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Aviation History
1941
1941 - 1015.PDF
MAY IST, 1941. 313 FRIEND OR FOE ? (Continued) forward as to set the wings almost amidships, has an angular transparent '' chin'' with a power-driven gun- _turret immediately above. The tailplane is approximately rectangular and the rear gun-turret projects well clear of the large strut-braced fins and rudders. So far as the spotter is concerned, the appearance of any three-engined machine should send his finger straight to the alarm button, for only Germany and Italy have any such aircraft in service to-day. It seems unlikely that the slow speed and limited ceiling of the Ju 52 would enable it to penetrate very far inland unless under cloud cover, but if seen in plan its wings will be observed to taper sharply on both edges to small square tips and to be fitted with slotted ^jailerons and flaps. As the two outboard radial engines are fitted squarely on the tapering leading edge, they " toe out" from the axis of the engine on the nose. The fuselage is typical of the airliner of several years ago with its straight sides and line of square cabin window^. The strut-braced tailplane has a straight taper to its leading edge its balanced elevators projecting at the tips, and the angularityof the fin and rudder is relieved from complete squareness by a slope on the leading edge. The fixed undercarriage isattached below the centre-section (the short engine nacelles being almost entirely above the wings), and althoughwheel spats were originally fitted, photographs of Ju 52s operating during the present war show them to be devoidof this little refinement. The retractable " dustbin " under turret, which was fitted when the machine was used as abomber, is no longer present, but the open gun-position above the fuselage, midway between trailing-edge and tail-plane, is still retained to give some measure of defensive* action. The metal covering to wings and fuselage is ofcorrugated alloy sheet. Next week : Saunders-Roe Lerwich and Dornier Do. 24. THE LIQUID-COOLED ENGINE A Reply to John Lpe^Tfhe Merits of the*p-cyl. Multibank By JOHN W. MORRISON MR. JOHN LEE'S paper, " Air-cd^ed v. Liquid-cooled Aircraft," in Flight of Marclhas been well presented and very carefully thought' out, but I find it unconvincing and, in certain respects,grossly misleading. One can prove anything with figures ; one can likewise disprove anything. America has made tremendous strides in the designorientation of the air-cooled radial engine both in the direc- tion of increased power and the reduction of drag. ThePratt and Whitney " DoutJfe-Wasp" engine, with its take- off power rating of 2,000 b.h.p. lor a volume of 45957 litresand a diameter of 52m., jg<an outstanding example of the progress that has been made. Not so very long ago, thepossibility of exceeding 400 m.p.h. with an air-cooled radial- engined aircraft seemed remote ; now, the new Pratt andWhitney engined Vought-Sikorsky fighter is claimed to be the fastest of all American aircraft with a speed appre-ciably in excess of 420 m.p.h. Even Germany has not altogether abandoned the air-cooled radial The B.M.W. Flugmotorenbau have been manufacturing Pratt and Whitney engines under licence fora number of years, and, apparently, a German.version of the " Double Wasp " is being installed in one of/Germany'snew fighters. The fact iemains, however, that the vast majority of the German air force is supplied with liquid-cooled engines. In so far as we in Britain are concerned, even the largest 2-row 18-cylinder radial engine cannotj&ope to compete with oui new liquid-cooled in-line engines in power output, speed and all-round efficiency. In design-ing new engines, oui principal concern must inevitably be the potential power of the new 24-cylinder in-liae Germanengines. Thus far, Jerry has contented himself with com- paratively Jow power per litre from his engines, relying dna large swept volume to provide the necessary outodt. The maximum engine speed has been 2,300 to 2,400 r.p.m., andthis low speed has been ascribed to the petrol injection system that sets a limit to the r.p.m. However, with avolume per cylinder approaching 3 litres, there has been plenty of scope for higher output, and the most recentDaimler-Benz engine is apparently rated at 1,500 to 1,700 b.h.p. The potential output of the new German engines havinga swept volume of up to 70 litres will be 3,000 to 3<4PO b.h.p. This output is 50 per cent, greater than ihatpfthe radial. Even should Germany have aban-ISned the standard bore dimension of 150 mm. for a smaller one, it is hardly likely that the 18-cylinder radial willproduce any more power. The B.M.W. 116 inverted V-12 water-cooled advanced trainer engine with a bore andstroke of 130 mm., may form the basis of an X or H-24 cylinder engine of 41.41 litres with an output of up to2,000 b.h.p. at 20,000ft. Below is given a 2,000-h.p, engine study: — Type and Cooling A. 2-ro\v raci. air B. 4-row rad. air C. X in-line air D. H in-line liquid E. X in-line liquid F. VV in-line liquid Number o> cyls. 18 ao Bore and stroke orxoj"5rx«r arxir r>i" xir 5J"X 59* 51"X4?* Volume! litres) 5o.-r> 53.111 4:',.0fl •1(1.14 4JJ.GO 41.50 Crank- shaft length 22" M\" V.<\" (2) 4llf 5.11" Power/litre and sq. in. p.a. :s:s.u & n.T'.i :!?.« \ .!.K"> 4.",.!l & 4.(14 411.4 it 11.8.1 41.!! & 4.04 IH.'> & :i.K5 In the above study, all the engines are assumed to IK;capable of delivering 2,000 b.h.p. at high altitude, the precise height being dependent on the type of supercharger.With an exhaust-driven turbo-blower the power would be available at 26,000ft., and with 2-stage blowers from 20,000to 22 oooft. The power available for take-off is set at 2,300 b.h.p., which is slightly in excess of that of the most power-ful 2-row radial. To avoid any misleading tendency, power per litre and per square inch of piston area are includedside by side. The figures have been compiled from a search- ing analysis of all high-duty engines, the particulars ofwhich have been released within recent years. In those instances where cylinder dimensions are the same as forengines that have been released, the dimensions are con- sidered the best possible when everything is taken intoconsideration. Mr. Fedden dealt very briefly with the 20-cylinder multi-bank engine some years ago. The projected Bristol engine -—an illustration appeared in Flight—had o.h. camshaftsand it was dismissed on the score of weight. Personally, I never could see why this should be so when comparedwith the 2-row radials. In so far as sleeve valves are con- cerned, I submit the 20-cylinder engine is incomparablymore attractive than the 2-row 18 and lighter than the X-24. The position of the ports in a sleeve-valve engine is
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