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Aviation History
1957
1957 - 0481.PDF
FLIGHT, 12 April 1957 The Changing Navigation Picture . . . (Right) AN/APA-95 Indicator, Position and Course, with its elaborate input and output arrangements. 483 Q Q & 6 r/i/s Co/Jins Radio AN/ARA-21 uses Tacan signals to compute a course between two preselected points. Bombing and Navigation Computers A.C. Electronics Division of General Motors Corp. THIS company is known to be engaged in the design (and possibly production) of bombing and navigation computers for the American Services, but no details of the equipment have been released. AN/APN-57 Seeburg Corp., Chicago 22, Illinois. COMPRISING three units, including a large indicator and control panel,APN-57 is a ground-position indicator giving information in latitude and longitude co-ordinates. Ground Track Plotter Loral Electronics Corp., New York 54, N.Y. ON a flat plan-position screen this device will automatically display acontinuous and permanent record of the ground track of an aircraft. The position of a target relative to the present position of the aircraft maybe automatically set into the unit. Nothing further has been released about this equipment. Airborne Navigational Computer Loral Electronics Corp., address as above. THIS is defined as an accurate and compact system which computesand indicates ground displacement of an aircraft in rectangular co-ordinates from an initial fix. The control panel includes poweron/off, variation and wind velocity setting controls and a compass card with two needles indicating drift and course. Nothing further has beenrevealed. Automatic Short-range Ground Position Indicator Loral Electronics Corp., address as above. WEIGHING 18 lb, this computer automatically indicates ground posi-tion derived from airspeed, course and wind information. There are two dials, one a modified compass-card with several indication scalesand the other a two-window instrument showing north-south co-ordin- ates and distance together and the other showing co-ordinates anddistance in the east-west direction. Nothing more has been published about this equipment. AN/ARA-21 (XA-4) Collins Radio Company, Cedar Rapids, Iowa. DEFINED as a navigational computer group, this equipment is ratherdifferent from the other computers here described in that it is a develop- ment of Collins' earlier NC-101 radio navigation computer, but designedto operate with the aid of Tacan signals supplied by a standard Tacan receiver. The ARA-21 shows deviation of aircraft positionfrom selected course line to an arbitrary destination, with manually selected course, to/from indication, and flag alarm displayed on theTacan course indicator. Compass course and computed course to the reference point are displayed on an R.M.I, dial and there is anindication of distance to the reference point. Bearing and distance of the selected reference point from the Tacan station are set in thecounters on the control panel. AN/ARA-21 was designed under U.S.A.F. contract. It weighs21.7 lb, less indicators (these may be duplicated, are of any of a number of standard U.S.A.F. types). Power requirements are 25 Wof 28 V D.C. and 40 VA or 115 V, 400 c/s, single phase. Bearing accuracy is approximately ± 1 deg. AIR DATA SYSTEMS AN air data computer supplies information about the atmo^sphere through which the aircraft is flying to autopilot,^ navigation computer, fire control, instruments and other systems. It provides information on speed and angle of attack, Mach number, T.A.S., pressure altitude, free stream air tempera- ture and air density. The information may also be required for flight control and powerplant management, and for the determina-; tion of range and flight-path in navigation. Indications from the standard aircraft instruments are not accurate enough to provide this information directly to the many systems which require it. The need for accuracy and speed in reporting air data means that for modern high-speed flight a central air data system is virtually indispensable. A central system is also important for co-ordinated operation and to avoid duplication. The arrangement of any particular system will be tailored to suit a certain aircraft, and air data computers are not generally items which can be bought "off the shelf." Both British and American companies are producing this type of equipment, but so far details of American examples only have been released for publication. Central Air Data Computers Eclipse-Pioneer Division, Bendix Aviation Corp., New York 17, N.Y.THE company plans production of a specific central air data computer, but can arrange variations to customer's requirement. Bendix recentlyreceived a U.S.A.F. contract worth $6,736,102 for central air data computers for the F-101 and F-105. They also supply this equipmentfor the B-58, together with the flight control system, manual powered controls and other items. Main components are an air data computer, a multiple outputconverter, static-pressure and angle-of-attack compensator, true-airspeed indicator and a combined airspeed and Mach indicator. The last twoare the cockpit instruments. The inputs used are static and total pressure from the pressure head, indicated free air temperature from a sensingprobe, and indicated angle of attack. The pressure compensator provides an error correction for indicated and true static pressures to the primarycomputer. Outputs are based on formulae standardized by the Bureau of Standards,Wright Air Development Center and N.A.C.A. Most functions are computed by magnetic means, gear train shafts, cam correcters anddifferentials, and outputs are adaptable to the system requirements of specific aircraft. The total weight of the units listed above is 49i 1b. Integrated Flight Instrument System Kollsman Instrument Corp., 45th Avenue, Elmhurst 73, New York.UNDER this rather misleading name, Kollsman have produced an air data system primarily serving the pilots' flight instruments. It has beenspecified for the Douglas DC-8 and Convair 880 jet transports. The system consists of a sensitive altimeter, a standard A.S.I., aMach meter, an angle-of-attack senser, an outside air temperature probe, and a computer. Servo components link the instruments to each otherand to the computer, so that information from one instrument can be used to correct the indications of another. For example, both Machnumber and angle of attack are fed into the altimeter to correct for the inherent error in the aircraft static pressure system. Altimeter instru-ment error is corrected by a scale error correcter in the computer. By combining Mach number with indicated outside air temperature, trueoutside air temperature and true airspeed are obtained. Angle of attack is passed to the A.S.I, where the minimum safe airspeed and bestlift/drag ratio speed are indicated. Five cockpit instruments are associated with the system. The sensitivealtimeter indicates hundreds of feet with a needle and thousands on a counter drum. It has overall errors of 50ft at sea level and 100ft at40,000ft. An A.S.I, reads from 60 kt to 450 kt; a striped needle shows maximum permissible speed for the aircraft's height and a coloured
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