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Aviation History
1948
1948 - 1593.PDF
SEPTEMBER 23RD, 1948 FLIGHT 385 Nimonic Alloys TABLE VICreep Characteristics of Nimonic 80A been developed. It is superior to Nimonic 80 in load-carryingcapacity at the lower temperatures and can be used for rela- tively short-time service at temperatures ranging up to 820-850 deg C. For design purposes involving high temperatures the use ofiactors of safety is somewhat complex but can conveniently ae sub-divided into factors of stress, temperature and time.In the moving blades of a turbine, for example, the centrifugal md bending stresses are known. A factor of safety is necessary•a cover departures from the nominal stress arising from error in ulade dimensions allowed on the profile and to cover the effectaf stress raisers, where occurring as machining marks or brought ibout in service. In applying creep test data to turbinedesign the following considerations should be kept in mind. (1) The total permissible deformation should not be ex-ceeded in the extended time provided by the assigned time "factor ot safety."(2) If the worst conditions of stress, temperature and time are assumed to be operating for the life of the component, -^. the rupture figure should certainly not be exceeded and pre-ferably the time defining the onset of tertiary creep should not be overstepped. The alloys commence to melt at about 1,380 deg C. Nimonic75 can be forged successfully in the temperature range 1,180- 1,230 deg C and can be continued down to about 1,050 deg C,although it becomes increasingly difficult. Forging of Nimonic 80 and 80A is performed satisfactorily in the range of 1,050-1,150 deg C. Stiffness of these materials increases rapidly below 1,000 deg C and frequent reheatings are necessary. Inforging turbine blades it is preferable to deliver only one or, Time and Temp. °C 100 Hour Data 650 700 750 300 Hour Data 650 700 750 1,000 Hour Data 650 700 750 Stress (tons sq in) to produce creep extension of 0.1 per cent 26.0 19.0 14.5 23.0 15.5 11.5 20.0 11.5 8.5 0.2 per cent 28.5 23.0 16.0 26.0 19.5 13.0 22.5 15.5 10.0 0.S per cent 29.5 24.5 17.0 27.0 21.5 14.5 24.0 17.5 11.0 Rupture 30.0 25.5 17.5 27.5 22.0 15.0 24.5 18.0 11.5 at the most, two_ blows between reheatings. The furnace atmo-sphere should be oxidizing and the fuel used should have a low sulphur content. The heat treatment of Nimonic 80 and 80A comprises a solu-tion treatment of eight hours at r,o8o deg C, followed by an ageing treatment of sixteen hours at 700 deg C. Air is thepreferred furnace atmosphere. The extended period at the high solution temperature produces an altered superficial layerhaving a maximum thickness of 0.003m. This should be removed by machining or other means, prior to placing the partin service. Both Nimonic 80 and 80A are adversely influenced by cold working, the effect of which is to increase the rateof creep under given conditions, thus leading to failure by rupture in a shortened time at a large elongation. SIDDELEY TROPHY COMPETITION/r is proposed this year to stage the handicap race for theSiddeley Trophy, presented by Lord Kenilworth, on Saturday, October 16th, under the joint organization of theRoyal Aero Club and the Wolverhampton Aero Club. It will be remembered that the race is open to club members flyingclub aircraft or private owners in their own aircraft, all professionals being expressly debarred. The race will be overa three-lap course of approximately 64 miles, and it is antici- pated that heats will have to be flown before the main race.The first prize is £50 and the Siddeley Trophy; the second ^25 plus a memento; and the third £\o plus a memento. A^5 prize is also to be offered for heat winners. The mementoes and heat prizes will be presented by the Wolverhampton Clubin addition to approximately half the main prize money. As soon as they are received from the printers, entry forms andregulations will be posted to all clubs within the A.B.A.C. organization, and other enquiries should be made to thesecretary of the Wolverhampton Club. Should the weather on Saturday, October 16th, be unsuitable for the contest planshave been made to hold it on the following day. GAS TURBINE PROSPECTS THE Director of the National Gas Turbine Establishment,Mr. Hayne Constant, F.R.Ae.S., M.I.Mech.E., in a recentinterview with the Press, said that his team at Pyestock are probably the world's leading specialists on axial compressordesign. ' On the subject of fuels, he then gave it as his opinion that in time it would be possible to use the heaviest andcrudest of fuels, and suggested that coal did not necessarily need to be pulverized before rendering it usable in a gasturbine; in addition, ordinary producer gas should be added to the list of possible fuels. Mr. Constant also went on to advise that there was noneed to worry very much about the present shortage of liquid fuel. By the time the gas turbine appeared in large numbers,one could expect that the whole outlook on liquid fuel supplies would have changed. He did not, however, indicate in whatdirection this changed outlook might be expected, other than forecasting that a fuel saving of at least 20 per cent couldbe expected in the consumption figures of engines turned out in the next year or two. Additionally, when the present"cooled" turbine came to fruition, a very big improvement in all-round performance could be expected. It is, of course,the temperature at which turbines can satisfactorily operate which sets the limit to the power delivered, and if a turbinecan be cooled with any degree of success, then the peak temperature at the blades can be allowed comparatively toincrease in order to give a greater expansion ratio. On the industrial side of application, Mr. Constant averredthat the general employment of the gas turbine to land and B 23 sea purposes was likely to take much longer than in the aero-nautical field, because the rate of progress was much slower and existing capital equipment would have to work out itsnatural life before replacement. However, the Director fore- saw that when atomic energy power stations were developed,we might expect the heat generated in the atomic pile to be converted into power in a gas turbine very similar to thosewe knew to-day. He also suggested that we might see the day when a firm will make gas-turbine components andassemble them to order in whatever system is required by their customers, in much the same way as xadio firms manu-facture components and assemble them at the present time. FORTHCOMING EVENTS Sept. 25th.—S.L.A.E. (South Eastern Area): "Aviation Gasolines," by G. L. Coles, B.Sc, A.R.C.Sc, F.lnst.Pet., Manson House, 26, Portland Place, London, W.I, at 3 p.m. Sept. 25th and 26th.—Butlin's Week-end Air Rally at jngoldmells, Skegness. Sept. 25th and 26th.—International air rally at Cervin, Sion, Switzerland. Sept. 27th to Oct. 1st.—Federation Aeronautique Internationale Con- ference, Paris. Sept. 28th.—R.Ae.S. (Graduates and Students): "Sailplane Design," K. G. Wilkinson, B.Sc., A.C.G.I., D.I.C., A.F.R.Ae.S. Sept. 28th.—R.Ae.S. (Glasgow) : Film Evening, Prestwick airport. Sept. 30th.—Royal Aeronautical Society : Fourth British Commonwealth and Empire Lecture : " Some Economic Factors in Civil Aviation, with Emphasis on Civil Aircraft and their Pros- pective Trends of Development." Peter G. Masefield, M.A., F.R.Ae.S. Oct. 6th.—Royal Aeronautical Society (at Birmingham) : " Some Aspects of Power Plant Development," Dr. E. W. Still, B.Sc., A.F.R.Ae.S. Oct. 9th.—The British Interplanetary Society: "Interplanetary Man," Olaf Stapledon. Oct. 13th.—R.Ae.S. (Hatfield) "Aircraft Photography," John Yoxall. Oct. 15th.—Second International Air Ball at London Airport. Oct. 21st.—Royal Aeronautical Society : " Cold Weather Operation of Aircraft," G. W.Wilson, A.F.R.Ae.S. and S/L. E. P. Bridg- land, R.C.A.F., B.Sc., A.F.R.Ae.S. Oct. 26th.—R.Ae.S. (Graduates and Students): "Flight Refuelling," Sir Alan J. Cobham, K.B.E., Hon F.R.Ae.S. Oct. 30th.—S.L.A.E. (South Eastern Area) : " High Speed Flight," by W. A. Waterton, Manson House, 26, Portland Place, London, W.I, at 3 p.m. Nov. 10th.—R.Ae.S. (Graduates and Students) : " Flying Experiences," Lt. Cdr. (A) E. M. Brown, O.B.E., D.S.C., A.F.C., M.A., A.R.Ae.S., R.N. Nov. 12th.—Redditch Society : " Aircraft Photography." John Yoxall. Nov. 17th.—R.Ae.S. (Hatfield) : " Design Problems of Large Flying Boats," H. Knowler, F.R.Ae.S. Nov. 20th.—Joint Meeting Royal Aeronautical Society and Helicopter Association of Gt. Britain. Full day Discussion on Heli- copters. Nov. 27th.—S.L.A.E. (South Eastern Area) : " Gas Turbine Power Plants," by D. H. Mallinson, B.Sc., Manson House, 26, Portland Place, London, W.I, at 3 p.m. Dec. 21st.—R.Ae.S. (Graduates and Students): "Production—The Dynamics of People at Work." J. V. Connolly, B.E., A.F.R.Ae.S. Feb. 14th.—The Institute of Transport : Brancker Memorial Lecture by Major R. H. Mayo, O.B.E., M.lnst.T.
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