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Aviation History
1945
1945 - 1304.PDF
JULY 5TH, 1945 FLIGHT Survey of Britain's Most Powerful Radial Engine : An Example of . r l^OgiCal Layout to Achieve Compactness with Power T has been eommbn knowledge far some time past that the Bristol Aeroplane Co., Ltd., have been engaged with the production of a larger and improved model in the age of radial, air-cooled, sleeve-valve engines with which ey have for so long enhanced their reputation. This mmon knowledge—the result of unofficial "leaks"— ibraced the facts that the new engine was an 18-cylinder lit of over 2,000 h.p. and was called the Centaurug.. ther than this nothing much was generally known until nctioned reference, to the engine was made with the lease of the Short Shetland flying boat (Flight, May 17th, 145), when it was revealed that the Centaurus was of 'er 2,500 h.p. Even now we are not permitted to give any indication the power output other than at it is well in excess of 500 h.p., so that, in assessing it'cific qualities' relating >wer, one can ily use the ;ure of 2,500 as 'datum and ite that the uated result is mewhat lower an the factual due. Probably the ost impressive ature to strike e casual ob- rver of the mtaurus is the mpactness of e unit in rela- )n to its power itput, and, as a irollary, the achieve- ent of a clean and efn- ent fairing by refine-. ent of design. It is, course, obvious that miponent in the engine is the suit of months, in some cases ;ars, of development, and that c only means by which such WOLIC- anship can bear fruit is by way of ie hard road of technical ability fol- wed strongly by the incessant trial" id error of testing. By such means a tremendous fund E data is amassed, such data being the "history" only uough which the future may be discerned. Looking ack in order to look forward applies equally in the tech- ical as in the ordinary world. . • • » Specific Powers From the aspect of arrangement analysis the Centaurus basically similar to its immediate forerunner, the Her- jles, with the chief differences that it has four more flinders and that entirely separate individual gear trains re embodied front arid rear for driving the sleeves in the -spective cylinder* banks. Swept volume is naturally irger, but so is the unit swept volume as, although the ylinder bores remain the same at 5.75m., the stroke of the entaurus is 7.0m. as compared with the 6.5m. of the lercules. This gives the new engine a capacity of 53.6 tres (3,270 cu. in.) in contrast to the Hercules' 38.7 litres 2.360 cu. in.), an increment of 38.5 per cent. In terms of apacity and power output, at the restricted Centaurus every Compactness without complication. Note the backswept exhaust stack cooling muffs and the collected exhaust tail pipes. •power figure of 3,500, the b.h.p. /litre of both Hercules Centaurus is 46.5, although we know that the latter engine is somewhat better than this, as may be rough!y indicated by the figures for b.h.p./sq. in. of piston area, these being respectively:. Hercules 4.93. and Centaurus better than 5.34. • f : Cooling Arrangements As an indication of refinement in the design of the cowl- ing, if. we take as a datum the frontal area of the Hercules at 2,122 sq. in. and give it the value of unity, then the Centaurus frontal area of 2,402 sq. in. gives a comparative ratio of 1.13:1, which is well below the relative h.p..ratio of 1.385 :1, itself a conservative figure. Put another way, this means that for an increase in power output of 38.5 per cent, over the Hercules, the Centaurus has only a 13 per cent, greater frontal area, its specific' power thus being 150.5 h.p./sq. ft. It must be appreciated that the goal of really close cowling ...- . . ,.., . -•.. is hindered in at- '."'•''/ tainment by the- very critical fac- tors of cooling, and Bristol's achievement is rendered the more deserving of praise by virtue of their having obtained, with it, an en- hanced cooling efficiency. To a - certain extent the employment of a cooling fan driven from the air- screw spinner can be deemed partially responsible for the in- crease in cooling efficiency— but by no means wholly. As the Centaurus is designed- as a power plant, the cowling, fairing and baffling arrangements naturally come into the picture in addition to the engine per se, so whilst on the sub ject of cowling we might as well deal with it before going on tc the engine' proper. The subject is well worthy of study. The main body of the engine in way of the cylinder -'banks is closely cowled by four panels, two per side, hinged together at top and bottom on the fore and aft centre plane of the engine and secured together with three toggle- type fasteners on each side. The latter are recessed to give a smooth surface line. Forward of the cowling panels is the-aerofoil-section annular nose fairing which, with the very unusual spinner extension fairing (fitted around the reduction gear casing), provides a smoothly contoured, but surprisingly small, annular intake duct in the entry of which rotates the- 18-blade cooling fan fitted to the rear of the spinner. It may thus be seen that cooling air entrained is ob- structed not at all until it reaches the front cylinders. Having done its due amount of fin circulation the air is then allowed to escape to the outside atmosphere through cooling gills in the skirt ring of the main cowling panels. In consideration of the amount of development design which has gone into producing the Centaurus, the instance
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