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Aviation History
1925
1925 - 0660.PDF
covered considerable expenditure towards the development of the heavy-oil engines, and the result of these researches would be of great value to the operators of heavier-than-air craft. (b) The cost of pilots' and mechanics' flying pay was a com- paratively small item, but was worthy of consideration. At present it was equivalent to 1 \d. to \\d. a mile, according to speed of aircraft. The biggest item of operational cost was, however, (c) the maintenance and overhaul of engines, which represented about 44 per cent, of the total. Referring again to that part of the paper dealing with reliability, the lecturer recalled that the four most serious troubles arose from the water system, the valves, the oil circulation, and the breakage of parts usually of small importance. Two of these categories—water system and oil circulation—totalled 38 per cent, of the whole : the cost of spares was scarcely involved. The other two— valves and breakage of parts—totalled 42 per cent., and involved considerable expenditure in spare parts as well as man-hours. All these cases involved many man-hours wasted in removing faulty engines and installing sound ones. From this he thought it would be safe to say that an increase in the • capital cost of the engines and spares would be justified if thereby the frequent removal of engines could be avoided and hours before overhaul lengthened. The next item of operating cost was (d) the maintenance and overhaul of aircraft, which accounted for about 20 per cent, of the total. The first cry of the operator was for simpli- city and ease of access to all important components. It was to be feared that war methods had led designers into bad habits, which had continued since the war, and it was only the economic pressure of commercial operation which had brought vividly to notice the fact that much money spent in maintenance could be saved if more attention had been paid to simplicity in design. Many of the defects in this respect could be eliminated in the future by a little careful thought and common sense. The thick-wing, cantilever monoplane had certainly proved easiest to maintain in efficient flying condition. It was claimed for the Fokker types that the planes need not be touched for a period of twelve months, and he thought that the Junkers lasted even longer without attention. Unfortunately, the lack of continuity in policy had made it difficult to obtain reliable data regarding the operation of the aircraft in use. Some of our machines had flown for as much as 2,000 hours, covering perhaps 170,000 miles, without undergoing a thorough overhaul, but inspection had revealed that it was not wise to permit such long periods of operation with wooden aircraft. The lecturer then gave an outline of the system in force on British air lines, according to which the machine undergoes a " dock overhaul " after every,250 hours' flying, and after three years' service the aircraft should be completely overhauled and practically reconstructed. Most of the defects discovered lately during periodic inspection had been directly due to the perishable nature of wood and fabric, and he was therefore forced to the conclusion that the adoption of all-metal aircraft seemed to be the next step towards reducing cost of main- tenance. The effect of improvements in design, leading to longer hours between overhauls, was of a twofold nature : not only would the actual spares and man-hours be lessened, but the amount of work which aircraft could accomplish in a given time would be increased. Insurance was a big factor in costs, and, since the beginning of civil aviation in 1919, insurance rates had varied between 12 per cent, and 30 per cent, per annum, on the capital cost of the aircraft, regardless of the number of hours it spent in the air during the year. Negotiations were, however, in progress with a view to putting insurance upon a mileage basis. The various possibilities of reducing operation costs were summarised as follows :—" I. Reduction in the weight of fuel consumed per horse-power, particularly in air-cooled engines. 2. The introduction of some cheaper fuel than petrol. 3. Once again, an improved power plant, even at cost of extra weight and expense. 4. Once again, the introduction of all-metal aircraft, even at greater capital cost. 5. The development of the thick-winged cantilever monoplane or biplane without external struts and bracing. 6. Investigation and prevention of corrosion in metal. " It will be seen that two of these steps towards greater economy in operation are similar to those already demanded for safety and reliability, and that none of the others need necessarily clash with the requirements of these two latter essentials." Hitherto the paper had considered the possibility of reduc- tion of operational costs for a fixed load. In the next section the question was examined of the possibility of carrying a greater paying load per horse-power for a fixed operational OCTOBER 8, 1925 cost. 74 per cent, of the total cost could be attributed to the maintenance and the fuel consumption of the engine. Further, the capital value of engines, and of most normal commercial aircraft, was closely related to the horse-power employed, and for this reason the contract with Imperial Airways had been modified from a purely mileage basis to a horse-power mileage basis. If they accept the plea that operational costs were directly proportionate to the horse-power enployed, the two problems which presented themselves to the designer in his struggle towards producing a really economic aircraft were : how could he carry a greater total weight per horse- power, and how could he improve the ratio of the weight of paying load to the total weight of the aircraft ? These two problems were closely bound up together, and yet offered different aspects. To commence from actual facts, the existing standard commercial machines gave the following results :•— h.p. 440 710 365 '53 +j CC x O oH &, (lbs.) 13-58-6 9-95 be'53 ^ P. "S (U H Pn (lbs.) 16-4 17-6 16-6 cd UC PH •|* PH P, (lbs.) 31 3-85219 ^ Type. Ue Havilland 34 Handley-Page W.8. Supermarine " Sea Eagle " It was on these figures that they must endeavour to make a definite improvement, and the following solutions presented themselves : (a) increased wing area ; (b) a good climbing wing section ; (c) the employment of flaps, slots and similar devices ; (d) variable pitch propellers ; and (e) the " ground boosting " of engines. Under (a), Sir Sefton Brancker stated that when new designs were being considered in the drawing office, speed was apt to lose its importance in the eyes of the designer, who was prone to sacrifice speed in order to attain the apparently more commercial attributes demanded, but speed had a very high commercial value. Sir Sefton admitted that possibly considerable experience of racing with darkness, and of long journeys carried out against high winds, had biassed him a little in favour of speed, but he thought that in normal conditions the cruising speed of 100 m.p.h. was necessary. In fact, for mails he thought that considerably higher speeds would be demanded in the future. Overseas it was found necessarv to fly long stretches against strong winds, and, for this reason, military opinion had put the proper speed for the Egypt-Iraq service at 120 m.p.h. It was possible, however, that goods services would fly at much lower speeds, and so, while maintaining his demand for at least 100 m.p.h. for normal traffic, he would suggest that designers should seriously consider the problem of how slow it was possible to fly economically with goods traffic in view. As regards b), Sir Sefton said that here he was very much out of his depth, but he thought that a thick-wing type of aircraft appeared to offer great possibilities. Under (c), the paper made reference to the various devices for increasing lift, such as the de Havilland flaps and the Handley Page slots, and it was stated that about five new types of aircraft were to be fitted with slot gear so that definite experience should soon be available. Under (d) and (e), reference was made to variable pitch propellers and " ground boosted " engines and, to get the best results, the two should, of course, be combined. With all these developments the paper stated that a total increase in total weight carried per horse-power of 25 to 30 per cent, should not be impossible, and it should be possible to design, even at the present time, an aircraft cruising at 100 m.p.h. and weighing, fully loaded, 25 lbs./h.p., which would be safe and easy to fly. A brief reference was then made to the flying boat or sea- plane, and the table showed that the small flying boat had a very small ratio of paying load but, on the other hand, the paper stated that the leading designers held the view that really big boats or seaplanes would work out to be lighter than aeroplanes of the same size, and would, consequently, give a better ratio of paying load. By way of showing what improvement one might hope to attain by incorporating all such features as were known at present, and which might be expected to give a greater ratio of paying load, Sir Sefton Brancker's paper took as a basis a standard aircraft closely approximating to one of those at present in operation. This aircraft carried a total load of 18 Ibs./h.p., of which only 3-5 Ibs./h.p. represented paying load. Its cruising speed was 85 m.p.h. and its endurance about 4^ hours. Its cost of operation, including only fuel, 660
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