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Aviation History
1952
1952 - 2094.PDF
126 FLIGHT (Left) The second call after leaving England was at Luqa Airfield, Malta. (Below) The inevitable but still impressive photograph when the Viscount 700 flew over Mount Kilimanjaro. PREPARING THE VISCOUNT . . . equipment has been fitted. Records show that of the four tyres new for the Famborough Display in 1950, the last was changed at Nairobi before leaving for home. This meant that approximately 80 landings had been made, including all the tropical tests. Nothing unusual was demanded during the take-off and landing tests, although these were of a particularly comprehensive nature. The pilots were asked to comment, for example, on the approach and the ease with which the round-out could be made during a power-off landing, bearing in mind the steep gradient and relatively large elevator stick-force involved under such unusual conditions for a four-engined airliner. In addition to the normal recordings made in the aircraft—I.A.S., engine r.p.m., altitude, aircraft weight, e.g. position and so on—the results of landing and take-off tests were recorded with a ground camera. The usual technique is for the pilot to make a normal short landing or quick take-off, and the camera, recording continuously, provides the soft-screen data. Because of the poor condition of the runway at Nairobi, which has frequently been used for landing and take-off tests in the past, Wadi Seidna was used in the case of the Viscount. The altitude of Wadi Seidna is 1,256ft and the air temperature is generally higher than at Nairobi, the August average being 41 deg C (106 deg F). The object of the take-off tests with four engines operative was, of course, to obtain figures for the minimum take-off distance consistent with recognized handling techniques. The e.g. position selected was the one giving maximum elevator loads. The aircraft weight for the first test was 50,000 lb; the wing flaps were set at 20 deg, and the landing gear remained extended up to 50ft. At least three tests were made in each of the selected configurations, both with and without water methanol. The Darts were set at 14,500 r.p.m. against the brakes, and the technique was to initiate "unsticking" at about 5 kt before the appropriate take-off safety speed, leaving the ground as late as possible to climb away immediately at a speed equal to the take-off safety speed. It was necessary to climb away sharply in order to prevent the speed building up over that desired. For the take-off-with-engine-cut tests the weights, flap angle and technique were the same, but the e.g. position was altered to that critical for controllability. Water methanol was used, and a series of tests were made at engine-cut speeds of 100, 95, 90, 85 and 80 kt I.A.S., in that order. Start-stop tests with engine cut were made for the same condi tions and at the same cut speeds, and, as before, the critical engine, No. 4, was stopped by closing the H.P. fuel cock. It may be added here that while at Wadi Seidna the Viscount was taken off, flown round and landed without even starting the fourth engine. Following the take-off and landing tests the schedule called for checks on climb performance and en route performance, and of level cruising. In practice some of these tests were made at any convenient point in the flying programme, regardless of the order laid down on the test schedule. Climb measurements were first made w'th all engines operative and landing gear extended, the rates being recorded at 5-min periods, commencing at ground level and at io,oooft for an aircraft weight of 50,000 lb. A further series of tests was made with one engine inoperative, both with wheels down and with them retracted, and figures were obtained for weights of 45,000,47,500, and 50,000 lb. Some actual figures recorded were as follows :— T.O. Climb At 50,000 lb, four-engine operation, flaps 20 deg and chassis down, 105 kt. At S.L.—1,480 ft min at air temperature of 36 deg C. At 10,000ft—1,000 ft min at air temperature of 12 deg C. At 50,000 lb, three-engine operation, flaps 20 deg, chassis down. At S.L.—680 ft min at air temperature of 39 deg C (102 deg F). At 10,000ft—360 ft min at air temperature of 10 deg C. En route performance checks called for measured rates of climb from ground level to ceiling in normal flying conditions, i.e., at maximum weight, I.A.S. 140 kt and with flaps and landing gear retracted. The engine speed for these conditions, without water, methanol, was 13,800 r.p.m. The same tests were made with one engine out and with two engines out. During a demonstration at Salisbury, Rhodesia, at a weight of 49,000 lb, the Viscount main tained height at 10,500ft with the two port engines feathered. For tests and demonstration purposes it is usual to cut the pert engines in order to keep two of the three cabin blowers, (those to starboard), in use. The main point to note about the two-engines-out case is that the Viscount has shown that it could safely go round again at all European fields should it be baulked on landing, even though the two inoperative engines are on one side. It is appropriate to mention at this point that the four engines have Rotol airscrews equipped for automatic feathering; the leading edges of the blades are electrically de-iced. During the tropical trials, the automatic feathering worked faultlessly on all occasions. Under the heading of "level cruising performance" the require ments were simply to measure performance on three and four engines, at 40 and 48,000 lb weight, at altitudes of 5, 15, 20 and 25,000ft. Various engine r.p.m. settings were used down to the minimum with which level flight can be maintained. Checks (paying particular attention to jet-pipe temperature) were, in fact, made at 13,800, 13,400, 13,000, 12,000 and 11,000 r.p.m. Tests at all the above altitudes were repeated at 45,000 lb all-up weight. The Viscount had arrived at Wadi Seidna on October 7th and a good proportion of the tests had been completed when it left for Entebbe and Nairobi on October 22nd. At Nairobi a few days were spent in completing tests and in certain cases repeating those which had already been carried out at Khartoum, at the higher altitude of Eastleigh Airport, Nairobi. It was at this time that political troubles were being experienced in the Canal Zone and all tests involving use of water/methanol had to be postponed because the supplies did not arrive in time. For approximately two weeks from the beginning of November the Viscount made a series of flights in East, Central and South Africa for demonstration purposes, and in several cases these provided valuable operating experience. Calls were made at Salisbury, Lusaka, Blantyre, Kasama, Entebbe and Johannesburg. Several demonstration flights were made at Salisbury and Johannesburg. According to reports—and this was before the Comet had started operating into Johannesburg —the reputation of British civil aircraft was not very high in South Africa (much adverse propaganda had been put out by foreign companies), but after some of the airline pilots and crews in that area had sampled the Viscount, they confessed that they were very favourably impressed. Passengers were apparently very pleased with the excellent view they obtained through the large oval windows, having previously believed that, with a highly pressurized aircraft, only small "portholes" could be fitted. While the Viscount was based at Salisbury arrangements were
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