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Aviation History
1957
1957 - 0022.PDF
22 Research, Development and Technical Issues ... of optimism do not seem to me to alter the following general indications. First, city-centre operation by jet-flap aircraft is not attractive, since the runway length below which cost rises rapidly is not short enough. Next, though the jet-flap aircraft is cheaper to operate than the conventional aircraft for field lengths below 2,OOO-2,5OOft, it is still substantially more costly than a conven- tional aircraft operating from a field of 4,000ft or more. There- fore, it seems to me that since 4,000ft is by no means a difficult length of runway to find, operators will not think the jet-flap type attractive. However, I expect to see interesting results coming from uncon- ventional approaches to the design both of the jet and the struc- ture, the aim being a higher lift/drag ratio, less structure weight, and high mobility in the direction of application of the thrust, . without weight penalty—or, indeed, with a reduction of weight. Applications to Civil Aviation. Long-range, high-subsonic, jet- propelled civil airliners (typified by the figures 480 kl speed, 5,000 , still-air nautical miles range, 25,000/30,000 lb payload) will show | distinctly lower costs of operation than the aircraft they will ! replace. This is the result of the larger annual earning capacity ' with which their speed endows them. At ranges much above ! 5,000 nautical miles the simple-jet high-subsonic aircraft is ' moving into the "difficult" class on the range equation diagram; ; if substantially longer non-stop ranges are required they can best [ be got by the use of a ducted-fan engine, without sacrifice of speed ! or, for even longer distances, by the use of a propeller as the driv- . ing element, with a drop of speed of 70 or 80 kt. But the 4,500- ! 5,000-miles-range aeroplane is undoubtedly capable of satisfying ; a very substantial part of the need, and in this class the jet- I propelled machine is the right answer; I think it will also be the right answer for the medium-to-long-range bracket. There are two particular ways in which greater economy can be brought to this class of machine. Its size can be increased, and it can use a ducted-fan engine. The pursuit of such developments depends on whether the high-subsonic regime is likely to remain a field of high commercial interest for a very long time. I think it un- doubtedly is and I will return to the subject after attempting to justify this statement/ Present-day long-range aircraft have a "formula" direct operat- ing cost, on British standards, of about 24 pence per long-ton n"utical mile. In practice, there is an addition to the formula cost which varies with the route, but in round figures it is about 10 pence. The indirect cost is about 22 pence. For comparative purposes, I will use the formula direct operating cost as a measur- ing stick. The high-subsonic jet aircraft suitable for non-stop trans-Atlantic operation will bring the formula direct cost down to about 11 pence per long-ton nautical mile. To achieve a cost within 10 per cent of this, a "low-supersonic" aeroplane, suitable for the same flight, would have to achieve a lift/drag ratio of about 14. Even if understanding of how to control wave-drag in the early supersonic regime extends further, it seems imprudent to expect anything better than, or even as much as, 14, having in mind that 16 is a very good figure to achieve in a conventional subsonic civil aeroplane. Therefore, long-range civil aviation in the low-supersonic regime will be more expensive than subsonic, and probably by a substantial margin. Looking next at Mach 2.5. an aeroplane capable of non-stop Atlantic operation is in the "very difficult" class. It is extremely sensitive to small departures from ideal in its design. Taking figures of lift/drag ratio and specific consumption that are reason- able on present knowledge, the direct operating cost per long-ton nautical mile cannot be less than 100 pence. This position could *Some hold that greater economy can also be had by the use ofboundary layer control to maintain laminar flow; I do not propose to discuss this here, having done so in another paper. (Jour. Inst. ofTransport: Brancker Lecture 19SS.) FLIGHT, 4 January 1957 improve as our knowledge becomes more exact, but it would be imprudent to suppose that such an ideal state could be reached quickly without substantial experience in this regime of flight. Although I have quoted figures in the previous paragraph for Mach number 2-5—whi.ch is where the combination of airframe and engine is in sight of its best performance—I think that, in considering civil aviation, it would be more prudent to think of Mach numbers in the region of 1-8 or 2, in order to avoid the more serious consequences of kinetic heating, thereby easing not only the structural problem, but also that of temperature control and air conditioning in the passenger cabin. Since overall effici- ency is rising as Mach number increases, figures quoted above for Mach number 2-5 are optimistic for the more prudent choice of Mach number 2. NON.STOP ATLANTIC 'v^-^_ PRESENT PRESENT - ONE STOP DAY COST DEPENDSON CONTROL OF WAVE DRAG ATLANTIC JET NON-STOP , 0, ATLANTIC BIGGER SIZE \^OR DUCTED FAN ' DECREASES COST) Y NON-STOP ATLANTIC / (EXCEEDINGLY OPTIMISTIC: PRESENT—p^KNOWLEDGE t 2,000-MILE STAGE f (MORE L/DLOWER FUEL CONSUMPTION 1 2 MACH NUMBER Fig. 13. Comparison of seat-mile costs for various transports. The place where supersonic civil aviation may become more immediately interesting is clearly at shorter ranges, so that the aircraft is moved out of the "very difficult" into the "possible" class. If one thinks of still-air ranges of 3,000 miles and less (stage lengths a little under 2,000 miles— and these are of interest to a large proportion of travellers), direct operating costs of about 30 pence per long-ton mile at Mach number 2 can be found on prudent assumptions of lift/drag and specific fuel consumption and if optimistic figures are taken, a price of 12 pence comes in sight. This, incidentally, shows how sensitive aircraft of this type are. However, I do not believe that in practice complete refine- ment can be achieved without development, and I would therefor^ rather base assessment of the immediate possibility on figures ir the region of 30 pence, with the knowledge that when experience is gained in this regime of flight there will be room for development that can be favourable to economy. To put the above figures in perspective, Fig. 13 contains a plot of total operating costs (i.e. the direct costs quoted above plus an element for indirect costs). The scale is arbitrary and no more should be read into the plot than that it gives a very rough indi- cation of the overall position. Cost is not the only criterion of service in aviation, but it does control the section of the market in which the greater part of the total demand is likely to be found. What these figures suggest is that on present established know- ledge, and on prudent assumptions about what we may learn in the future, there is no great incentive in cheapness to impel a move- ment of long-range civil aviation into the supersonic regime, as there has been to bring about the present increase of cruising speeds towards 500 kt. But the figures also show that costs may well be achieved which are sufficiently good to attract the smaller section of the market which is concerned more with time and comfort. (To be concluded). NEW RUSSIAN ROTORCRAFT (continued from page 18) the Russian equivalent of the term "helicopter." The prototype was lost in an early stage of flight-development but Kamov went on to evolve the well-known A-7 gyroplane, built in small num- bers for liaison and A.O.P. duties and still in service in 1941. Immediately after the war with Germany Kamov—having in view a "popular" helicopter for purely sporting purposes— embarked on the design of an ultra-light single-seater. It was fitted with two-blade (N.A.C.A. 230 section), contra-rotating, co-axial rotors and had an open-frame steel-tube fuselage and a pontoon-bag undercarriage. To this formula were produced suc- cessive models, culminating in the Ka-10 illustrated. Known as the "Flying Motorcycle" in the Soviet armed forces, the Ka-10 is powered by an AI-4G engine, rated at 55 h.p. at 4,500 r.p.m. The latest variant has a single fin and rudder. Rather larger, but unknown in detail until now, the Ka-15 is used by the Red Air Force as a light general utility vehicle, some- what in the class of the Bell 47 and Hiller H-23. Of particular interest is the rotor, which comprises twin, counter-rotating assemblies each with three blades of wooden and plastic construc- tion with multi-ply covering. The blades are fully articulated in both flapping and drag planes, and are painted and hand-polished to achieve a mirror-like finish. Of very simple form, the fuselage is all metal, the central portion housing the powerplant, gearboxes and accessories and a forward extension supporting the cabin and the twin nose legs. The rear fuselage is a stressed-skin structure, heavy sheet doublers being fitted where the shear is passed from the skeleton structure to the skin. Side-by-side seats for two are provided in the neat and- roomy cabin, which has excellent glazing and a neat instrument panel on the centre-line. The engine is a specially adapted ver- sion of the widely-used 200-260 h.p. nine-cylinder radial family, equipped with a single-speed supercharger and cooling fan. A particular advantage of the Ka-15 is claimed to be its unusual ease of maintenance.
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