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Aviation History
1964
1964 - 1386.PDF
FUGHT International, 7 May 1964 765 BASIC UNSCHEDULED REMOVAL RATE TIME BETWEEN OVERHAUL I TOTAL CONWAY ENGINE HOURS | Tll€ BETWEEN OVERHAULS WITH PART-LIFE SHOP CHECK ENGINE HOURS ENTERS SERVICE The Conway's unscheduled removal rate remains constant at about 0,1 per I.OOOhr—an excellent level 6th -M YEARS IN SERVICE ponents. The improvement was confirmed by repeating the load measurements. RCo.42 Accessories Many of the engine systems, such as the fuel system, are logical developments of those of the RCo.12, i.e., they are basically the same but include numerous detail modifica- tions to improve performance and reliability. There are, however, certain areas in which fundamental changes have been made, some of these based on RCo.12 experience. On the RCo.42 the fuel-cooled oil cooler has been moved from the h-p to the 1-p fuel system upstream of the fuel heater, resulting in a considerable reduction in unit weight and—perhaps even more important—a significant degree of fuel heating upstream of the 1-p fuel filter. As a result it has been found possible to reduce the fuel-heater size; in addition, the time during which actual operation of the fuel heater occurs is very much reduced in comparison with that of the RCo.12. This not only reduces the penalty in s.f.c.— by reason of the reduced engine hot air bleed required for the heater—but there is also strong evidence to suggest that the reduction in thermal cycling to which the heater is exposed will result in improved matrix reliability. This does mean, however, that the fuel pump now runs at a higher inlet temperature; and this factor, as well as the increasing likelihood of running on wide- cut fuels, has led to the introduction of carbon-topped slippers on the pistons in the h-p fuel pump, so that they are better suited to low-viscosity fuels. Control of fuel heating is another area in which changes have been made. The somewhat complicated electrical control system of the RCo.12 has been replaced by a very simple system consisting of a poppet valve mechanically operated by a Vernatherm element, in which the fuel-heater outlet temperature is sensed by the Vernatherm, the expansion of the latter's wax element being transmitted via a simple push-rod to operate the valve controlling the air inlet to the heater. This system has so far operated with complete reliability and although the temperature control band- width has to be somewhat wider to achieve stability, the overall s.f.c. penalty of the system is very low, owing to the relatively small degree of fuel heating required. Overhaul-life Development An accompanying diagram shows the rate of overhaul-life development, the service unscheduled removal rate and total engine hours plotted on a time base since the introduction of the Conway into service. The first passenger- carrying flights with the RCo.12 were carried out in March 1960 • ^d over the first year of operation the basic unscheduled removal rate was approximately 0.5 per l,000hr. Towards the end of the first year, as the various engineering cures for the service teething troubles were fed into the fleet, the rate started to fall and continued to do so during the second year of operation, following which it has remained sensibly constant at approximately 0.1 per l.OOOhr. During the same period the overhaul life was raised from the initial starting life of 700hr to 4,000hr without any intermediate attention, or to its present level of 5,7O0hr by use of the "shop check" technique at an intermediate life. It is expected that with the incorporation of various modifications now becoming available it will be possible to increase the straight overhaul life beyond 4,000hr. While it is still too early to forecast the service reliability of the Conway Mk 540s in the standard VClOs operated by BOAC, the changes incorporated in these engines on the basis of RCo.12 service experience suggest that it should be better than that of the RCo.12, particularly in the early days of service operation. One engine at 400hr, two at 700hr and one engine at l,000hr have been dismantled for examination, with very encouraging results. A second engine is about to be removed for inspection after com- pleting l,000hr in the route-proving aircraft. On the basis of the satisfactory inspection of these engines an initial service life of 1,200hr was agreed, followed by a normal service life development programme. VC10 Flight Testing Since the first flight of a VC10 in June 1962 a total of 16,500 engine hours have been flown during the certifica- tion and route-proving programmes. So far a total of 11 aircraft have flown, including the prototype, G-ARTA, and during this period there has been only one basic unscheduled engine removal, the cause of which is under investigation. The flying, during which the above engine reliability picture has been accumulated, included performance trials at Madrid and Johannesburg in August and October 1963 respectively, systems trials in Aden in August 1963, the l,000hr route-proving exercise carried out jointly between BOAC and BAC on aircraft G-ARVF, and also a large amount of crew training at Shannon. The route proving trials on G-ARVF are perhaps the most significant as a pointer to service behaviour of the engines. These flights were mainly to East and West Africa; some were to the Middle East, and others westward to Montreal and Toronto for cold-weather trials. The engine performance during the whole of this programme was completely satisfactory and the aircraft utilization was comparable with that experienced in normal airline service. , Pref>,'oration of a Conway for thrust-reverser tests
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