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Aviation History
1948
1948 - 2101.PDF
DECEMBER gra, 1948 FLIGHT 701 Development of a New Aircraft only a fifty per cent chance of success.Consequently, unless he could sell his products abroad, he must find other workto do, or he would lose valuable technical staff and fail to keep in touch with advances.'in modern technique. .- Comments on the effect of delayed develop-, ment and on the traditional policies of firms followed. DEVELOPMENT COSTS _TF the firm's production capacity was*• JL already occupied with a large order that •.would keep the shops busy for sometime to come, a Chief Designer w ' .-•would be free to proceed with long- SSrange planning and embark on new "~ 'projects. It frequently happened,however, that the immediate need was for what might be termed a"bread-and-butter" type; one that, requiring a small amount of projectwork, would fill the shops at short 5^ 0 18 notice. One of the most attractive g^.types of "bread-and-butter" air- _.° 014 craft from the manufacturer's pointof view was a major conversion of an established type.In a country so short of technical resources as ours, every effort shouldbe made to meet a new demand by means of a variation of an existingtype, before launching forth on an expensive and unknown new design.A major cause of the troubles ex- perienced from official routine wasthe disparity between military and civil requirements. The cure wasthat civil aircraft should be de- rived from basic military types, the originalspecification being laid down by the Direc- tor of Requirements, Air Ministry, advisedby civil operators. The facilities for exhaustive trials in theservice far exceeded those available to civil operators. That essential process familiarlyknown as "getting the bugs out" of a new design would be completed, as far as thecivil version was concerned, at the ante- natal stage. One of the chief difficulties confrontingthe civil operation of turboprops was the absence of previous military operation. It was the author's opinion that the alter-nating of new and conversion types in the production programme also provided oneof the most satisfactory contributions the manufacturer himself could make towardsa solution of current problems. It was not intended to imply that eachnew type should be limited to a single major conversion. - A really sound basictype might be capable of producing several versions, both military and civil. First-class aircraft came seldom enough to warrant their being discarded after they had satis-id their original purpose. Talking of new types, Mr. Edwards saidthat he believed it would be advantageous if, while drawing up the specification,selected firms in the industry were consulted at an early stage in order to get their viewson the feasibility of the project. ENGINE DEVELOPMENT THE present state of gas turbine develop-ment made it difficult to assess future events. Present experience was largelyconfined to centrifugal types, and medium performance civil and military aircraftmight well continue to be powered by them. The higher compression ratio and smallerfrontal area associated with the axial com- pressor would make it the future engine for \ \ < /•(j ^— CON\0___ 0 ERSIO - 8w P^ NS 0 — — — — 030 O26 022 O-1O — 0O6 ' a 02 20.O0O 30,000 4QOOO 50.000 LIGHT WEIGHT mates, the third project stage, and aero-dynamics were considered next. If there was one branch of aircraft designlikely to give rise to a greater number of problems than another, during development,it was aerodynamics. Few aircraft during recent years had not been threatened withdelay because of this. The fundamental reasons for this state ofaffairs might be listed broadly under four headings, in ascending order of seriousness.1. The increasing severity of requirements. 2. The difficulty of making basic struc-tural alterations alter the aircraft has flown. 3. The inaccuracy and insufficiency ofresults from obsolete equipment unable to Cope with modern speeds and aircraft sizes. 4. The complications introducedby so many additional design para- meters—compressibility, sweepback,shock waves, extreme altitudes— and the lack of sufficient relevantdesign data to guarantee success. It was unlikely that such a drasticintroduction of higher standards in so short a time would occur again. Time spent by senior designers inattending committees concerned with the formulation of national re-quirements was by no means so wasteful as it might seem, whenconsidered in conjunction with the actual design time thereby saved. 60,000 70,000 AERODYNAMIC TEST EQUIPMENT Comparison in drawing office times to first flight for new types and major conversions. 1 TIME TO FIRST FLIGHT- NEW TYPES ZZJ LAPSE TIME TO rt*R,£UCHT - CONVERSIONS r3 LAPSE TIME TO FIRS'fT'lteDUCTIQN 20,000 30,000 1O.OOO 5O.OOO LIGHT WEIGHT- LB. Time comparisons between new types and major conversions. An important saving in lapsed time between formulation of the requirements and the start of pro- duction is apparent. T 37 high-performance types, particularly whereburied installations were feasible. The author would make a plea for a long-termlimitation in size change so that the engine bays in buried installations could be de-signed to accommodate all types of engines which might be fitted during the life of theaircraft. The declared power should be based on an engine certain to be ready forthe prototype, rather than on a higher- powered projected engine which might novalter all, materialize in time. Mr. Edwards next said that he proposedto follow the aeroplane through its succes- sive development stages, and in so doing toconsider its relation to the various depart- ments concerned. By far the biggest contribution a manu-facturer could make towards cutting cost; was sometimes overlooked. That was, get-ting the aircraft right the first time. When examining the original require-ments a designer had first to decide when special emphasis should be placed on anyparticular feature or aspect of the aircraft. It was inadvisable to embody too many• untried features in a single new design. PROJECT OFFICE THE first stage in preparing a tender,which would occupy some six months,took place in the project office and was • concerned chiefly with the basic characteris-tics of the aircraft. This was the stage at which a Chief Designer must be preparedto make firm decisions. The example of German project methods as exemplified bythe Messerschmidt organization was a case in point. There, up to 1,000 combinationsbased on 20 variations of a project were con- sidered. It was here that sound judgmentwas required; two or three alternatives at most might be considered at this early stageand the sooner they were reduced to one, the better. Mr. Edwards then discussed design con-siderations with relation to a specific aircrait required to carry 32 passengers at a cruis-ing speed of 240 knots over a still-air rangr of 900 nautical miles. The production process was then carried to the stage of sub- mitting the tender, with data and necessaryproject drawings, together with a time pro- gramme and a target date for prototype amifirst production aircraft. Planning and esti- A LTHOUGH derided by some,I\ there could be little doubt that on the wind tunnel fell the bruntof aerodynamic design, whether the data so obtained took the form ofad hoc information on specific models or of empirical formula1! of a generalnature. With one or two notable exceptions, wind tunnels now in use were built sometwelve or more years ago when the average speed was of the order of 200 m.p.h. and anaircraft weight of 25,000 1b was considered excessive. Since then, speeds of 600 m.p.h.and weights of 100,000 lb were not unusual. The need for accuracy in wind tunnel datahad increased tenfold, a demand which none but the newest tunnels could meet. Theneed for new wind tunnels of sufficient size and speed was imperative if we were evento keep pace with requirements. Some idea of the cost might be obtainedfrom the Co-operative Wind Tunnel at Pasadena, which was used by four majoraircraft firms. The tunnel was operated for 11 to 14 hours a day, and apparentlycosts each firm about £50,000 a year. The addition of new fundamental variableswas necessitating exhaustive tests on almost all new designs. Because of the very limitedhigh-speed testing facilities available in this country, and because existing wind tunnelscould not operate for more than 24 hours a day, the supply of basic empirical dataon which the industry relied was unlikely to mature. This bleak outlook was extremely serious,and the aircraft industry could not afford to allow the situation to continue. TheGovernment must encourage the industry to build for itself subsonic and supersonic windtunnels in order to relieve the load from the research establishments at the earliestpossible moment. Without these, we should be forced to fall back on the time-honouredcustom of analysing American data on air- craft bearing some resemblance to the onein hand. This inevitably led to inferior design and to aircraft which could not com-pete with American types derived from the original data. A similar plea for the energetic construc-tion of research aircraft was made. The amount of information now available onthe effect of sweepback in delaying the onset of compressibility was small and mainlyconfined to model tests. Invaluable full- scale flying tests could be made on aircraftderived from basic square-wing fighters in which the addition of sweepback was theonly design change. (The conclusion and discussion will htPublished, next week.)
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