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Aviation History
1960
1960 - 0554.PDF
554 FLIGHT, 22 April I960 Cranfield's Flight-Test Symposium ON Thursday and Friday, April 7-8, over 200 people attendeda symposium on flight-test instrumentation at the Collegeof Aeronautics, Cranfield. They included representatives from aircraft firms and instrument manufacturers having connec-tions with this specialized branch of aeronautical engineering, and overseas delegates from Australia, USA, Holland and France. Many delegates commented on the timely nature of the sym-posium; with new-generation aircraft such as the TSR.2, D.H.121 and Bristol 188, a radical change is taking place in the techniquesassociated with prototype flight-testing. A great deal of interest was shown in radio telemetry and magnetic-tape recording asbeing the only airborne data-acquisition systems which would provide the answer to the problem of the large number of quan-tities to be measured in these aircraft. The meeting was sponsored by the Department of Flight at thecollege, and the papers were arranged to cover a wide range of subjects including transducers, recording techniques, datahandling and analysis, and future flight-test requirements based on research being carried out in Ministry establishments. Thefull list of papers was printed in the April 8 issue of Flight. The present trend in the number of measurements to be madewas illustrated (see diagram) by T. Kerr of Aero Flight, RAE Bedford. Tracing events back to the early 1900s when flighttesting was carried out by a sensing element known as "seat of the pilot's pants," he was able to show the tremendous increase sincethen in the number of measurements required. There is certainly a limit to the amount a pilot can be asked todo in a modern aircraft. One way of helping him, and an argument that was put forward as a case for telemetry, was described ina paper by T. Heffernan of A & AEE, Boscombe Down. During the spinning trials of tho Scimitar, he related, certain informationwas telemetered to the ground and another pilot familiar with the aircraft was able to re-orientate the pilot in the aircraft duringthe spin, if necessary, by using this information. The telemetered quantities were airspeed, altitude, rate of roll, rate of yaw, andaileron and rudder angles. Although this seemed a convincing argument for the use ofradio telemetry, some delegates were doubtful as to whether it would form the sole method of obtaining accurate flight data. Itcertainly performs a useful monitoring function, however, and W. L. Horwood and J. Walsh (Radio Department, RAE) indicatedhow this monitoring function could be improved to provide a complete data-acquisition system. On the question of accuracy, however, D. M. Ridland (RAE,Bedford) surprised many delegates by showing the order of accu- racy required to evaluate aircraft transfer functions. Typicalvalues for the longitudinal case were: — Elevator IncidenceC.G. acceleration Rate of pitch Range4° 2' lg14°/sec Resolution required0.0067° 0.0033°0.0017g 0.0233°/sec Instrument designers and manufacturers must obviously strivefor an order of accuracy higher than that currently accepted for flight testing. Mr Ridland thought that this could not be achievedwith electronic aids and black boxes, which he seemed to distrust. This opinion caused a certain amount of argument, especially inview of remarks by D. A. Drew of Rolls-Royce that the flight-test engineer of the future must be a qualified electronics engineer. Two instruments which are capable of the above order ofresolution were described by W. R. Macdonald (RAE Farn- borough) and W. Horath (SFIM, France). The force balanceprinciple or, as it is sometimes called, the servo transducer, can give as an accelerometer a range coverage of +0.01g to ±10g Airborne units of the Ampex AR200 all-solid-state magnetic tape- recording system, displayed at the Cranfield symposium full-scale in one instrument with, according to Mr Macdonaldextremely high stability in its dynamic behaviour. These trans- ducers have been used in the USA and also in Holland, accordingto T. Van Oosterom of NARI, Amsterdam, for in-flight thrust measurement. M Horath gave details of the design and performance of asemi-floated rate gyroscope with an extremely good threshold performance and which incorporated a novel multipole inductivepick-off. One instrument nominally rated at ±20° /sec full-scale with a resolution of 0.001 per cent and a natural frequency of30c/s had a linear range extending to 120°/sec. The Instrumentation Department of RAE Farnborough waswell represented at the symposium. Dr G. E. Bennett gave a review of the techniques of magnetic tape recording and the scope mI • I 2- 6CO-, 4OO- 5 CO 2OO- MAGNETIC TAPE t TELEMETERY l«. REQUIREMENT FOR ELEVATOR ANGLES TRACE RECORDERS I9IO I92O I93O I94O I95O I960 Variation of number of measured quantities with time (from paper by T. Kerr), from seat-ot-pants days to the present of its application to aircraft flight-testing, considered in terms ofdata capacity, data bandwidth and accuracy. He also showed a new tape deck designed by RAE to an SBAC specification, anddemonstrated the miniaturization possible in the associated elec- tronics. These modules were completely transistorized and formedpart of a miniature tape-recording system for ballistic missiles. The capacity of a magnetic tape system was shown by P. Bellerbyof Blackburn Aircraft; in the case of the NA.39, he said, 107 quantities ranging from wing strains to airspeed and altitude wererecorded on one machine. Twenty exhibitors at the symposium, including Ministry estab-lishments, showed items ranging from complete radio telemetry systems for aircraft to miniature differential pressure transducersjust over one half-inch long. The highlight of the show was the first appearance in this country of the new all-solid-state airbornetape-recording system by Ampex (see photograph). At the in- formal dinner which concluded the meeting, guest speakerF. W. Page (English Electric), chairman of the SBAC aircraft data-reduction committee, stressed the need for a closer liaisonbetween design and flight-test departments. The general feeling among delegates and organizers was that thesymposium had proved a great success in bringing together flight- test engineers and the designers and manufacturers of instruments.In addition, Cranfield was able to show its own current work in the field of flight-test instrumentation. It seems probable thatthis symposium could become an annual or bi-annual event in the aeronautical calendar. Proceedings of the meeting may be pub-lished if there is sufficient demand, and enquiries should i>e addressed to M. A. Perry, Department of Flight, The College ofAeronautics, Cranfield, Bletchley, Bucks.
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