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Aviation History
1958
1958 - 0583.PDF
2 May 1958 599 As to variable-speed alternators, there is nothing new in the asynchronous induction machine. It is over thirty years old. It has a disadvantage in that the range of speeds over which it will maintain constant frequency output is very limited—far too limited for aircraft use. Unless this can be extended—and present indications give little hope for optimism—it is useless and contri- butes nothing to what has already long been known about the machine. Fundamentally there is nothing in an aircraft system which justifies the use of three-phase A.C. Where space is limited and high starting torques on small motors are required, then D.C. stands supreme. This has been proven indisputably on rail-traction schemes. Even with overhead A.C. lines the current is rectified before being applied to the motors. By all means let us have higher generated voltages but for the maximum load needed on the largest of aircraft there is no need to exceed 112 volts, which in only very exceptional cases can cause physical hurt through shock. For the A.C. requirement of electronic equipment, single- phase supplies avoid all problems of differing voltages on phases and cross-phasing. Gyro motors will run just as well on single- phase as on three-phase. Fundamentally it is the right system for the particular field of application. Why, then, are we shy of using it? There appear to be two objections. First, the output of an alternator is far greater than that of a generator within the same frame size. Second, there is the brush-wear problem, on which I have already commented at the symposium. The first is valid but I am certain that a redesign of the generator on an inverted basis is possible which could almost, if not quite, meet the equivalent output D.C. of the alternator. Development costs? Let us say £100,000. Chances of success? Extremely high. The second has been within an ace of solution in many research programmes which have been prematurely cut without valid tech- nical reasons. The commutator has not changed either in con- struction or design over the last 50 years, not because it is incapable of being improved upon but because it has so far satisfied the bill. But that is not to say it cannot be improved. Let us put the development cost at £50,000. For £150,000—and this is a realistic outside figure to a deter- mined development group—the objections to the D.C. system could be removed. (Compare this with the millions of British and American public money spent on A.C. system development.) It has already been established that the 115 volt D.C. system works and works well. Consider the Valiant. This, as the chief electrical engineer of Vickers-Armstrongs recently said before a distinguished American audience, "is an exercise in forward design which has contributed much to our present-day knowledge and practice and its influence has been felt not only in subsequent military aircraft but in civil airliners both current and future." That is a fully justified remark. Electrically the Valiant is one of the most reliable military machines in any country. Of course, some "clangers" were dropped during its development and the lessons properly and truly learned; but, compared with those on rectified A.C. and paralleled A.C. systems both past and current, they are as the tinkling of a bicycle bell to a full-blown peal. It seems such a pity to waste this valuable knowledge. Now why should this be? So far as I can see, ; 1 British aircraft design- Lull ers are largely governed U i/i in their choice of system " •' ^ by the airline operators. They, in turn, in this ". . . 05 the tinkling of a bicycle bell to a full-blown peal." country, being a nation- alized industry, are ad- vised by the Ministry of Supply who, in turn, are advised by the R.A.E., who, in turn, are influ- enced by NATO deci- sions which tend towards the acceptance of American standards, right or wrong. In this sort of business the Gadarene swine have nothing on the aircraft industry. Yet we have, if we care to exer- cise it, the aptitude and the technical knowledge to stand four square on our own feet. * * * Now on a personal note. One of the symposium authors in his reply asked: "Are all the aircraft electrical engineers except Mr. Hill out of step?" Even if this were true the answer is still "Could be!" Gallileo, in his time and place, was the only one who insisted that the world was round. But that did not make it flat. In matters of fact majority opinions just don't count. However, I am by no means the first or the only one who holds to these views, otherwise the Valiant system would never have seen light. It has not been my practice constantly to blossom forth into print or to read papers before learned societies; but for more than thirty years I have been closely associated with electrical technical and design matters in every field, both A.C. and D.C., from the highest voltages to the lowest, and I have clung all the while to sound fundamental precepts. I think I may claim to have a fair know- ledge as to which supplies are most suitable for which services. In my own small sphere I have a reputation for being right far more often than being wrong. I wish the same could be said for many who hold responsible positions in the industry today. Well, those are my personal views and I intend to stick to them. To borrow a phrase from the old Western pictures, "Them's fighting words," and I may be taken to task for uttering them; but, seriously, matters are now far too critical for personal con- siderations to count. Both in Great Britain and America the future of the aircraft industry— with its tens of thousands of workers, its millions of capital, most of it held by small investors 'Them's fighting words!" —and, above all, the safety of air travellers of all ranks and ages, will depend upon the cool and accurate judgment—I might add selfless judgment—of those who now hold the reins. A decision for political reasons, leading to a false selection of a wrdng system can mean, at the very least, long delays in the delivery of an aircraft urgendy needed to compete in the world's markets or, worse, an even longer record of unserviceability with the airlines. Possibly, since aircraft systems are today inextricably tied with air safety, it may lead to disaster. I am practically certain that unless the industry shows a remark- able change of heart and is prepared to sacrifice gimmicks to sound fundamental design it will not need the foregoing views; but at least, for once, they are on record. EXPERIMENTAL AERODYNAMICS TRAINING NOW in its second year of operation, the Training Centerfor Experimental Aerodynamics (T.C.E.A.) at Rhode-Saint- Genese in Belgium was established to train scientists and engineers from NATO countries in the techniques and operation of a modern aerodynamics laboratory and also to disseminate information on aerodynamics and related subjects. So far, students from eleven NATO countries have taken the course. It lasts nine months, starting on October 15 and ending on July 15, and includes the following aspects of study: wind tunnels and basic instrumentation; basic electronics; measure- ments in steady and in non-steady flow; and transonic and hyper- sonic aerodynamics. The present aerodynamic facilities consist of two wind tunnels, one supersonic and the other low-speed; and it is planned to increase these facilities so as to cover the whole speed range up to hypersonic. There are also electronic, optical and photographic laboratories and shops for metal and wood machining. The electronic laboratory has a wide range of instru- ments for studying and developing equipment used in aerodynamic tests; and the optical one is equipped to cope with most problems encountered in the photographic and film recording of aero- dynamic phenomena, and to develop devices such as the Schlieren systems. The chairman of the directing board of T.C.E.A. is Professor Theodore von Karman, the technical director is Dr. R. Paul Harrington and there is a total staff of about 50. Scientists of international repute are invited throughout the year to give lectures and demonstrations. There is no tuition fee for the course but those wishing to take it must have a B.Sc. in engineering, science or mathematics (or the French or U.S. equivalent degree) and a knowledge of incom- pressible and compressible fluid mechanics; while some know- ledge of basic electronics is desirable. A limited number of scholarships is available; tuition is in both English and French; and at the conclusion of their course successful students are awarded certificates. Application forms and further information may be obtained by writing to the Technical Director, Training Center for Experimental Aerodynamics, 72 Chaussee de Waterloo, Rhode-Saint-Genese, Belgium.
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