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Aviation History
1949
1949 - 1804.PDF
568 FLIGHT, 27 October 1949 THE RELIABLE HERCULES Overhaul Period of 630 Series Engine Further Extended SINCE the days of its first extensive application in militaryaircraft, such as the outstanding Beaufighter, the BristolHercules has proved itself to be one of the most reliable and popular units in the piston-engine category, and the newsof A.R.B. approval for still further extension of the overhaul life of the 630 series to 900 hours represents yet another stepin the long career of a highly successful power unit. The Her- cules 630 series, based on the original Hercules 100 engine, isa version designed exclusively for civil use. Some 57,000 of the 100 series •units were manufactured for <use«in „military air-craft during the war. Under the stimulus of wartime development and withbackground provided by such an enormous total of engine running hours, the power output and overhaul periods of themilitary Hercules had shown very rapid increases, and the 100 series was already producing 1,800 h.p., compared withthe 1,325 h.p. of the original mark, when the time came for thoughts to be turned to development of a version for civiluse. The first, the 630 series, designed for ope'ration at medium altitudes and consequently fitted with only a single-speed super-charger, was type-tested in May, 1945, and produced 1,690 h.p. fitted with flight-type exhaust system (after boost pressure hadbeen raised 1 lb/sq in to compensate for exhaust installation losses). The next civil design to appear—in keeping with moderntrends towards increased take-off power—was the Hercules 730 series, incorporating such improvements as the copper-based cylinder head to provide the increased cooling necessi- tated- by higher power output. Although take-off powerof the "730" was originally 1,860 h.p., the output was steadily increased by modifications and improvements untilthe present-day figure of 2,040 h.p. with exhaust system was attained. This is no mean achievement for an engine with aswept volume of 38.7 litres. In order to provide adequate power for the high-altitudeoperation of pressurized airliners, the development of the 760 series, fitted with two-speed superchargers and an additional150 h.p. drive for cabin blowers and large generators, was the next step. The latest variation, the 763 series, now installedin the Hermes IV, gives 2,100 h.p. for take-off. Increases in power output were not the full extent of Hercules develop-ment : in fact, they were eclipsed by the rate at which the over- haul life of the '' 630 '' was improved in the short span of three 1,000 OVERHAUL LIFE APPROVED BY A.R.B. 00 JUN. SEP. DEC. MAR. JUN. SER DEC MAR. JUN. -SEE DEC. MAR. JUIM. SEf? DEC 1946 t947 1948 1949 This graph emphasizes the steady rats of increase in over- haul life of the Bristol Hercules £30 series engines. years from 250 hours for the initial installation in the Viking aircraft to the 900-hour lile approved on October 14th, 1949. First of the engines to reach 900 hours was a Hercules 634installed in a Viking operated by Airwork, Ltd., which since manufacture had completed a total of 2,025 hours' running.The rapid manner in which overhaul life has been extended is emphasized by the fact that previous overhauls of thisengine had been carried out at 500 and 1,222 hours respec- tively, the third period of its life being 50 per cent longerthan the second. The accompanying graph shows the rate of increase in theoverhaul life of the 630 series. An indication of the high proportion of hours actually achieved is the fact that outof a total of 124,150 permissible hours, four leading airlines have achieved an average of 92.2 per cent of those hours inactual running time. This is particularly notable when it is considered that this average includes all engine changes, someof which were made somewhat ahead of time as a matter of convenience to the individual operators. A trial batch of engines is now being run to 1,000 hours,and the makers have little doubt that approval will soon b6 obtained for this period. LOOKING BACK Dr. A. P. Thurston Recalls Memories of Maxim SOME interesting reminiscences of the early days of aviationwere given by Dr. A. P. Thurston," M.B.E., D.Sc.,M.I.Mech.E., F.E.Ae.S., in his presidential address to the Newcomen Society, delivered at the Science Museum,South Kensington, on October 12th. In 1903 Dr. Thurston became chief assistant and designer toSir Hiram Maxim, who at about that time had conceived the idea of making the public "air-minded" (and, incidentally,of making them pay for the privilege) by means of rides in his "captive flying machines," one of which was erected inthe grounds of the Crystal Palace, to be a popular attraction for many years. As older readers of Flight will recall, thislarge and impressive structure consisted of a series of long radial arms resembling umbrella ribs, braced to a central steam-driven shaft; from the extremities of the arms were hung cars equipped with wings and other aircraft features.. Dr. Thurston, who designed several of these devices forMaxim, recalled that when the first was erected and had been tested with sandbag ballast the engineer-in-charge invited theyoung designer to make a "test flight." "Speed was in- creased/' recalled Dr. Thurston, "until centrifugal force wasO.87 g. After a mighty mental struggle I fell unconscious to the botfom of the car. Fortunately I had with me in themachine a workman who was in a more advantageous position, and he was able to give the signal to stop. I recovered con-sciousness at about 3 g. and was able to walk when we stopped. Sir Hiram put me in the car again after lunch and ran me upto 3 g. ; I took this all right." Maxim and his assistant actually used the Crystal Palacemachine for aeronautical research. In 1904 Dr. Thurstoh was able to drive a model through the air at 100 m.p.h. and measure the lift of the wing, which worked out at 7lb/sq ft—a figure which appeared to disprove current mathematical theories of maximum lift obtainable. During the period 1905-09 Maxim was busy designing his second aircraft and its power unit. The lecturer recalled that the wings were of thin section, strengthened by longitudinal spars and ribs, and were double-surfaced. Provision was also made for the eventual incorporation of automatic control by gyroscope. A new type of petrol engine was designed with a novel carburettor, unconventional lubricating system and skew- gear-operated overhead valves, vanadium steel cylinders and spun German silver water jackets; that unit was now in the Science Museum. • First trials were made with the machine held captive to a mast with a swivel-head attachment for the cable. The engine drove a small central airscrew and two large outboard airscrews by means of cable belts. This drive gave much trouble. Dur- ing the final trials one of the aluminium driving wheels.on one of the large airscrews broke and the cable wound up on the engine and collapsed the machine. It was while these experiments were being made that the great aviation meeting was held at Rheims, when Latham's Antoinette monoplane climbed to the then amazing height of 500 it. During World War I Dr. Thurston served ia the R.F.C. and became a technical inspector, in which position he was able to replace by more scientific procedures many of the rule-of- thumb methods then used for investigating structural failures. Recalling the highly successful S.E.5, conceived by the then B 28
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