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Aviation History
1928
1928 - 0425.PDF
MAY 24, 1928 THE BRISTOL " JUPITER" FAMILY (I) Leading Particulars of Seven Standard Types IT IS an old saying that imitation is the sincerest form offlattery. In the aero engine world, the modern form of imita- tion, fortunately, often takes the form of building underlicence, and on this basis probably no aero engine in the world has been the subject of a greater amount of sincere flatterythan the Bristol " Jupiter," which is being, or about to be, manufactured under licence in a great number of foreigncountries. Thus, at the present moment, the " Jupiter " is being manufactured in no less than eleven different countries.This fact speaks for itself. Moreover, the " Jupiter " is in use in the military and naval services of more than 20 Euro-pean countries, while an ever-increasing number of engines are being employed in commercial aviation, the recent typeswhich have been added to the " Jupiter " family having been produced largely with the requirements of civil aviation inview. The popularity of the Bristol " Jupiter " engine being by now well established, we have thought it would interest our readers, both at home and abroad, to have a fuller account than has hitherto been possible of the number of types now available, the details of their design and construction ex- plained and illustrated. We have, therefore, made special arrangements with the Bristol company in the matter of plac- ing at the disposal of FLIGHT much detailed information which has not yet been published, so that our readers will be the better able to understand the reasons which have contributed to the favour with which.the " Jupiter " engine is regarded at home and abroad. One feature of the engine, of vast importance in itself, which no amount of description or illustration can adequately convey, is the exquisite work- manship put into these engines by the Bristol Company. A tour of inspection of the new engine works at Filton, such as we were privileged to make recently, leaves one amazed. Firstly, that it should be possible, and secondly, that it should be commercially practicable. We have not the space here to go into details concerning the manufacturing side, but perhaps some little idea of the degree of care bestowed upon the manufacture of the Bristol " Jupiter " engines can be formed when we point out that already a large percentage of the components from which the engine is made are machined all over. At the moment this applies to the crankcase, for instance. It is likely to be extended to even more compli- cated parts, such as cylinder heads. But the point to keep in mind is that nothing but the best is regarded at Filton as being good enough. It might be argued that such refinement is not really neces- sary. Mr. Feddon has a good reply to this. His argument is that, if under peace time conditions something better than merely good enough is produced, then in case of emer- gency, when mass production must inevitably reduce quality to some extent, the engine will still be thoroughly sound and reliable. It might be thought that such meticulous care as is taken in the manufacture of the " Jupiter " must resultin a very high price. Actually this does not appear to be the case. Probably this is due, in no small measure, to thegenius of Mr. Wriitehead, who presides over the engine works, and who appears to have solved the problem ofcombining laboratory workmanship with quantity production. One can see directions in which some of the extra cost ofmachining operation may be regained in a saving in scrap and waste of castings, etc., but even so, the layman is puzzledto reconcile such perfection of workmanship and finish with a reasonable commercial price. Probably the truth is onewhich Mr. J D. North is fond of expressing somewhat as follows : " When a critic complains that a thing is expensiveto make, it usually merely means that he does not know hovr to make it." However, to return to the family of "Jupiters" nowavailable, since the beginning of the present year the Bristol company has standardised seven distinct types of engine,of which three are of the direct drive " Jupiter VI " series, known as the VI.A (compression ratio 6-3 : 1), the VI A.M.(compression ratio 5-3: 1), and the VI A.L. (compression ratio 5:1). One is a standard service engine with gear-drivensupercharger, and is known as the Series VII. The remaining three are geared engines fitted with the 2 : 1 Farman reductiongear for which the Bristol company has secured the British rights, and are designated as Series VIII, IX and XI, respec-tively, according to compression ratio. The VIII is a stan- dard service engine, with a compression ratio of 5-8:1.The IX is a general purpose engine, with a compression ratio of 5-3 : 1, and the XI is the commercial version, with a com-pression ratio of 5 : 1. In the same way, the Series VI consists of a high-compres-sion type, standard service engine, the VI.A., the VI.A.M. general purpose engine, and the VI A.L. commercial engine. The main particulars of each type are given in the tablebelow. It is not intended here to go into details concerning thedesign and construction of the " Jupiters," but a few remarks may be of assistance in forming an opinion as to the mainfeatures of the different types. To begin with, the " Jupiter " VIA, is the famous VI with certain detail improvements.For instance, the cylinders and pistons have been improved, the former having additional cooling fins, triple valve springsand ball-bearing rocker gear. These improvements have been included in the whole series, making them interchange-able as regards cylinder components. As already stated, the difference between the Series VI A and the VI A.M. andVI A.L. is one of compression ratio only. The Series VII " Jupiter " is interesting on account of thefact that it is fitted with a gear-driven supercharger designed to maintain ground-level power up to 12,000 ft. The gearingand drive for this blower has been the subject of very careful Leading Particulars of Bristol " Jupiter " Engines Engine, Series Bore, inchesStroke, ,, Swept vol., cub. in. ,, litres Compression ratio Normal engine r.p.m. Gear ratioPropeller id f Normal r.p.m. of prop.§ J Normal h.p. g I Max. r.p.m. of prop. O I Maximum h.t). T3X) "S -^ -<«2 < ' Altitude, ft Normal r.p.m. of prop... Normal h.p.XT Max. r.p.m. of prop.Maximum h.t). . . Icrnition . .... Oil pressure lb./sq. in . . Oil return, normal r.p.m., gals./hr. . . Tachometer drive, fraction of engine speedStandard weight, bare lbs. Engine control .. VI A. 5-75 7-501,752 28-7226-3:1 1,700 Nil L.H.T.1,700 415 '.. 5,000 1,700 415 1,870 460Fixed 40 45 i720 Gate Throttle * Gate throttle VI A.M. 5-75 7-501,752 28-7225-3 : 1 1,700 Nil L.H.T.1,700 440 1,870 480 Ground — —— —Fixed 40 45 i720 Standard boost gauge 389 VI A.L. 5-757-50 1,752 28-7225 0: 1 1,700 Nil L.H.T.1,7001 420 1 1,870 f 460 J Ground — — — —Fixed 40 45 \ 720 Standard VII 5-757-50 1,752 28-722 5-3 : 1 1,775Nil L.H.T. See fPower < Curve 12,000 1,775 420 1,950 —Fixed 40 40 i760 * VIII 5-757-50 1,752 28-7225-8 : 1 2,000 2 : 1L.H.T. 1,000 450 3,000 1,000 4551,100 490Fixed 60 65 J880 Gate Throttle IX 5-757-50 1,752 28-7225-3 : 1 2,000 2 : 1L.H.T. 1,000485 1,100 525 Ground — — — —Fixed 60 65 \ 880 Standard XI 5-757-50 1,752 28•722 5-0 : 1 2,0002 : 1 L.H.T.1,000 460 1,100 500 Ground — — — —Fixed 60 65 88C Standard
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