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Aviation History
1956
1956 - 1631.PDF
FLIGHT, 16 November 1956 CENTAURUS 373 ... Hobson/R.A.E. system, this unit senses the boost, atmosphericpressure and exhaust back-pressure and charge temperature; but instead of altering the orifice through which the fuel passes (as itdoes in all present Centaurus engines), it varies the delivery of the plungers of the injection pump. Fuel is delivered direct to thecylinder heads through a total of over 100ft of high-pressure steel piping. The nozzles are of a Bristol design whichhas improved the behaviour at low r.p.m.; each nozzle lifts at about 650 lb/sq in, the peak delivery pressure being around2,000 lb/sq in. Flight trials of the Centaurus 373 are about to begin and, inview of the fact that the aircraft has now been granted full C. of A. clearance, the D.P.I. Centaurus could become the standard power-plant for the Beverley and the civil Universal. The D.P.I. has been so engineered that it is quite practicable toconvert existing Centaurus to 373 standard, and there is no reason why this should not be done during overhaul periods. To effecta conversion the chief requirements are the following: change to new cylinder heads incorporating injection nozzles; installation ofthe injection pumps to drives which already exist; modification to the Hobson control system; installation of fuel-delivery piping;and modification to the existing cylinder sleeves to conform to the revised valve timing. As far as the powerplant is concerned the onlymodifications necessary are: fining of a new air intake and cleaner suitable for the larger air consumption of the engine; installationof a vent pipe between the injection pumps and the fuel tank; and modification to the cut-off control, fuel and oil pipes. Nochanges are anticipated to the propellers or ancillary equipment. As the accompanying curves show, the D.P.I, engine will beable to deliver considerably more power than previous Centaurus marks. The cooling of the engine has also been improved topermit full use to be made of die increased power, and it will be possible to take higher powers on weak mixtures without 791 Provisional power curves for the Cen- taurus 373 under i.s.a. conditions. The curves are: A, max. take-off and operational ne- cessity with water/ methanol; B, as above but without w/m. in- jection; C, max. con- tinuous; and D, max. weak-mixture. The curves assume 100/ 130-grade fuel and a flight exhaust system, but without ram. WOO I BpOO I &000 I 35000 0 IO000 20PO0 30.000 AQO00ALTITUDE (tt) detonation. The possibility of back-firing (never a failing of theCentaurus) does not exist, as there is no petrol-air mixture in the induction system. Further increases in take-off and climb ratingspresent little difficulty, but advancing the weak-mixture power would normally have necessitated fuel of a higher octane ratingthan die standard 100/130 grade. In order to provide more w.m. power on die same fuel further research is being carried out on aCentaurus 373 in which the compression ratio has been reduced from 7.2 to 6.75. This will permit a considerable increase inxatingover that at present offered by the 373, at some expense in increased specific fuel consumption and head temperature. CANADIAN INDUSTRY PROGRESS IN his presidential report at the recent annual general meetingof the Air Industries and Transport Association of Canada, Mr. E. H. Moncrieff said that the past year had probably been oneof the best in the history of the Canadian aviation industry. For the air carriers it had been a year of unprecedented activity, whilethe industrial side of the industry continued to provide an essential link in the defensive strength of Canada. Preliminary figures for 1955 showed die air carriers to have hadan operating income of $6,162,483, compared with $1,876,920 in 1954. Bulk transportation services were almost trebled, largely asa result of DEWline and Mid-Canada-line airlift activity, and revenue freight lifted was morethan double that for the previous . year. Estimated figures for thefirst six mondis of 1956 showed diat "tonnages carried by diecarriers are up by 25 per cent over the same period last yearand the number of passengers carried is up 33 per cent." The tempo of the radar-chainoperations was now gradually slowing down, Mr. Moncrieffstated. Transport of die largest proportion of materials and sup-plies for die construction of these projects had now beensuccessfully completed and, in the near future, flying require-ments would probably be re- duced to the maintenance andsupply of the various radar sites. The level of activity of the manufacturing industry during 1956had been governed largely by die fact that the initial build-up of die country's air defence programme had been completed. Asa result there had been a shift in emphasis from manufacturing production to design and development of future equipment andthe re-supply and maintenance of existing equipment. The acquisition of new research and design facilities had provided newtechniques and skills and had created additional sources of supply. AlUiough total current expenditures for air defence remainedat $872m, approximately the same level as last year, the current trend was indicated by die drop in appropriations for new aircraftand engines to $197m from die 1955-56 figure of $293m. From 1954 to 1955 die total employment in the aircraft and ancillaryindustry had remained at about the same level, and the total value of aeronautical production had increased from $346m to $353m."Generally," Mr. Moncrieff said, "I wouldsay die industry pre- sents a fairly healthy picture at this time." Mr. Moncrieff, A.IT.A., President, J955-56. HELICOPTER DESIGN PROBLEMS AS reported in last week's issue, a lecture on Design Problems** of a Large Helicopter was given by Dr. G. S. Hislop (Fairey Aviation Company) to die London Airport branch of the RoyalAeronautical Society on October 30. Some 90 members were present. Dr. Hislop began by emphasizing the tremendous undevelopedfield for die use of large helicopters (over 20,000 lb gross weight) as short-range transports between city centres. To be successfulin such operations, be said, die helicopter would need a cruising speed of some 150 m.p.h., a seating capacity of 40 to 50 persons,an operating cost less dian 6d per seat mile and a safety standard equal to that of modern civil aeroplanes. Turning to die problems encountered in the design of such ahelicopter, die lecturer first mentioned that of obtaining a suitably low ratio of rotor-blade weight to aircraft weight. Blade weightwas influenced by factors such as rotor diameter, tip-speed limita- tion, blade coning angle and shaft torque. The complete weightof die rotor system resulted from the structural requirement to transmit die power and to react the blade loads, plus the control-system requirement. The problem of designing to maintain constant blade angular-velocity under flight conditions widi cyclicvariation of airflow over the blades was next discussed. Appreciable penalties in structural weight and power wastagewere imposed in shaft-driven rotors by the power transmission shafting and die need for torque-reacting devices. Distinct advan-tages on diese points were offered by the use of tip propulsion. The speaker went on to consider die relative merits of the fourbasic types of tip units; ramjet, pressure jet, pulsejet and rocket. The forward speed of current types of helicopter was limitedby factors directly associated widi stalling of die retreating blade. This limitation, however, could be overcome with die help ofconventional propellers and wing surfaces to unload the rotor in cruising flight. Boundary-layer control techniques could beapplied, but it was too early to assess dieir overall economic merit. Other design problems arose from the requirements of stabilityand of fatigue. The former, as affecting the fuselage as a whole, could be met largely by die application of conventional methods.To reduce overhaul costs, fatigue must be catered for by design- ing on fatigue criteria for the materials concerned, with due regardto the role of die various structural components. In diis respect die helicopter designer was placed somewhere between the enginedesigner, who had always needed to design for fatigue conditions, and the airframe designer, who had in die past been primarilyconcerned widi design on ultimate strength criteria. In conclusion Dr. Hislop referred to operating costs as dieyaffected the design of helicopters. A cost-range diagram indicated diat, on a basis of seat-mile costs, the large helicopter would becheaper than die best present-day conventional aircraft over stage lengths up to ISO miles.
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