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Aviation History
1964
1964 - 0122.PDF
fliCHT International, 16 January 1964 85 is any hope of accommodating the car parks now dominating the layout of all airports. In most US cities, the airport buses are not allocated to specific flights. Frequently they start from the airport with a load of incom- ing passengers, drive round the downtown area, stopping at say four strategic points, and then return directly to the airport. Depart- in 'A passengers are picked up at any of the stops, and the service runs every 10 or 15 minutes. Apart from passenger convenience, this improves the productivity of the buses and drivers over our "han.iabout" system. From the airline viewpoint it makes the passenuer responsible for getting himself to the gate on time, and it eliminates the cost of a town terminal. Though a town terminal survives in New York, its future as anything more than a bus depot seems uncertain. Taxi fares from the airports are modest, by American standards, and the numbers using the buses seem to be small—a dozen were the most observed in six journeys. Amongst all these symptoms of high staff productivity it is ironic that the aircraft themselves should be provided with so few seats by comparison with our "sardine style" layouts. In a recent flight by BEA Comet, the seat pitch was measured to be 30in, though whether this was standard or due to a mistake in the engineering department was not established. In North America, two aircraft only, a TCA Vanguard and a Continental 707 in economy class, had a seat pitch of 34in, and the Canadian aircraft had three-by-two seating in contrast to BEA's three-by-three. Otherwise coach-class passengers had 36in or 38in. A local service DC-3 provided a luxurious 40in, with seat rows of two-by-one. Perhaps in Britain it is that competition has not been enough to force the airlines to concentrate sufficiently on cost analysis and *«• The Eastern Air Lines terminal at New York International, one of a dozen airline terminals at that airport, is as big as the Gatwick terminal "Flight International" photograph cost reduction. Some of the figures produced by BEA in particular bear the marks of an academic, traditional accounting approach in which the emphasis is on allocating every penny of overhead rather than on the "marginal" approach more appropriate to air- line operation. Perhaps there is again something to be learned from the past. At a recent administrative inspection of the Royal Army Medical Corps, the outside experts congratulated the Corps on the simplicity and functional excellence of their costing system, and asked who designed it. The answer was "Florence Nightingale." A. B. C. BODY Under the ll-18's Cowlings MORE has recently become known in Western Europe about the Ivchenko AI-20 4,000 h.p. turboprop engine which powers the 11-18 four-engined airliner, standard equipment with Aeroflot, LOT, CSA, Malev and other national airlines of the Communist bloc. The Ivchenko AI-20 has a number of very unusual features, when compared with western turboprops, not least its reduction gearbox. With overall dimensions similar to the Dart gearbox, this transmits almost twice the shaft horsepower. Compactness is achieved by splitting the torque path along two routes, the two-stage epicyclic gear having a differential feature between the two gear trains, as shown in the accompanying diagram. The torque-meter system is similar to that of the Rolls-Royce Tyne engine, employing six piston and cylinder assemblies restraining one of the planet cages. The sys- tem is sufficiently accurate for test as well as flight purposes. It seems a fair assumption that the same torque-splitting gear technique is used in the 15,000 h.p. Kuznetsov turboprops which power the leviathan Tu-114 now in Aeroflot service, with the likely difference that once the torque path has been split the individual drives go to individual components in the two-part propellers. Propeller oil lines on the Ivchenko AI-20 are fed along cored pas- sages through the reduction gear casing, over the gears to a large transfer sleeve around the propeller shaft. There is a third oil line to break-down propeller locks. Propeller blade actuation is similar to that on the Rotol Dart propellers, featuring a large piston with link pins to each blade root. Main rotary components are a ten-stage axial compressor and a three-stage turbine running on a single shaft. The compressor end •s of the balloon type, made up of separate rings, one for each stage. These rings are spigoted into each other with heavy intervening rings and are assembled hot, on a 25-ton press. The compressor blades are dovetailed into these rings and the lock tang for each blade features a small dowel which is an interference fit in drillings going through the spigot of each adjacent ring, so that each blade tang forms a dowelling feature between adjacent rings. It is not normal practice to dismantle the shaft at overhauls but if necessary •t is possible to replace individual rings. The turbine assembly is very similar to that of the Dart RDa.7, utilizing ten long bolts to hold the turbine wheels together and on to the shaft. Short dowels are fitted between adjacent rings and oversize dowels can be fitted, enabling any one disc to be replaced 'our times in one disc set. The turbine blades are set in the wheels the normal fir tree roots and are unshrouded, but feature a !^ ^n Sea* similar to that in the Napier Eland engine.1 en cans in a common casing and duplex downstream burners comprise the combustion system. The fuel manifold is a rigid, small-bore steel-tube construction. The control system is com- pletely automatic and there are no ground adjustments whatsoever to be made in service—a notable advantage for an operator over some much-used western turboprops. But in overhaul life the Ivchenko AI-20 does not match such engines as the Dart, Tyne and Proteus. Recently, the overhaul life of the engines in the Polish airline LOT's II-18 fleet was 75Ohr for a new engine and 600 for one already overhauled, though these figures may now have been increased, for Aeroflot is thought to be running its AI-20s through to l,500hr. Engine life development follows a similar practice to that adop- ted by British engine manufacturers—12 per cent of engines are trialled to 300hr more than the approved life. Aerofiot aims at an unscheduled removals rate of less than 0.3 per 1,000hr and this rate is being achieved. The most common failing is distress in the tur- bine resulting from temperature effects. Oil is changed every 400hr. The engine is of handsome and "expensive" appearance; an engineer who recently saw some in Il-18s after lengthy operating lives said that they were immaculate, without a trace of an oil leak to be seen. All fuel lines, oil lines and so on are coloured according to their function—fuel lines and filters being bright red, oil lines and filters being brown. Schematic diagram of the split torque-path technique which enables the Ivchenko AI-20 reduction gearbox, transmitting 4,000 s.h.p., to be no larger than a Dart gearbox transmitting about half as much. The figures indicate the number of teeth on each spur gear 97 T. SIX TORQUE PISTONS AND CYLINDERS RESTRICTING 2 ND. PLANET CARRIER 97 T. 31 T. 35 T.
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