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Aviation History
1948
1948 - 0165.PDF
FEBRUARY 5TH, 1948 FLIGHT 141 Bristol Brevities Power for the M.R.E. ; Hercules 630 Overhaul Periods : Free-exit Cowl DEVELOPED from the Centaurus 630, already builtfor the Airspeed Ambassador, the Centaurus 663,just announced by the Bristol Company, is scheduledfor installation in the new Bristol Medium Range Empire aircraft designed for use on the B.A.O.C. routes. The new engine employs a compression ratio of 8:1 and, operating on 115/145 grade fuel, will have a specific consumption over the major portion of the cruising range in "M" gear, of below 0.4 lb/ b.h.p./hr. Notwithstanding the high compression ratio, the sea-level take- ,j^power is 2,810 b.h.p., rising to 2,985 b.h.p. at 8,500 ft. The ability to deliver maximum power at heights of this order renders the engine par- ticularly suitable for use from high- altitude airfields in the tropics— notably, of course, Nairobi, which is situated at 5,500 ft. Provision is made for a cabin blower and, including the Bristol torquemeter, the unit weighs 3,170 lb. The maxi- mum continuous power output is 2,405 b.h.p. at 7,750 ft. in "M" gear and 2,280 b.h.p. at 16,000 ft in "S" gear. In lean mixture the maximum continuous power is 1,830 b.h.p. at 15,500 ft in " M "' gear, and 1,745 b.h.p. at 23,250 ft in "S" gear. , Hercules 630' f A conservative policy has been adopted by the Bristol Company in regard to the overhaul periods allowed on its Hercules engines designed specifically for the Vickers Viking and Bristol 170 types of aircraft. The 630 series engines, as they are known, are moderately rated and axe backed by long experience with the earlier types of military Her- cules ; it was, nevertheless, decided to start by dismantling the first two engines for inspection after 250 hours. So satisfactory were the results of this and subsequent in- spections that the period was progressively increased and a number of engines were run on to 500 hours, again with excellent results. In May, 1945, 500 hours was established as the standard overhaul period but since that date, in agreement with the Air Registration Board, eighteen en- gines have been run to 600 hours and inspection has shown tht this period is well within the capabilities of the 630 series. Although a 600-hour overhaul period has now been allowed, it must be recognized that much depends on the proper care and handling of the engines and approval of the new " life " is restricted to those operators who have demonstrated in practice that this is consistent with the operating conditions imposed. With a possible further ex- tension in view, certain selected engines—again with A.R.B. approval—will be run to approximately 700 hours. A life of 200 hours between spark-plug servicing has been established and experience has shown that, given satisfac- tory operating conditions, engine replacements required after 500-600 hours' service are very moderate. All the following major components were in excellent condition after 500-600 hours in Vikings and Wayfarers and needed no replacements: crankshafts, connecting rods, big-end bearings, reduction gear bevels, crankcases, cylinder barrels, complete blower assemblies and airscrew shafts. Free-Exit Cowl Another item of interest concerning Bristol engine de- vebpment is the new " free-exit" cowl. It will be appre- ciated that certain types of aircraft and their engines are, on occasions, required to fly at high power output but rela- tively low forward speed. Such conditions present some- thing of a cooling problem unless the power plant has been designed specifically for the work. The Bristol free-exit cowl has been produced specially to meet these require- ments, and mention was made of it when discussing the latest Bristol piston engines in our issue of January 8th. The special baffles and air flow system which characterize this free-exit cowl are illustrated on this page and compared BAFFLES S€RAfiATiN CYLINDER HEAD » CYLINDER BARREL COOi.f*l& AtR .NGWCCOOUNS- FREE-EXiT COWL CONTROLUWtE GUI- TYPE COWL Comparative diagrams of the free-exit type (left and controllable gill cowls. Approximately one seventh of the total airflow is by-passed over the cylinder heads in the free-exit design. with the standard type of cowling. It will be noticed that there are two annular outlets and that neither is fitted with controllable gills. (As a result of a typographical error it was previously stated that "gills are fitted.") Through the forward outlet is discharged about one-seventh of the total cooling air flow, which has been by-passed directly over the cylinder heads. The remainder of the cooling air emerges from the fixed annulus further aft. Thus a rela- tively large exit area and low static pressure at the exit are permitted without causing high drag. A1 INDIAN INTERNAL SERVICESIR INDIA, LIMITED, have ordered two Vikings, whichwill make a total of eight aircraft of that type for opera- tion on their non-stop services radiating from Bombay to Calcutta, Delhi and Karachi. Dakotas are used on the routes Bombay-Ahmedabad-Karachi, Bombay-Ahmedabad- Jaipur-Delhi, and Bombay-Madras-Colombo. The latest southern service now includes Coimbatore, and on this route— Madras-Bangalore-Coimbatore-Cochin-Trivandrum—six flights a week are made. PLEASURES IN STORE AUSTERE as the year threatens to prove, there is someexcuse for anticipatory pleasure in a glance at the aero- nautical calendar. True, realization will be denied to manyenthusiasts by the "basic" ban, but, on the other hand, the joys of Continental visits may be multiplied by the re-valua-tion of the franc, though we could have wished for some less grave reason for "this advantage. There is warmth merely in noting than the Cannes Inter-national Rally is billed for May 17th; that the Shannon, Netherlands and Wolverhampton Aero Clubs will be "athome" respectively on May 22nd-2_3rd, May 29th-3oth, and June 12th; and that June igth-2ist is set aside for the RoyalAero Club Week-end for Foreign Guests. Gliding enthusiasts will make their various ways to Switzerland for the Inter-national Gliding Competitions beginning on July nth, and the British venue for aeromodellers will be Eaton Bray (July 31st-Angust 8th). Under the patronge of the Aero Club de France the "Tour" will start on August 27th and continueuntil September 5th, thus, it must be noted, clashing with the Cinque Ports International Flying Meeting at Lympne onAugust 28th and 29th. It is good to note that a whole series of Butlin Rallies—at Filey, Pwllheli and Skegness—promise further to relieve the drabness of the year.
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