FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1973
1973 - 0392.PDF
232 AIRCRAFT PRODUCTION When the cutter reaches it, the check surface usually becomes the drive surface for the next cutter movement. In the sequence of actions needed to simulate the machining of a part, the cutter symbol is first called up on the screen and set in position in contact with the first drive surface on the component image. The light pen is then nsed to indicate the first check surface. This action causes the first cutter movement to be calculated by the computer and displayed on the screen, and leaves the cutter symbol in contact with the first check surface. When the second check surface has been indicated by the light pen the first check surface becomes the new drive surface and the second cutter motion is calculated and displayed. Point-to-point cutter movements are simple to process, requiring only an indication of the point to which the cutter is required to move. In two-and-a-half axis contour ing (that is, continuous-path machining in the x and y axes, with only incremental or intermittent movement in the z axis), point-to-point movements are mainly used for initial setting of the cutter position, returns to datum and changes in z-axis height of the cutter. Lines, circles and tabcyls are regarded as vertical sur faces and constitute the drive- and check surfaces for any cutter movement. Other GPP programming facilities are automatic pocket-area clearance and play-back of the computed cutter-path for verification. If errors are found, it is possible to "edit" them out. Both the component geometry and the cutter-centre path data can be filed on a magnetic-disc store and automatically retrieved when required for correction or to make design changes. The light pen is used to display the list of draw ings stored in the computer and to indicate which one is required. A/", / / / / J4 / / /CO / / / FLIGHT International, IS February 197J B t ^-^-^>x *!"** A ^-V-A t i i t c i i i i i Diagram illustrating how the "cutter" is traversed round the profile of a component diagram on the screen of the console, in the simulation of machining A—Drive surface I B—Check surface I and drive surface 2 C—Check surface 2 and drive surface 3 GPP has been used in production jobs at Warton to generate control tapes for 25 components, many of which have been subsequently machined. Although the graphic display costs £35/hr to use, the cost of control tapes is reduced by 18 per cent by using GPP and processing man-hours are reduced by 55 per cent. Moreover, control tapes are usually correct when they go for the first time to the shop floor. About four man-years have been devoted by BAC Warton to the development of GPP to its present state. • AVIONICS interest in Omega and several manu facturers, including Canadian Marconi, have developed suitable airborne equipment. Designated AD1800, the Canadian Marconi system is designed for civil and military use. It weighs 521b, excluding connectors and installation trays, can provide a fix with an accuracy of 2 n.m. anywhere in the world, and it is suitable for single- pilot operation. It consists of four units: - a loop aerial, pre-amplifier, receiver-processor and control/display unit. Electronically, the AD1800 employs a fairly conventional receiver, using standard MSI (medium-scale integra tion) components throughout, as does the 16-bit, 8,000-word, 2/*sec general- purpose computer, used for processing the incoming information. This unit is based on a commercial desk-top Hewlett Packard unit. The control/ display unit contains all display and visual annunciator read-outs, along with a mode-selector and push buttons for the insertion of informa tion. Operation of the equipment is again straightforward and requires only the time, date, latitude and longi tude of the start and destination co-ordinates. A further facility enables the pilot to select up to nine en-route waypoints. On start-up the equipment is switched on and can be checked by selecting the Test function, which illuminates all the seven-segment light- emitting-diode display elements and annunciator lamps as the computer is checked. The pilot then selects the GMT/D function (Greenwich Mean Time and Date), punching in the time—say, 1232-5, signifying 12hr 32-5min, followed by 15273, indicating the date as being February 15, 1973. This in formation is taken into the system by depressing the Insert button. These insertions need to be accurate to en sure that the correct propagation- correction factors are used. These change every 20min. Compiled from naval oceanographic tables, this aspect of the software has a fairly long period of validity and the current pro gramme will remain good up to 1980. The next step is to move the display mode switch to WPT and enter the co-ordinates of the desired waypoints and destination and select the first leg. The present position is one of these waypoints. Once the aircraft is airborne the arithmetical processing function of the computer can be selected and the pilot is supplied with the following informa tion: bearing and distance to fly to any specified waypoint; ground speed and estimated time en route; aircraft present position in latitude and longi tude; desired track and actual track error angle; track and cross-track distance from a great circle track between the selected waypoints; and wind direction and speed. In the event of the loss of Omega signal input, the computer automatic ally switches to a dead-reckoning mode. Other indicators alert the pilot to a systems fault, including such external failures as loss of heading reference, lack of synchronisation in the received signal, and the possibility of lane ambiguity. The performance of the AD1800 system was demonstrated during a recent flight over a triangular course, bounded by Southend Airport and the Ongar and Clacton VORs. During this flight, which took place below 2,500ft a.m.s.l., the maximum error did not exceed 1-2 n.m., although signals were being used from transmitters as far afield as North Dakota, Trinidad and Norway. The last two stations were radiating at only lkW, as opposed to the lOkW from North Dakota. Early equipment-proving trials have already been made by a major European inde pendent airline and further evaluation by three more operators will begin next winter. By that time all eight Omega transmitters (in Norway, Aus tralia, Japan, Hawaii, North Dakota, Trinidad, Argentina and the Reunion Islands) should be operating at full power. The equipment is priced at about $40,000 and an operating cost of about 25 per cent that of a full airline- standard inertial system is claimed. The system is marketed in Britain by Marconi-Elliott Avionic Systems. •
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
