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SUPPLEMENTTOFLIGHT NOV M R 28, 1930THE AIRCRAFT ENGINEERwhenx= L

- Eldyjdx = WL 2 M 'L- ~ (Mo 2M')= j (3WL+ 6M') - j (M + 2 M')6 fa= L (3M + 3M' - M - 2M')6

dyjdx = 6E1 (2M + M')A difficulty arisesin thecalculations. Foranexact solution,theendloads m ustbeknown beforetheslopesmay befound.Therearetwoalternatives. Eitherthetorsionin themembersmust firstbeneglectedtoobtain approximateendloads whichmay thenbeusedtogivethevaluesof theslopesintermsofthe bending moments,or theeffect of endloadon theslopesmust beneglected. Thebetter assu mption depends on thegeometry of the undercarriage.

Tobe concluded.)

TECHNICAL LITERATURESUMM RIESO ERON UTIC L RESE RCH

COMMITTEE REPORTSThese Reports arepublished by HisMajesty's StationeryOffice, London, and may be purchased directly fromH.M.Stationery Officeat thefollowing ad dresses: Adastral House,Kingsway, W.C.2; 120,George Street, Ed inb urg h; YorkStreet, Manchester ; 1, St.An drew 's Cres cent, Cardiff ; 15,Donegall Square West, Belfast; orthroughany bookseller.

OK THE PR OB LEM OF HYDR ODYNAMIC STAB ILITY . 1. UNIFOR M SHEAR ING MOTION IN A V I SC O U S F L U I D . ByR . V. Southwell, F.R.S., and Letitia Chitty. R. & M. No.1200. (Ae. 361). (54pages and 17 diagrams.) Jan uary ,1930. Price 2s. 6d. net.

The repor t lays down thefollowingas theonly k nown cases where.thes tabi l i tyof thes teady motionof fluidshasbeen d emonstrated.(a ) Thelamin ar flowof a fluid, under uniform pressure gradient or bodyforces, betweentwo fixed parallel planes (Lam b, Hydrodynamics , 330).(6)Thelaminar flowof a Buid betweentwoplaneandparallel bo undarieswhich havea uniform velocity relativeto oneano therin a direction parallelto their planes (ibid., 330 (a).)(c) Therectilinear flowof a fluid, under uniform pressureor body forces,rougha straight pipeof uniform section (ibid.,331,332). d) Two-dimensional rotatory motionof fluid abouta fixed axis, betweentwo co-axial cylindersof infinite length (ibid, 333).This repo rt describes work whichhasbeen don ein ana t t empttoexaminethe s tabi l i tyof themotion (b). The aim hasbeentodevelopa generalisedtheoryof thekind which K ayleigh employed so successfully in relation toproblems of vibrat ion, wherebythecritical velocity of steady flow mightbeestimated approximately in cases where exact solutions are unobtainable.Attent ion isconfined to disturbances whicharetwo-dimensional . .SectionIII of therepor t descr ibesthe Method of Normal Co-ordinateswhich entailsa s tudyof disturbances varying accordingto a simple expon-ential factor of thet ime . It is shown that the method may be used toobtaina complete solution(forinfinitesimal disturbances)in thespecial caseoftheproblem, wheretheplane boundariesare atrest. Themethodisthenappliedto thegeneral case (with moving b oun darie s); it isfound to breakdownonaccountof thefailure,inthis case,ofcer tain conjugate relationswhichare an essential basisof themethodin its existing form.Other linesofat tackon theproblemarediscussedand arcbeing co ntinued.E X P E R I M E N T S ON THE IGNITION OF G A S E S BY S U D D E NCOMPRESSION. By R. W. Fenning, M.B.E. , B.Sc, D.I.C.and F. T. Cotton, B.Sc. Work performed for the Depart-m e n tofScientificandIndustr ial Research. R. &M.No. 1324.

(E . 36). (43 pages and 18 diagrams). Novemb er, 1929.Price2s. 6d. net.Whils t exper imenting at Cambridgeon theignition tem peratures of air-gas mixtures having high ignition temperatures, Messrs. ' l izard and Pyeobtaine d results which were somewh at erratic. Subsequently, the com-pression ignition apparatus wassentto the Nationa l Physical Labora tory,in order that this anomalous behaviour might be investigated.(a) Exper iments on air-hydroge n, air-acetylene, air-benzene, and air-hexane mixtures were carr ied out, using the appara tus as received,anddiscordant results obtained despite the efforts mad e to secure constancyof conditions. . .

b)The appara tus wasmodifiedso as toelimin ate friction effect*and tipabletos tudytheinfluenceof (i)surface friction,(ii) thepresenceoflubricat-in goil. and (iii)fine metallic particlesinsuspens ion; all a t roomte inpera tun(initially).(c) Theexper iments unde r(ft) indicated th at consistent results shouldbeobtainablein a well-lubricated cylinderat room temperature,and this formof apparatus wasused for subsequent work (on air-methane mixtures).There is strong evidence in favour of the highest values given by tinapparatus ,asreceivedandasoperated,approachingthe most closelyto thitrue valuesof the igni t ion tem perature.The values of the igni t ion tem perature, under the cooliu? conditionsper taining to these particular bulb experiments, are of the order :7- 6percent, acetylene,92-4 percent ,air .. .. 440C.

8-9percent, m ethane,91-1percent ,air .. .. 82 0sC.' 29 1 percent , hydrogen,70(1percent .air. . .. 670C.An increasein the gas concentrat ion tendstolowertheignitiontem-perature.

Compressions in a cylinder (at room temperature) by meansof a pistonflooded with castoroil,appearto give consistent results.Incidentally, theinfluence of particlesof cotton woolin themixturewasexamined anil their presence wasfound to result in a substantial loweringof theignition tem peratu re. This is possibly of some significance in con-nection with investigations relating to explosions in mines.PER FOR MANC E OF A C OMPR ESSION IGNITION UN IT W ITH

R E D U C E D I N T A K E AND E X H A U S T P R E S S U R E S . By P HStokes,B.Sc. Presentedby theDirectorofScientific Researc h.Air Ministry. R. & M. No. 1328. (E. 38.) (20pagesand21 diagram s.) December, 1929. Price Is. 6d. net.

Tests were carried out on the K.A.E.20.T. compression ign ition u nit inorder to determine the rate of fall off in power with reduced intakeandexhaust pressures,therateof increaseof power with boostand thechangein power andthe rm al efficiency w ith chan ge ofexcess air atreducedlpres-sures.W hen the maxim um c ylinder pressure was maintained by increasingthe injection advance at reduced pressures, the indicated horse-powerdecreased in direct p roportion to thedecrease in absolute pressure, whenmaintaining30 percent, excessair. Thefuel consumptionperB.H.P.-hoursiremained constant, while on an I .H.P. bas is it decreased slightly withdecrease in pressure. Mechanical losses decreased w ith decrease in intakeand exhaust pressure owingto thereduced pump ing andfrictlonal losses.When a fixed fuel injection timing wasemployed, themaximum cyl inderpressure dropped from 800 to 450lb./sq. in., as the absolute intakeandexhaust pressurewasdecreased from 28 to 20 in. Hg. Over this pressurerange there was an addi t ional8-5 per cent, decrease in B.H.P., comparedwith theconsta nt m aximum cylinder pressure tests.The rateof decrease of fuel consum ption w ith theincrease in excessaircoefficient wasfoundto bemore rapidat thelower ab solute pressures. The

amountoffuel injection adv ance nece ssaryto maintain constant maximumcylinder pressure atreduced loads increased more rapidly as the airdensitydecreases, thus an unsupereharged compression ienition engine at al t i tudewould require a wider range of fuel injection advance than wagapparentfrom ground level conditions. Thetests with va rying excessair coefficientand constant fuel injection timing, when compared with thepreceding tests,demonstratedtheadvantages, especiallyinfuel econom y,to beobtainedbyadvancing thet imeof fuel injec tion.When increasing the intake pressure above th at of the exhaus t , theincrease inpowerwas 37 percent , for a 40 per cent, increase in intakipressure, maintaining 30 per cent, excessair.C OMPAR ATIVE HANDLING TESTS OF T H R E E B R I S T O L

F I G H T E R A I R C R A F T W I T H D I F F E R E N T T Y P E S OF SLOTS. ByFlight-Lieut. C. E. Maitland, D.F.C.,andFlight-Lieut.J. H.C. Wake. Communicated by the Director of ScientificResearch, Air Ministry. R. & M. No. 1332. (Ae. 464).(8 pagesand 9diagrams.) October,1929. Price9d. net.Comparative handling trials were required on three typesof slot, namely

Coupled control slot, auto control slot, andcoupled pilot slots. Accord-ingly, tests were carried out in normal and in stalled flight, and the effectof the three types of control on recovery from prolonged spins wasalsoinvestigated.The centresof gravi tyof theaircraft for mostof thetests were14-4 in.behindtheleading edgesof thelower main planes, tha t isapproximatelyonthe. aft Air Ministry limit.The general conclusion is t h a t the coupled control slot is consideredtobe the better device all round, except perhaps for checking a prolongedspin. PHOTOGR APHIC R EC OR DS OF F L O W IN THE B OUNDAR YLAYER. BVL. F. G.Simmons, M.A.,A.R.C.Sc, and N. S.Dewey, M.A. R. & M. No. 1335. (Ae. 466.) (9pagesand13 diagrams.) May, 1930. Price Is. net.The experiments here described form acont inuat ionof theearlier investi-gationof R. *. M.3334, underta ken withtheobjectof developing method-of photographing airflow in theboundary layer .

Various meansforindicating airflow were exam ined, includingthevapourof volatile liquids, smoke formed through chemical combination of twndifferent vapours,and smoke produced by thechemical actionof a vapourinthepresenceof mois tair. Tocomparethemeri tsof theoptical systemof E.&M. 1334 and the Schlier.m method, a seriesof photographsofturbulent f low were taken with thedifferent indicators used to revealthestructu re. Some atte mp ts were also made to devise a simple methodforindicating theregionofturbulencein theboundary,buttheselea tonegativeresults.The investigation clearly demonstrated thesuperiority of t i tanium tetra-chloride over otner methods as a means for revealing airflow. A typicalse t of photographs of turbulent f low taken over a range of wind speed-u p to 50ft. .pe r second isappendedto therepor t .

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