals. A parking brake is provided, and a skid toprotect the tail rotor. Eight interconnected bag tanks give atotal usable fuel capacity of 145 Imp. gal. Delivery is by engine-driven pump andtwo immersed booster pumps. For all ser- vices a 30-volt d.c. system is employedwith air-cooled generator charging a single * 24-volt 25-amp-hr battery. The radiocompartment is aft of the main cabin and provision is made for V.H.F. STR.9Xradio. Quick removal of Dzus-fastened panelsgives access to the main gearbox and flying control system, and the radio bay isreached by removing a single panel on the starboard side. Servicing platforms arebuilt into the fuselage to facilitate inspec- tions of rotor head and gearbox. Features of the rotor head include offsetflapping hinges giving a wide e.g. range and consequent freedom of loading. Drooprestrainers ensure adequate clearance between the blade tips and the fuselage atslow rotor speeds, making starting pos- sible in high and gusty winds. Blade pitchcontrol is transmitted from the hydraulic servo jacks by swash plates and push-pullrods to the blade levers. Freight up to 2,000 lb, which may be toobulky to accommodate in the cabin, can be carried externally below the fuselageon a sling. An electrical quick-release is mounted on the pilot's control column witha secondary mechanical release on the cockpit floor. Loads are attached with thehelicopter hovering above, and can be accurately positioned on landing so thatfurther crane or ground handling is not necessary. Sling installation or removaltakes less than ten minutes. An item of extra equipment is the hydraulicallypowered hoist with a jib mounted above the main cabin door. It will lift two peopleor a load of 400 lb. The engine is mounted in the nose andis readily accessible by opening two clam- shell doors. The installation ensures easymaintenance and servicing. A complete power-plant change can normally be madein five hours, including time required for fuel-flow test and engine run. All-metal main rotor blades, made up ofa robust extruded leading-edge spar to which are attached light-alloy trailing-edge pockets, are utilized, as on all West- land helicopters, and are claimed to affordimmunity to temperature and humidity effects thus remaining in balance and obvi-ating the necessity of constant retracking. They are matched to master blades and Model of Westland Westminster.
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