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Aviation History
1962
1962 - 0292.PDF
294 FLIGHT International, 22 February I%2 FLIGHT SYSTEMS requirements, tyre and brake wear and similar factors can all be improved whether the weather factor is taken into account or not. Beyond a basic safety level, the actual elaboration and cost of equipment depends on the weather minima it is required to over come; and this is an economic factor discussed elsewhere in this review. Handling capacity of airfields could also eventually be improved. The only arguable point in the process is the timing of the introduction of the various stages. At the moment, the target for routine automatic landing is still 1969 or 1970. The multiplex SEP. 5 was designed for more than just automatic landing. It was intended to provide a new flight control system for full-time use with a very wide range of operational facilities. The complete system, including air data sensors, instruments and radio, has been conceived and developed as a single entity. Application to each type of aircraft is supervised by a separate team of engineers who run the final tests on every one of the 2,000 items involved, wherever the detail design and manufacture were carried out. Smiths Para Visual Directors fitted in a 80AC Boeing 707. KLM are also evaluating PVD and a fare computer in a DC-8 Cables and connections, interrelation of components from different suppliers, in fact the overall integration, are controlled by the one small team. A full rig for each aircraft type is set up at the Smiths factory near Cheltenham so that the whole system can be assembled and run in conjunction with simulators, computers and gyro test stands, all designed and made by Smiths. In parallel with this development work, Smiths have already made a complete Trident systems training rig so that both air- and ground- crews can gain experience before the aircraft reaches BEA. Thorough training is perhaps more important for this project than for any before. Appreciating that maintenance away from the central base could be a problem, Smiths have also designed servicing methods as an integral part of the system. The object has been to allow the local maintenance engineer to progress as quickly as possible from a pilot snag report to the appropriate black-box change without necessarily knowing the system intimately, using complex test equipment or having to open up the black boxes themselves. The main sensors can be exercised on the ground to produce outputs from which overall responses may be checked. For in stance, the gyro mountings can be tilted in a predetermined cycle on their racks. In the azimuth computer, mechanical shafts indi cating radio demands and bank demand are brought out to dials at the front of the box so that they can be directly visually checked. Flight instruments can be quickly and simply removed through the front of the panels without disturbing wiring. Units which have to be precisely aligned with the airframe datum can be changed with out disturbing their alignment. As far as possible, the system is split up into small units—there are many i ATR cases—both to preserve the appropriate degree of segregation and to simplify unit changes. Modules are generally soldered in so that there are hardly any plugs and sockets within the boxes. Though soldered in, modules are generally mounted on hinged frames so that they can be folded out for accessibility. Smiths have developed their own very success ful micro-relay, about the size of a normal resistor, and several hundreds of these are incorporated in the SEP.5. In any instance where a box has more than a 30- or 40-pin connection to the racking system, it is arranged to be jacked in and out of its mounting to ensure good contact and avoid damage during installation. Major factors in simplifying and speeding up maintenance are a very small, portable signal injecter, which can be plugged in on the flight deck to produce a range of test inputs, and a portable tape recorder on which step-by-step test sequences are voice recorded to lead maintenance men through complete checking routines. The tape recorder gives one spoken instruction at a time, demanding first all the settings necessary for initiating a certain test. The man then follows each new instruction, making a control setting and observing that visible reactions on instruments and autopilot fall within specified tolerances. If a reaction is correct, the engineer passes on to the next move. If a response is incorrect, he switches to another tape routine which then takes him through sub-routines to investigate the particular fault. In the final phase he is instructed to select a test card and can finally identify and change the faulty unit. The test tape stays with the aircraft and can be easily altered to take account of any system modifications. Assembly of the various boxes on the production line has been very carefully planned and coloured photographs of wiring and component layout at various stages of assembly are extensively used as guides for production work. Wiring routes are in all cases planned in detail and an exceptionally large number of tie-backs are used. To avoid possible contamination from smoke-laden cabin air, no box requires forced cooling. Smiths own ATR box con struction is, of course, used for all electronic units. Like the micro-relays, the Smiths miniature rate gyros used in the attitude sensors have a history of their own and are finding many applications beyond the SEP.5. They are extremely small and highly accurate, and were originally developed in slightly larger form for a missile project. The main controller is a particular example of SEP.5 system philosophy. Containing all the manual controls for the autopilot and the flight system, it has separate frames for mechanical and electronic portions, bolted together. Segregation of the parts con cerned with the individual multiplex channels and with the three separate power supplies is rigorously maintained, despite dense packaging required by a limited installed volume. Electronic modules here, as in other units, are wired into the overall circuit, but arranged to swing out on hinges for servicing. All components likely to require replacement are mounted on the outside of a module. The whole controller is arranged to be jacked out of its well in the central console and is aligned by guides, so that the multi-pin connectors cannot be damaged during removal or installa tion. All levers and switches are sealed against entry of fluids spilled in the cockpit. Leads from the three power supplies are of different colours and are routed and tied-back to preserve fullest segregation. About half the detailed functional and precision checks have now been completed on a production model. A notable feature of the flight instruments, and one which directly results from the overall design approach, is that all dials have a consistent styling in markings and lettering. It was possible to make a free choice in the early days between roller blind, pointer or counter instruments and to match the presentations of different instruments to provide the minimum possibility of confusion and the clearest reading. The main a.s.i.s are of the helical-face, single- needle type which provide a 90° movement of the needle between cruising and VNE speeds as well as allowing a reading accuracy of 2kt in the approach range. As is well known, roller blind presenta tions are used for director horizon and compass. "Human engineer ing" has been very carefully watched in all control and instrument layout and is being systematically checked by flight testing. One new device is the instinctive cut-out button for the autopilot, designed so that the pilot can positively feel the trigger pressure applied to disengage the autopilot and also feel by touch whether it is engaged or not. Everything possible has been done to make the instrument and control panels for all crew members coherent and clear. Behind all the detailed work now in progress lies the multiplex
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