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Aviation History
1948
1948 - 0038.PDF
FLIGHT JANUARY 8TH, 1948 Latest Bristol Piston Engines Some Details of the Civil Hercules and Centaurus Series : High Take-off Power and Low Consumption THERE is little doubt that even those who predictedseveral more years' use for the large piston engineinstalled in commercial aircraft did not anticipate all the delays and setbacks which have been experienced by the manufacturers of large airframes and the gas turbine power units for them. The fact now is that intensive development of piston engines is still going on and speci- fications for large passenger aircraft to fly in 1950 and later still call for piston engines. Two of this country's most important piston engines are the Bristol Hercules and Centaurus, and more details of the latest marks of these units have recently become available. It is often stated that conditions of operation are such that civil power plants must now be designed for their purpose from the start, and that it is no longer possible successfully to adapt military units. To some extent this is true, but the operative word is adapt. If this is taken to mean a substantial redesign of certain components to meet the different requirements of civil operation, there is no reason why the previous experience in military aircraft with other components of the unit should not be of great value. Both Hercules and Centaurus engines were origin- ally designed for military purposes, but trie Hercules, and to a limited extent the Centaurus, have proved that they can be operated successfully in freight and paj6enger transports. Multiplicity of type numbers still tends to appear confus- ing at first sight, but the differences in Hercules mark numbers, with a series, for instance between 730 and 759, refer only to the type of airscrew, type of mounting, type of cowling and, in the case of odd or even numbers, whether or not torquemeters are fitted. Reference was made in Flight of April ioth last to these numbers and to the addition of 500 to the mark of a military unit when adapted for civil use. Hercules 730 and 750 Series The latest civil 14-cylinder, air-cooled Hercules engines the 730 and 750 series, differ from the immediately previous 630 in having several components redesigned to permit an increase in take-off powei. The engines are .intended primarily for medium-altitude operation and, likie the 630, have single-speed superchargers. The redesign is chiefly^, concerned with stiffening-up of the power section of the ? engines, but in view ol the higher b.m.e.p. us£(f /#r take-off, cooling problems also had to be faced. The com- pany's new composite copper-based cylinder heads have proved to dissipate heat much better than the. previous aluminium heads. The alterations to meet the increased power output have not affected the reliability or the over- ENGINE AND POWER PLANT WEIGHTS (Without Airscrew) Hercules 730,734 engine ... 2,0601b 732, 738 engine 2,0701b Torquemeter 351b Baffles, screens and exhaust system ... ... ... ... l75/l80lb 730 series power plant with wing entry intake 2,9501b 730 series power plant with external intake scoop ... ... 2,9301b 730 series power plant with external intake scoops and free- exit cowling ... ... ... ... ... ... ... 2,8651b 762 series engine 2,2651b 762 series power plant with wing entry intake 3,1951b 762 series power plant with external intake scoops ... ... 3,3151b 760 series power plant with free-exit cowling 3,1601b Centaurus 630 engine 2,9801b Torquemeter 551b Baffles, screens and exhaust system 2201b Typical Centaurus 631 power plant 4,4041b DETAILS OF EQUIPMENT DISTINGUISHING TYPES INDIVIDUAL Hercules Mark Equipment 730, 750 4-point engine mountings 732, 752 6-point engine mountings 734, 754 Free-exit cowl, 4-point mountings. 738, 758 Free-exit cowl, 6-point mountings 760 6-point mountings, 100/130 grade fuel 762 6-point mountings, 115,150 grade fuel 750s and 760s have provision for reversible-pitch airscrews, 730s have not. Addition of I to make odd numbers of above indicates fitting of a torque meter. haul period of the engines, which normally operate at between 40 and 50 per cent of the take-off output. More- over, under economical conditions a fuel consumption of 0.415 lb/b.h.p./hr has been achieved. The 730 and 750 series units and also the 760s, which are referred to below, are normally sup- plied as complete power plants of which there are alternative ver- sions according to airframe re- quirements. For aircraft with high cruising speeds air-intakes in the wing leading edge would normally be used, but in cases where this is not permitted, because of the wing structure, external scoops can be provided on the power TAKE -OFF (5 MIN. LIMIT) MAX. EMERGENCY MAX. CONTINUOUS MAX. CONT. W.M. d 1,000 Performance curves for Hercules 730 and 750 series. 10 15 JO ALTITUDE FT.x 1OOO plant cowling. For aircraft which may re- quire a high power output from the engines for relatively , low v forward speeds a third power plant known as thep free-tptit-cowl type can be provided. In this, controllable air outlet gills are fitted and the air which cools the cylinder heads, about one-seventh of the total flow, is discharged through a short, unobstructed annular passage separately TAKE-OFF POWER (aoOO B.H.P.):-O74/O 8 (RICH MIXTURE MAX.CONT. POWER (tfOS B.H.P.): (RICH MIXT SOO 6OO 7OO 8OO 9OO 1.00O 1.1OO WOO VOO f-uel consumption curves for Bristol Hercu.'es 710 and 750 series. from the main stream. Thus, without causing excessive drag a relatively large exhaust area and low static pressure at the exit is achieved. All three power plants incorporate a shutter arrange- ment which enables the pilot to select either cold air, cold filtered air, or hot air, and provision is made for auto- matic opening of the warm-air shutter should the cold intake ice up rapidly. In keeping with modern practice, all main
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