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Aviation History
1955
1955 - 0276.PDF
276 FLIGHT, 4 March 1955 CORRESPONDENCE The Editor of "Flight" does not hold himself responsible for the views expressed by correspondents in these columns; the names and addresses of the writers, not neces- sarily for publication, must in all cases accompany letters. The Hawker Fury referred to in the letter horn Mr. S. Dayies. High-lift GenerationT HE article by Mr. A. R. Weyl on "High-Lift Generation," inFlight for January 7th and 14th, was interesting not only in itself, but also on account of the comparisons to be drawn withlow Reynolds number aerodynamics. Mr. Weyl omitted to state (though perhaps correctly so, as it was self-evident) that the devicesdescribed are applicable only at Reynolds numbers of full-size aircraft. However, it is interesting to review briefly the practical methodsfor lift-augmentation used in low Reynolds number aerodynamics, i.e., in "free" aeromodelling (normally in the range between 7,000,for indoor models, and about 150,000, for large powered free-flight models—tethered speed models reach some 250,000). As theoperating conditions of the aerofoils of many models, especially those of high-performance sailplanes, fall within their sub-criticalregion, characterized by a laminar boundary layer and very low L/D ratios, it is often necessary to introduce energy through arti-ficial turbulence into the boundary layer, as only this ensures an adequate flow pattern over the aerofoil without separation of themain airflow. This is generally done in one or both of two ways —either by using special aerofoil sections which operate, even atlow Reynolds numbers, in over-critical conditions, or by using artificial turbulence generators on, near, or in front of the leadingedge. Both methods are in use today. As to aerofoils, low fineness-ratios (e.g., 4.4 per cent on asection evolved by the writer), moderate to high centre-line camber and sharp trailing edges are considered necessary in modelsailplane wings. Turbulence in the boundary layer is generated mostly with theaid of the following devices. The turbulence wire is the one mostly used, and, correctly placed in front of the leading edge,gives very good results, increasing Ci values by up to 300 per cent on normal aerofoils (e.g. from 0.45 to 1.3—which is con-sidered high in a model! —for a given constant Cd at RN = 80,000 on a Clark Y type aerofoil). Sharp-edged turbulence strips areglued, in some cases, on to the upper surface just behind the leading edge. Sometimes sawdust is sprinkled on the upper sur-face, which even has been painted black, at least in two cases, in order to turbulate the boundary layer by heat convection! Jerusalem, Israel. N. KADMON. RJV.F. Bands Strike a Dull Note I AM surprised that the Air Council have not done somethingto improve the R.A.F. Central Band and the R.A.F. College, Cranwell, Band. These bands, in my view, are hopeless to marchto and deplorable to listen to. A number of suggestions could be made, including the follow-ing : establishment of the ranks of band sergeant and bandmaster in the R.A.F.; formation of R.A.F. and W.R.A.F. brass bands forevery unit of sufficient size; the holding of R.A.F. brass-band contests; the composition of a quick march and slow march foreach squadron of the Service, as in the Army regiments; forma- tion of an R.A.F. school of music to teach airmen and airwomenfull theory and practice; and establishment of a boy entrant and apprentice scheme for the trade of R.A.F. musician. There are thousands of airmen in the R.A.F. today who canplay brass band instruments, but they are refused permission to enter station voluntary bands or established bands in the R.A.F.They are not allowed to practise on the station and they are refused permission to play in civilian bands. This is a remarkablecontrast to the Service encouragement of sport and similar occupations. In conclusion, it may be added that some years ago three Norfolkbrass band instrumentalists went to Uxbridge to be examined by the R.A.F. Central Band trade test board. They were turneddown. Subsequently, after auditions at the Royal Military School of Music, they passed out with ioo per cent marks on the wholemusical curriculum, and today they are commissioned officers and directors of music. One is in charge of the R.C.A.F. CentralBand, another of the R.C.A.F. Training Command Band and the third of the R.A.A.F. Central Band. I personally was told thatI was "no good as a musician," but I am now a tuba player in the B.B.C. Scottish Orchestra. Peterborough, Northants. W. S. WHALES. Collecting the Empties THE implication, in a recent statement by the Under-Secretaryfor Air, that Hunters are to be fitted with external link and cartridge containers suggests that a lesson learned as long agoas the 1930s may have been forgotten. I refer to the fitting, as illustrated in the enclosed photograph, of collector boxes on theHawker Fury biplanes in R.A.F. service. Subsequent Hawker fighters, of course, had wing-mounted guns, and presumably thesame problems did not arise. Broadstairs, Kent. S. DAVTES. Pressure Cabins RESULTING from the Comet Inquiry, one point would appearto be highly relevant in that problems of construction which have always been present during the fabrication and shaping ofmetal into unnatural attitudes becomes magnified as we enter the region of rare air which necessitates the boosting of cabin internalair pressures beyond a given differential. I feel that we could safely categorize high-flying commercialaircraft as any machines with normal differential pressures above 5.45 lb/sq in, giving us around the 8,000ft cabin altitude at25,000ft. For reasons of fuel consumption alone, all pure-jet commercialaircraft will automatically be outside this range. Comet Series 1 aircraft, the forerunners of a new era in commercial flying fromall aspects (i.e., block-to-block speed, passenger comfort and ease of en route maintenance) cruise at up to 39-4O,OOOft altitude,with maximum normal cabin pressures at about 8.25 lb/sq in. Series 2 and 3 aircraft, with superior performance and range will(possibly due to the problems surrounding cruise control of the jet engine, and in order to hold speeds within the desired Machnumber) wish to exceed such altitudes as 40,000ft as all-up weight decreases with fuel burn-off for the longer stage-lengths. Later on it may even suit us to fly higher still, with furtherincreases in cabin pressure differentials. No one can possibly be in any doubt that we are able to designsatisfactorily a modern fuselage that will continuously stand a pressure of 8-10 lb/sq in for any safe economical life which theplanners may lay down having regard to capital outlay. Then surely the only problem is die one already existing withall the mechanics of aviation, i.e., strength/weight ratio. In simple terms, were we to construct a Series I Comet with a pressure cabinand general wing construction so robust diat "prepared-for-service weight" began to approach to maximum all-up weight, this in itsnew form would be an extremely safe aircraft with a life far beyond any practical requirement, but commercially valueless. From this we surely see that it is only a matter of intelligentapproach to the subject. We do not yet know what new steps our aircraft designers will take in this matter. Methods of fabricationmay have to be revised, metal gauge stepped up, steels be intro- duced; and one's mind automatically strays to forms of geodeticconstruction where skin thicknesses could be held within reason by two or three laminations wrapped in varying directions for grainflow stagger to give the equivalent of a plywood in metal. It would also appear advisable to keep cut-outs to a minimum,and to this end the modern passenger, with the aid of pleasing aircraft interior layout, may have to be enticed away from thewindow-per-seat-row idea. Technique in modern aircraft construction, both military andcivil, tends towards machining from the solid, of quite large sec- tions of aircraft, on giant millers. A good example of this is a32in X 4in x ljin inner section of the underwing surface, port and starboard, of the Lockheed Super Constellation. There may wellbe some future for such fabrication along cabin windows and escape hatches of the modern high-flying pressure cabin. I wonder whether we are approaching a point where fuselage designs will have to be standardized and serialized and pressure ^n1«Lbu,iltnand tested t0 cover the 40-50,000ft requirement for110,000, 210,000 lb m.a.u.w. requirement, available for release to builders of modern aircraft. To me this would not appear sounhkely. There must be an optimum aerodynamically and static- ally efficient shape for a fuselage and this is rather borne out bya rapid glance at the Boeing 707 and Comet Scries Heliopolis, Egypt. j
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