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Aviation History
1949
1949 - 0590.PDF
By M. G. K. Byrne, A.F. R.Ae.S. TEST INSTRUMENTATION « Automatic Observation and How it Functions K S the title of this article includes the word "Instru-mentation," it is logical to start by defining a termwhich, until recent times, was associated with the An additional consideration is that flight research hasmade such strides that the aerodynamicist now demands.a complete history of the aircraft's behaviour. To satisfy arranging of music for a combination of instruments. In- • the specifications of the Air Ministry it is now obligatorystrumentation is a collective noun covering every procedure apertaining to instruments, whether for standard or test purposes: but in this instance only the latter will be considered. Instrument readings are recorded during test nights in order to gain data not previously obtainable and to shorten, the test-flying period: these time histories are used to augment, and give reasons for, the test pilot's' assessments of controls, aircraft behaviour, and so on. ' * One's conception of instrumentation should not be ob- scured by recollections of a pre-war film in which a " super fighter'' was dived at terminal velocity and began to shed its wings. Before baling out the pilot wrenched the dashboard plus instruments from the cockpit mounting and floated to earth with them clutched tightly to his manly chest. Upon landing, with a resounding crash, all the instruments were found still to be indicating the correct r.p.m., speed, height, etc.—a most useful attribute! In the era of low-performance aircraft there was ade- quate time for a pilot to note the requisite A.S.I., alti- meter, temperature and pressure readings. For example, in IQ-35. if the performance figures on a Gloster Gladiator, climbing at combat rating, were recorded at intervals of 1,000ft the pilot had approximately half a minute in which to write down each set of results. To-day, a machine such as the Gloster Meteor IV has an initial rate of climb of 7,35oft/min., i.e., a thousand feet is now achieved in just over eight seconds. • 7 he author is Flight Observer for BUxkburn and Ai Fig. 2 (left). An instrument panel photographed by standard lighting, use of polarized lighting, as shown in Fig. 3 (right). to measure air speed, height, aircraft attitude, accelera- tions in the three planes, all control angles and forces, engine speed, pressures, temperatures, etc.—in fact, to record every movement and force associated with flight. In order that this data may be obtained and analysed at leisure, prototype and research aircraft are fitted with automatic observers. These devices consist fundamentally of an instrument panel suitably lighted so that cine cam- eras can photographically record the various dial readings. The films so obtained are processed and projected on to screens at a magnification greater than the original, and the instrument readings are first of all accurately logged and then plotted. In dealing with the component parts of an automatic observer, consideration must first be given to the cameras ; in the majority of instances these are of 35 mm type, although the range of films actually varies from 4m in width down to 16 mm. According to the task in hand, the cameras may be set to take single shots or may have their running speed varied from one frame per minute to 60 frames per second: the former exposure rate would be suitable for a long-range endurance flight and the latter for any high-speed manoeuvre. Four typical cameras which have been utilized for widely differing tests are shown in Fig. 1, namely : — (1) The Vinten "K," which has a magazine holding 200ft of 35-mm film and runs at 16 or 24 frames per second. A camera speciall3Cde*MSd fctyutftaatic-ohserver work, fln ana shadows are entirely eliminated by the )u strain shadows In the boost-gauge l I lid rr^. (2) A camer specia dard lighting. Tmyusual reflections *«. »: . r : :T:-: • \ .-« .' • • li n* »» v« <o" iJ
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