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Aviation History
1950
1950 - 0351.PDF
FLIGHT, 16 February 1950 DE-ICING THE VISCOUNT . . . The slightly modified production de - icing system in diagram- matic form. Exhaust- gas heat exchangers are used in place of a simple jet-pipe bleed. prevent the use of a simple jet-pipe bleed." Exhaust-gas heat exchangers are therefore used instead. The two systems are illustrated diagrammatically. In the production version equal efficiency is maintained, but at the same time any doubts about the ducting of exhaust gases through the airframe are eliminated. Flight and laboratory tests so far carried ont do not, in any case, indicate that there would be trouble from corrosion or soot caused by the exhaust from kerosene fuel. So far as the Dart turboprops themselves are concerned, the earlier marks in the prototype, as used on the trials to which the report refers, have no de-icing system. How- ever, to ensure economical operation • on the production aircraft, it is in- tended that the later marks of Dart shall embody thermal de-icing for the intakes to avoid a risk of increased fuel consumption as a result of ex- treme intake blockage. The airscrew blades on the prototype are de-iced by fluid overshoes, but those on the pro- duction machines will be electrically heated. Thermostats and flownieters were in- stalled in the wings and tailplane during the construction of the Vis- count so that the de-icing system could be thoroughly checked during a series of clear-air proving nights, but to augment these tests it was considered desirable to fly deliberately in search of ice. At the appropriate time it was reported by the Meteorological Office that intense icing •was likely to be met in the vicinity of Shannon. The main objects of the trial were to study the handling charac- teristics of the aircraft when carrying a considerable quantity of ice, and to assess the efficiency of the de-icing system in preventing its formation and in removing ice after it had formed. The report continues : "... in all, four separate flights were made in temperatures varying from o deg C to - 18 deg C O.A.T., and at heights between 4,500ft and 15,000ft. Trials were made with main and tail systems on and off alternately and photographs were taken of the results. The accretion of approximately 2in of ice on the tailplane (see illustration on previous page) had no effect on the con- trol characteristics of the aircraft, and the damping effects of both rudder and elevator were very positive. When flying hands-off in bumpy conditions there was no tendency for the control column to move. The ice was of very rough formation, building up 4 to 6in aft of the leading edge, but completely covering the tip. - . • . " When the tailplane de-icer was turned on at the con- ; elusion of this test, the ice began to break up after about four minutes and came away in large pieces without any sign of run-back. Run-back experienced in other tests, at ' lower temperatures, was in the form of narrow chord-wise streaks (as illustrated) causing no adverse aerodynamic effects. On no occasion was there any tendency to form spanwise ridges.'7 The heading photograph shows the nature of ice. forma- tion around the turboprop power units. It is recorded that "a build-up of some 2.3m was observed round the engine air intake and a thin-lipped ridge formed around the de- icing air scoop, as seen in the picture. The large piece, some ••37 CONTROL VALVE - --" ~:- HOT GAS FROM JET PIPE STARBD t t BETWEEN TURBOPROPS OUTER WWG Section through the leading edge of the Viscount mainplane showing double skin, D-shaped duct, and slot for hot air. gin long, which is seen to have broken off from the engine intake, went into the engine without any harmful effect. " When the heating to the mainplanes and tail unit was switched on before entering the icing zone, the surfaces remained clear of ice, although on the aerial masts, which are not de-iced, the build-up was quite considerable. Under the coldest conditions encountered (- 25 deg C true tem- perature) the thermal de-icing system cleared the main surfaces of ice but the fluid de-icing system failed to cope satisfactorily with ice on the windscreen—a significant fea- ture when considered in the light of the linn's faith in the former method." The Company concludes its report: "As a result of these trials Vickers- Armstrong feel more than satisfied with the behaviour of both the aircraft itself and the thermal de-icing system, / as the Viscount was flown in s considerably more severe - than those likely to be encountered during the normal routine operation of high-altitude aircraft of this type. Not only was the thermal system able to dispose of the ice formations deliber- ately accumulated by entering ice- forming clouds with the system not working, but the machine remained stable and controllable when carrying a fairly heavy build-up of ice. "Even in the worst conditions encountered, the bulk of the ice was dispersed after the system had been turned on for a relatively short time, and the only remnants of run-back were of such a nature as to be negligible, either from the point of danger or of efficiency." These trials complete the Viscount prototype test pro- gramme, and the aircraft is now with the Civil Flight at Boscombe Down. During its 400 hours of test flying, the prototype has undergone intensive and comprehensive tests particularly, in the later stages, of the pressurizing system. The attainment of 400 hours' flying since the first flight in July, 1948, speaks well for the serviceability achieved on both power units and airframe. The prototype Viscount received a British noimal-cate- gory C. of A. last September, but at that time it was without its pressure or de-icing systems. The slightly en- larged Viscount 700s will, of course, have to obtain a separate C. of A. B.E.A.'s 40-seater version will be the model 701 and B.O.A.C.'s the 702. Assuming that approximately one hundred Viscount 700s will be built, a provisional selling price of £167,000 has been announced. They will probably commence operation on Corporation routes by mid-1952 and reference is.made to B.E.A.S, plans for them on page 239. - - EUROPEAN TOUR FOR THE VISCOUNT /COMMENCING in. the third week of March, thr VickersV_/ Viscount is to make a demonstration tour of the principal cities of Western Europe. The aircraft will he demonstratedto airline officials in Amsterdam, Brussels, Zurich, Rome, Madrid, Lisbon, Copenhagen, Stockholm, Oslo and Paris. Onboard will be Sir Hew Kilner, M.C., deputy chairman of Vickers Armstrongs Ltd., Capt. J. Summers, chief test pilot,and Mr. R. C. Handasyde, sales manager of Vickers Aviation Division.
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