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Aviation History
1953
1953 - 0170.PDF
168 FLIGHT, 6 February 1953: FOIL-GAUGE DEVELOPMENTS ONE of the most significant developments in the tech nology of strain-gauge manufacture is the appearance of the Foil gauge Flight, September 19th, 1952), evolved jointly by Saunders-Roe, Ltd., and Technograph Printed Circuits, Ltd., 32, Shaftesbury Avenue, London, W.i. During the past year, use of the technique—a thin, metallic foil cemented to a lacquer sheet and then etched to the strain-gauge profile—has permitted the production of a number of specialized types of strain-gauge which could not conveniently have been pro duced with the use of wire. The Foil-gauge technique is, to quote Saunders-Roe, "so flexibly simple that it is possible to produce any conceivable pattern in two dimensions." The patterns under consideration and illustrated here are for the measurement of torque and fluid pressure respectively. Although accurate measurement of torque is frequently required in aircraft experimental work—particularly where helicopters are involved—it is rarely possible to achieve it by absorbing the torque completely, as can be done with a dynamometer on an engine test-bed. In fact, it is desirable that a minimum of power shall be absorbed by the torque-measuring device. The classical method involves the use of wire strain-gauges applied at 45 deg to the principal axis of the torque-carrying member, the circuit usually being a four-gauge bridge to provide full compensation for bend ing of the member under test. The new Foil torque-gauge is produced as a parallel-sided rib bon in standard lengths of 6 or I2in; there are two parallel pat terns sensitive to strains at 45 deg and 135 deg to the major axis of the strip. All that has to be done is to cut off the required length and cement it around the torque-carrying member. The electrical connections can readily be soldered to the large tags shown as white discs in the drawing. It will be appreciated that the marking out of the shaft, normally a somewhat tedious task, is no longer required. The torque-gauge has, to quote the manufacturers, "all the advantages of the Foil gauge in respect of sensitivity, robust ness, etc., and as an additional aid to the all-important cause of ^sensitivity, if used as described, the strains in the shaft are inte grated circumferentially, and not picked up at only four points as in the case of the wire gauge application." Strain-gauges are also proving singularly useful in the measure ment of hydraulic and pneumatic pressures, the gauge being used to measure the deflection of a flexible diaphragm subjected to the pressure. An application of this nature cannot conveniendy be met by the use of standard linear gauges, and the diaphragm gauge (the double spiral in the drawing) has been developed to integrate the circumferential strains over the diaphragm area. The actual pattern shown is designed for use on relatively stiff diaphragms with small total deflections, but other types of gauge are being developed for application to very flexible surfaces. This last-mentioned type could not be connected to the external measuring circuit in the usual manner because of space restric tions; Technograph Printed Circuits, Ltd., have overcome the problem by preparing a printed and etched copper foil pattern which is laid over the gauge and soldered at the appropriate points. At the present time, there does not appear to be any foreseeable limit to the possible variety of Foil gauges which can be developed. It is significant that, although the technique was initiated by the aircraft industry, the Foil gauge has already found applications in every sphere in which the wire gauge had been used, and by virtue of its simple and robust nature can also be used in more arduous fields. Finally, it may be recorded that Saunders-Roe, Ltd., and Technograph Printed Circuits, Ltd., have entered into an agree ment with H. Tinsley and Co., Ltd., of London, S.E.25, by which Foil gauges will be sold with measuring equipment by the latter company. Tinsleys state that they are developing improved equip ment to make full use of the potentialities of the Foil gauge, includ ing new bridges for accurate static measurement, and robust simple apparatus for general purposes; they also hope to use the Foil gauge technique in electrical measuring instruments. These drawings show the metal foil in white on a black background; the limit of the lacquer base is shown as a broken line. The parallel strips (left) are for torque measurement and the double spiral for the measurement of fluid pressure on a diaphragm. MORE ABOUT THE FLYING SCHOOL CLOSURES ANXIETY about the effect of the Government's decision to i- close down certain flying schools was again expressed in the House of Commons on January 28th, when Dr. Barnett Tanner (Lab., Leicester N.W.) asked the Under-Secretary for Air whether he would reconsider the decision in view of the adverse effect on air training. Mr. George Ward replied that he would not. The Secretary of State was satisfied, he said, that the future requirements of the Royal Air Force for pilots and navigators could be effectively met without making use of the 16 schools. Mr. Janner asked if Mr. Ward was aware that that was not the opinion held by those who had been studying the problem outsie'e the Ministry. Mr. Ward replied that very careful consideration had indeed been given to the matter in the Air Ministry, and that the step was being taken with the greatest possible reluctance. Mr. W. R. D. Perkins (Con., Stroud and Thornbury) was then informed that the Minister had written to B.A.L.P.A., who had again requested a meeting with him, and had made clear that both he and the Under-Secretary were only too anxious to meet them at any time to discuss the problems arising from closure of the schools. It had also been made clear, however, that the question of costs could not be discussed with them. Mr. A. C. Manuel (Lab., Central Ayrshire) said that the pilots and navigators concerned had been asked to make superannuation contributions after one year's service. Was it proposed to give them employment to ensure the continuation of the superannua tion they had been paying in the past? Mr. Ward replied that the question of superannuation was one between employer and employee, and the terms of the contracts between the civil firms and the Air Ministry were perfectly clear. A. Cdre. A. V. Harvey (Con. Macclesfield) then interposed that the terms of contract made no allowance at all for pension rates and the onus was quite clearly on the Air Ministry. Mr. Geoffrey de Freitas (Lab., Lincoln) asked for consideration of the position at Kirton-in-Lindsey which opened only last year and where, according to the Under-Secretary's own statement on a previous occasion, the staff were led to believe there was a three-years' agreement. Mr. Ward repeated that he could only assure Members that the matter had been examined in all details. While the Ministry always kept an open mind, he could assure them that the decision was not a hasty one. G/C. Wilcock (Lab., Derby North) then asked the Under- Secretary whether, in view of the anxiety which had been caused to flying instructors and ground staff of V.R. schools by the uncertainty of the future of V.R. training, would he now give an assurance that no such schools would be closed other than those already notified. Mr. Ward replied that, while appreciating the anxiety of instructors and other staff at V.R. schools, he regretted that he was not yet in a position to make a statement about the Ministry's future reserve requirements. He promised to deal with the matter fully in the Air Estimates debate. G/C. Wilcock asked if the Under-Secretary was aware that, owing to the uncertainty of the future, pilots and ground crew mechanics of these schools were now seeking employment outside aviation and outside the country. He asked for an assurance that no further damage was to he done to the training organization of this country by the closing down of further schools. Mr. Ward said he could not accept the implication that such damage had been caused. Mr. Frank Beswick (Lab., Uxbridge) observed that the Under- Secretary had in fact created "alarm and despondency" throughout the industry, and ought to do something to stabilize the position.
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