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Aviation History
1939
1939 - 0439.PDF
FEBRUARY 16, 1939 FLIGHT. g- •* ^. - - - H..I . 11 • •*• AQUILA Displacement (litres) 15.6 (cu. in.) 950 Take-oS (b.h.p.) 710 Max. .. (b.h.p.) 725 Weight (lb.) 795 PERSEUS XII 24.9 1,520 830 905 1,105 TAURUS 1,010 1,065 1,280 HERCULES II 38.7 2,360 1,300 1,375 1,650 The four Bristol sleeve-valve engines compared. The views are to the same scale so that they give an idea of relative size. because the whole layout was based on attaining a velocity head at the upper front section and allowing the air to leak through finned cells to the lower-pressure air of the rear. Development on sleeves had also taken place, and, in ad dition to the use of nitriding, increased port area had been provided and control of swirl obtained. The piston, also, had been subjected to many thousand hours of work. It is a light alloy drop forging with two compression rings and two scraper rings. Of the standard driving ball assembly used in the Bristol sleeve-valve engines, Mr. Fedden said that this had been ab solutely reliable. A test rig was employed to facilitate investi gations over long running periods under arduous conditions. The success of the present engine was a result of the consider able design and research efforts. Fortunately, the drive assembly adopted had proved to be the simplest of those tried. On the test rig it had been found possible to transmit more than 4 h.p. through the sleeve drive. As a result of suitable detail design, an appropriate selection of materials, and the nature of the motion, wear had been almost eliminated from the production series of sleeve drive. Main Engine Development Mr. Fedden proceeded to review the various types of Bristol sleeve-valve engine. Designs for a complete engine were put in hand after four years of single- and two-cylinder research. In 1932 the Perseus I, a nine-cylinder radial, was type-tested at 515 b.h.p. normal rating and 638 b.h.p. maximum. This PISTON SPEED FT./kMN. 2400 2600 2BOO 3400 MOO 2SO0 PISTON SPEED ri./um. Comparative breathing efficiencies of two-valve, four-valve and sleeve-valve cylinders. was subsequently increased to 700 b.h.p. and the engine endurance-tested in a Bulldog. It appeared in public at the Royal Air Force Display of 1934. Due to an incomplete understanding of the fundamental problems involved when the rating was increased, considerable setbacks were encountered during the development of the evolution : The original sleeve-valve cylinder compared with a modern Perseus cylinder. Most noteworthy is the increase in finning. slightly modified Perseus II, but the engine was finally type- tested in 1934 and submitted to a 250 hours' cruising test at 420 b.h.p. and 2,150 r.p.m. Its satisfactory condition at the end of the test showed that it had great possibilities for com mercial operation. Five of these engines were then loaned by the Air Ministry to Imperial Airways and four were put into service in a Short Scylla type. The engines fully demonstrated the reliable service to be expected from the single-sleeve valve in commercial operation. Fitted to a Squadron of Vildebeests two years ago, the Perseus VIII was the first Bristol sleeve-valve engine to be tested under Service conditions. Results had been most satis factory as regards reliability, ease of maintenance, and, especially, continued serviceability. Other types of Perseus had now been produced and, as com pared with the Perseus I, the b.m.e.p. had been raised by some 40 per cent, and the b.h.p./sq. in. of piston area by 65 per cent. A number of improvements in design have been introduced, such as the accessory gear box adopted in 1936. The latest Perseus engine was now in large-scale production and was being instaDed in a number of military aircraft, in cluding the Lysander II and the Blackburn Skua, while two civil types so equipped were the latest Short flying boat and the D.H. Flamingo. Another single-row sleeve valve was the Aquila, type-tested in 1934 and subsequently test-flown in the Vickers Venom fighter and the civil Bristol 143. Rearmament work had in terrupted the development of this engine, but a recent resumption had resulted in its passing its civil test with satis factory figures. Turning to the two-row type, Mr. Fedden said that endur ance flight trials of the Hercules were proceeding in a special Northrop. Of 2,360 cu. in. capacity, the Hercules was type- tested in 1936. It was then rated at 1,375 b.h.p. at 2,400 r.p.m. Other types of this engine would be developed for con siderably higher powers with both 87- and 100-octane fuel. The lecturer went on to describe the Bristol unit installation system, which was particularly happily developed in the case of the Hercules. He recalled that there was nothing really new in the idea of "an interchangeable power egg." In the Bristol Brandon produced 14 years ago, there was a swinging engine mounting, and the present-day Vickers Venom had a similar installation. The latest Bristol sleeve-valve engine to be publicly announced was the Taurus, type-tested last summer for a ' • "''MJIMAHA^
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