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Aviation History
1974
1974 - 0036.PDF
34 Avionics PILOTS WHO FLEW the LTV A-7D and A-7E in action in South East Asia spoke highly of the accuracy of its navigation and attack system. It is based on the AN/APQ426 forward- looking radar, AN/APNil90 Doppler, AN/ASN-90 inertial system and AN/ APN-141 radar altimeter. The infor mation supplied by these systems is digested by the A-7's digital computer and passed on to the Computing Devices of Canada AN/ASN-99 pro jected map system and the Marconi- Elliott Avionics head-up display. When A-7 pilots returning from South East Asia were asked by a re search organisation on behalf of Computing Devices to comment on the use of the projected-map system (PMS), the majority were enthusiastic. They found it a useful navigation aid —especially when operating close to sensitive borders in IFR conditions— and used it mainly in conjunction with the radar display. The close proximity on the instrument panel of the radar and PMS displays made it straight forward to correlate the two systems (see illustrations) and pilots found they had little need for a hand-held map. Because the PMS is slaved to the aircraft computer it provided a good reference, when cross-checked with the radar return, of any errors in the navigation system and allowed the pilot to up-date the computer manually. The PMS fitted to the A-7 has the Computing Devices designation PMS4 and over 1,000 sets have been ordered. It is a two-box system being fed with data from the aircraft's central com puter via the Computing Devices electronics assembly unit which in cludes built-in test equipment for self- checking, automatic performance monitoring and fault isolation. The screen of the PMS is 5in, 12-7cm in diameter and provides a full colour image of standard aeronau tical charts. For tactical-fighter appli cations scales of ,1:500,000 and 1:2,000,000 are used; at 11:500,000 the area visible on the screen is about 25 miles, 46km in diameter. Computing Devices offers its PMS5 system based on the same map, but with a navigation-control unit and a larger electronics assembly unit that includes a navigation computer, for aircraft with less comprehensive The close proximity on the A-7 instrument panel of the radar (left) and PMS (right) make it straightforward to correlate the two systems No 163 PMS in action avionics systems. It is designed to accept inputs from navigation sensors such as Doppler, inertial platform and air-data computer and perform all navigation and display calculations. The company says the projected map is ideally suited to civil operations for flying in terminal areas and for inte gration with area navigation equip ment. For these applications Comput ing Devices has built and flown its PMS 8 which is directly compatible with VOR/DME, Tacan and inertial systems. The company has also built an automatic chart display known as the PMS6 to Arinc standard 561. Although a simplified map coupled to VOR/DME and designed for general aviation is technically possible and appears attractive (Marconi-Elliott Avionics has already developed its prototype VOR/DME Radiomap), Com puting Devices thinks it would be diffi cult to manufacture a fully moving map system at a reasonable price. Moving map displays were pioneered by Kenneth Honick at the Royal Air craft Establishment, Farnborough, and in the early days there were problems of viewing displays in sunlight. Ron McNab, director of avionics marketing for Computing Devices, told Flight re cently that the brightness level of the image of the well proven PMS4 is such that the map can be viewed in bright sunlight at angles of up to 25° from the optical axis. The type of display Computing De vices will propose for the Rockwell B-IA for the USAF will combine the optical map projection with the elec tronic display of other data on a cathode ray tube. The system will allow details of radar returns and data from various electronic sensors to be superimposed on the PMS. (Ferranti is supplying a similar system for the MRCA; see Flight, August 31, 1972.) FLIGHT International, 10 January 1974 The marketing director says that this is the way in which the PMS is likely to develop in the future. Despite uncertainties over timing, Ron Macnab sees the Canadian re quirements for a long-range patrol air craft to replace the Argus and a fighter to replace the F-104, F-5 and F-101 as two long-term applications for developments of the moving map. Computing Devices—a division of the Control Data Corporation—has a wide background in data-processing and computing systems and supplies a wide range of equipment for a num ber of aircraft, including the Nimrod. It is perhaps only natural that the company should capitalise on its PMS and computer technology to offer a complete navigation and attack system. Testing of individual com ponents has already taken place although flight testing of a complete system is still some way off. It is based on a Computing Devices digital com puter and interface unit, computer- control unit, head-up display and PMS. The company does not manufacture optical equipment and these items are supplied by Pilkington, Perkin-Elmer and Farrand Optical. Optics for the head-up display (HUD) are supplied by Farrand Optical of New York, a relative new comer to HUD manufacture. The Far rand HUD has a particularly wide angle of view (35° horizontal to 25° vertical) and has a semicircular curved combining glass. Ron Macnab says that the close integration of the display and processor which the Com puting Devices system achieves brings significant savings in size, weight, power and cost over current designs. It is suitable for helicopters and other light attack aircraft and the design and reliability philosophies reflect this. The computer has a storage capacity of 64K (16-bit words and can carry out more than 450,000 operations per second. It is ideal, says Macnab, for wave-form generation as well as for solving navigation and fire-control cal culations. When used to generate a synthetic shell trace for display on the HUD to aid the pilot during air-to-air combat (a system known as hot-line or snap-shoot) it will be capable of showing up to 50 tracers rather than the five or six available from current systems. A.N.H.
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