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Aviation History
1959
1959 - 1206.PDF
591 Tha latest version of the Minneapolis-Honeywell miniature inertial platform. A window is provided to allow initial optical alignment together with trimming potentiometers. The picture on the right, of the gyro and gimbal assembly, shows some of slip-rings and gyros LIGHTWEIGHT INERTIAL-NAVIGATION SYSTEM Joint Anglo-American Development and Production By D. O. FRASER AND B. A. C. STACK* OFTEN the first question when considering a new naviga-tion device is its weight; and inertial navigation dependson the conservation of momentum, a principle not easily associated with lightness. Nevertheless, the Minneapolis-HoneywellRegulator Company has developed a complete all-attitude inertial platform weighing only 28 lb and contained in a .cylinder of lessthan lOin diameter by 14in long. All the associated electronics are contained in a separate pack, smaller in volume, weighing 26 lbso that total weight of the system is only 54 1b. The secret of this compactness lies in the use of miniature components and integrateddesign. The three GG49 miniature integrating gyros used are fully floated, inertial-quality gyros developed by Minneapolis-Honeywell from the principles first enunciated by Dr. Draper of the Massachusetts Institute of Technology. Although its per-formance is comparable to that of any other inertial gyro in pro- duction, the MIG, as it is called, is less than one-tenth as heavyand weighs under 8 oz. The three GG56 accelerometers on the platform are of the pendulous current-balance type and weighonly 7 oz each. A number of parts are common to both the gyro and accelerometer. An early version of this platform was des-cribed in Flight for May 16 last year. An important feature of this platform, and one also contribut-ing to its compactness, is that it was designed from the start as an integral unit, the specifications for the MIGs and GG56accelerometers together with the gimbal system having been derived from the overall platform specification. Common powersupplies have therefore been provided for all components, an advantage in view of the fact thai slip-rings must be used totransfer power from the external source, through the gimbal bearings to the gyros and accelerometers mounted on the inner-most gimbal. The components also operate at a uniform tem- perature of 180 deg F at which the platform is maintained by aninternal heater. The high operating temperature is of great advantage in applications where high ambient temperatures areexpected, because it avoids the need for refrigeration; considerable weight penalty might otherwise be incurred. It is the remarkable sensitivity of present-day gyros andaccelerometers which has made inertial navigation possible and these components form the nerve-centre of an inertial platform.But such a platform is much more than a simple assembly of these sensitive components. If their accuracy is to be fully exploited,much attention must be given to the design of the limbs and muscles of the system—the gimbals, torque motors, synchros,slip-rings and so on. Many development problems and teething troubles had to be overcome during the development of theHoneywell miniature platform assembly, quite apart from those concerned with the gyros and accelerometers. Because the strengthof the gimbals and power required to drive them are functions of the weight of the gyro and accelerometer assembly, the totalweight of an inertial platform is nearly proportional to that of the gyros and accelerometers. The use of miniature components there-fore results in a saving of overall platform weight of an order of several times compared with equivalent systems. The small size and weight of the MIG has been achieved with-out any significant sacrifice in performance. Moreover, further developments of this miniature gyro promise to put it in a per- formance category even superior to that of instruments ten timesits weight. This may have far-reaching effects on inertial-gyro technology, because the weight saved in miniature platformsbased on instruments of this kind might allow an extension of weapon performance. Inertial systems of this type could also beapplied to a much wider range of aircraft and missiles than has been considered so far. The miniature platform shown above uses the three rate-integrating gyros for stabilization in azimuth, roll and pitch. Accelerometers are mounted in the two horizontal axes and providevertical stabilization by sensing components of the gravity vector when the platform is not vertical. Their outputs are used to slavethe two levelling gyros so as to keep the platform horizontal and also to indicate lateral acceleration signals which can be integratedin turn to provide velocity and distance flown. The azimuth gyro gives direction of horizontal motion. The third accelerometer canbe used to indicate motions in the vertical plane. The miniature platform is in itself a short-term inertial-naviga-tion system and can be used for guidance of missiles or manned aircraft of limited endurance. Alternatively, the system may becombined with other navigation aids such as Doppler, in which case the short-term stability of the inertial system smooths thevelocity signals of the Doppler in addition to providing a memory during lapses in Doppler signal reflections, such as might occurduring pronounced manoeuvres. Apart from inertial navigation, the platform provides a stabilized reference which may be put to anumber of uses in any weapon system. It could, for example, be used as a heading- or vertical-reference for aircraft control, flightinstrumentation, radar stabilization or bombing devices. A par- ticular instance is the provision of an accurate heading referencefor use with Doppler where the compass is the main source of navigation error. The miniature platform and other Minneapolis-Honeywellproducts are available in this country through Honeywell Controls Ltd. of Greenford, Middlesex. Manufacturing licences in thiscountry for the full range of Minneapolis-Honeywell gyros are held by English Electric. Delivery of the first few MIGs builtentirely from British components is expected early this summer. These inertial components are being manufactured in a newlyequipped factory forming part of English Electric Guided Weapons Division at Stevenage, Herts; the plant is probably the bestequipped of its kind in Europe for production of precision instru- ments of this class. The Aeronautical Division of Minneapolis-Honeywell Regulator Co. and English Electric collaborate closely both in production and exchanging information on future develop-ment by both companies. Both already have considerable experi- ence in inertial navigation developments, and their combinedresources should lead to rapid progress. The importance of this area of development cannot be over-stressed, and it appears that inertial navigation will be as universal in its application as the time-honoured celestial methods. Thenew techniques are already being used in vehicles ranging from submarines to spacecraft. * Mr. Fraser is with English Electric Aviation Ltd. and Mr. Stackwith Honeywell Controls Ltd.
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