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Aviation History
1946
1946 - 0566.PDF
292 FLIGHT MAKCH 2IST, 1946 R.Ae.S. DEBATES THE CAS TURBINE flying must be done before a heat exchanger has paid for itsown weight. In addition, the problems to be faced in its development make it the radiator problem in excelsis. On the score of performance with jet propulsion. Dr. Hookerillustrated some rather entrancing examples. First, a Lan- caster fitted with four Nene engines which gave the aircraft acruising speed of about 400 m.p.h. at all altitudes up to 35,000ft. At 10,oooft each engine will consume 430 gal/hr, sothat the air miles per gallon are 0.23. At 20,000ft the corre- sponding figure is 0.31 a.m.p.g., and at 30,000ft 0.43 a.m.p.g.Admittedly these are low figures, but it should be remembered that four units of this type when fully installed only weigh atotal of about 7,000 lb, whereas the present four Merlins fully installed weigh 13,000 lb. Further, jet fighter aircraft such as the Meteor, Vampire andLockheed Shooting Star have drag figures very much lower than airscrew-driven machines of a similar category, e.g., the dragcoefficient of the Meteor is only about two-thirds that of the Spitfire, and figures for the Vampire are even better. Conse-quently, at a conservative estimate the previous figures of a.m.p.g. ran, in actual fact, probably be increased by about25 per cent, and in addition jet engines with a fuel consumption some 14 per cent less than that of the Nene can be designedand made. So far as take-off is concerned the Lancaster with four Neneswill have a static take-off thrust of 20,000 lb, which is con- siderably greater than that from four Merlins, and although itis improbable that the Lancaster would be able to fly the Atlantic it is respectfully suggested that it will have littledifficulty in crossing the English Channel and reaching very attractive places like Paris, Stockholm, Copenhagen and Zurich. To consider another case, namely, the celebrated D.C.3. Acruising speed of 400 m.p.h. at 1,000 ft and 5,000 lb payload coupled with a range of 1,000 miles can be obtained at a take-off weight of 27,000 lb, using jet propulsion engines of about 6: 1 compression ratio and a static thrust of 6,000 1b. In consideration of the effect of altitude upon range, thepreceding figures for the Lancaster give an indication. But to analyse the effect in more detail we may consider a machine ofabout Spitfire size having a drag of about 1,000 lb at 300 m.p.h. at sea level. For a sea level speed of 500 m.p.h. a thrust of 2,400 lb will be required, and the air-miles/gallon of the machine will be reduced to about 1.0. At 40,000ft the drag of the aircraft at the same speed of 500 m.p.h. will be reduced to about 800 lb, due both to the lower density of the air at this . . . four air miles per gallon on a jet propelled Spitfire at 500 m.p.h. at 40,OOOft. . . . it should be clearly understood that jet propulsion is efficient at any altitude, at a greater speed than 500 m.p.h. height, and also to the change in angle of incidence of themachine. Consequently, at this altitude the air-miles/gallon will be about 4.0. In going from sea level to 40,000ft thethermal efficiency of the engine is improved from about 18 to 25 per cent, and this improvement is due to the lower air-intake temperature to the engine and the consequent high compression ratio of the cycle. On the other hand, the pro-pulsory efficiency of the jet has fallen from 64 to 58 per cent, due to the increased jet velocity at 40,000ft brought about bythe increased thermal efficiency of the engine. Thus the balance is as follows:— Improvement in thermal efficiency of engine from 18 to 25 per cent, i.e., 1.39.Reduction in propulsion efficiency from 64 to 58 per cent, i.e., 0.90.The overall improvement of the engine is, therefore, 25 per cent, but the range of the aircraft has actually been quad-rupled. Hence the improvement in range of a jet-propelled machine at altitude is not so much due to the engine, but int|je main due to the aircraft. ' In actual fact, at 40,000ft and 500 m.p.h. this machine doesthe same air-miles /gallon as a Spitfire, and consequently all the objections to jet propulsion can be overcome by flying highand fast. It should be clearly understood that jet propulsion is efficient at any altitude provided the speed is greater than500 m.p.h. It should also be remembered that the higher the altitude the more efficient the aircraft. THE NXJFFIELD CENTBE, WARDOUR STREETS INCE it opened in September, 1943, the Nuffield Centre forService men and women at 15, Wardour Street, has pro- vided meals, dancing, entertainment, and the facilities of writ-ing rooms, games rooms, tailor's and barber's shops, etc., for nearly three million members of the Forces. The premises, which are a combination of the former EmpireRestaurant and the Cafe de Paris, are pleasantly " non-Service- Club " in appearance, and at the present time there are stillmore than 25,000 visitors each week. Members of Flight staff were recently guests at the Centre onthe occasion of one of its bi-weekly variety-entertainment even- ings. With a list of artistes volunteers topped by TommyTrinder and compered by Peter Waring, the two-hour show was first class. It is to be hoped that this excellent club, which is sponsoredby the Nuffield Trust for the Forces of the Crown, will be able to continue with its good work as long as there are young menand women in uniform. Great credit and thanks are due to the organizers and staff—the majority of whom give theirservices voluntarily—and the enthusiasm and obvious pleasure of their visitors must in itself be a reward to them. Service men and women below commissioned rank who havenot yet visited the Centre are strongly recommended to do so next time they happen to be in London. Jet Propulsion and Military Aircraft (Concluded from page 2S5) that the aircraft should respond to precision control undei all conditions. It can be seen that the working-out of a new equilibrium between attack and defence has only just begun, and that the problems associated with this outlook have become greatly intensified as the tempo of events has been speeded-up. More effective armament installations are also likely to be required, and these may profoundly influence the general trend of design and development. At no other time in the history of aeronautical events have so many intricate and. formidable problems been presented for solution. In this brief review only a few of the aspects concerned with the application of jet propulsion to military aircraft have been mentioned. There are, however, many secondary considerations no less important than those which relate more to the fundamental aspects of design. These associated effects mostly involve the safety and comfort of the pilot, a matter for special consideration now that speed and altitude ranges have been so greatly increased. However good the aircraft may be as a means of transporta- tion for offensive weapons, so much depends upon the man in making the most effective use of the military machine. FORTHCOMING EVENTS March 28th.—*R.Ae.S., "The Electrical Measurement of Strain," by Dr. S. C. Redshaw. March 28th.—R.A.F. Club annual meeting at 128 Piccadilly, London, W.I, at 6 p.m. April 4th.—jMetropolitan Region luncheon meeting, Institute of Motor Industry (London). April 10th.—*R.Ae.S., " The Silencing of Aircraft," by Dr. Fleming. April 16th.—**R.Ae.S. Graduates and Students Section ; " Flight Refuelling," by Sir Alan J. Cobham. April 25th.—fR-Ae.S.. Manchester Branch. April 25th.—*R.Ae.S., "Modern Aeronautical Materials," by Dr. L. Aitcheson. May 2nd.—**R.Ae.S. Graduates and Students Section ; "Trans port Aircraft," by F, Ratcliffe. * Lecture Hall, Institute of Civil Engineers, Gt. George St.. S.W.I. ** The Library, 4 Hamilton Place, W.I. f Lectures by Air Comdre. F. Whittle.
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