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Aviation History
1952
1952 - 3150.PDF
FLIGHT 556 THE development of the Vickers V.C.i Viking in service with B.E.A. makes a story that is well worth recording, even in these days of rapid advances in the operation of British turbojet and turboprop transports. Designed as an interim-type aircraft to fill the immediate post-war gap, the Viking was the first British post-war transport to go into service, and a glance at its six-year record is now due. It is a far cry from the first 21-seat Viking of 1945, with fabric wings, to the 38-seat Admiral class of 1952, and much has hap pened to the aircraft and to factors such as its overhaul life and annual utilization between these dates. An attempt to describe every modification made during the Viking's life with B.E.A. would be of little value : this article, therefore, refers to specific aspects of the Viking's development, and gives a general account of the Admiral conversion, with examples of detailed changes particularly relevant to the story. The introduction of the Viking into B.E.A. service came at the same time as the Corporation itself was developing, almost from scratch, its route network and operational method. The absence of a tried system of new-aircraft introduction, together with the lack of operational data on the Viking from any other airline, made this early period especially difficult, and extended the time taken up by it. Direct costs were increased by the inevitable low utilization, lack of maintenance experience, inefficiency of a small initial fleet, training of crews and ground personnel, and miscel laneous unknown operating factors. In addition, the indirect costs of project and development engineering, and planning of maintenance, traffic, commercial and flight operations aspects (all normally present when any new type is introduced), had swollen rapidly at this time, owing to the expansion of these departments to do this introductory work. This should be borne in mind when considering the following particular phases and aspects of the Viking's airline life. Early Flight Tests.—In April 1946, at the request of B.E.A., the third prototype Viking G-AGOM was delivered to the develop ment flight of B.O.A.C. for handling trials. The first production machine, G-AGON, was delivered for the same purpose the following month, and a complete investigation was made into the operational suitability of the aircraft and its radio equipment, its handling and maintenance features, and its performance. Both machines were of the Mk iA "short-nosed" type, with geodetic fabric-covered mainplane, tailplane and fin, and Hercules 630 engines; G-AGON was fitted with a T.K.S. airframe de-icing system. The handling trials included 73 hr and 37 hr respectively on the prototype and production model, during which every aspect of the aircraft's performance was thoroughly examined. On G-AGOM, after test instruments had been fitted, checks on general handling, climb performance and speed/power consumption variation were the first to be made, followed by V.H.F. signal range tests, and maintenance check 2 (the 25-hr inspection). Airscrew vibration checks, single-engine handling and night flying were then followed by tests of catering equipment, vibration, noise and booster-pump utilization, and the machine was re-weighed at Boscombe Down. After D/F. loop calibration and swinging, and tests of take-off, rated and maximum cruising power, the 100-hr maintenance check 3 was carried out, and the Viking was returned to the makers. After a similar but shorter period of test flying and appraisal, the second machine, G-AGON, was delivered to the aircrew training school at Aldermaston. Following these trials, modifications prior to the aircraft's operational use were suggested, some believed essential before de livery, others desirable subsequently. Thirty-seven modifications were recommended to improve maintenance, together with eight essential and 33 desirable changes to the aircraft equipment (excluding radio) from an operational viewpoint. Eleven faults in THE VIKIN( Detailed History, from B.E.A. and otl the cockpit layout, and 17 essential and 63 desirable changes in the radio equipment, were also reported. • • The De-icing Problem.—The first major problem in the operation of Vikings arose in December 1946, and was concerned with ice accretion on the tailplane. At this time 12 aircraft (Mks iA and 1) were in service on eight European routes, and a further six were being used for training. On December 4th, a B.E.A. Viking 1 developed an overbalanced elevator when a moderate accretion of ice occurred on the tailplane leading edge, and more serious over balancing occurred with iin of rough ice during a test flight the following day. B.E.A. decided to withdraw the Vikings from ser vice and, in co-operation with Vickers-Armstrongs, to carry out a most extensive series of flying tests in severe icing conditions. There were two problems : (a) to ensure that the de-icing equip ment could prevent ice from forming and could remove any ice which had already formed; and (b) to improve the handling charac teristics of the aircraft with ice on its surfaces. As Mk iA machines had carried ice without any change in elevator control arising, it was thought that some change in elevator balance had been introduced with the metal tailplane of the Mk 1. Wind-tunnel tests confirmed that the basic elevator without ice was too closely balanced, and this aerodynamic problem, being the more important, was tackled first. Suggested solutions were spring-tab modification, cusped trailing edges, built-up trailing edges and modified horn balances. The tab gearing was increased, and 516m tubing was added to top and bottom surfaces of the port elevator; but the most significant improvement was due to the reduction and increase of the port and starboard elevator horn balance areas respectively. Even on the earliest Vikings the port horn balance had been smaller than the starboard, due to the destabilizing effect (on the port side) of the asymmetric slipstream; but by reducing its area still further—to 62 per cent of the original —it became completely shielded and was in effect a mass-balance arm only. With the above modifications (and a spring-compensator giving an elevator down-force of 25 lb, fitted temporarily until the starboard horn balance was further increased), improvements in longitudinal stability and elevator hinge moment linearity were achieved. During January and February 1947, an exhaustive series of flight tests were carried out, in order to study handling characteristics under icing conditions and the effects of varying the rate of flow of the de-icing fluid. Capt. J. W. G. James, then B.E.A.'s chief pilot, and now their director of flight operations, was the pilot in charge, and he was accompanied on the flights by other experts from B.E.A. and Vickers-Armstrongs, including Mr. George Edwards, the constructors' chief designer. Areas of heavy icing were sought, and elevator damping tests with de-icing equipment switched off showed that the behaviour of the aircraft was satisfactory, both on one and two engines, and when landing. The rates of flow of de-icing fluid used pre viously proved to be insufficient to prevent ice forming on the tailplane; and an increased emergency rate was adopted until optimum rates could be subsequently determined. The main conclusion from the tests was that the Viking, as modified, was safe under icing conditions; the question of the rate of flow of the de- icing fluid was obviously not confined to the Viking alone, but concerned, in addition, other types of aircraft. The modifications mentioned above were made to all B.E.A. Fig. 2 (below) Passenger capacity variation with range for the "Admiral," assuming fixed fuel reserves, two-crew operation (plus steward) and the 36-seoter arrangement; 38 passengers could in fact be carried over the short-distance routes. ZOO 400 6OO BOO 1.000 STAGE DISTANCE (similes) Fig. 1 (left) "Aircraft costs" per seat mile, assuming 2,000 hr utilization. These costs correspond broadly to direct operating costs, and represent in this case be- 200 tween 45 and 50 per cent of the total cost. •»v 30 <.zo u IO 2C KJ 4C O 60 RANGE O 8C (st miles) O IOC O 1.2CX
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