FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1957
1957 - 0743.PDF
FLIGHT, 31 May 1957 749 Comet 4B Postscript — and Further Thoughts on Jet v Turboprop Economics By J. M. RAMSDEN "Flight" copyright drawing Comet 4B: more pay load, less drag and lower price add up to a more economical Comet. THOSE who have tried to make sense of the jet versusturboprop cost controversy which has been aired in thesepages during recent months may be feeling a little bewildered by it all. But they may at least be clear on one point: the trendof the arguments thus far has been,towards establishing not which is the more economic form of transport, but by how wide a marginthe turboprop is more economic than the turbojet. It is significant that no convincing academic case has yet been put for the jet.No doubt keenly aware of all the pro-turboprop arguments, and perhaps because of them, the de Havilland Company lastweek made this claim for the Comet 4B: — "During the period of development of the Comet jet airliner, whichincluded two years of accurately costed operating experience by the British Overseas Airways Corporation and other carriers, it has beengenerally argued that contemporary propeller-turbine airliners would cost a few per cent less to operate per seat-mile or ton-mile than wouldthe pure jet of comparable function. "With steady development of the Comet design, including superiorengine performance and consumption, the situation has improved in favour of the jet, until we see the Comet 4 intercontinental liner, andthe Cornet 4A continental (shorter-stage) liner, offering highly competitive figures of operating cost."A further advance [the Comet 4B] becomes possible in the field of shorter-stage operations which reduces the seat-mile cost of the Cometby about 15 per cent, a margin great enough to establish without doubt the superiority of the pure jet in regard to operational economy."This is indeed strong, challenging stuff, and it is certain to make people reach for their slide-rules. It is the first time that the word"superior" has been used to describe the jet's economy relative to the turboprop: always in the past the carefully chosen descriptionhas been "highly competitive." Are de Havilland justified in making this claim? Because if theyare—or, rather, if the airlines (who always do their own cost sums) agree that they are—D.H. should have few worries about sellingthe Comet 4B in quantity. Of all the factors that influence an airline in its choice of equipment, economy is paramount. It hasto be, in an industry which is always sailing so near to the wind in its pursuit of profits. Speed, and other factors such as delivery,reputation and trust, are high on the list, and may sometimes over- ride economy—as when Capital chose the 4A. But superioreconomy is the prerequisite of a transport if it is to sell in quantity, particularly in the U.S. market. If high speed andother advantages can be had for good measure, the airlines should be tumbling over themselves in the rush to buy. What exactly should one take the phrase "superior economy" tomean when applied to the Comet 4B? It might be taken to imply that the aircraft has a lower operating cost per seat-mile over allthe ranges for which it is designed (300 miles to 2,000 miles). Or, to bring in the revenue angle, it could be taken to mean that the4B has a lower break-even load factor. But both these interpreta- tions would be contested by the protagonists of the short/medium-stage turboprop, except perhaps over 1,000-mile-plus ranges. The trouble with operating cost as a measure of "economy" isthat it may not always tell the whole story. This was the limitation of the many attempts which have been made to establish a com-parison between jet and turboprop economics on the basis of operating cost alone.Lord Douglas (whose Brancker Lecture last February really prompted all the fuss) estimated that, for any given class ofoperation, the jet would always be 10 to 15 per cent more costly to operate than the turboprop. This estimate was partly basedon B.E.A.'s and B.O.A.C.'s measured Viscount 701 and Comet 1 results, from which Lord Douglas assumed that a jet will alwaysprove eight per cent worse in its ratio of actual costs to formula costs. Flight thought this latter assumption rather Unfair To Jets,and submitted that there should be no discrepancy in formula-to- actual costs between the two types—with the result that, on LordDouglas's figures, the jet would only be 6 to 9 per cent more costly to operate. But more costly.And so the discussion went on, with Mr. F. H. Robertson weigh- ing in even more heavily on the side of the turboprop, using hisshort-cut cost formula to calculate that the margin was as h:gh as 26 per cent. "The public is not going to get a fair deal from theairlines," he wrote. His cost method was not as perfect as it might have been, as correspondence in the R.Ae.S. Journal and in thesepages suggested: but even with adjustments it still showed the jets to be considerably more costly to operate. No one from the turbojet camp committed himself to takingexception to these conclusions—perhaps because, as we have said, operating costs may not tell the whole story. Break-even loadfactor gets closer to the point; but even this may be meaningless if the fares assumed could never achieve the break-even loadfactor claimed. After all, a pedal-propelled flying machine for two passengerswhich requires one drop of oil per year should have a low operating cost per seat-mile. But several million of them might be requiredto handle a given traffic flow, and an airline might find that a fleet of conventional airliners would require a smaller capital invest-ment. (It might also find that passengers prefer to ride the faster, more comfortable way, especially at the same fare.) Such a reductio ad absurdum may be overstraining the pointwhich jet protagonists have been promoting for years: that the jet offers higher work-capacity because of its higher speed. Thereis no special magic in this—unless the capacity can be produced cheaply, and unless the speed can be used. The Comet 4B docsproduce capacity considerably more cheaply than its 4 and 4A predecessors in terms of operating cost per unit-load-mile. Itmay not produce load-miles more cheaply than a comparable turboprop (though the margin appears from the manufacturer'sfigures and curves published last week to be small); but fewer may be needed to shift a given amount of traffic at a given frequency,and therefore the airline's total capital investment in a new fleet will be less. Thus operating cost need not always be the decidingfactor—though obviously it must be low. But one has to be careful with the "higher work-capacity" argument: the higher block speedto which the jet largely owes its higher work-capacity may well be vitiated on the shorter stages. The word "economy" when applied to a transport aeroplanelooks as though it is taking on a broader meaning, embracing not only low operating cost but also the high unit work capacity whichin theory produces a required available-traffic-capacity for a lower capital cost. "Economy" may be said also to embrace in itsmeaning the intangible earning powers of speed and comfort, commodities which cannot be discounted as mere jet sales-talk. If all this is accepted, then the phrase "superior economy"applied to the Comet 4B may be justified. It will certainly be disputed in the temples of the turboprop: but perhaps not sovehemently as in the past. Both Bristol and Vickers have their eyes on the jet-transport markets, and as these words are beingwritten the last-named firm has (as recorded elsewhere in this issue) secured a B.O.A.C. order for its VC-10 medium jet project. It will be enlightening to see what Vickers, a firm steeped inthe traditions of the turboprop, have to say about the comparative economics of their new project. JOHNSTON TROPHY PRESENTED ^ the Falkland Islands Dependencies survey ship OlujSven reached Harwich on May 13 the Johnston Memorial Trophy—awarded to Mr. J. H. Saffery and the pilots and navi-gators of Hunting Aerosurveys, Ltd., for their work during the 1955-56 season [as announced in Flight for March 8, p. 295]—waspresented to Mr. Saffery on the quayside by Mr. J. Lankester Parker on behalf of the Guild of Air Pilots and Air Navigators. Mr. Peter Mott, leader of the expedition, said it had been"a complete success"; 40,000 square miles of the world's most southerly ice-free area had been accurately surveyed by aerialphotography and ground survey. Mr. Saffery, the flying manager, had said in an earlier report on the two seasons' work that about75 per cent of the contract area had been photographed.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
