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Aviation History
1957
1957 - 1384.PDF
474 FLIGH7 THE FOLKESTONE CONFERENCE . . . flight, compared with the types of VTOL horizontal-attitude air-craft described in the lecture, but would have a speed penalty. Dr. T. P. Wright of Cornell Aeronautical Laboratory adapteda Stout quotation to the VTOL concept; the problem, he said, was to obtain a vehicle that would support itself financially in theair. The need was great for the final vehicle at which the N.A.C.A. research was aimed. Air. J. J. Foody of Shorts expressed surprisethat qualitative agreement between the stability and control be- haviour of models and full-scale aircraft had been found: couldnot stability investigations be carried out, he asked, by wind- tunnel tests plus computing procedures? Extensions of both classical aerodynamic theory and experi-mental techniques were required by these new concepts, suggested Mr. Raoul Hafner (Bristol Aircraft). Mr. F. H. Robertson(Shorts) asked whether calculations of the relative economics involved had been made. Replying, Mr. McKinney said that, on the military side, therewas a clear-cut need, and the ability to pay, for VTOL and STOL aircraft. Detailed studies were needed to decide the possiblecommercial applications. It seemed that intermediate ranges would be best suited to these aircraft, with helicopters or convertiplanesfor the very short stages. An intermediate-size VTOL aircraft for stage-lengths of 1,000-1,500 miles could probably be built, butwould be 50 per cent larger and more expensive than conven- tional machines in this class. Interest in the subject of the lecture had been so great that aninformal continuation discussion took place elsewhere in the hotel while Dr. Dunworth was presenting the conference's secondpaper. At this meeting, in reply to suggestions that the free-flight modeltechnique suffered from severe limitations caused by the higher model frequencies and low Reynolds number, Mr. McKinneystressed that the information gained from such tests was essen- tially qualitative. It had shown very good agreement with full-scale flight, however, when allowance was made for the effects of size on the frequency of oscillations. In contrast, simulatorstudies had often proved very misleading because of lack of know- ledge of some of the derivatives—and in some cases importantderivatives had been neglected entirely. In connection with the optimum designs for various duties theimportance of specifying the hovering time was stressed. It seemed to be generally agreed that if an appreciable period ofhovering was required, or if short flights were involved, then the helicopter layout was the best choice. It was confidently expected that military VTOL and STOLaircraft would appear in the next few years, but views were divided on the commercial side. On the one hand it was arguedthat the poorer direct operating costs of the VTOL aircraft would be all-important; on the other hand, the saving in both moneyand land for airfields, it was submitted, would outweigh the increased operating costs. While the economics of civil-aircraft operation was undoubtedlyimportant, it was considered that the problem of engine failure at take-off was even more vital. Interconnection of the lifting unitswas essential, and some reserve of thrust over weight was neces- sary. The attraction of having a large number of separate liftingengines as suggested by Griffith of Rolls-Royce was very evident. Concerning the take-off and landing manoeuvres, it was sug-gested that these should be carried out entirely automatically. The lecturer said that, in his view, the aircraft should be controllableby the pilot in these manoeuvres, but he admitted that the N.A.C.A. was divided in its views on this subject. Noise was another problem that came up for discussion. Againthere was controversy, one school arguing that the VTOL aircraft would confine its noise to a smaller area, other speakers arguingthat, although this was true, the aircraft would often be operating closer to densely built-up areas. Under the chairmanship of Rear Admiral Laurence B. Richard-son of the General Dynamics Corporation, the second technical session was concerned with the paper by Dr. J. V. Dunworth,Nuclear Mobile Propulsion with Particular Reference to Aircraft. The lecturer, who is head of the reactor division of the U.K.Atomic Energy Authority Research Group, said that preliminary work associated with an aircraft project would probably takeseveral years. The design, construction and investigation of proto- type and experimental systems would take several more years, andit would be unreasonable to think that an aircraft project could reach the stage of completion of a prototype in less than 15 years. Commenting on his written paper, Dr. Dunworth said thatanything that was worth saying (concerning nuclear propulsion for aircraft) was, on the whole, secret. Admiral Richardson opened the discussion by suggesting thatthe first nuclear-powered aircraft might be seaplanes, for reasons of safety. Dr. T. P. Wright emphasized that nuclear aircraft wereinevitable; engineers were more optimistic than basic scientists, he said, as to the time period involved. Dr. J. W. Drinkwater(Ministry of Supply) criticized the lecturer's pessimism: why TAKE-OFF Fig. 4. Estimated take-off and landing distance for max' ALLOWS FOR CLIMB \ AT FULL POWER FULL POWERS 8=70° 0 .2 .4 .6 T/W should reactors occasionally suffer sudden and complete shut-downs, and were not some of the paper's weight estimates unduly conservative?Some of the technical problems of designing a nuclear propulsion system for aircraft were raised by Mr. G. E. Preece (de HavillandEngines), who said that, in addition to establishing the technical feasibility of such a project, it must be shown to fulfil a vitalmilitary role or to have economic possibilities as a civil transport. Monday afternoon's papers were both concerned with powerplants, Control of Supersonic Propulsion Systems, by John C. Sanders of the N.A.C.A. Lewis Flight Propulsion Laboratory,dealing with air-intake diffusers; and The Electrical Control of Power Plants, by G. M. Sturrock of Ultra Electric, referring to the"electric throttles" of the Bristol Britannia. The problems covered in Mr. Sanders' paper, which was pre-sented at a session chaired by Dr. E. S. Moult of de Havilland Engines, arise from the fact that the variation in critical airflowfor efficient operation of the diffuser at supersonic speeds does not correspond in general to that required by the turbojet or ramjet.Thus control of diffuser and engine to make these requirements compatible can improve aircraft performance.In the discussion following the paper, Dr. J. Seddon (R.A.E.) emphasized that the overall control problem involved a numberof specialist approaches—by the airframe and intake aerodynami- cists; by the engine aerodynamicists; and by the control-systemengineers. If shock-sensing was by simple tapping or probe, would there not be a boundary-layer effect? Mr. H. Pearson of Rolls-Royce described the effect of an ejector nozzle on intake matching; the ejector type appeared to have advantages over bodi fixed andvariable convergent-divergent nozzles. Mr. J. E. P. Dunning (R.A.E. Westcott) suggested that theengine designer should ignore the aircraft (when considering intakes) and should use pods, enabling the intake to do its jobwithout compromise. At speeds of Mach 3-4, the matching problem could be minimized by using turbo-rockets. Mr. W. J.O'Donnell (Republic Aviation) described his company's approach which, accepting a lower value of pressure-ratio, involved the useof a known type of intake for an initial programme. Variable-area inlets had been flown, with good results. Mr. Sanders commented that the boundary layer did tend togradualize the pressure-change across the Shockwave, but this had not affected the control. The shock could "hang on" to aprobe, however. It was not known from laboratory work how important it was to guard against the diffuser operating away fromoptimum conditions. The suggested ejector nozzle appeared to form part of a difficult problem. Mr. Sturrock's paper described the "electric throttles" used tocontrol the Proteus engines in Bristol Britannia aircraft, as an example of the general approach to the problems of the electricalcontrol of aircraft powerplants. This installation was felt generally by B.O.A.C. to be very good, only three in-flight failures of thesystem having been experienced by the Corporation up to September 6. Chairman of this session was Dr. E. R. Sharp ofthe N.A.C.A. Lewis Flight Propulsion Laboratory. Mr. Sanders opened the discussion by pointing out that thebasic assumption of temperature control demanded electronic control. With temperature control one was sensing a basic damagelimit. Disillusionment with the reliability of many kinds of elec- trical components was emphatically voiced by Mr. D. Gerdan(Allison Division of General Motors): "Capacitors won't capaci- tate; resistors won't resist; and—strangely—connectors won'tconnect . . ." The elimination of vacuum tubes by magnetic amplifiers—or by transistors, as his own company was doing—was only the start of a long process of improvement. Mr. Sturrock, replying, referred to the problems of magnetic-amplifier stabilization and of thermocouples; the sensitr ity demanded was 0.04 mV/deg. Temperature control was accurateto ± 5 deg C over the ambient temperature range — 50 to + 70 ieg C; and his company was aiming at 100 deg C as the upper limit.
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