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Aviation History
1926
1926 - 0940.PDF
DECEMBER 9, 1926 A.D.C. AIRCRAFT Ltd. TWO SUCCESSFUL AERO ENGINES FORMED originally shortly after the Armistice—and knownthen as the Aircraft Disposal Co.—for the purpose of handling the very large stocks of Government surplus aircraft,aero engines, and accessories, A.D.C. Aircraft have now joined the ranks of British aero engine constructors. Theirfirst effort in this direction was the 120-140 h.p. " Airdisco," an 8-cylinder V air-cooled engine which, fitted in such machinesas the Avro type 504 and D.H. 51 has given very satisfactory results. Two other engines were then produced by A.D.C. Aircraft,which have obtained a very satisfactory position in the ranks of British aero engines—the A.D.C. " Cirrus " and the A.D.C." Nimbus," some brief particulars of which follow :— THE A.D.C. "CIRRUS." The A.D.C. " Cirrus " aero engine—of which there are twomodels, the Mark I and the Mark II—was designed to meet the requirements of the Light Aeroplane Constructor for areliable power unit of low horse power at a moderate price. From the view of the private owner, it was essential thatthe engine should be free from complicated mechanism, and should be easily accessible for adjustments. No undue sacrifice has been made to obtain extreme light-ness, and to achieve the desired result it was necessary to adopt a progressive and original design, differing from thelight engines already available, and this necessitated con- siderable experiment and research. As a result, the " Cirrus " engine was produced, and shortlyafterwards successfully passed the Air Ministry 100 hours Type Test—incidentally being the first British low-poweredaero engine to achieve this distinction. In its simplicity the engine ranks with the average motor-car engine, and no specialised knowledge of aero engines is necessary to operate or maintain same. It is a 4-cyl. in line air-cooled engine, with a bore of 105 mm.(Mark I) or 110 mm. (Mark II) and a stroke of 130 mm., the Mark I developing 60 h.p. (normal) at 1800 r.p m. and theMark II 75 h.p. at same r.p.m. ; the maximum horse power, at 2,000 r.p.m., is in each case 65 h.p. and 80 h.p. respectively.Constructionally, the Mark I and Mark II engines differ only in details, so that the following remarks apply to both. Thecylinders are of cast iron, with detachable heads of aluminium alloy carrying overhead valves. The latter are operatedthrough rockers by push rods, the rockers being supported by brackets cast on the cylinder heads. The valve springs areof the double helical type and are interchangeable. The pistons are of aluminium alloy, fitted with two (Mark I) orthree (Mark II) cast-iron rings. The hardened steel gudgeon pin is a floating fit on the piston, and is fixed in the connectingrod by a special stud and nut or circlip. The connecting rods are of H section, Duralumin stampingsin the case of the Mark II, with the big end bearing of white metal in a bronze shell. The crankshaft is carried in fivebearings, which differ in the two models as follows :—In Mark I, three inner bearings of white metal in bronze shells,and front and rear bearings of the ball type ; in Mark II these latter bearings are of the roller type. The upperportion of the crank case contains the three central crankshaft bearings, the top half of the end bearing housings, and alsothe camshaft. The lower portion forms the oil sump and carries the oil pump relief valve and oil strainer, and alsoforms the lower half of the ball bearing housings. The camshaft is supported on three plain phosphor-bronzebearings. All cams and bearings on this shaft are case hardened. A spiral gear on the camshaft drives the oil pump. The latter is arranged at the lowest part of the crankcase,so that it is always primed with oil. This pump forces the oil through the gauze filter and thence through oil ways to con-necting holes opposite each main bearing, the oil being thus forced under pressure directly to each of these. The standard engine is provided with 2-4 cylinder B.T.H.magnetos, one being fitted with an impulse starter. Each magneto operates a separate set of plugs, thus providing twoindependent ignition systems. THE A.D.C. "NIMBUS" ;This engine, which has passed its Air Ministry Type Tests, was developed, or evolved, from the well-known Siddeley,"Puma" engine, of which engine A.D.C. Aircraft, Ltd., holds large stocks, with spare parts. It is, however, to allintents and purposes really quite a different engine, develop- ing a higher power, although it is designed to fit standard" Puma " bearers and several of the original " Puma " parts, where opportunity presented itself, have been incorporatedin its construction. Nevertheless, it is still of the " Puma " family, especially as its designer, Major Halford, was one ofthose responsible for the design of the " B.H.P." engine, the forerunner of the " Puma." Its construction, however, differs considerably from the" Puma"; the "Nimbus" is a 6-cylinder inline water- cooled engine, with steel cylinders screwed into the bottomof the water-jacket blocks, and secured at the top to the aluminium alloy cylinder head blocks by the valve seatingswhich are screwed into the head-blocks. The water-jackets are formed by two aluminium castings, each block enclosingthree cylinders and being secured to its respective cylinder head block by a number of bolts. Each cylinder has one inlet and two exhaust valves, operatedby an overhead camshaft—directly in the case of the exhaust and through short rockers for the inlet valves In fact, thevalve gear is much the same as in the " Puma." An entirely new and considerably strengthened crankshaft is,however, fitted in the "Nimbus," whilst aluminium alloy pistons of special design are employed, which, althoughof larger bore, are lighter than the original. Finally, it may be added, that the outstanding features of the " Nimbus "are :—Lightest engine per h.p. of its type ; exceptionally low petrol consumption ; installation interchangeable with" Puma " ; small frontal area. Specification.—Bore, 152 mm. ; stroke, 190 mm. ; com-pression ratio, 5-4:1 normal r.p.m., 1,450; maximum r.p.m., 1,600; normal b.h.p. (at 1,450), 305 ; maximumb.h.p. (at 1,600), 335; petrol consumption, at 305 h.p., 0-58 pts. per/h.p./hr. ; oil consumption, 0-017 pts. per/h.p./hr. ; weight, dry, in running order (less radiator and water), 670 lb. ; weight per h.p. (as above), 2 1b. (approx.). The A.D.C. "Cirrus." The A.D.C. " Nimbus.' 8105
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