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Aviation History
1957
1957 - 0069.PDF
FLIGHT, 18 January 1957 69 BRISTOL 192 The R.A.F.'s First Twin-rotor Helicopter: Design Details and Sketches THE Bristol family of twin-rotor helicopters at present com-prises two versions of the Type 173, powered respectivelyby two Alvis Leonides (550 b.h.p.) and Leonides Major(850 b.h.p.) engines. Following last year's cancellation by the Ministry of Supply of the order for Type 191 machines for anti-submarine duties with the Royal Navy, the next in line is the Type 192, on order for varied duties with the R.A.F. The 192 is, of course, a derivative of the Type 173, which isessentially a research vehicle for the tandem-rotor configuration, and considerable design changes are likely to be necessary forService use. The following description, however, indicates the design thinking to date. Following on from machines powered by Leonides Majors willbe versions incorporating Napier Gazelle gas turbines. Another Bristol design-study, mentioned by Mr. Peter Masefield in arecent lecture, is the Gazelle-powered Type 194 which, showing the way to even larger helicopters, would carry 21 passengers,cruise at 160 m.p.h., and have a gross weight of 20,000 lb. Airframe. Orthodox semi-monocoque construction with light-alloy stringers and frames is used for the 192 fuselage structure, which has a transport joint at the forward front-fuel-tank bulk-head. A duct at the top of the fuselage carries the synchronizing shaft, flying controls and other services; a similar duct carryingother services forms the bottom of the fuselage structure. The inner surfaces of these ducts form the normal skin of the aircraftand the outer covering panels (shaped in the lower duct to minimize ditching pressures) are quickly detachable to facilitatemaintenance. Light-alloy castings mounted in the top duct and bolted through the frames carry bearings for the synchronizingshaft and the control rods. The cockpit incorporates controls and instruments (includingblind-flying panel) arranged for the pilot to fly from the star- board seat, with a folding port-side seat for navigator or (whendual controls are fitted) instructor or second pilot. The entrance doors have large moulded windows and are upward-opening andjettisonable. The port side of the fuselage is bulged to permit access to the main cabin (past the front engine and fuel com-partment) through a door behind the navigator's seat. The main cabin comprises the fuselage section between thefront engine compartment and the forward fin frame, and is of : constant ovoid section. In the bare condition it is 24ft lin long, I 5ft 3in wide and 4ft llin high. The main entrance, 50in x 54in, | is covered by a zip-fastened canvas door (or, alternatively, an| upward-hinging metal door carrying winch and searchlight). I There is a fixed window on each side of the fuselage and ajettisonable window and escape hatch, 36in x 28.6in, at the port after end of the fuselage. Internal doors give access to the rearf engine and, past the forward engine, to the cockpit. Two bulkheads separate the front fuel tank from the maincabin and the engine compartment. The forward one, together with an auxiliary bulkhead beneath the floor, carries the frontundercarriage loads. A port-side passage is formed from the main cabin to the cockpit through apertures in the bulkheads,between the bulged fuselage-skin and the panels enclosing the engine bay and fuel cell.The front engine is mounted in a near-vertical position. Vertical engine loads are carried, via flexible couplings at thebase of the engine mounting, by two longitudinal keel members and the forward bulkhead. These keel members extend fromthe fuel compartment through the engine bay and continue for- ward to form the main support structure for the pilot's cabin. The engine is installed and can be serviced through a largeaperture in the underside of the aircraft, bounded by the two keel members and the bulkhead at each end of the engine bay.The engine bay as a whole serves as a plenum chamber for engine and gearbox cooling air, which is admitted through an intake ontop of the fuselage. The floor structure for the cockpit and forward fuel bay is completed by transverse frames and members. There are two rear fuel-cells, one situated immediatelyforward of the rear engine bay and the other aft. The forward bay is enclosed by two main bulkheads, which carry the loadsfrom the rear undercarriage. The rear engine-bay structure and the engine installation is similar to that in the front bay. Therear cooling-air intake is positioned at the top of the fin and pro- vides air for the rear and intermediate gearboxes. Servicingaccess to the engines, intermediate gearbox, tail structure and the flexible bag-type fuel tank in the rear of the fuselage is pro-vided by an access door in the underside of the rear fuselage. Total fuel-capacity is 560 Imp. gal. The rear rotor-hub and gearbox are raised high above thefuselage to reduce rotor interference and are mounted on top of the fin, loads being carried by a box structure formed by thethree fin spars and the side skin between them. The leading and trailing edges are light, non-load-carrying fairings, the leadingedge being detachable for access to the rear-rotor control run. Structure of the tailplane consists basically of a main spar and atorsion box with stiffened skin, with the addition of a short auxiliary spar at the root end. Behind the main spar, diaphragmribs support the light-alloy trailing edge. Power Unit. The two Alvis Leonides Major engines eachprovide 850 b.h.p. under I.S.A. sea-level conditions. The engine is an aircooled radial having 14 cylinders arranged in two banks,the two-throw crankshaft providing a direct drive through a clutch to the transmission system. While the forward clutch ispneumatically operated by the pilot, the aft unit is centrifugal and engages at a predetermined engine speed. A single-speed centrifugal supercharger is utilized. Accessorydrives from the engine include tachometer, Koffman starter and a 4Kw D.C. generator. A Hobson master control unit suppliesfuel to the eye of the supercharger impeller. Automatic adjust- ment of the fuel supply to the engine to compensate for varyingengine conditions is obtained with a fuel-metering valve and a boost control valve, which are interconnected to give a singlelever control. Each engine is housed in a removable titanium cowling. Thetwo oil systems are independent, separate oil tanks and oil coolers being located in the front and rear engine compartments. Theair intakes are equipped with filters, and by-pass valves permit air to be drawn from the engine bays in icing conditions. Coolingair is provided by a fan mounted on the clutch. The design of the 192 is such that the Napier Gazelle gasturbine, when available, can be installed in place of the Alvis Bristol's twin-rotor family: (reading from left to right) Types 173, 792 and the projected 194.
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