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Aviation History
1962
1962 - 0483.PDF
FLIGHT International, 29 March 1962 481 with the almost circular SR.N1 the new design has a hull more like that of a ship, with a 2 : 1 length/beam ratio, an excellent bow form and buoyancy tanks to enable the craft to float and travel at much reduced speed as a ship. To minimize e.g. problems, the SR.N2 is designed round a central load carrying cabin 20ft x 16ft, with fore and aft lift fans discharging into a plenum chamber below the deck. Power for lift and propulsion is integrated. Two pairs of free- turbine engines situated in an aft engine room drive through gear boxes and shafts to the lifting fans and propellers. One pair of engines drives each fan/propeller system, and the ability to continue with any two engines out was regarded as very desirable in a civil craft. The thrust axis of each propeller can be turned in order to control the craft, and propeller pitch may be reversed. Structurally, the SR.N2 could scarcely be simpler. Aircraft-type jigging is almost unnecessary, the machine being built from the keel up like a ship. The buoyancy chamber is ogival in plan-form. Two main longitudinal beams (keelsons) and 17 full-depth trans verse frames constitute the principal members. Certain transverse frames, in conjunction with the keelsons, partition the buoyancy chamber into watertight compartments. Two such compartments amidships on either side of the keelsons house the flexible fuel tanks, each having a capacity of 425 Imp gal, while compartments at the Fig 9 One of the two pairs of Blackburn Nimbus powerplants. Each engine has twin jetpipes and a rear free-turbine drive bow and stern incorporate a controllable water ballast system. The chamber is pierced by diagonal slots through which air can escape from the plenum chamber to increase stability. Fore and aft between the two keelsons are located the fan gearboxes, reached from hatches in the deck via an access tunnel through the trans verse frames. Skin plating stiffened by stringers completes the structure of the buoyancy chamber, the plating round the edge being shaped to form the inner wall of the lift duct nozzle. On top of the chamber a main athwartship wall and a partial fore and aft wall constitute the main load-carrying members for the deck. Additional support is provided by vertical posts, those at the edges employing interpost bracing. The deck consists of transverse I-beams joined by closely spaced intercostal stringers and double- skinned. The outer skin of the lift duct nozzle is formed by a curved extension of the deck plating, and sweptback deflector vanes in the nozzle deflect the air backwards to provide forward thrust. Between the underside of the deck and the buoyancy chamber is a completely open space which forms the plenum chamber in which are housed the two fans on the fore and aft centreline. The bow is formed by a series of frames which provide attachment for the plating. These frames carry the bow structure above the deck level and are profiled to transmit shock loads from wave impacts to the main structural members of the deck. Above the deck the structure is based upon four plate bulkheads, which run right across the superstructure ahead of and behind each of the two pylon assemblies and their flanking fan air entry ducts. These bulkheads and the load-carrying tunnel along the centreline of the roof bear all the main loads imposed on the superstructure, and behind the rearmost bulkhead are the tubular engine mountings. The superstructure is completed by enclosing the engine room and control cabin, adding the propeller pylons and fin and rudder, and attaching the two covers over the central payload space to form the main cabin. These two covers can be removed to provide an open deck for carrying bulky freight. From the fact that Westland intend to use the SR.N2 to prove the transmission, propeller and fan system for future Hovercraft it can be deduced that these components require more development effort than does any other part of the vehicle. In the SR.N2 they have been sized so that, when fully developed, they should be capable of being used directly on Hovercraft of up to 300 tons. Four fans and propellers would be matched with a vehicle weighing about 125 tons, and this size will probably prove to be a very important one. Originally the transmission to the forward unit was expected to pass along the keel box, but it was found preferable to run it along the top of the superstructure. Another minor change is that Fig 10 A "Flight International" drawing of what may variously be considered as the flight deck, bridge, driving compartment or cockpit. The method of operation of the prin cipal control is illustrated overleaf 1 Control wheel for pylons and rudder 2 Fan r.p.m. 3 Air-speed 4 Water-speed 5 Propeller pitch 6 Pylon angle 7 Engine fire suppression 8 Jetpipe temperature 9 Inlet guide vane position 10 Water ballast 11 Gas-generator r.p.m. 12 Fuel gauges 13 Oil-cooler temperature 14 Engine output torque 15 Propeller torque 16 Power levers for engine pairs 17 Propeller pitch levers 18 Water ballast switch 19 Engine start and warning lights 20 Directional gyro 21 Radar display
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