FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1964
1964 - 2152.PDF
FLIGHT International, 30 July 1964 171 PAN AMERICAN GOES INERTIAL EXERCISING its absolute right to be first in all things, Pan Ameri- can has decided to adopt inertial navigation for all its present 48 Boeing 707s and for seven others on order. In so doing Pan Ameri- can have placed what is believed to be the largest-ever airline order for electronic equipment, valued at $12.5m. The system chosen is the new Sperry New York SGN-10 in which two major break- throughs have made the scheme commercially feasible. One is the development of the non-floated inertial gyro, using Sperry Rotorace bearings, and the other is the microcircuit digital computer, which offers a new standard of reliability. Even six months ago, such a system would still have been too expensive and too demanding in maintenance to have been economic for a civil operator. The first SGN-10 hand-made to production standard is to be flown next January and the first Pan American aircraft will be fitted next June. The whole fleet should be equipped by June 1966. The system provides a 50 per cent circular error probability of 1.8 n.rh. per flight hour and is intended to run without up-dating throughout1 any of Pan American's long over-water flights. Forecast accuracy is such that, if all aircraft were fitted, separations on the North Atlantic might be reduced. Pan American at present run their trans- oceanic flights with a four-pilot crew, one acting as flight engineer and another as navigator. With SGN-10 they might be able to reduce the complement to three, thus alleviating the present acute pilot shortage. It was the FAA-sponsored Pan American trial with a Litton LN-3 inertial system last year which convinced both Pan American and the FAA that the method was feasible for civil operations. PAA then evaluated six inertial and two Doppler systems before choosing the SGN-10, and it is significant that they rejected Doppler. Problems are provision of a sufficiently accurate heading reference, deterioration of performance with age, minimum altitude problems and the fact that certain sea-crossings still involve long periods of memory operation because of smooth sea. To match inherent Doppler accuracy some kind of gyro platform compass system is necessary, and this is in itself the basis of an inertial system. The Pan American SGN-10 installations will be duplicated, each complete system weighing 1041b—an additional weight reduction of 301b has been effected in the computer—and the computers will have a plausibility check between them. The two control panels will be positioned adjacent to the weather radar indicator, accessible to each pilot, and course directions will be switched into the normal Sperry course director instrument, thus minimizing the familiar- ization time involved. Long-distance navigation will therefore become an entirely pilot-operated function. If successful, this programme will establish inertial as the general navigation system for flights in regions not well covered by ground- A Sperry engineer, framed by the vast gimbal cage of the Sperry sub- marine inertial navigator, holds a plastic model of the SGN-10 platform. The Pan American control panel is beside him based navaids. But Sperry London are also pushing the SGN-10 for forthcoming British military projects and for the Concord. It is already accepted for the American SST. Sperry London have considerable experience of quantity manufacture of Rotorace gyros and twin-gyro platforms. SGN-10 has a four-gimbal gyro platform in which the three single-axis Rotorace gyros and two Bell Aerosystems accelero- meters can be extracted by undoing only ten screws. Gyros, accelerometers and gimbals can be replaced without special align- ment equipment and all run in a plain-sealed container cooled by normal airflow. No special heating is required. The complete platform is set on a mounting bore-sighted in the airframe, so that complete platforms can be changed without special realignment. The gyros themselves can be serviced and repaired in a normal airline instrument shop, without the specialized cleanrooms hitherto associated with inertial systems. Platform electronics are contained in an ATR-shaped case and made up of circuit modules on easily removed aluminium cards. The Univac microcircuit computer is separated into calculator and core-memory sections, individually ATR-contained, and has no moving parts. Circuit elements are in flat cases and TO-5 transistor cans, so that unrepairable "throw-away" components cost only $1. A self-checking routine within the computer identifies faults down to a module replaceable on the flight line without special equipment, greatly simplifying servicing. Self-checking and plausibility cross-checking between the two computers continue in flight. All power is taken from a d.c. buss protected by a battery, and all necessary a.c. is generated within the system's own power pack. The platform will align itself without any magnetic or external reference in 15min in any ambient temperature. Using a free- azimuth system the computer is slewed to match existing platform attitude and a statistical "least mean square fit" technique is used during coarse alignment to isolate disturbances caused by aircraft motion resulting from fuelling, wind and passengers boarding. The system is ready to run on the ramp before the aircraft moves off. On the control panel, the pilot sets departure latitude and long- itude to an accuracy of 0.1 n.m. He can see by counters how nearly the platform is aligned. He also sets latitude and longitude for up to ten way-points, and can reset them in flight if flight plan is changed. The course indicator shows distance to go and distance right or left of great circle track between two way-points, with a warning light 20 miles before a turning point is reached. Special provisions are made for navigation in Polar latitudes. Both SGN-10 systems run together, but indications from only one are switched into the course directors. Sperry point out that the maintenance and reliability features of the SGN-10 have finally brought the "cost of ownership" within the range of a commercial airline. Microcircuitry and other features have also led to a forecast MTBF of no less than 940hr, which is essential for a company flying its aircraft for 12 or so hours per day. In addition, customers can specify three grades of gyro, of which Rotorace is the simplest. If floated gyros are to be used, the slip- rings needed for Rotorace bearing rotation are available for floated gyro heating. A third accelerometer may also be incorporated for such applications as the SST, where vertical as well as horizontal navigation are required. Progress in the computer field is so rapid that the weight of SGN-10 may well be significantly reduced by the time it goes into service. LAST VORTAC CONTRACTS PLACED COMPLETION of the FAA's implementation of the VORTAC navigational system throughout the 50 states of the USA will result from the commissioning of equipment ordered under two contracts, totalling SI7m, recently placed by the FAA. One con- tract is for $13.3m-worth of TACAN beacons, with test, monitor and control equipment, placed with Raytheon, and the other, worth S3.52m, is for aerials and aerial control equipment from ITT Federal Laboratories, of Nutley, NJ. Delivery of the Raytheon-supplied equipment will begin in June 1966 and continue at the rate of 15 units a month, and delivery of the ITT equipment will begin in June 1965, at the rate of 25 a month. VORTAC is the United States' primary short-range navigational system.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
