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Aviation History
1959
1959 - 0539.PDF
266 FLYING AID8 . . . FLIGHT, 20 February 1959 Part of the computer for the Achiever inertia!-guidance system made for the Douglas Thor by A.C. Spark Plug division of General Motors Inertial Navigation The development of inertial-quality equipment has reached apoint where the special gyros used for stable platforms (and in some cases as accelerometers) are small and cheap enough to beincorporated in master dynamic reference systems. While it is safe to say that genuine inertial navigation is not likely to finda place in airline use for some years to come, a number of master references are being planned to include inertial-quality gyros sothat they are theoretically capable of being applied not only to flight control and instrumentation but also to short-termnavigation. Under the stimulus of military requirements during thedevelopment of the ballistic missile, tremendous progress was made in inertial design in a relatively short time. Many differentapproaches were tried and a great variety of gyros, accelerometers and computers is now available. But because the main applica-tion was in missiles with a flight time of about 30 minutes, the first few minutes of which would give anything an exceedinglyrough ride, the main effort went into short-term systems capable of withstanding a distinctly hostile environment. In its review of flying aids of May 16 last year, Flight recordedthat inertial systems were not yet suitable for long-term navigation such as might be required during a trans-Atlantic flight. The sub-sequent voyages under the polar ice cap by the nuclear submarines Nautilus and Skate proved that a long-term inertial system, typi-fied by the Autonetics Ships Inertial Navigation System (SINS), had now come of age. The application of a similar long-term pure-inertial system to aircraft use depends mainly upon reducing the weight of the equipment and increasing its tolerance to vibrationand extreme temperatures. Although work began on inertial systems in Britain at a rela-tively early date, rapid advances were mostly made in America where financial backing was virtually unlimited. The followingrecord of achievement by the Autonetics Division of North Ameri- A stable platform for the Sperry inertial system for the B-58 Hustler being tested in a transport aircraft can Aviation is, in view of this, not surprising, though nonethelessimpressive. Autonetics flew the first "all-inertial autonavigator,' the XN-1, in a C-47 in May 1950. Since then more than 800flights with various systems have been made. During 1952 the XN-2 stellar-inertial autonavigator successfully tracked stars auto-matically during flights in daylight and picked up stars at night after the aircraft had taken off and climbed above cloud. By 1954Autonetics had produced a completely manoeuvrable inertial plat- form and was currently testing five inertial systems of threedifferent types. The following year a stellar-inertial system guided a U.S.A.F. T-29 during a 13? hr flight from Los Angeles toPatrick A.F.B., Florida. During 1956 a pure-inertial system guided the X-10 experimental vehicle through an out-and-returnflight of several hundred miles at supersonic speeds. It also guided a test version of Navaho at Mach 3. By 1957 Autonetics hadachieved in-flight alignment of an inertial navigation system from a cold start using an independent velocity reference. An idea ofcost can be gained from the fact that development of the inertial guidance system for Titan by the American Bosch ArmaCorporation cost slightly over $140 million. The first production application of an inertial system to amanned military aircraft is the AN/ASQ-42 primary navigation system made by Sperry for the Convair B-58 Hustler. Almost ahundred of these aircraft are being ordered. Late Republic F-105s and the Norih American A3J Vigilante will have inertialsystems. The ASQ-42 is, in fact, a Doppler-inertial hybrid capable of providing accurate information over a period of hours.It is probable that the Doppler element would be used only inter- mittently to check the inertial element. In addition to providingnavigational information, ASQ-42 supplies attitude and other information to nearly a dozen sub-systems such as those forreconnaissance and flight control. The navigation system can operate anywhere in the world and will automatically control therelease of the Hustler's 50ft-long pod. The ASQ-42 is 20 per cent lighter and occupies 37 per cent less space than presentsystems such as that of the B-52, and it is claimed that it is more versatile and reliable. In Britain, the Sperry Gyroscope Company flew an inertialnavigator designed for manned fighters in November 1954. The company now holds the contract for development of the guidancesystem of the British ballistic missile. English Electric announced last year an agreement under which they will produce some ofthe range of Miniature Integrating Gyroscopes designed by Minneapolis-Honeywell in America. In addition to producingthis equipment under licence, English Electric are designing com- plete stable platforms as well as the necessary gyroscopes for them.Elliott Brothers (London) Ltd. are designing the inertial naviga- tion system for the Avro stand-off bomb. During last year's S.B.A.C. Display, one of the six MiniatureStable Platforms which had then been produced by Minneapolis- Honeywell was publicly displayed for the first time. Althoughintended as a master dynamic reference, it is based on three GG49 Miniature Integrated Gyros which are of inertial quality.The two units comprising the platform weigh a total of about 40 lb, can be started up in three or four minutes and do notrequire a highly stable power supply. In one application, thirty different outputs have been supplied. Instead of being used asa master dynamic reference, M;S.P. can be used as a short-term or hybrid inertial system. Five years ago S. G. Brown Ltd. produced the first two-gyromaster reference unit (described in Flight for April 12, 1957). The Mk 1, which is fitted in all the latest British fighter and veryhigh speed research aircraft, has now been succeeded by the Mk 2 which is 14in long, 7in wide and 8iin high, including the mount-ing frame and amplifiers. Because the vertical and azimuth gyros are set in line with the fore-and-aft axis of the platform theirwheel diameters and therefore their efficiency have been increased. The rate of roll of the platform is 450 deg/sec. Only a 115 V,400 c/s, three-phase power supply is required. The gyros have random wander rates of better than 0.25 deg/hr and platformvertical accuracy is 0.2 deg. A computer introducing appropriate signals to allow for the earth's rotation, sphericity and coriolisaccelerations can be provided if the M.R.G. Mk 2 is to be used for navigational reference. S. G. Brown last year concluded an agreement with AmericanBosch Arma (and not with Kearfott as stated in Flight for Sep- tember 12, 1958) providing for an exchange of information. As aresult of this, a Mk 3 M.R.G. is being planned to incorporate a pair of two-degree-of-freedom, Arma-Brown floated gyros. Thisequipment will be suitable for inertial navigation purposes. The Sperry Rotorace vertical gyro, with the remarkably lowdrift (for a non-floated unit) of 0.25 deg/hr, has now been in service with Sperry C-ll compass system for more than a y:ar.In this equipment gimbal-bearing imperfections are to a great extent cancelled out by rotating the concentric ball-bearmghousings at about 20 r.p.m., the direction of rotation being
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