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Aviation History
1957
1957 - 0053.PDF
FLIGHT, 11 January 1957 53 Research, Development and Technical Issues . . . plate, to which stress was then applied. The graph shows howthe crack grew under additional stress. Rapid growth starts in each case at about the threshold for an unreinforced plate; thissuggests that the condition for the start of self-propagation is local in character and is uninfluenced by the presence of the stoppers.Thereafter, rapid growth took place in the specimen using a rivet- ing stopper, until it was arrested at the inner rivet-line; the speci-men then took a higher stress until it failed. When the stoppers were attached by an adhesive (Redux) the growth was slower;when the stopper was machined integrally with the plate, the growth was also slower but failure took place earlier than in theReduxed specimen, occurring when the crack reached the fillet On the stopper. With the accumulation of empirical data of this kind, it is likelythat before long the mechanism of cracking and tear resistance will be much more understood, and "fail safe" design will becomefirmly based. Noise from Aviation. The noise on the ground from aircraft inthe air is not unnaturally becoming a considerable issue in public affairs. It is sharpened as an issue by the fact that, at presentanyway, the people on whom the noise descends are, for the most part, not the people who enjoy the benefits of aviation. I thinkthat there is no doubt that those who do enjoy its benefits must be willing to pay a little more in order to reduce the impact onthose who do not. In this section I want to discuss, in the broad only, what has caused noise to emerge more importantly andwhat the cost to the traveller will be to keep it in bounds. I am indebted to Mr. Greatrex of the Rolls-Royce Company fordiscussions on this matter that have cleared my own mind and I have quoted figures from a recent paper on the subject writtenby Mr. Greatrex. First, it is important to realize that the size and cruising speedof an aircraft controls the noise it makes, because this is related to the power of its engines. A large part of the present day worryabout noise is caused by the fact that aircraft are larger than they used to be. There will, of course, be detailed differences in designbetween aircraft which will affect comparison of the noise they make, but in the broad it is inevitable that an increase of weightfrom 30,000 lb to 300,000 lb will involve an increase of noise of about 10 decibels. This is a factor which has some bearing onwhether aircraft will get bigger, and therefore more economical, as discussed in a previous section, though it is an open questionwhether a louder noise less often would be preferable to a lesser noise at higher repetition rate. It will also have a bearing onwhether jet-elevated vertical take-off aircraft could be used for city-centre operation; they have an installed-thrust which exceedstheir weight and must be very noisy. Then there is the influence of the introduction of jet propulsion;the character of the noise from a jet engine is different from that due to a propeller engine. In a propeller-driven machine, thepropeller itself is a major source of noise; this is added to by the engine exhaust to an extent that depends on the type of engineand on its installation. Making allowance for increase of size and cruising speed, on apessimistic basis future jet-engined aircraft of the 300,000 lb class, without provision for noise suppression, will be about 18 decibelsnoisier than quiet present-day pistoned types, and 8 decibels noisier than noisy present-day types. We are now confident inEngland that we can more than bridge the gap between the large jet transport and present-day noisy types. The use of a by-passengine, which gives a lower jet velocity than the simple-jet, for the same thrust, drops noise by about 3.5 decibels. In passing,the use of a ducted fan would drop it much further. Next, means have been found by the use of a development of a corrugated nozzleto produce a further reduction of about 7.5 decibels, giving a com- bined reduction of 11 decibels. This will make the future largejet quieter than present noisy piston types, though still rather louder than present quiet piston types. To produce this effectthe nozzle must be very corrugated indeed: relatively minor corru- gations have a much smaller effect. Jet engines need thrust reversers and it is therefore desirablethat the jet pipe should incorporate a noise-supressing nozzle and a thrust reverser. Successful designs have been evolved incorporat-ing both, but these are not, of course, without their cost. It is difficult to separate penalties resulting from each of these twoitems, but dealing with the noise suppression alone, and taking together the effects of loss of cruising thrust, the drag of theinstallation and the weight penalty, it emerges that the overall result on a large long-range jet aircraft is equivalent to an increasein cruising specific fuel consumption of about 2 per cent. If take-off length is critical, the effect of loss of take-off thrust mightbe equivalent to another 1 per cent increase in specific fuel con- sumption. The increase in the cost of the seat-mile will dependon the flight plan; but in very round figures the passenger will pay about 6 per cent more on internal routes and 9 per cent moreon trans-Atlantic routes than the fare the aircraft could other- wise offer, in order to relieve the people on the ground. The field remains a fruitful one for research. We have by nomeans a full understanding yet of the way in which corrugated nozzles produce their effect, though there are some theories inoutline. Conclusion. I have not set out in this lecture to reach, or toadvocate, any particular conclusion. But in writing about aero- nautical research and development, and on some of the technicalfactors which will influence the next phase of aviation, it is diffi- cult to resist the temptation to think in broader terms of whataviation has done and will do. The world has needed aviation, and has set out to get it, to an extent that has caused it to be abovemost other things the mainspring under which the methods of organized research have developed; these methods are now rapidlyspreading throughout other technologies. But the reason aviation has been so much sought after—and will continue to be so—is thatit has exerted a greater influence in a shorter time over a wider area of politics and sociology than most other developments, andits powers in this respect are still nearer their beginning than their end. Mobility of people and of heavy goods has had as great an effecton the broad trend of world affairs as most other factors. Political integration has been greatly influenced by it, because it is thecapability of moving men and material with reasonable dispatch to the limits of a political area that gives point to the rule of what-ever law applies within it. Internal transport and internal com- munication systems have set a limit to what it was reasonable toattempt to govern, and it has generally been the case that when that limit was exceeded the outlying districts did not for long—in historical terms—stay within the orbit. By providing a method of movement at much greater speed, with a by-no-means negligiblecapacity for quantity, and with greater indifference to geographical features than most other systems, aviation has already had adecisive influence on world affairs and will in future exert an even greater one. In recent years civil aviation has matured and is in sight ofhaving tools for its job which are excellently suited to it; that this is so will become quite clear when the ancillary services on theground have been adapted, as they can and must be, to meet the needs of the new aircraft. Civil aviation has before it an enormousexpansion; this will come from a pursuit of economy in the cost of the seat-mile, which will succeed, and which will open up airtravel to a far wider cross-section of the world's population than use it now. Civil aviation has expanded in recent years at a ratewhich exceeds that achieved by most other industrial enterprises at a comparable stage in their development; on airlines operating inthe Western World, two million passengers were carried in 1937, and over fifty million in 1953. Air freighting has also shown aconsiderable expansion; there was a tenfold increase in freight ton-miles carried by Western World scheduled operators between1946 and 1955, and this has been done largely with adapted air- craft rather than with machines particularly designed for thepurpose. Freight will follow the passenger trend—it will go faster and be turbine-propelled—and it is likely that the market willrespond to the increasing availability of machines particularly suited to its purpose. In the military field aviation's first major influence was to restoreto land battles the mobility that they had lost, and so to alter radically the character of land war. Land battles had becomestatic in the first world war because it took a long time to con- centrate for an attempt at a break-through, and during this- timethe other side, becoming aware of the build-up of strength before it, were able to group to meet the attack when it came. Tacticalaviation changed this; improvement on ground transport per- mitted more rapid concentration, while, if air superiority had beenattained, interference from the air frustrated counter-grouping. This was the major effect of aviation on the second world war.But, throughout the development of long-range aviation, the con- cept of dominance by the bomber being decisive in itself had beencanvassed. This latter possibility was not in fact in sight until thedevelopment of atomic explosive which, by providing a vast increase of hitting power at a moderate weight, permitted thedesign of aircraft for its delivery having far longer ranges than those previously used for bombing. This has made possible thepolicy of the "nuclear deterrent"; it has also made a radical change in the distribution of the air threat. The political reaction ofcountries to world situations are inevitably governed by the direct threat to their homeland and one of the big influences whichaviation will have on world affairs in the next decade will arise from the fact that the U.S.A. has joined the other major Powersin being under a heavy direct aerial threat. The extent to which the political effects arising from this willbe moderated by technical advance in air defence remains to be seen. The nuclear bomb, by multiplying something like a milliontimes the explosive power that can be delivered by a single aero- plane, has relieved the offensive of restraint in range, in end-point accuracy and in sensitivity to losses, and defence has there- fore a large burden to overcome if it is to be of account. Thisburden is made the heavier by the fact that defence depends vitally
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