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Aviation History
1951
1951 - 0682.PDF
422 FLIGHT ON RECORD Hawker's Adopt a Voice-on-wire Recorder to Replace the Test-pilot's Knee-pad The comport layout of the Wirek device: on the left is the cockpit remote-control switch unit and in the foreground is the connector. THE knee-pad and pencil have for very many years beenindispensable to the test pilot; but there is little doubt that,as observations become more and more detailed, and the pilot has to study the behaviour of an ever-increasing number of components, accessories and services, some form of "automatic notebook" must be the logical successor to the aforementioned two simple tools of his trade. A new and promising device of this kind, a "voice-on-wire" recorder, has now been developed in this country as a result of co-operation between Hawker Aircraft, Ltd., and Wirek,, Ltd., of Edgware, manufacturers of wire recording equipment. It should be said in fairness that the idea first originated in the United States, where it has already found great favour among test pilots; but the British equipment, now in production, was made in response to a request from the test department of Hawker's, and has been "tailored," from the thought to the finished job, to meet the requirements of British aircraft. Standard wire recorders, as already in use with the three branches of the armed forces, were quite out of the question for airborne test work; both their size and weight (57 lb) were excessive. Hawker's specified a unit of less than 15 lb in weight and of not more than half the size. It had also to be suitable for stowing in any place but an already overcrowded cockpit: something, in fact, that could be remote-controlled, and whose operation would not interfere with or complicate the existing R/T. and intercomm arrangements. The manufacturers decided that it would be inviting trouble to design a fundamentally new unit for aircraft use, for the standard mechanism and amplifier had already been proved as a result of six or seven years of really tough field use, and any major departure from standard would bring its inevitable batch of teething problems. The answer was found by discarding half the entrails of the ground unit, which is a combined recorder and play-back instru- ment. The pilot needs only to talk; he is not interested in what he has said until the flight is over. Accordingly, a unit based on the standard mechanism was used, with a very small amplifier, suitably modified to operate on an aircraft D.C. supply. All unnecessary switchgear, etc., were dropped, and the finished job, very much condensed, was housed in a strong, light-alloy case. The result can be seen from the accompanying photograph of the first prototype. It weighs only 9| 1b, its volume has been reduced to approximately a quarter of the original, it is fully remote-controlled, and it records for a period of 60 minutes. The power drain on the batteries is of the order of only three- quarters of an ampere. From right to left, in the main unit illustrated above, are the take-up spool, guide pulley, recording head, guide pulley, wire- piling guide, and loaded wire spool. The wire travels at the inter- nationally agreed speed of 30 insec, and provides excellent speech quality over a frequency range of from about 300 to 3,500 cyc/sec. A calibrated scale shows the amount of recording time in hand. In the foreground of the picture is the connector, and the cockpit remote-control unit is on the left. This unit is fitted with a two- way toggle switch with a large knob for gloved hands. Plug-in points for pilot's microphone and for R/T.-intercomm connection can be seen at the front. The small switch at top left is the on-off control for the recorder, and the tell-tale lamp at top right lights up when the machine is on; in accordance with convention, it is out during actual recording. At the lower, or "stand-by" position, the pilot is switched through to R/T. and intercomm for multi-point crew working in large aircraft. At the top or "record" position of the switch, he is connected direct to the recorder. The first prototype was supplied to Hawker's and installed in a single-seat aircraft. Apart from a valve failure, due to a fault which was corrected, this instrument is reported to have worked excellently ever since, and to have provided much useful data for the later models. It has also proved beyond doubt that the system of automatic recording has a big future in most flight test work. After considerable use by the Hawker test team, it was decided that two modifications were advisable. It was found, first of all, that the absence of side-tone had a worrying effect. When one is used to hearing one's voice in all everyday telephone conversations, it is unnatural to speak into a microphone and to hear nothing happening in the earphones. Side-tone has therefore been added. More important was the absence of an indication that the amplifier was actually recording; and this was discovered on the occasion when the valve failed. The indicator lamp showed that the instrument was "on," whereas, in fact, a ten-minute record was lost. The outcome is that current production models include a method of taking side-tone from the actual recording-head. This means that, so long as side-tone is heard, the amplifier is working; lack of such tone will therefore indicate an electrical fault, and the pilot can then resort to his notebook, which he will still carry as a precaution. At the end of a test night, the wire spools are removed from the recorder and played back on a standard Service Type A unit, through the built-in monitor speaker, and the pilot can make additional notes whenever references jog his memory. After that, the wire is turned over to a stenographer, who prepares a typed draft with the aid of stethoscope-pattern earphones. It is of interest that pilots who have used the system find it necessary to get into the habit of talking of what they are doing while they are actually doing it. It is comparatively easy—as it is with pencil and notebook—to make a summary of, say, a dive after levelling out; but in order to use the full benefits offered by wire recording, one must "natter" continually. This is definitely an acquired art, as will easily be seen by making an imaginary recording when driving a car. Once mastered, however, the process can become instinctive, and an exceptionally comprehensive flight summary is the result. Another point of interest is the initial "freezing-up" effect that a microphone and recorder have on some people; though it should not worry any pilot accustomed to R/T. it may be increased, as a form of stage fright or self-consciousness, by the knowledge that one is, in effect, talking to others who will be listening later. A natural conversational manner is the best and quickest cure; and the "asides" can always be deleted in the typed draft! It is easy to see that, coupled with a camera record of instrument readings,* the wire recording of a test flight will yield valuable data. By spoken references to the aircraft clock, which will tie-up with the photographically recorded time, a reasonably well synchronized log is possible. Unbreakable spools are proposed to airborne use, and the wire itself is virtually indestructible. This fact could be of the greatest importance, and might well provide vital evidence after an acci- dent. Tests have shown that the wire will retain its speech- induced magnetism even after exposure to considerable heat in the event of fire. To end on a happier note, the full possibilities of automatic wire recordings have yet to be discovered. The medium is now available, and the next few years will doubtless see it well ***"' not merely as an aid for the test pilot alone, but for many jobs, including (with intercomm connections) crew-training_work.___ • A method of instrument-lighting for photographic recording, used by Hawher's, was illustrated in "Flight" for November 23rd, 195°-
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