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Aviation History
1947
1947 - 2226.PDF
FUG DECEMBER 25TH, 1947 IN recent months the gas turbine activities of ArmstrongSiddeley Motors, Ltd. have been of absorbing interest,and the development of the Mamba and Python has fully occupied the company's time. The Mamba, althoughit was introduced after the much larger and more compli- cated Python, was later given top priority, and became thefirst of the two to commence flight testing. The Python should also be airborne early in the New Year. In the background of these aircraft engine activities latemarks of Cheetahs, the only survivors of a long and varied line of piston engines, continue to flow from the productionline. No news of so well-established a power unit may be taken as good news, but it is of interest briefly to recordand recall the present and past applications of this widely used seven-cylinder radial. Although Armstrong Siddeleyengines have been installed in almost every kind of aircraft it is probably their association with this country's trainingprogrammes which has been, and still remains, their best known application. The earlier company, Siddeley Deasy, laid a good founda-tion with the water-cooled six-cylinder Puma of the 1914-18 war, and an exceptional production rate of 700 engines permonth was achieved at that time. Between the wars the familiar range of air-cooled radials was produced and sawservice in a great variety of aircraft. To quote some examples the 14-cylinder Jaguar powered the Siskin andthe Flycatcher Fleet fighter. Panthers were found in Gordon day bombers of the early 1930s. Servals in A.W.15Sand other commercial transports, also in an amphibian, while the later Tiger was installed in the T.S.R. Shark,and the Whitley which became the first R.A.F. "heavy" bomber of the world war. In addition to these, many lightsingle and twin designs had Genet or Lynx power units. The first Cheetah, produced in 1932, was a developmentof the 215 h.p. Lynx. Like the Lynx it had seven cylinders, but an increase in cubic capacity enabled the power outputto be raised to 260 h.p. By 1934 the power figure had been increased to 310 h.p. After the earlier marks, the2A and 6, came, perhaps the best known of all, the Cheetah 9. This unit, which first ran in 1934, wasmoderately supercharged to give a take-off boost of T\ lb with an impeller ratio of 6.52: 1. It was in many waysvery advanced, and incorporated an automatic mixture and boost control. From the beginning of the war a new generation ofairmen was introduced to applied flying and aircrew duties on Oxfords and Ansons powered by Armstrong "Siddeley CHEETAH GENEALOGY Fifteen Years' Development Have Led to the 475 h.p. Mk. 25 : Association with Training Cheetahs. Many pilots before themhad learned to fly on Lynx-engined 504NS and Tutors. Very large num-bers of the two-engined trainers were produced, and in the case of the Ansona new lease of life has quite recently been granted by a new order for the latest Marks XX, 21and 22 for R.A.F. training in crew duties. Some 8,000 pilots received at least a part of their training on Oxfords andAnsons in various parts of the world under the Common- wealth Air Training scheme, and by the end of the warover 35,000 Cheetahs had been built to Government order. Even under the distinctly arduous conditions of wartimeinstructional flying an overhaul period of 1,200 hours was achieved for Cheetah 9s and 10s. Many Oxfords and/Ansons are, of course, still in use, and the post-war civil; light transport versions, the Consul and Avro XIX respec-tively, are giving very good service at home and abroad. The Later Marks Cheetahs had by 1945 reached Mark 25, units very similarto the 15s, but designed to give exceptionally high take-off power of 475 b.h.p. at 2,700 r.p.m. These engines arealso concerned with training, many having been installed in D.L.22 trainers for the Argentine Government. Cheetahsare being built under licence in the Argentine. The new R.A.F. Ansons referred to above are fittedwith Cheetah 15s which develop 420 b.h.p. at 2,550 r.p.m. These later engines, the first of which was the Mark 10 of1937, carry variable-pitch airscrews. The Mark 10 closely resembled the 9, having 80 per cent of its componentsinterchangeable with that unit, but the front cover was redesigned for the new airscrew. In 1943 this was againredesigned to incorporate a reduction gear of 0.732 ratio to take advantage of the constant-speed airscrew which hadbecome available. The 1943 Mark 10 was thus the first * Cheetah to incorporate all the latest refinements of thelarge power units. With a new crankshaft carrying pen- dulum-type vibration dampers, fully feathering Rotol air-screw, and an authorized rated boost pressure increase to 2| lb, a new mark for the engine was obviously called for,and in this way the Mark 15 came into being. In case it should be wondered where the Cheetah 19 -fits into the picture it may be added that this hybrid unit; was derived from an admixture of the 9 and io, and it wasichiefly brought about by the introduction of a power-" operated undercarriage on the Anson. This required ahydraulic pump which was not provided for among the •' accessories on the Cheetah 9. The 10, however, as fittedto Oxfords, carried the necessary pump. The Mk. 10 auxiliary drives were therefore fitted to the Mk. 9 engineand the resulting unit was distinguished by the mark number 19.
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