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Aviation History
1951
1951 - 0314.PDF
200 FLIGHT, 15 February 1951 TURBINE AIRCRAFT in CIVIL AVIATION B.E.A.'s Chairman Lectures in Denmark : Cost of Fuel : More Operational Experience to be Obtained : Operating Technique : Traffic-control Problems ON Wednesday, February 7th, Marshal of the RoyalAir Force Lord Douglas of Kirtleside, chairman ofBritish European Airways, gave a lecture, under the above title, before a most distinguished audience of guests and members of the Royal Danish Aero Club in Copen- hagen. Among those present were H.R.H. Prince Axel; Lt.-Gen. C. Forslev, Chief of the Air Force, and members of his staff; Sir Alec Randall, British Ambassador, with his Service Attaches; the Swedish and Norwegian Ambassadors; the Danish Traffic Minister and Minister of Civil Aviation and members of their staffs; Civilingenior Per Kapmann, chairman of D.D.L.; and representatives of British and foreign airlines in Copenhagen. Introducing his lecture, Lord Douglas said: "When makingcomparisons between different types of aircraft I shall try to relate the qualities of the turbine-engined variety to those ofpiston-engined aircraft of current design which are capable of doing a comparable job. This, to my mind, is the most usefulyardstick." We in Britain [continued the lecturer] firmly believe in the engineering correctness of turbine engines as a class. Weclaim that the outstanding characteristics of turbine engines are simplicity, efficiency and reliability in operation. ... Reliability islargely an outcome of this relative simplicity, and our experi- ence with the Dart engines in the Viscount has been most en-couraging in this respect. Experience with pure-jet aircraft is similar. In the matter of efficiency there are two opposing characteris-tics which make it difficult to assess the final result. In the first place, turbines tend to be much lighter than comparable piston-engines, but their specific fuel consumption is decidedly higher. Development, however, is entirely on the side of the turbineengine, and we can look forward in the not-too-dista/it future to engines showing substantial improvements in specific consump-tions which will tip the balance decisively in favour of turbines. It is a matter of some importance here that the military ex-penditure on engine development is now going almost exclusively into the turbine variety, and we know from past experience thatthe money spent on military developments is reflected later in the equipment available for civil use. One of the important benefits we are expecting to gain fromturbines is a smoother and more comfortable ride for the passenger. There are certain engineering differences between the twomain classes of turbine engine. At first we feared that the gear- ing and airscrew of the turboprop would lead us into inherentlygreater unreliability. Some careful development work has been necessary to avoid this pitfall, but we now feel satisfied that theaddition of the airscrew to the turbine engine is unlikely to land us in any severe difficulties! In return for the extra complicationof the airscrew and its control gear, we are, of course, getting a high propulsive efficiency, and this results in more operationalflexibility and a relief in respect of traffic control and operational problems. B.E.A.'s Viscount Order B.E.A. has placed an order for 28 Vickers Viscounts driven byturboprop engines. Last summer we" had the useful experience of some 122 hours of commercial operation with an early proto-type version of the Viscount and we now feel that we have some foundation in experience for our earlier conclusions on thepotentialities of turbine aircraft. So confident am I of this that I am prepared to stick my neck out and say that the pistonengine is already obsolescent, and that in ten years' time there zoill be no piston-engined aircraft in air transport except onshort local routes. We are very conscious that in taking on this aircraft we arein fact pioneering civil operations with a new type of prime mover. Although our experience has been highly satisfactoryto date, we are making plans to get some more substantial ex- perience with this engine type before commencing our large-scale passenger carrying operations. Rolls-Royce are fitting Viscount-type Dart turboprops to two of our Dakota airframes,and this summer we shall be running freighter operations with these aircraft in the United Kingdom and in Europe, withspecially trained crews and with special arrangements for tech- nical observation of the engines' behaviour. We are planningin this way to accumulate about 5,000 engine hours represen- tative of the cycles of treatment which our Viscount engines willencounter. We also hope to repeat our last year's experience with the Viscount prototype on certain passenger services, buton a larger scale. This will give us a further 2,000 engine hours of experience. Quite apart from the mechanical engineering advantageswhich I have mentioned, we expect to reap an economic benefit from turboprops . . . our most careful assessments suggest thatwe shall be some 20 per cent better off on direct operating costs per passenger-mile than with a piston-engined aircraft of com-parable type. I might mention here how very important we have found thefactor of fuel prices in studying this kind of aircraft. The large fuel consumptions tend to make this item on the budget a moreserious one than with the older piston-engined types, and it is no exaggeration to say that the profitability of a turbine aircraftcan depend on the trend of fuel prices and taxation. Here again, of course, we are less vulnerable with turboprops than a com-pany backing pure jets. Linked with the advantages in economics is the matter ofcruising speed. It is possible to use the light weight of turbine en- gines either to install more power in a given airframe or to carryhigher payloads. The latter, we think, results in better economy. We have therefore chosen an aircraft which will give us only amodest increase in cruising speeds compared with piston- engined types. We intend to cruise our Viscounts at about 300m.p.h., which is some 40 m.p.h. faster than a comparable piston- en'gined aircraft of to-day. We could have asked for an aircraftwith lower power loading, having the same economy as a piston- engined aircraft but cruising at still higher speeds. . . . Thesolution we have chosen will not necessarily be best in all circumstances for all operators. "f The Traffic-control Aspect | Operational problems and in particular air-traffic control prob-lems, always loom large in any discussion of turbine aircraft. Our experience suggests that turboprop types present no majorproblem. They are sufficiently flexible to fit into present traffic- control systems, albeit somewhat less economical in this respectthan piston-engined aircraft. We are satisfied, however, that we can achieve economic operations with present facilities andcarry adequate fuel reserves as well as a profitable load. Successful operation of turboprops will call for a higher degreeof fuel consciousness on the part of the crew, as compared with current practice with piston engines. It will be quite easy, bylack of sufficient attention in flight planning and control of the flight, to waste more fuel than would result from quite extensivestacking. Crew " fuel consciousness " is, of course, closely allied to thecalculation of saleable space on the aircraft for booking purposes. Care by the crew in conserving fuel will result in less fuel beingcalled for (therefore more payload being available) when condi- tions are favourable. To clarify your appreciation of the traffic control and associa-ted problems I will now discuss in rather more detail the prob- lem as it affects a pure jet airliner, such as the Comet, whichB.O.A.C. will shortly be operating. The essential differences between jet and piston-engined aircraft are that the jets arefaster and are also very much more sensitive to altitude. It will not be long before we have to contend with pure jet aircraftcruising at 450 to 550 m.p.h., so that aircraft approaching each other along an airway are closing at speeds up to 1,100 m.p.h.It is quite obvious that fundamental differences in traffic control and operational handling are necessary to .deal with this situa-tion, for it can no longer be left to the pilots to avoid collision by visual means only. The traffic control problem also has torecognize the most economical flight paths that are typical of these aircraft. After take-off, it is necessary to make continuousascent, generally speaking at about the same gradient of climb as is customary with the piston-engined aircraft, but at far greaterspeeds, of the order of 350 m.p.h. The rates of climb which are occurring are therefore considerably greater than at the moment.The most economical cruising technique will be to fly the aircraft near to its operational ceiling, using engine speeds as close aspossible to the maximum continuous. Any change in engine condition or weight will tend to produce a change in cruisingaltitude, and similarly, any change in altitude, imposed for traffic control reasons, will change the economy of cruising flight. Thedescent to destination from cruising altitude has also to be B u
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