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Aviation History
1969
1969 - 0392.PDF
368 NEW SUB-INERTIAL NAVIGATION SYSTEM mix. During periods when Doppler-lock is lost the vertical gyro resumes its first-order state. Design aims of the Decca Doppler 72 sprang from a market survey which Decca made some seven years ago when inertial systems were beginning to come into favour in civil applications. The survey revealed that what potential customers required from a Doppler system (in descending order of importance) were: high reliability; low cost; low weight; ease of installation; one equipment for all speed ranges; and, lastly, accuracy—consistent with present-day requirements. That "ease of installation" came before accuracy reflected the fact that modifying aircraft structures to accommodate the then current Doppler aerials often cost more than the equipment itself. But the fact that accuracy was last on the list meant that Decca knew it need not offer the world's most accurate Doppler. (This, they claim, is the equipment supplied for TSR-2, costing twice as much as Type 72). Even so, they have achieved good accuracies; velocity range is 50kt-1,000kt, with a velocity output to a computer of 0.3 per cent (2a- value). Meter display accuracy is +0.5° drift; +3kt groundspeed at lOOkt; and 6kt at 600kt. Altitude range is 0ft-50,000ft and tempera ture range —40°C to +70°C (the writer has sat with the equipment in the Boscombe Down Comet at both extremes). To reduce weight in the Type 72, Decca raised the CW operating frequency into the J-band (13kHz) and used a fixed antenna, smaller waveguides, micro-miniature circuitry and so on. In this way all the equipment, including antenna?, fits into one box 16in square. This contains the flush-fitting radome. antennas, tracking circuits and associated electronics on plug-in printed modules. The power pack, also in the box, has no FLIGHT International, 6 March 1969 voltage higher than 115V; in fact, all high-voltage devices such as klystrons have been eliminated and replaced by solid-state crystal-controlled oscillators. Two beams are transmitted forward of the aircraft and one behind. The system will lock-on only when all three signals have been received back. Initial lock-on can be 20sec from switch-on, no inching being needed. There is a built-in self-test system and "power-off" and "memory" warning. One of the claimed advantages of an inertial system is its capacity to align itself without external help. Called gyro- compassing, the process takes some 20min, during which the platform must not move and must have a constant power supply. The advocates of sub-inertial systems say that these two conditions are unlikely to be met during transit stops for civil aircraft, as even the movement of people (e.g., crew and cleaners) up and down the aircraft will tend to upset the gyro- compassing. Initial alignment of the SGP 500, which will not gyro compass, can be via a transfer gyro, magnetically, optically, or simply by alignment with the runway during take-off. In addition, provided the aircraft is not moved during a time when power is switched off on the ground, the original heading will be retained when power is restored. Of the two basic parts which make up the system, the Type 72 Doppler has the most experience behind it. It is already fitted in One-Elevens, 707s, DC-8s, Comet 4Cs, HS.125s and Transalls and will appear in the Jaguar. Two pre- production models of the SGP 500 are undergoing bench- running at Sperry's and another four will 'be ready by June. A production unit will be ready by the year-end. The system will be checked in Decca's Prince this year, and may also be checked jn Boscombe Down's Comet 4C this summer. The aim is to pack the SGP 500. its electronic unit, and Omnitrac into a 1 ATR case. LETTERS (continued from page 366) through cleared altitude. On descent any mistake will be on the safe side, i.e., levelling off above cleared altitude. Thus, at top of descent one sets the airfield height, removes the blanking device, and the height-above-air field will come into view. Strictly speaking, this reading will only be approximate as long as the pressure setting is standard. At top of descent this hardly matters; the accurate height-above-airfield will come up as soon as QNH is set on the sub-scale. Henley-on-Thames, Oxon o. R. RICHARDSON [Several more letters on this subject are awaiting their turn in the stack—Ed] History: Help Wanted SIR,—In an issue of Flight last year it was stated that Bristol Blenheims were first issued to 114(B) Sqn in 1937. I was a serving airman in 139(B) Sqn at RAF Wyton in April 1938, at which time 139 had Blenheims whilst 114 still had Hawker Hinds. In our village school hall there is a plaque stating that Capt Vivian Hewitt was the first man to fly the Irish Sea from Holyhead to Dublin, on April 26, 1912. Flight gives the honour to someone else who flew on April 22. I haven't the issue of Flight to hand and can't remember the name given. Would you please tell me which is correct? Pen-y-Parc, Llanfairynghornwy, J. c. OAKES Holyhead, Anglesey [We do not know to which issue Mr Oakes refers, but there is certainly no question that Vivian Hewitt flew from Holyhead to Dublin in a Ble'riot monoplane on April 26, 1912; possibly there has been some confusion with D. JL. Allen, who had set out from Holyhead about ten days earlier and was never heard of again. Can any reader help our correspondent with his Blenheim query? We believe that No 114 did in fact receive Blenheim Mk Is in March 1937.—Ed] DIARY Mar 6 RAeS Belfast Branch: "Sabotage in the Air," by E. Newton; Main Lecture Hall, Ashby Institute, Queens University, Stranmillis Road, 7 p.m. Mar 6 RAeS Rotorcraft Section: Half-day symposium, "Future Rotorcraft Research in the USA," by P. F. Yaggy; "Experiences in the Development of US Military Helicopters," by Maj Gen G. P. Seneff; 4 Hamilton Place, London Wl,2.15p.m. Mar 6 RAF Reserves Club Ball, Hilton Hotel, London. Mar 10 RAeS Cranwell Branch: 12th Trenchard Memorial Lecture: "50/50 Phantom," by D.J. Whitehead; Whittle Hall, 8 p.m. Mar 11 RAeS Air Transport Group: "Development of UK Air Services," by G. H. G, Threlfall; 4 Hamilton Place, London WI, 6.30 p.m. Mar 11 RAeS Dublin Branch: Symposium, "Pilot Training—From Chipmunk to 707," Lecture Theatre, Shell BP House, Fleet Street, Dublin 2, 8 p.m. Mar 11 RAeS Gloucester and Cheltenham Branch: "Project Apollo," by Sqn Ldr McMaster; St Mary's College, The Park, Cheltenham, 7.30 p.m. Mar 11 RAeS Prestwick Branch: Debate, "Prestwick Airport has no Future," Golden Eagle Hotel, 7.45 p.m. Mar 12 RAeS Manchester Branch (main lecture): Nth Chad wick Memorial Lecture: "History of the Vulcan," by S. D. Davies; Renold Building, University of Manchester Institute of Science and Technology, 7 p.m. Mar 12 RAeS Bristol Branch: "Propulsion Prospects," by R. Weir; Bristol University Main Engineering Lecture Theatre, 7 p.m. Mar 12 RAeS Christchurch Branch; "Concorde," by M. G. Wilde; East Cliff Court Hotel, Bournemouth, B p.m. Mar 12 RAeS Hatfield Branch: "The Red Arrows," by Sqn Ldr R. G. Hanna; HSA Senior Staff Restaurant, S.30 p.m. Mar 12 RAeS Luton and Stevenage Branch: "Man-powered Flight—the Puffin," by E. Vann; English Electric Co, Luton Airport, 5.30 for 6 p.m. Mar 13 RAeS Southend Branch: "New Generation of Aero Engines," by H. Cundall; No. I Committee Room, Southend-on-Sea Civic Centre, 7.45 p.m. Mar 13 Institution of Mechanical Engineers: Internal Combustion Engines Group: Discussion, "Closed-cycle Engine—The only Powerplant of the Future?," I Birdcage Walk. London SWI. Mar 13 RAeS Cambridge Branch: "The Highlands and Islands Service," by Capt A. C. McLean; Lecture Theatre O, Cambridge University, 8.IS p.m. Mar 13 RAeS Chester Branch: "Concorde Supersonic Aircraft." by G. Worral; Stanley Place, Watergate Street, 7.30 p.m. Mar 13 RAeS Yeovil Branch: Annual general meeting and Junior paper evening, Yeovil Technical College, 6 p.m. Paris Show: May 29-June 8 "Flight" Light Aviation Show, Cranfield, Beds: July 24-27.
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