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Aviation History
1957
1957 - 0221.PDF
FLIGHT, 15 February 1957 223 CIVIL AVIATION POINTS FROM THE BRANCKER MEMORIAL LECTURE "AIR transport is at present embroiled in perhaps the most *»• controversial issue of the whole 37 years of its existence.This is concerned with the future roles of pure jet and turboprop engines in the propulsion of transport aircraft." These remarkswere among those with which the chairman of B.E.A., Lord Douglas of Kirtleside, began the fourteenth Brancker MemorialLecture. His paper, The Economics of Speed: An Examination of the Future Roles of Jet and Turboprop Transport Aircraft,was delivered at the Institute of Transport, London, on the evening of February 11.* The core of Lord Douglas' lecture was a comparison of the"formula costs," calculated according to B.E.A.'s cost method, of nine hypothetical jet and turboprop transports. Having establishedthese formula costs, and having adjusted them to actual costs on the basis of Viscount and Comet 1 experience, he then estimatedthe number of aircraft of each form of propulsion which will be required between now and 1970. The jet/turboprop controversy was summarized by the lectureras follows: "The advocates of the turboprop claim that their favoured engine will offer substantially lower operating costs.If these lower costs can be passed on to the public, it is claimed that they will more than justify lower speeds from the point ofview of the great majority of the air traffic of the future, which, above everything else, will want lower fares. The jet enthusiasts,on the other hand, claim that their aeroplanes will be as economic, or more so, than the turboprop—and 100 to 150 m.p.h. faster!Both claims cannot be true and it behoves the airlines to establish the facts themselves before entering into commitments for newaircraft costing many millions of pounds." The nine hypothetical transports used by Lord Douglas for thecomparison of formula costs covered the three main classes of transport—short-, medium- and long-haul. He studied three"comparable" machines for each class: a 575 m.p.h. jet, a 375 m.p.h. turboprop, and a 460 m.p.h. turboprop. Each transportwas assumed to accommodate a 25;000 lb payload (100 passengers) and to be designed to carry this payload over practical designstage lengths of 1,000 miles (short haul), 2,500 miles (medium haul), and 3,500 miles (long haul). The result, at an "average" utilization of 2,250 hours for eachtype, was that the 575 m.p.h. jet had operating costs 3 to 9 per cent higher than the 460 m.p.h. turboprop, with an increasingeconomic advantage for the latter as stage length diverged from design figure. The disparity in cost between the jet and 375 m.p.h.turboprop was even greater—from 10 to 14 per cent higher. The lecturer then adjusted these formula costs to actual costslikely to be achieved in service, the basis for his adjustment being B.E.A.'s operating results with Viscount and B.O.A.C.'s resultswith the Comet 1. His conclusion, which allowed for a settling-in period, was that the differential between formula and actual costsmight be 8 per cent more for jets. Applying this differential to his formula costs for the hypothetical transports, and usingB.E.A.'s factor of 160 per cent for the conversion from direct to total costs, Lord Douglas concluded that the difference in costbetween jet and turboprop would be as shown in Fig. 1 below. * Lord Douglas's paper was the result of teamwork by a number ofindividuals. He paid tribute particularly to the work of Mr. Peter Brooks, who was mainly responsible for assembling the data, and forthe help given by Mr. Stephen Wheatcroft, Mr. R. H. Whitby and Mr. K. G. Wilkinson in formulating the conclusions. Generalizing, he said that over equivalent ranges the 575 m.p.h. jet emerged as 10 to 15 per cent more expensive per seat-mile than comparable 375 m.pJi. and 460 m.p.h. turboprops. On the question of speed the lecturer concluded that die time saved by the jet would not be competitively significant on stages of less than about 500 miles. On the "intangibles" which affected the argument, he concluded that "they will tend to increase the turboprop's economic advantage over the jet, particularly on the shorter hauls." Drawing his conclusions, Lord Douglas suggested that the turboprop would have a long innings on the shorter short-haul routes where its block-time handicap was small. The turboprop should have a useful—but probably shorter—career on long and medium hauls, where its lower operating costs might give it a useful application in the lower-fare mass-travel market, particu- larly if a fare differential were accepted by I.A.T.A. The longer- range turboprop's future might, however, largely depend on whether the type succeeded in establishing itself in service before the big jets appeared in large numbers. Lord Douglas went on to discuss what is, for the manufacturing industry at any rate, the most crucial issue of all—the numbers of jets and turboprops that will be required between now and 1970. This was a further contribution to the many forecasts which have been made on this subject, and was real fulfilment of the promise implicit in the lecture's title. We record it in full: — "Past experience suggests that although roughly two-thirds of theworld's passenger-miles will be generated on the shorter hauls, about half this traffic will be carried in medium- and long-range aircraft oper-ated on short sectors. Because of this, it is not unreasonable to assume that about a third of the total airline passenger-miles will be providedby short-haul aircraft, a third by medium-haul, and a third by long- haul types. If this division is accepted and the average passengerload-factor is assumed to be 65 per cent on all types, the numbers of aircraft required can be estimated on the assumption that aircraftutilization, service life and wastage remain the same as they were during the past ten years. The passenger-miles provided by short-,medium- and long-range jet and turboprop aircraft are assumed to be divided as follows ::— "Short-haul aircraft—one-third by jets, two-thirds by turboprops;medium-haul aircraft—one-half by jets, one-half by turboprops; long- haul aircraft—two-thirds by jets, one-third by turboprops. "The numbers of new transport aircraft required by the airlinesbetween 1957 and 1970 which result from the above assumptions are as follows [see Fig. 2 below]. It has been assumed in the calculationsthat the aircraft in each category will be broadly similar in productive capacity to representative types already on order or projects: —"Short-haul: jets, 800—turboprops, 2,500; medium-haul: jets, 700 —turboprops, 800; long-haul: jets, 600—turboprops, 500." It was tantalizing that no basis was given for the divisionsbetween jet and turboprop assumed for each range category, which is the question to which all the world's manufacturers areseeking the answer. Nevertheless, the conclusions are there, in black and white, and they are the conclusions of the world'smost experienced operator of turbine aircraft. Footnote: It is of interest to compare Lord Douglas's estimate of 700medium jets and 800 medium turboprops (which included orders already placed) with the prediction of future capacity made in Flight ofDecember 14, "The Hungry Airlines," Part 2, The Medium-Haul Market. We said : "Forward projection of the results of this analysiswill be found to show that just about 1,500 medium transports, turbo- prop as well as jet, will be required between 1960 and 1970 in additionto those already ordered." 20% ts% . . 10% *SOmph TUHeoPnOP . STSifcph JET 20* 3.000 Fig. 1 (left). The percentage fay which the jet will be more expensive to operate than "com- 2500 15% parable" turboprops. 2.000 1500 5% Fig. 2 (right). An estimate of world airliner production, 1957-1970. 1.000 500 tooo 2.000 aooo STAGE DISTANCE (st mils*) 4.000 3,000 2500 2JD00 1500 1.000 500
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