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Aviation History
1963
1963 - 2310.PDF
JGHT International supplement, 24 October 1963 LETTERS TO THE EDITOR The Editor of "Air-Cushion Vehicles" is not necessarily in agreement with the views express ed by correspondents in these columns. Names and addresses of writers, not for publication in detail, must in all cases accom pany letters. Comparative Costs SIR,—In your September issue you refer to the second part of Mr Trillo's study of costs and the surprising conclusions he reaches particularly in respect of the unit costs of liners and helicopters. I cannot comment upon the figures for helicopters but the figures for liners are certainly surprising, particularly their derivation. For example, a com parison is made between a 707-320B jet airliner and the liner France. The respective work capacities are quoted at 10,560 ton-kt (18,960 ton-kt for the freighter version of the aircraft) and 11,200 ton-kt for the liner. This is, of course, a misleading method of comparing these two vehicles. In the case of the liner carrying over 2,000 passengers, the weight of the pay- load itself is not a design feature that has any real significance, the space and weight of the luxury accommodation being much more a limit to the earning capacity of the vessel. The only reason able economic comparison between the two vehicles would be on a passenger- knot or -mile basis (for comparable fare- class ratios) and also this should be related to the annual utilization of the two vehicles, which, in the case of the liner, is approximately double that of the airliner. Worked out on this basis, it will be found that the passenger-mile capacity of the France is approximately three times as high per annum. If Mr Trillo wishes to compare the ton-mile or knot capacity of air freighters with those of ships, he must compare like with like; for example, one of the largest and heaviest air freighters in service, such as the 707-320C with, say, a 100,000 or 120,000 ton tanker where at a cost approximately three times that of the aircraft an output in ton-miles per "our something like 100 times as high as that of the aircraft is achieved by a marine vehicle specially designed to do the job. . Arguments such as those put forward m Mr Trillo's article are interesting, but care must be taken not to bring into the comparison factors which apply to one vehicle and not to another, e.g., the absolute limitation in the liner of space as opposed to weight. The "payload" used for the France, of 362 tons, could be increased very many times with hardly any effect on the performance of the ship if it were so desired, and in fact no naval architect ever uses the weight of passengers as the sole payload in a passenger ship. Clearly, 10 per cent added to a displacement of about 60,000 tons would not have a very deleterious effect on the performance of the ship as length is the primary con sideration, but would nevertheless in crease the so-called payload by a factor often or thereabouts, which would make the comparison look rather different. Basingstoke, Hants E. C. B. CORLETT [Mr Trillo comments: "I feel that this letter attaches a quite disproportionate amount of importance to the reference to the Boeing 707-320C freighter, which appeared in parenthesis in the caption to the photo graphs of the Boeing 707-320B passenger jet and the France. This mention of the Boeing freighter was inserted by Flight International purely as supplementary information. From it, however, the writer appears to have in ferred that a comparison was being made between the Boeing freighter and the France. Such was most certainly not the intention and I am sure this must be appreciated, since the title of the article specifically refers to trends in first cost of over-water passenger transport. "Now the next point to emphasize is that the article is dealing with the first cost of craft and is not dealing with a full economic comparison. In this connection, however, I am rather puzzled by the statement in Mr Corlett's letter that 'in the case of the liner carrying over 2,000 passengers, the weight of the payload itself is not a design feature that has any real significance, the space and weight of the luxury accommodation being much more of a limit to theearning capacity of the vessel.' Surely the payload is the stuff that brings in the revenue, and to have this at a sensible maximum in the craft is of the utmost importance. The luxury accommo dation is only there because of the relatively long journey times involved. Your corres pondent says that 'the only reasonable Air-Cushion Vehicles economic comparison between the two vehicles [Boeing 707-320B and the France] would be on a passenger-knot or -mile basis ... related to utilization.' Well, again, my article was not concerned with a full economic comparison, only a facet of it. However, here I must disagree with the writer over a number of points. He says that in the case of the liner the utilization is approximately double that of the airliner and that the 'passenger-mile capacity' of the France is approximately three times as high per annum. These statements do not appear to be supported by the facts, and I do not see the significance of 'passenger-mile capacity* in this context. The utilization of some of the transatlantic jets is between 3,000 and 4,000hr and some are over 4,000hr/annum. The figures in the accom panying table can only be approximate, but they do show the order of things. "The comparison which Mr Corlett makes between the Boeing 707-320C freighter and a 100,000 to 120,000-ton tanker suffers from the fault of not com paring like with like. He is simply compar ing two of the largest craft existing instead of two craft having the same work capacity. I agree of course that the tanker of the size mentioned is supreme for the job of transporting high density loads. "As a basis for comparison of transport craft, the payload density and the work capacity are the factors to hold constant and the suitability of the craft will then be determined according to its weight and space limitations. "I agree that in theory the payload of the France or any passenger liner could be increased many times with little serious effect on the performance of the ship if it were so desired. So why is it not done? Clearly because the economics of the business would dictate otherwise. In mak ing a comparison between craft one can only be concerned with fact. Hypothetical changes which 'would make the comparison look rather different' must surely be ruled out. "In judging the liner beside the transport aircraft, the liner, because of its low speed, not only transports one, but also gives one a holiday en route. In other words, the liner provides something more than a pure transport craft for the capital outlay. Inversely, a high-speed hovercraft could make an over-night ferry service unneces sary, but in this case, no holiday is lost, only a night at sea!"] "France" New York - Southampton - Le Havre. Distance, 3,270 n.m. (estimated mean) "Average" speed 30.3(1) kt Distance travelled per annum, 137,200 n.m. .•. utilization (assuming block speed 137,201 =96% "average" speed) No of trips = 137,200 3,270 42 30.3 X 0.96 = 4,720 hr Passenger accommodation: 2,032(2) No of passengers/annum — 65,000(1) 65,000 |0/ Load factor: , .„ — /6.1/0 ««,„ 42 X 2,032 (a value of "nearly 80% is quoted in Ref I) References I. Modern Transport, Feb. 2, 1963 p. 12. 2 5.S. France Greets You, French Line booklet. 3 AA.C. World Airways Guide, Sept. 1963. 4.' BOAC Boeing 707-320B New York - London. Distance, 2,990 n.m. 2 990 Timetable block speed •= ' • = 4l7kt /. 167 (where 7.167(3) is mean time in hr for eastboundand westbound crossings) Assuming 4,000 hr, distance covered - 4.000 X 417 = 1,670,000 n.m. .ti / • 1,670,000 .-. No of trips = ,°",~r 2,990 = 559 Passenger accommodation: max all coach (3) 189 typical mixed (4) 20 first 117 economy 137 Load factor, assumed = 55% .'. No of passengers/annum: = 0.55 X 189 X 559 - 0.55 X 137 X 559 = 58,100 -42,100 81
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