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Aviation History
1958
1958 - 0335.PDF
14 March 1958 351 Research THE ELEVENTH LOUIS BLERIOT LECTURE ON March 5 the eleventh Louis Bleriot Memorial Lecturewas read before the A.F.I.T.A. in Paris. The author ofthe paper was Professor W. J. Duncan, C.B.E., D.Sc, F.R.S., F.R.Ae.S., M.I.Mech.E., Professor of Aeronautics andFluid Mechanics at Glasgow University. His paper ranged far and wide across the fields of aerodynamics, propulsion, politics,finance, air traffic control, the dissemination of knowledge, educa- tion and other diverse factors. The paper began with an assessment of the future outlook foraviation generally, and Professor Duncan was emboldened to state: "In my opinion the aircraft industry of the world has a tremen-dously important future and those nations who have a lead in this industry will unquestionably reap a great reward." He did, how-ever, note that, although it was possible that (for example) it might fairly soon be practicable to send a reconnaissance satelliteto the moon, astronautics in general would not have much influence on the aeronautical industry "for a long time to come." Going on to discuss the basic aims of research, Professor Duncansuggested that aeronautical research was notoriously expensive, being carried out in an atmosphere of extravagance stemming fromthe need to win wars regardless of cost. Even in commercial avia- tion an atmosphere of extravagance was engendered by considera-tions of national prestige and, in the past, the readiness of the public to pay extravagantly for the real advantages of aerial trans-port. A related factor was that aeronautics had been given "an extravagant licence to become a nuisance to the public," and itwas the lecturer's view that an important aim of research would be the elimination of aeronautical nuisances of all kinds. The major part of Professor Duncan's paper was devoted to astudy of eleven aspects under which aeronautical research is at present being conducted. First and foremost—since it was theaeronautical science par excellence—came aerodynamics. Under this heading Professor Duncan briefly discussed flows at very highMach numbers and very low mean densities, and went on to point out that it was now realized that in certain circumstances, suchas those pertaining to very thin wings in high-speed flight, it was advantageous to permit flow-breakaway to occur. Turning next to the kindred subjects of materials, structuresand strength, Professor Duncan emphasized the widening appre- ciation of the fact that the strength/fatigue/creep complex wasa single subject which could be understood and mastered only through the avenue of the fundamental physics of metals. As inthe case of aerodynamics, the problems of stress analysis and dynamics of aircraft structures were becoming far too complexfor exact solution. On the subject of propulsion, Professor Duncan said: "I offer no opinion about the ultimate feasibility of the atomic propulsionof aircraft. ... It appears that the aircraft must be enormous by present standards and atomic propulsion seems unlikely tocome into use for some decades." Next topic for discussion was entitled special aircraft and projects, and under this heading theauthor compared helicopters and other types of VTOL and STOL machines and went on to suggest that, if land-based and water-based [transport] aircraft competed on a fair footing, the latter might be found the more economical. After discussing groundinstallations, communications and navigation, the lecturer spoke of meteorology and made a plea for intensive work into atmo-spheric turbulence and for the further investigation of jet streams. On the number and complexity of the mathematical calculationsrequired in the design of an aircraft, Professor Duncan suggested that, while recognizing the importance of the electronic computer,he was convinced that there was still great scope for the improve- ment of the mathematical techniques employed. He then turnedto a discussion of the problems posed by the need for disseminating the enormous output of scientific and technical papers—"so enor-mous that research workers are in danger of smothering themselves beneath their own products." It was not easy to make constructivesuggestions, but the ultimate solution would have to depend on international and voluntary co-operation. Conferences were valu-able, owing to the personal contacts made and the dynamic inspira- tion of the spoken word. In some countries the writers of text-books deserved increased support, and a thought-provoking sen- tence at this point of the paper is "in spite of the glamour ofdiscovery, it may soon be a more valuable service to the com- munity to publish a lucid and accurate account of the subject thanto discover new knowledge, except of a very fundamental nature." In the next section, Professor Duncan discussed education forresearch. He outlined some suggested qualities which a good research worker should possess, and in his opinion the mostimportant was "interest in the subject, coupled with energy and dogged determination" Several of the good qualities desired ina research worker truly stemmed from basic character formed at a very early age. In his conclusion, the lecturer reiterated the view that,in future, aeronautical activities would have to be conducted in a truly economical manner and that in aeronautical research realefficiency was needed rather than narrow financial economy. Carried to the extreme, strict application of the rule "no duplica-tion of effort" implied a complete international pooling of research programmes which at present was plainly out of the question.Actually it was the lecturer's view that, although extravagance was to be avoided, some duplication was desirable. ROCKET GUIDANCE AND CONTROL AT its meeting on March 1 the British Interplanetary Society- heard a lecture on the guidance and control of long-range rockets. The paper was by Professor G. A. Whitfield, of theCollege of Aeronautics, who discussed the aiming of ballistic missiles, at the end of burning, to hit a chosen target. He notedthat, to avoid too much mass being carried in the missile, the guidance was best performed while the engines were still firing,so that side-thrust could be got by tilting them. This required that, at cut-off, a combination must be obtained between missilespeed, elevation angle and azimuth angle which suited the position at which cut-off occurred. There was always a value of the elevation angle which resultedin a minimum launching speed, and operation at this angle had the further advantage that errors in angle did not have much effecton the impact point. For the errors which might be tolerable in a ballistic missile—say, two miles at 2,000 miles' range—the cut-off velocity had to be kept within an error of 7ft/sec in about 12,000ft/sec, with anerror in azimuth of about 0.1 deg. The lecturer went on to show that radar and Doppler can giveestimates of range and radial velocity which are sufficient for this purpose, and that lateral resolution is also good enough, providedthere are no errors due to imperfect radio propagation. In the high atmosphere, in the presence of ionization, the velocity ofpropagation is appreciably different from that in vacuo, and considerable refraction may also occur. Alternatively to radiomethods, use may be made of an inertial navigation system. This consists essentially of a platform in the vehicle which is stabilizedin space by having three gyroscopes mounted on it. Three accelerometers are carried on the platform, which, by integration,give an indication of the position and velocity at any time in the flight of the vehicle. Severe limitations are given to the errorswhich can be tolerated in the gyros and accelerometers which are actually used: a drift of 0.2 deg/hr in the gyros, compared withabout 30 deg/hr for aircraft instruments, is all that can be allowed, while zero error and hysteresis in the accelerometers must beminimized. When solid-propellant motors are used for ballistic missilesit is not usually possible to arrange cut-off at an exact velocity, but the motor must be allowed to burn out completely. It is thusnecessary to adjust the elevation angle to resist the velocity, and this is done continuously during firing so that the target erroris minimized. For the successful placing of a satellite vehicle in an orbit, theaccuracy required in the navigation system is very much less than that needed in ballistic missiles, since quite large variations in theheight of the vehicle above the Earth can be tolerated. For 100 miles' difference between apogee and perigee altitudes, a 500m.p.h. error in cut-off velocity, or a 1 deg error in elevation, could be accepted. However, the satellite system is more compli-cated than the ballistic missile, since it is necessary, for efficient working, to burn the first-stage propellants fairly quickly andthen let the vehicle coast up to the orbit height. This means that, unless special precautions are taken, the attitude of the later. stages may be anything but horizontal and in the right azimuth when they are due to be fired, and so some stabilization must beprovided. In the American Explorer vehicle, this is done by making the three solid-propellant stages, mounted on the nose ofthe Redstone which forms the first stage, into a large gyroscope; the cluster of motors can rotate about die launching-vehicle axis,and, before launch, it is spun up to some 750 r.p.m. This main- tains the attitude of the vehicle constant in its coast after first stagecut-off; this coasting flight is made of such length that the trajec- tory starts to droop before the solid stages are fired, so com-pensating for the upward component resulting from the up-tilted attitude of the vehicle, and giving a reasonably circular orbit.
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