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Aviation History
1954
1954 - 0869.PDF
2 April 1954 391 re-align if left by itself—several hours for 180 deg. But this is immediately noticeable, and resetting is simplicity itself. The pilot merely presses the clearly marked button and turns it until the dot and cross in the annunciator window (two o'clock in the dial rim) alternate steadily. If for some reason the magnetic detector unit fails, the compass can be employed as a plain gyro D.I. Sperry produce three versions of the instrument, the C.L.I (and C.L.1A), the C.L.2 and the C.L.3. These correspond respectively to the Services' G.4.F, G.4.B, and G.4.F.T. The C.L.I is a straightforward gyro-magnetic compass using magnets for deviation correction of the detector unit (usually located in the tail or wingtip), an amplifier and the indicator. The C.L.I A is similar, but utilizes an electro-magnetic compensation system, so that this can be carried out from the cockpit. The C.L.2, intended primarily for large aircraft, is the instrument specified for the B.O.A.C. panel. It has a detector unit, an amplifier and a master indicator located at the navigator's position, with a control panel. One or two gyro units almost identical in appearance with the C.L.I are fitted in the pilots' panels. If required, local magnetic variation can be set in at the master indicator so that all indica tions will be in relation to true north. The C.L.3 is a combina tion of the C.L.I and 2; it is intended for aircraft in which a navigator is not carried, but where variation control and azimuth monitoring of Air Position Indicator or radio compass are required. The compass dial in this case is identical with that of the C.L.I. It can be said that a compass of the G.4.F type is now regarded as vital for jet aircraft where accurate and constant directional information must be provided, even during violent and prolonged manoeuvring at high speed. Artificial Horizons. Principally under the stimulus of jet- aircraft requirements, a great deal of development has gone into producing an artificial horizon which will provide accurate attitude-reference in almost any flight condition. Because of the rapidity with which the jet aircraft will lose height, flying on primary instruments is no longer to be contemplated except in emergencies. In a Meteor, for instance, it could prove fatal to lose control in cloud at less than 5,000ft above ground level, since that is the height required for recovery from a vertical dive. The best way to avoid losing control is to have a fully free artificial horizon. The Sperry Company has gone a very long way towards providing such an instrument. Firstly, the gyro horizon must be electrically driven, because of the difficulty of obtaining an air drive at very high altitudes; secondly, it must be as free as possible. A series of Sperry horizons has been produced, leading up to the H.L.6 and H.L.8. The H.L.6 is now in production, but the company's Anson was fitted with a prototype version in the first pilot's panel. Many present military aircraft have an early type of H.L.6 known in the Services as the Mark 3. This is fully free in roll and allows 85 deg of dive or climb. It does not topple, but only ceases to function for a short time. In practice it is possible to carry out all aerobatic manoeuvres without losing the use of it for more than a fraction of a minute. The H.L.6 will have the same working limits as the Mark 3, but will embody three new features. First, the small "aircraft" in the centre of the dial will be in the form of an inverted gull wing; this has been found the most suitable reference to align with the horizon bar. Second, it will be fitted with a small flag at the top of the dial which will show "OFF" either when the instrument is switched off or if power fails. Third, and probably most important, it is provided with a fast-erection device. If the horizon is upset the pilot has merely to press a button (at the rim of the dial) marked "Fast Direction PUSH" to re-erect the instrument in level flight in the space of a few seconds. This device may also be used for initial erection before take-off. The H.L.8 is an air-driven version of the H.L.6 with the same limits but without the "OFF" flag or fast-erection device. Both instruments have a roll cut-out which greatly reduces turn errors. Sperry have, incidentally, produced a horizon—the H.L.4— specially for helicopters, but this, of course, was not fitted in their Anson. Basically the instrument is intended to give attitude information against a datum that is variable to allow for fuselage attitude. In the co-pilot's position in the Anson the artificial horizon was, in fact, a horizon gyro unit Type B (H.L.5), an instrument required to provide attitude information for either an auto-pilot or the Zero Reader. The first pilot's artificial horizon is a separate instrument so that on his panel the Zero Reader and artificial horizon are completely independent to allow effective cross check ing in flight. The Sperry Anson is a remarkable aircraft; it is full of instru ments, yet its passenger cabin has the opulent air of a V.I.P. machine and the cockpit is a model of what such places should be. It was, indeed, our first impression on sitting in the pilot's seat that the instrumentation was particularly well arranged. The B.O.A.C.-type blind-flying panels are a great improvement on previous layouts. Fixed to the centre pillar of the windscreen is a radio compass which we used during I.L.S. approaches as a check on the markers. On the bulkhead behind the first pilot's seat there is an array of control panels used to check the extensive electrical system. Each instrument is individually selected by circuit-breakers on a special panel designed by Rotax. From this bulkhead rear wards, a series of shelves is fitted, on which are mounted all the various "black boxes." The compartment is open, well lit and easy to reach. On the bulkhead at the rear of this compart ment facing the passenger seats there is a third full blind-flying panel. Extra instruments can be installed here for tests if required, or a number of people can watch the behaviour of a series of instruments without crowding into the control cabin and leaning over the pilot's shoulder. The Anson is also fitted with the Sperry A.L.3 autopilot which is designed for medium-sized aircraft of this type. From its own independent gyro vertical it directs pneumatic control servos through valves operated by air pick-offs. Pitch-and-turn controls are provided for the pilot, together with a sensitivity control to allow for varying atmospheric conditions. It is connected to the gyro magnetic compass to maintain a selected heading. The autopilot can be manually over-ridden at any time. This description gives some idea of the way in which aircraft flight instrumentation is progressing. We have not gone into details of the working of the devices described; the pilot, in any case, is concerned principally with the function, accuracy and limitations of his instruments, and with their appearance and clarity. The Sperry Anson is an impressive and encouraging machine, and we regard the two hours we spent flying it as a most valuable experi ence. If the all-weather pilot, either civil or military, can be provided with such instrumentation his prospects are far from bleak. C.M.L. W. L. ALLARDYCE HIS very many friends in the industry will be grieved to hear of the death of Mr. W. L. Allardyce, production manager of de Havilland's Hatfield works. He passed away last Friday morn ing in Hertford General Hospital following a short but severe ill ness involving two operations. He was 56. "Jock" Allardyce joined Sir Geoffrey de Havilland at the Aircraft Manufacturing Co. at Hendon immediately after World War I, in which he had served in the Scots Guards. He did not at once go over to the de Havilland Com pany when it was formed in September 1920 but joined it in January 1924 after three inter mediate years with Handley Page, Ltd. He worked in the fitting shop—as he had done at Hendon—but was promoted to the staff in 1925, thereafter rising by stages to be assistant production engineer and—in 1940— works superintendent. He held mat post throughout the critical war years and after, until his recent appointment as production Mr. Allardyce. manager, with responsibility for the entire output of aircraft and components. "The efficient running of the factory was his concern," writes one of his colleagues, "and in his energetic and cheerful mastery of the continuously changing scene he always had his finger on the pulse of every department and section; he knew literally hundreds of people personally, and understood their work and problems. The responsibility was a very great one and he gave himself unsparingly to it. "Jock did much to make the character of the firm, and with his passing a part of that character is irretrievably lost, despite the fact that his influence will be felt and appreciated for many a long day." Mr. Allardyce leaves a widow. A funeral service was held at Hatfield Parish Church last Tuesday, followed by cremation at Enfield Crematorium. AERONAUTICAL ART TTHE Society of Aero Artists, whose formation was announced in •*- a letter in our correspondence columns on March 26th, is to hold its first exhibition in London this summer. The venue will be the Guildhall Art Gallery, and Viscount Templewood, president of the Air League, will perform the opening ceremony on June 15th. The secretary of the Society is Mr. M. B. Bradshaw and the headquarters are at 23 Albemarle Street, London, WL
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