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Aviation History
1955
1955 - 0211.PDF
FLIGHT, 18 February 1955 •m- 211 TODAY'S RESEARCH for TOMORROW'S TRANSPORTS Sir Arnold HaWs Brancker Memorial Lecture THE 1955 Brancker Memorial Lecture was delivered onMonday last, February 14th, at the Institute of Trans-port by Sir Arnold Hall, F.R.S., M.A., F.R.Ae.S., Director of the Royal Aircraft Establishment, Farnborough. Sir Arnold's paper, entitled The Influence on Civil Aviation of Some Current Researches, was particularly concerned with ways of improving not only the performance and economics of transport aircraft, but also their safety and regularity. Lucid in both thought and expression, it promises to receive early recognition as one of the most significant of post-war aviation lectures. The first part of the paper is given below; we expect to conclude our summary next week. The lecturer began by "confessing to the feeling" that civilaviation, already a substantial influence, needed greater reliability and safety if it was to become, as it should, a great force in worldaffairs. It was particularly to these matters, rather than the very- long-term possibilities, that attention should be, and no doubtwould be, directed. The accident due, for example, to troubles of navigation, to storm, to landing in bad weather, must be totallymastered, and achievement of this aim would be assisted by developments which were now in hand, or which could be foreseen.It was usually the case that advances in the performance of aircraft could be taken in several ways (for example, in lifting greaterweight, in reducing operating costs, in lower approach and landing speeds). Improvements representing a considerable potentialeconomy were likely to occur in the next decade, and Sir Arnold hoped that some part of them would be taken in features whichenhanced reliability and safety, rather than entirely in economies in the cruising phase. There should be enough in plenty toprovide the right service, reliability and safety at the right price. Saying that he could not hope to cover the subject of this lectureexhaustively, the lecturer remarked that he had chosen topics of general interest, and particularly those in which the Royal AircraftEstablishment had been able to make some contribution. The Next Generation of Long-Range Aircraft.—During thelast ten years [continued Sir Arnold Hall] research has greatly increased our knowledge of the aerodynamic problems encounterednear the speed of sound, and has brought the gas turbine engine to a high state of development. As a result, long-range civil air-craft capable of cruising at high subsonic speeds—500 to 600 m.p.h.—can now be designed, and such machines are likely toform the generation of long-range aircraft which will follow the machines now about to come into service. ... High-subsonic-speed aircraft can be powered with turbopropor turbojet engines, and the wings can take several forms, typified by the straight wing—for speeds up to 500 m.p.h.—and theswept-back wing of about 40 deg (leading edge), or the delta wing of 45-50 deg, for speeds up to 600 m.p.h. The operating heightof this class of aircraft will be in the 35,000-45,000ft altitude band, the turboprop types flying at rather lower levels than the turbojet.The economic characteristics of such aircraft differ substan- tially from those of present long-range types and, in particular,their operating costs can be considerably lower. Characteristics are, of course, to some extent influenced by the choice of wingplan-form and propulsion system, but the economic variation between the arrangements is small compared with the change TABLE "Formula" direct operating cost ..."In practice" addition to "formula cost" Indirect cost Cost: pence per capacity long-ton nautical mile Typical present-daylong-range aircraft (Paylood; 15,500 Ib) 24.5 10.5 22 Typical high-subsonic- speed aircraft (500-600 ^lfayioad 35.000 Ib) (120 passengers) 11 20 (assuming present level of over- heads) IN these pages, in very slightly abridged form, is the first part ofSir Arnold Hall's lecture. As all except one_ of his illustrations (Fig. 5) are included, the original figure numbering is retained in order to assistsubsequent discussion. from present-day standards. Apart from remarking that I believethat the turbojet type can be designed for comparably cheap operation at speeds substantially higher than the turboprop type,I will leave die argument as to which layout and powerplant is to. be proclaimed the best to the protagonists of particular arrange-ments, and attempt to.bxingjo«ijJae Jgeafl«al-£h«acteristics of the •class. As compared with a direct operating cost of about 35 penceper capacity long-ton nautical mile for present-day long-range aircraft, high-subsonic aircraft will show direct costs of about18 pence, and will, in addition, be capable of operating over considerably greater stage-lengths. Assuming the present levelof indirect costs, the total cost (direct plus indirect) of high sub- sonic aircraft will be about 38 pence, as compared with thepresent-day 57 pence, per capacity long-ton nautical mile. In what follows, the "formula direct operating cost" means,the direct cost, including the element for annual charges on the aircraft, according to an established costing formula which isdetailed in Appendix 1 [see page 214], wherein also will be found the "make-up" of the formula cost in typical cases. Direct costs asthey are found in practice differ from "formula costs" by an amount which depends on the route, and type of operation. Inquoting the figures in the preceding paragraph, a typical addition, as found in practice on a particular route has been made for thepresent-day aircraft, and an estimated "in practice" allowance as it might be found in a high-subsonic aircraft operated in similargeneral circumstances has been added for that case. The general magnitude of the elements making up the total cost in a typicalcase is shown in Table I, which is intended to do no more than put them in relative perspective.For comparative purposes, it is convenient to work in terms of the "formula cost," and this is done in what follows.In Fig. 1 are shown some of the economic characteristics of the high-subsonic class, as typified by aircraft designed for the non-stop London to New York flight, at 550 m.p.h. This is a stage- length of 3,000 nautical miles; the still-air range, to provide normalallowances for wind and fuel reserves, is 4,800 n.m. The figure shows the formula direct operating cost, as a function of thepayload and the landing approach speed for which the aircraft is designed. The take-off weight is indicated at particular points.(The landing approach speed quoted is the "speed over the hedge"; some prefer to quote the speed in the early stages of theapproach, but the two are usually related in a simple way.) If the wing of the aircraft is made only sufficiently large lo carrythe fuel needed for the specified still-air range, the economy of operation in the cruising phase approaches the maximum obtain-able, since the wing is then the smallest upon which the aircraft can make the journey. A smaller wing would suffice were fuelcarried in the fuselage, a practice some designers prefer to avoid, or if additional fuel were carried in nacelles attached to the wing.Such arrangements, at high design-payloads, result in a fast land- ing approach speed, which, for reasons I will discuss later, I wouldprefer to see avoided, though new ideas on obtaining more lift from the wing, or additional lift to that given by the wing, to ease thetake-off and landing problem, may allow such additional economy as can be obtained by "podding" the fuel to be taken. Leavingaside these possibilities for the moment, the "wing-full" aeroplane is the design giving maximum cruising economy, and if lowerlanding approach speeds—and incidentally, better take-off charac- teristics—than are provided by the "wing full" design are needed,the wing area must be increased, with the adverse effect on economy of operation which is indicated in Fig. 1.Examination of the influence of designed capacity payload (Fig. 2) shows that there is economic benefit to be derived fromincreasing the designed payload as compared with that carried by contemporary long-range aircraft, if the traffic available, andfrequency of service needed, will permit. The influence of annual utilization can be gauged from Fig. 2 where a comparison is madeof the 3,000 hours per annum and 2,000 hours per annum "wing-
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