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Interactive computer-aided technology
Interactive computer-aided technology C H English A description is given of a powerful computer-operated three-dimensional graphic system and associated auxiliary computer equipment used in advance design, production design and manufacturing activities. This system has made these activities more productive than when using older and more conventional methods to design and build aerospace vehicles. The process of designing and manufacturing the complex parts of an aerospace vehicle requires the coordinated efforts of many technical disciplines. Effective interface among these groups demands that each understands the design engineer's concept completely. Heretofore, the only medium for communicating the concept has been the twodimensional engineering drawing, often subject to misinterpretation. Today, the designer is no longer restricted to creating part or entire vehicle definitions within the constraints of two-dimensional descriptive geometry. With the use of this computer graphic system, he is now able to define parts using a wide variety of geometric entities, defining them as fully surfaced three-dimensional models. Once geometrically defined, he is able to take section cuts of the surfaced model and automatically determine all the section properties of the planar cut, or lightpen detect all the surface patches and automatically determine the volume and weight of the part. He may also view the model from any vantage point desired by rotating it about any designated spatial axis, thus providing better visibility of its geometric definition. Further, his designs are defined mathematically at a degree of accuracy never before achievable. The mathematically defined mode/, stored in a central computer, is accessible to other engineering disciplines, tool designers, loft, manufacturing planning, quality assurance, and other personnel having a need for these data. This provides them with a single source set of geometric data with which they are able to address the tasks of analysing the designs for performance, structural integrity, fit and function, part fabrication, and inspection of parts after fabrication. These tasks are accomplished using various computer-aided techniques, software modules and computer hardware, each tailored to do the job for which it is best suited. The use of this computerized system has proved to be both cost and time effective in the conduct of our business. With continued use and development, even greater cost and time-saving techniques are anticipated. In today's very competitive business world, each business firm must continually seek improved methods of conducting its varied activities if it is to survive and retain McDonnell Aircraft Company, Box 516, Saint Louis, Missouri 63166, USA
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its competitive position. These improved methods are normally measured in terms of reduced cost, reduced manhours, reduced leadtime, better products and maintenance of a creative work environment. The design of an aerospace vehicle is predicated on a multitude of requirements of each of the systems and technical disciplines comprising the total design activity. In order that each technical discipline be properly interfaced with all other disciplines, and the integrity of the vehicle performance and specification requirements maintained, close intergroup coordination is mandatory. During any design program, several design interactions are required as a result of loads analysis, weight and balance requirements, aerodynamic considerations and other design ramifications. As a result of these necessary design interactions, there is often difficulty in effecting a smooth and orderly response to the required alignment of the specific design tasks to satisfy these requirements. Reaction time by all affected parties must be closely coordinated to prevent jeopardizing major program milestone schedules. Design changes vary from being minor in nature to the very complex, but all require that we exploit every available technique, talent and design tool at our disposal to assure that the changes are made on a timely basis to prevent schedule compromises. Computer-aided technology, which is comprised of numerous types of computer hardware and software and used by our engineering and manufacturing disciplines at MCAIR, is helping us to meet these goals. MCAI R has formed a CAT (computer-aided technology) project, made up of representatives from departments that use computers in their work, for the purpose of providing the coordination necessary to effect smooth and costeffective interfaces between each of the activities and to identify and ejiminate duplication of efforts in the development of software. Our CAT project activities are similar to those of other companies currenly developing interactive computer graphic capabilities, but is probably structured differently. Our computer system has been modularized into several specific packages in order that each department using computer graphics be required to develop and maintain only the software necessary to accomplish its required departmental tasks. Training of the console operators for each module is therefore simplified compared with having to instruct the operators how to use a single large module that would be used by all departments. Our CAT project personnel are colocated, providing close coordination and a direct line of communication between the various disciplines in the development of their modules. There are currently 15 basic graphic modules under development or coordination by the CAT project. They are CADD (computer aided design-drafting), ICADE (interactive computer-aided design evaluation), CALL (computer
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aided loft lines), CGSA (computer graphics structural analysis), GNC (graphic numerical control), CAQA (computer-aided quality assurance), DBMS (Data base management system), CGAA (computer graphic aerodynamic analysis, CSMP (continuous system modelling program), CAST (computer-aided structural technology), FASTCUT, WTDS (wind tunnel data system), MATLOC (matrix locus) CALA (computer-aided loads analysis) and GNP (graphic nesting program). There are also several special technical programs used by our Engineering Technology Divison. Several of these systems are discussed in the following paragraphs.
SYSTEM DESCRIPTION MCAIR'S software packages utilize a user-oriented programming language that is specifically tailored for the types of problems typically encountered in an aerospace engineering and manufacturing environment. They were developed to allow engineers to utilize the speed and accuracy of a large digital computer to assist in solving analytical and geometry-oriented problems and to present engineering data to other disciplines, both engineering and manufacturing, in the form of computer-stored data or as a hardcopied engineering drawing. The output of the computer, which consists of geometric figures and relevant information relating to them, is visually displayed on a CRT. The engineer can interact with the computer based on what he sees displayed on the CRT or by inputting specific instructions to the computer by means of the functional and alphanumeric keyboards. In essence, he has replaced his drawing board with the display console. Because of the immediate information feedback aspect of the designer's visual relationship with a computer, he is able to complete his tasks in a shorter period of time. Each of our 44 CADD consoles is remotely connected to, and used in conjunction with, IBM 370 Model 168 computers. Each console consists of a display CRT, a typewriter-like alphanumeric keyboard for typing in dimensional data or special instructions to the computer, a 32-button function keyboard for ordering the creation and manipulation of geometric data (points, lines, arcs, conics, cubics, planes, surfaces, etc.) on the CRT, an electronic lightpen for detecting specific displayed data to be manipulated, a closure hood with a Polaroid camera for quick-reference pictures and a 'hot-line' telephone to the CPU (central processing unit) operator. Figure 1 shows a typical CADD console arrangement. The console operator inputs information and orders to the computer using the various input devices at the console The output of the computer, which consists primarily of geometric entities, is displayed on the screen of the CRT. Some simple examples of functions which can be performed using the CADD system should illustrate the types of things that can be done. For example, one of the ways in which an operator can generate a point is to hold the lightpen in close proximity to the screen at the desired location and depress the function key labelled GENERATE POINTS. Figure 2 shows the function keyboard arrangement. A point will be generated and displayed in the vicinity of the location of the lightpen tip. The position of the point, while mathematically precise, is only an approximation of the place or point where the lightpen is held. If the designer wished to generate a point at a mathematically precise location, he
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Figure 1. CA DD console arrangement
Figure 2. CA DD function keyboard overlay
must depress the function key labeled POINT. A message (called a menu) will be displayed on the screen requesting the operator to input the desired 3-D coordinates of the point. With this accomplished using the alphanumeric keyboard, the computer generates and displays the point. Although the lightpen was used to indicate the approximate position of a point to be generated in the first example, its primary use is in detecting screen images of entities with which the operator wishes to work. Detection is accomplished by positioning the lightpen over the image on the screen, then depressing its spring-loaded tip against the screen. The light from the image registers on a photocell located within the pen and when detected, the image disap-
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pears, indicating that it has been detected. As soon as the operation on the detected element is completed, all detected entities are redisplayed, along with any new ones that have been created. One way of generating a finite length line is for the operator to detect with the l ightpen two end points, having any x, y, z coordinates and depressing the function key labelled LINE. (Depression of a specific function key tells the computer what kind of entity it is to generate, i.e. line, circle or arc.) The two detected points give the computer all the information needed for it to generate the line. The result is a line between the two detected points. Should insufficient data be supplied to the computer for an entity generation, such as detecting one point with the lightpen and depressing the function key labelled CIRCLE, a message will be displayed on the screen asking for a radius to be keyed in. Thus, the logic programmed into the system has been well planned in a natural engineering mode. These examples illustrate how entities can be generated by using the function keyboard and the lightpen (GENERATE POINTS and LINE) or the function keyboard and alphanumeric keyboard (POINT), but the more general case for generating geometric entities would utilize all the input devices in combination. For instance, to offset a line parallel to another line, the operator would detect the original line with the lightpen and depress the LINE function key. The CRT would then display a menu requesting the distances from and the side of the detected line on which the parallel line is to be generated. When that information is supplied via the alphanumeric keyboard and the lightpen, a parallel line is generated and displayed. In addition to points and lines, our graphic system is capable of generating many other kinds of geometric elements. Separate function keys exist for POINT, GENERATE POINTS, LINE, ARC, CIRCLE, CONIC, ELLIPSE, SURFACES and CUBIC entities. Furthermore, since there are a number of different ways each element can be generated, virtually any figure can be defined by various combinations of the basic geometric elements. Using the computer in the design process has resulted in additional benefits and capabilities that enhance the basic attractiveness of the system. Admittedly, one of the chief attributes of computer graphics is its capability to define geometrically an object far more rapidly and accurately on the CRT, with the aid of the computer, than an engineer could on a drawing board. Once a computer is utilized and integrated into a graphic system, it lends itself well to various tasks associated with generating, displaying and manipulating geometric data. All the geometric data displayed on the CRT are physical representations of what is modelled in the high-speed core memory of the computer. Once the computer has been programmed to deal with data in terms of a model, it is then possible for the computer to manipulate that model. Data-manipulation functions such as SCALE (expand or contract the displayed drawing) FLIP (reflect a display about a line, i.e. mirror image) and TRANSLATE/ROTATE (translate and/or rotate a picture from one position to another) all make it easier for the console operator to work with the display. Beyond these, however, functions such GEOMETRIC PROPERTIES (calculated geometric properties of selected figures), SECTION CUTS (display the cross-section of the displayed model when it is intersected by a plane) and VIEW (automatically view the displayed model from any desired vantage point) extend the utility of the system to a point where the
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computer is capable of accomplishing tasks easily which, if they were even possible on the drawing board, would normally be time-consuming and often result in some degree of inaccuracy. This is one of the initial payoffs of computer graphics.
CAT SYSTEMS DEVELOPMENT Our CAT systems development at McDonnell started in the late 1950s and, in 1959, the first computer-stored loft surface was generated. In 1962, our manufacturing division made their first direct access to computer-stored loft surfaces. Additional systems development occurred over the years and, in August 1974, the CAT project was formed with objectives of assuring efficient use of computer resources, coordinating software development and assuring effective use of the computer systems in a project environment. Our current capabilities have provided a number of cost benefits to us; we are currently expanding our capabilities and broadening the areas of interface between the various technical disciplines tO increase the payoffs. In the area of flight technology, CGAA (computer graphic aerodynamic analysis), G&C, (guidance and control), and other technical programs yet to be determined (CGXA) can or will be able to access the design geometry files created by the CADD system, and the Engineering Technology Division (ETD) files created by the CGSA, loads and structural-dynamics modules. In addition, the structures-technology modules access both the ETD files and the design-geometry files which are created by the CADD module.
I C A D E (interactive computer-aided design evaluation) When an aircraft con'figuration has been synthetized on the CRT and stored in the computer, members of the design team responsible for performance analysis can access geometric data at the same console used to create the configuration and apply an interactive parametric sizing analysis program called ICADE (pronounced eye'-kaydee), to determine if the flight performance requirements and vehicle size are compatible. It also has the capability of sizing the aircraft configuration to satisfy a specified set of flightperformance requirements, i.e. size wing, engine and/or fuel volumes to meet or exceed performance requirements and determine concomitant changes in the aircraft geometry, mass properties, aerodynamic characteristics, installed engine performance and life-cycle cost characteristics. The system is quite effective when used to conduct studies for determining the effect of parametric variations in aircraft design parameters, (e.g. wing geometry, wing loading, thrust to weight ratio and structural load factors) on the aircraft size while holding the performance constant or determining the effect of parametric changes in performance parameters (e.g. mission radius and specific excess power) on aircraft size. In addition, ICADE can be used to evaluate specific design or performance tradeoffs; determine the sensitivity of aircraft size to incremental changes in engine size, fuel quantity, fixed weight, aerodynamic drag, specific fuel consumption, etc., while holding the performance constant; and generate data required for the PDAP (parametric design analysis procedure), a separate batch-analysis program, which is used to determine 'optimum' design parameter values which maximize or minimize a measure of aircraft effectiveness (e.g. takeoff gross weight and life-cycle cost).
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All input data required by ICADE have been divided into 13 categories to facilitate the editing process. These data categories are: • • • • • • • • • • • • •
Design parameters Program control indicators Sensitivity parameters Mission performance parameters Manoeuvre performance parameters Miscellaneous performance parameters Geometric characteristics - baseline aircraft Weight characteristics - baseline aircraft CG characteristics - baseline aircraft Aerodynamic characteristics - baseline aircraft Propulsion system characteristics - reference engine Cost characteristics -- baseline aircraft Payload characteristics
The analyst initiates the editing process by detecting with the lightpen the data category to be edited from a menu display. The data from the selected category are then displayed in card-image form identical to that used for the batch version of the program. A menu of commands is also displayed on the CRT. During execution of the ICADE sizing iteration, the iteration number and current values of fundamental aircraft sizing parameters are displayed. These data provide the analyst with information on the convergence behaviour of the sizing iteration, but do not allow him to interact with this phase of program execution. After the sizing iteration has converged to a solution and the cost and mission-performance characteristics have been calculated, the following summary of the sized aircraft characteristics is displayed • Geometric characteristics (comparison with baseline aircraft) • Weight characteristics (comparison with baseline aircraft) • C G characteristics (optional) • Mission performance • Manoeuvre performance • Cost characteristics (optional) • Aerodynamic characteristics Some of the programs we are currently using include a generalized sizing and scaling routine that provides a tradeoff option for conventional twin engines, podded engines and single engine, and the option for wing and control surfaces. Another capability features geometry scaling for the wing, fuselage, fuel volume, lift engine, thrust sizing for energy manoeuverability, mission, takeoff, thrust balancing and ground effects for V/STOL type aircraft.
ETD (Engineering Technology Division) interfaces In order that each of our technology disciplines takes advantage of the analytical computer programs being used by the other disciplines, we are developing an interface that will provide a rapid transfer of data among all of the ETD analysis programs. To accomplish this, it was necessary to define all of the design activities in the aircraft development process, identify the data-transfer requirements and computation methods used, document the form and format for the data transfer, and create the files and compatible programs.
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In addition, we have created an interactive program called CGAA (computer graphics aerodynamics analysis) that provides the analyst access to vehicle configurations stored in the CADD drawing files which he will convert to a format that is suitable for running aerodynamic analysis programs such as the Vortex Lattice, Middleton-Cartton, Emington-Weber, Woodward and NASA Wave Drag. This program provides a time compression in the analysis process allowing a more complete analysis of each of the configurations. Data c o n t r o l To provide protection of data stored in the computer, an executive program is being created that checks the user authority and will provide a tutorial step-by-step guide through the various menus to the desired program. In addition to its provision of file protection, authorized access to the various files and routines will be more rapid. Loft The basic function of the loft department at MCAIR is developing a computer-stored mathematical shape definition within which the aircraft is designed and from which tools and parts are manufactured. This definition must be compatible with the exacting tolerances of today's highspeed aircraft and the requirements of modern tooling methods. It must be available to all computer users. To accomplish this end, the loft department has developed many computer-aided techniques to assist in the timely acquisition of this database. Starting in the advanced design environment, loft assembles critical parameters from all design disciplines and assembles either a graphic representation (Figure 3) using the CRT application named CALL (computer-aided loft lines). These representations are used by the design department in preparing preliminary drawings to verify such items as proper fuel volume, sufficient room for equipment, structural integrity, etc. At this time, the configuration is still very fluid and loft must react quickly to continuous design changes. Coincident with this is usually a large amount of wind-tunnel model testing. One of the several methods of providing wind-tunnel wing models is accomplished with an NC program called WINGMILL. The only required input data to the computer are the wing planform geometry, model scale, cutter tool radius, tool feed rate, machining tolerance, stock thickness, and the basic equations of the airfoils and camber information, if applicable. The output of this program is either NC milling tapes or DNC (direct numerical control) data stored on disc. Figure 4 shows a wind-tunnel wing model that has been partially completed using this program. One of the areas of system improvements being addressed by our loft department is the conversion of the various mathematical formats of all our graphic programs into a common mathematical database. For example, in the past, the loft department has provided computer-stored lofted surface definitions with cubic surfaces: When the design department wanted a cross-section of a surface, the cut was represented by a series of points, reconnected with a series of conic curves and then displayed on the CRT. This curve-to-point-to-curve conversion provides an extremely close approximation of the actual lofted surface and more than adequately satisfies the engineering and manufacturing needs; however, it does mean that dual
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Figure 3. Advanced design loft surface definitions
mathematical definitions of the same geometry exist. Providing a single mathematical definition of a surface will result in a more efficient use of computer resources.
Computer graphics design applications CADD is being used for a wide range of design applications a few of which are • Geometry studies and layouts • Composite materials • Machined parts • Sheet metal flat pattern • Assemblies and installations • Hydraulic tubing design • Mechanism design One prime reason for using CADD for these applications is its unique 3-D capability which provides rapid and accurate solutions to complex spatial geometry problems, direct readout of all spatial relationships, natural part depiction, efficient utilization of computer resources and the provision of defining geometry in an unambiguous manner. Ambiguity of conventional two-dimensional orthographic projections results from the fact that each of the x, y, z coordinates must be defined twice to properly describe part geometry. In the case of the part being defined as a single three-dimensional model, each point of the model is defined with a single x, y, z coordinate, thus eliminating ambiguity. Figure 5 shows a comparison of these two methods of part definition. Another example of CADD's ability to solve spatial geometry problems is depicted in Figure 6. The geometry of McDonnell's MACS III flight simulator installation was recreated via CADD and stored in our central computer. Included in the computerized definition of this installation are all the target projection cameras, missile and horizon projectors, and all the support and base structure of the in-
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stallation. With these data stored in the computer, the cockpit of any aircraft can be recreated with CADD, stored in the computer, merged with the simulator definition and viewed from the pilot's eye position to determine if the projectors and support structure are out of view from the pilot, as shown in Figure 7. This may all be done before building a simulator cockpit and provides early information to determine whether cameras and equipment will have to be relocated to keep them out of the pilot's view. Volumetric studies are also readily accomplished with CADD. Figure 8 shows an example of a fuel-tank volume study where the tank has been defined with surfaces. By lightpen detection of all the surfaces, and utilizing the geometric properties key on the function keyboard, all of the properties shown are immediately displayed. The TFP (triangulated flat pattern) routine in CADD is particularly useful in the application of composite material design. On the F-15 fighter aircraft, the composite speed
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brake (Figure 9) is comprised of both machined hardware and a series of 0.0054in (0.13716mm) thick graphite composite plies that are preimpregnated with epoxy. There are 76 plies at one section of the speed brake, each of which is mould-line related. In the past, it was necessary for the designer to describe each ply in the installed configuration, but he was unable to define the flat-pattern dimensions required by manufacturing to cut out the plies from raw stock. Personnel from master layout section of the loft department would have to manually lay out each ply, which was costly and time consuming. With the TFP routine in the CADD system, our designers now define the installed, curved configuration of each ply, then instruct the computer to unroll them into a flat pattern. In an instant, the flat pattern of the ply is displayed on the CRT screen. Each of the flat patterned plies are then hardcopied at full scale and input to manufacturing as a template for cutting out the material. Thus, manual-layout errors are
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eliminated and the design/fabricate cycle time is reduced. Figure 10 shows a typical example of a curved flat pattern that has been rolled out from its curved installation position. Figure 11 shows a hardcopy of a: ply as it appears in the released drawing format, depicting type, ply number, dash number, the filament direction and a reference outline of the overall speed brake. With a dramatic increase in the number of machined parts on modernday aircraft cut with 5-axis milling machines, it has become prudent for us to devise a new method of defining parts in the computer and to establish a more automated means of creating drawings having the necessary data to interpret its definition. Figure 12 depicts a canard rib defined with surfaces, each of which has been uniquely labelled. Although this model is mathematically defined in three dimensions and stored in the computer, additional information is required for interpretation to facilitate its analysis and for manufacturing planning purposes. As a result, we are looking at methods of creating a batch-operated automatic drafting package and a batchoperated automated dimensioning package. This would eliminate the designer having to model each section-cut and view of the part (duplication of effort and computer
Figure 10 Triangulated flat pattern Figure 8. Fuel volume studies
Figure 9. Composite speed broke
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storage) and would eliminate the tedium of manually keying in dimensional data. Figure 13 shows a hardcopy of the sections of the part. All surfaces are automatically and uniquely labelled to assist the parts programmer in planning the machine cutting of the part. The only dimensions shown are the dimensions deemed critical for analysis and inspection of the part. Large-part definitions such as an F-15 fuselage bulkhead (Figure 14) have presented problems to both engineering and manufacturing personnel due to the 48 kbyte limit on model size. Figure 15 shows how the bulkhead must be modelled in segments with as many as 40 models required for a complete definition of the bulkhead. Even though these models are merged during the hardcopy process to provide a drawing of the complete part, accessing specific portions of the part definition from the computer might require retrieving segments from several models and merging them at the console, which is time consuming. An approach to solving this problem is currently being worked on, which we call Schematic File/Retrieval. This would require the creation of a simplified two-dimensional sketch of the part where each pocket or specified area of the sketch would be labelled and programmed to 'point' to the model stored in the computer, when lightpen detected, and retrieve and display the desired segments of each of the models. Thus, only the desired elements from several models would be displayed in a region less than 48kbytes in size. Another method of handling the problem of large-part definitions which is currently being addressed is data compression. This technique allows the designer to design
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by rules, where only a minimum of geometric details would be modelled and the remainder of the parametric design details would be implied. For example, the pocket of the part shown in Figure 16 would have the bottom surface modelled, a depth keyed in and the corner and fillet radii implied, resulting in an implied surfaced model without actually having the entire pocket modelled and stored in the computer. This will provide the data compression necessary to define much larger models than we can currently display.
CGSA (computer graphics structural analysis) CGSA is a module that has been developed to aid structural analysis and design. CGSA is used to provide internal loads, stresses and strains for structural sizing, and documentation of structural integrity. This system functions in conjunction with the CADD system. CGSA is used to prepare three-dimensional finite-element model input data for either the CASD or NASTRAN structural analysis programs. CASD, an acronym for computer-aided structural design, is a structural analysis program developed by Douglas Aircraft Company before the development of NASTRAN by NASA. Basic geometry is developed from loft data, conventional engineering drawings or the three-dimensional geometry of the vehicle constructed and filed in the computer by the designer. This results in a point-line model (which is converted to a finiteelement model by defining bar/panel/membrane element properties, applied loads and external boundary condition). The model can be viewed, checked and edited at the console for verification of the input data. Hardcopies are produced displaying input properties and element labels and the model is then stored in the CADD drawing files for future retrieval. The CASD or NASTRAN input card images are automatically created on a disc data set for submittal to the structural analysis program. The utilization of CGSA for model generation eliminates the need for manually creating the models, input sheets and punched cards. Upon completion of the CASD or NASTRAN structural analysis program (which performs a minimum strain energy solution), the results are stored with the model in the CADD drawing file and are also output in the more usual manner on an alphanumeric printer. The answers can be displayed at the console and hardcopied for all structural
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elements. The display options include magnitudes of bar load, bar stress, panel shear flow, panel shear stress, membrane stress, membrane strain and membrane running loads. Bar loads, bending moments and deflected shapes can also be plotted. The displays and hardcopies in the form sheets are used by engineering supervisors to gain an overall feel for the structural analysis, and also by the detail stress analyst as inputs for his computations. This type of graphic presentation eliminates the need to manually prepare loads sheets. This was previously done by reading the printed output data and associating it with the pictures of the structural idealization. CGSA is also used to transmit, within the computer, structural flexibility influence coefficients or a reduced stiffness matrix to the loads and structural dynamics departments. Additional geometric data are passed to the loads department who then generate panel point loads which are transmitted back to the CGSA module. CGSA is effective when used in both advanced design and project environments. The advanced design department requires smaller models, quick turnaround and good visibility, and it adds to the technical credibility of technical proposals. In a project environment, it is effective in handling large quantities of data (the F-15 wing model has 10000 card images) and in providing the design and strength department personnel with essential data when responding to design changes and updates.
Some of our current activities integrate several of the structures technology disciplines' computer programs with the CADD package. These include aerodynamics, loads, weights, strength, materials and process, and structural dynamics. This integration will yield the interactive flow of technical data necessary to provide rapid convergence to a proper design resulting from the iteration process.
CADD-GNC/APT interfaces Once a part definition has been created and stored in the computer, manufacturing can access the 8eometry from the computer files and, using the GNC (graphic numeric control) module, automatically generate APT source statements
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This method of part programming is more rapid than methods previously used. In addition to creating the part program for machining the part, the part programmer must also add lugs to the part to hold the part to the cutter bed during the machining operation. The lugs are then machined off after the rest of the part has been completed. After all the part programming has been completed, the programmer can usually review the path of the cutter at the console (Figure 18) to assure that he has no errors in his program.
CAQA (computer-aided quality assurance) Upon completion of the machining operation, inspection of the part is necessary to determine if it accurately represents the design definition. A copy of the part definition that was defined by the designer is retrieved by the quality assurance programmer. Using the lightpen, he generates points on the surface of the part that the DNC inspection machine is to probe (Figure 19). Vectors are displayed (Figure 20) on the part at the points which the probe is to make contact
Figure 15. Large drawing file capability at the console. These source statements are used as instructions to drive the machine tools for cutting the parts. The key to the success of this interface is the automatic labelling of the surfaces when they are created by the designer. Figure 17 exemplifies how the part source program is generated. The pocket of the part is completely defined with uniquely labelled surfaces. The part programmer need not know what the geometric definitions of these surfaces are, only what the label names are. In this example, the programmer would identify the part number of the machining and that it would be cut on a 3-spindle, 5axis milling machine. He would then identify the set point location from which the cutting tool would move to position (1) where the first plunge of the cutter would be made. This position is defined by the intersection of the three labelled surfaces: RSO001, PLO005 and RS0033. The next instruction would be for the cutter to move along surface RSO001 to position (2), then along surface RSO002 to position (3), where surface RSO003 starts, and so on.
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Figure 20. 'Blasting'points on surface of port when probe is to make contact
and APT statements, which will guide the probe to these points on the actual part, are created as vectors appear. He next reviews the program, using data set edit if required and then, as in the case of the cutter path plot, it is visually verified (Figure 21), edited if required and finally sent to an IBM 1800 computer for the inspection operation. During the actual inspection operation, the inspection probe is driven by DNC to each of the preprogrammed inspection points until contact of the part is made. When contact is made, the probe stops and the actual surface coordinates, the programmed surface coordinates, the allowed tolerances and out of tolerance conditions are automatically printed out on a high-speed line printer. This process eliminates many hours of inspection setup time and the human error that can result from more conventional inspection methods. This inspection method is primarily used for first article
F/gum 21. Plotting the peth the probe treversesend the points of contact
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inspections, for checking out modified GNC programs or for checking parts to determine the effects of cutter-tool wear. For inspecting subsequent parts after a first-article inspection, a F I A T (film inspection apply template) is sometimes used. It is made of clear polyester plastic (Mylar) sheet 0.19mm thick. When a FIAT is required, a console operator in the loft department will call up a copy of the engineering drawing, display it on the CRT and input a request to the computer for a scribecoat hardcopy. When the hardcopy is completed, a photo-sensitive sheet of Mylar is overlaid on the hardcopy, exposed and run through a development processor. Within a matter of minutes, an inspection template made of a dimensionally stable base material is ready for use. These templates are used by the quality assurance department to check a finished machined part for proper machining of flanges, webs and caps by overlaying the FIAT on the machined part. Any deviation from the intended configuration is readily detectable.
SUMMARY The use of CADD, CGSA, GNC, CALL, CAQA, ICADE and all the other programs and systems comprising computeraided technology at MCAIR, has effected many changes in traditional work methods of our various interfacing disciplines. We have streamlined our tasks by utilizing the various cost/time saving techniques afforded by these systems and plan additional development efforts which will further improve it. One might argue whether these activities are evolutionary or revolutionary, but in either case, it must be recognized that there is never an 'optimum' method of operation in the design/manufacture cycle. We are never satisfied with the tools for accomplishing the required tasks and are always seeking improvements. Our final objectives or goals cannot accurately be defined since they are in a constant state of change, but we are confident that the enhancements afforded by computeraided technology will continue to provide increased productivity in the years to come.
ik===l alllil;alll
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by John Paterson, Department of Construction Management, University of Reading. Fragmentation of the construction industry has caused problems of communication for all the participants in the design and construction of buildings. Furthermore, concepts of data and information are changing more rapidly than the processes are being changed. These and other aspects of information methods are examined and discussed and positive proposals made which range from simple manual systems to complex computer systems which may precipitate dramatic changes in the structure of the industry. Contents: Introduction; Man: Designer and User; Data;
Information Flow; Design; Communication: Design and Cost; Construction; Maintenance; Policy; The Machine: The Future; Appendixes; References; Name Index; Subject Index. About the Author: John Paterson has been a principal in private practice, consultant and lecturer in Construction Management at the University o f Reading since leaving West Sussex County Council where he was Deputy County Architect until Local Government Reorganization. Whilst he was in West Sussex he achieved an international reputation for his pioneering work in computer aided architectural design and energy conservation in building. He has served on many committees relating to these subjects and is at present a member o f the Transport and Civil Engineering Committee o f the Science Research Council and its building sub-committee. As an articled pupil before the war and a student at the Architectural Association School o f Architecture after the war, he has seen both types o f architectural training which has been a continued influence on his approach to design and construction.
0471 99449 9
254
208 pages
April 1977
$15.001£7.95
computer-aided design
volume 9 number 4 october 1977
its competitive position. These improved methods are normally measured in terms of reduced cost, reduced manhours, reduced leadtime, better products and maintenance of a creative work environment. The design of an aerospace vehicle is predicated on a multitude of requirements of each of the systems and technical disciplines comprising the total design activity. In order that each technical discipline be properly interfaced with all other disciplines, and the integrity of the vehicle performance and specification requirements maintained, close intergroup coordination is mandatory. During any design program, several design interactions are required as a result of loads analysis, weight and balance requirements, aerodynamic considerations and other design ramifications. As a result of these necessary design interactions, there is often difficulty in effecting a smooth and orderly response to the required alignment of the specific design tasks to satisfy these requirements. Reaction time by all affected parties must be closely coordinated to prevent jeopardizing major program milestone schedules. Design changes vary from being minor in nature to the very complex, but all require that we exploit every available technique, talent and design tool at our disposal to assure that the changes are made on a timely basis to prevent schedule compromises. Computer-aided technology, which is comprised of numerous types of computer hardware and software and used by our engineering and manufacturing disciplines at MCAIR, is helping us to meet these goals. MCAI R has formed a CAT (computer-aided technology) project, made up of representatives from departments that use computers in their work, for the purpose of providing the coordination necessary to effect smooth and costeffective interfaces between each of the activities and to identify and ejiminate duplication of efforts in the development of software. Our CAT project activities are similar to those of other companies currenly developing interactive computer graphic capabilities, but is probably structured differently. Our computer system has been modularized into several specific packages in order that each department using computer graphics be required to develop and maintain only the software necessary to accomplish its required departmental tasks. Training of the console operators for each module is therefore simplified compared with having to instruct the operators how to use a single large module that would be used by all departments. Our CAT project personnel are colocated, providing close coordination and a direct line of communication between the various disciplines in the development of their modules. There are currently 15 basic graphic modules under development or coordination by the CAT project. They are CADD (computer aided design-drafting), ICADE (interactive computer-aided design evaluation), CALL (computer
243
aided loft lines), CGSA (computer graphics structural analysis), GNC (graphic numerical control), CAQA (computer-aided quality assurance), DBMS (Data base management system), CGAA (computer graphic aerodynamic analysis, CSMP (continuous system modelling program), CAST (computer-aided structural technology), FASTCUT, WTDS (wind tunnel data system), MATLOC (matrix locus) CALA (computer-aided loads analysis) and GNP (graphic nesting program). There are also several special technical programs used by our Engineering Technology Divison. Several of these systems are discussed in the following paragraphs.
SYSTEM DESCRIPTION MCAIR'S software packages utilize a user-oriented programming language that is specifically tailored for the types of problems typically encountered in an aerospace engineering and manufacturing environment. They were developed to allow engineers to utilize the speed and accuracy of a large digital computer to assist in solving analytical and geometry-oriented problems and to present engineering data to other disciplines, both engineering and manufacturing, in the form of computer-stored data or as a hardcopied engineering drawing. The output of the computer, which consists of geometric figures and relevant information relating to them, is visually displayed on a CRT. The engineer can interact with the computer based on what he sees displayed on the CRT or by inputting specific instructions to the computer by means of the functional and alphanumeric keyboards. In essence, he has replaced his drawing board with the display console. Because of the immediate information feedback aspect of the designer's visual relationship with a computer, he is able to complete his tasks in a shorter period of time. Each of our 44 CADD consoles is remotely connected to, and used in conjunction with, IBM 370 Model 168 computers. Each console consists of a display CRT, a typewriter-like alphanumeric keyboard for typing in dimensional data or special instructions to the computer, a 32-button function keyboard for ordering the creation and manipulation of geometric data (points, lines, arcs, conics, cubics, planes, surfaces, etc.) on the CRT, an electronic lightpen for detecting specific displayed data to be manipulated, a closure hood with a Polaroid camera for quick-reference pictures and a 'hot-line' telephone to the CPU (central processing unit) operator. Figure 1 shows a typical CADD console arrangement. The console operator inputs information and orders to the computer using the various input devices at the console The output of the computer, which consists primarily of geometric entities, is displayed on the screen of the CRT. Some simple examples of functions which can be performed using the CADD system should illustrate the types of things that can be done. For example, one of the ways in which an operator can generate a point is to hold the lightpen in close proximity to the screen at the desired location and depress the function key labelled GENERATE POINTS. Figure 2 shows the function keyboard arrangement. A point will be generated and displayed in the vicinity of the location of the lightpen tip. The position of the point, while mathematically precise, is only an approximation of the place or point where the lightpen is held. If the designer wished to generate a point at a mathematically precise location, he
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Figure 1. CA DD console arrangement
Figure 2. CA DD function keyboard overlay
must depress the function key labeled POINT. A message (called a menu) will be displayed on the screen requesting the operator to input the desired 3-D coordinates of the point. With this accomplished using the alphanumeric keyboard, the computer generates and displays the point. Although the lightpen was used to indicate the approximate position of a point to be generated in the first example, its primary use is in detecting screen images of entities with which the operator wishes to work. Detection is accomplished by positioning the lightpen over the image on the screen, then depressing its spring-loaded tip against the screen. The light from the image registers on a photocell located within the pen and when detected, the image disap-
computer-aided design
pears, indicating that it has been detected. As soon as the operation on the detected element is completed, all detected entities are redisplayed, along with any new ones that have been created. One way of generating a finite length line is for the operator to detect with the l ightpen two end points, having any x, y, z coordinates and depressing the function key labelled LINE. (Depression of a specific function key tells the computer what kind of entity it is to generate, i.e. line, circle or arc.) The two detected points give the computer all the information needed for it to generate the line. The result is a line between the two detected points. Should insufficient data be supplied to the computer for an entity generation, such as detecting one point with the lightpen and depressing the function key labelled CIRCLE, a message will be displayed on the screen asking for a radius to be keyed in. Thus, the logic programmed into the system has been well planned in a natural engineering mode. These examples illustrate how entities can be generated by using the function keyboard and the lightpen (GENERATE POINTS and LINE) or the function keyboard and alphanumeric keyboard (POINT), but the more general case for generating geometric entities would utilize all the input devices in combination. For instance, to offset a line parallel to another line, the operator would detect the original line with the lightpen and depress the LINE function key. The CRT would then display a menu requesting the distances from and the side of the detected line on which the parallel line is to be generated. When that information is supplied via the alphanumeric keyboard and the lightpen, a parallel line is generated and displayed. In addition to points and lines, our graphic system is capable of generating many other kinds of geometric elements. Separate function keys exist for POINT, GENERATE POINTS, LINE, ARC, CIRCLE, CONIC, ELLIPSE, SURFACES and CUBIC entities. Furthermore, since there are a number of different ways each element can be generated, virtually any figure can be defined by various combinations of the basic geometric elements. Using the computer in the design process has resulted in additional benefits and capabilities that enhance the basic attractiveness of the system. Admittedly, one of the chief attributes of computer graphics is its capability to define geometrically an object far more rapidly and accurately on the CRT, with the aid of the computer, than an engineer could on a drawing board. Once a computer is utilized and integrated into a graphic system, it lends itself well to various tasks associated with generating, displaying and manipulating geometric data. All the geometric data displayed on the CRT are physical representations of what is modelled in the high-speed core memory of the computer. Once the computer has been programmed to deal with data in terms of a model, it is then possible for the computer to manipulate that model. Data-manipulation functions such as SCALE (expand or contract the displayed drawing) FLIP (reflect a display about a line, i.e. mirror image) and TRANSLATE/ROTATE (translate and/or rotate a picture from one position to another) all make it easier for the console operator to work with the display. Beyond these, however, functions such GEOMETRIC PROPERTIES (calculated geometric properties of selected figures), SECTION CUTS (display the cross-section of the displayed model when it is intersected by a plane) and VIEW (automatically view the displayed model from any desired vantage point) extend the utility of the system to a point where the
volume 9 number4 october 1977
computer is capable of accomplishing tasks easily which, if they were even possible on the drawing board, would normally be time-consuming and often result in some degree of inaccuracy. This is one of the initial payoffs of computer graphics.
CAT SYSTEMS DEVELOPMENT Our CAT systems development at McDonnell started in the late 1950s and, in 1959, the first computer-stored loft surface was generated. In 1962, our manufacturing division made their first direct access to computer-stored loft surfaces. Additional systems development occurred over the years and, in August 1974, the CAT project was formed with objectives of assuring efficient use of computer resources, coordinating software development and assuring effective use of the computer systems in a project environment. Our current capabilities have provided a number of cost benefits to us; we are currently expanding our capabilities and broadening the areas of interface between the various technical disciplines tO increase the payoffs. In the area of flight technology, CGAA (computer graphic aerodynamic analysis), G&C, (guidance and control), and other technical programs yet to be determined (CGXA) can or will be able to access the design geometry files created by the CADD system, and the Engineering Technology Division (ETD) files created by the CGSA, loads and structural-dynamics modules. In addition, the structures-technology modules access both the ETD files and the design-geometry files which are created by the CADD module.
I C A D E (interactive computer-aided design evaluation) When an aircraft con'figuration has been synthetized on the CRT and stored in the computer, members of the design team responsible for performance analysis can access geometric data at the same console used to create the configuration and apply an interactive parametric sizing analysis program called ICADE (pronounced eye'-kaydee), to determine if the flight performance requirements and vehicle size are compatible. It also has the capability of sizing the aircraft configuration to satisfy a specified set of flightperformance requirements, i.e. size wing, engine and/or fuel volumes to meet or exceed performance requirements and determine concomitant changes in the aircraft geometry, mass properties, aerodynamic characteristics, installed engine performance and life-cycle cost characteristics. The system is quite effective when used to conduct studies for determining the effect of parametric variations in aircraft design parameters, (e.g. wing geometry, wing loading, thrust to weight ratio and structural load factors) on the aircraft size while holding the performance constant or determining the effect of parametric changes in performance parameters (e.g. mission radius and specific excess power) on aircraft size. In addition, ICADE can be used to evaluate specific design or performance tradeoffs; determine the sensitivity of aircraft size to incremental changes in engine size, fuel quantity, fixed weight, aerodynamic drag, specific fuel consumption, etc., while holding the performance constant; and generate data required for the PDAP (parametric design analysis procedure), a separate batch-analysis program, which is used to determine 'optimum' design parameter values which maximize or minimize a measure of aircraft effectiveness (e.g. takeoff gross weight and life-cycle cost).
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All input data required by ICADE have been divided into 13 categories to facilitate the editing process. These data categories are: • • • • • • • • • • • • •
Design parameters Program control indicators Sensitivity parameters Mission performance parameters Manoeuvre performance parameters Miscellaneous performance parameters Geometric characteristics - baseline aircraft Weight characteristics - baseline aircraft CG characteristics - baseline aircraft Aerodynamic characteristics - baseline aircraft Propulsion system characteristics - reference engine Cost characteristics -- baseline aircraft Payload characteristics
The analyst initiates the editing process by detecting with the lightpen the data category to be edited from a menu display. The data from the selected category are then displayed in card-image form identical to that used for the batch version of the program. A menu of commands is also displayed on the CRT. During execution of the ICADE sizing iteration, the iteration number and current values of fundamental aircraft sizing parameters are displayed. These data provide the analyst with information on the convergence behaviour of the sizing iteration, but do not allow him to interact with this phase of program execution. After the sizing iteration has converged to a solution and the cost and mission-performance characteristics have been calculated, the following summary of the sized aircraft characteristics is displayed • Geometric characteristics (comparison with baseline aircraft) • Weight characteristics (comparison with baseline aircraft) • C G characteristics (optional) • Mission performance • Manoeuvre performance • Cost characteristics (optional) • Aerodynamic characteristics Some of the programs we are currently using include a generalized sizing and scaling routine that provides a tradeoff option for conventional twin engines, podded engines and single engine, and the option for wing and control surfaces. Another capability features geometry scaling for the wing, fuselage, fuel volume, lift engine, thrust sizing for energy manoeuverability, mission, takeoff, thrust balancing and ground effects for V/STOL type aircraft.
ETD (Engineering Technology Division) interfaces In order that each of our technology disciplines takes advantage of the analytical computer programs being used by the other disciplines, we are developing an interface that will provide a rapid transfer of data among all of the ETD analysis programs. To accomplish this, it was necessary to define all of the design activities in the aircraft development process, identify the data-transfer requirements and computation methods used, document the form and format for the data transfer, and create the files and compatible programs.
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In addition, we have created an interactive program called CGAA (computer graphics aerodynamics analysis) that provides the analyst access to vehicle configurations stored in the CADD drawing files which he will convert to a format that is suitable for running aerodynamic analysis programs such as the Vortex Lattice, Middleton-Cartton, Emington-Weber, Woodward and NASA Wave Drag. This program provides a time compression in the analysis process allowing a more complete analysis of each of the configurations. Data c o n t r o l To provide protection of data stored in the computer, an executive program is being created that checks the user authority and will provide a tutorial step-by-step guide through the various menus to the desired program. In addition to its provision of file protection, authorized access to the various files and routines will be more rapid. Loft The basic function of the loft department at MCAIR is developing a computer-stored mathematical shape definition within which the aircraft is designed and from which tools and parts are manufactured. This definition must be compatible with the exacting tolerances of today's highspeed aircraft and the requirements of modern tooling methods. It must be available to all computer users. To accomplish this end, the loft department has developed many computer-aided techniques to assist in the timely acquisition of this database. Starting in the advanced design environment, loft assembles critical parameters from all design disciplines and assembles either a graphic representation (Figure 3) using the CRT application named CALL (computer-aided loft lines). These representations are used by the design department in preparing preliminary drawings to verify such items as proper fuel volume, sufficient room for equipment, structural integrity, etc. At this time, the configuration is still very fluid and loft must react quickly to continuous design changes. Coincident with this is usually a large amount of wind-tunnel model testing. One of the several methods of providing wind-tunnel wing models is accomplished with an NC program called WINGMILL. The only required input data to the computer are the wing planform geometry, model scale, cutter tool radius, tool feed rate, machining tolerance, stock thickness, and the basic equations of the airfoils and camber information, if applicable. The output of this program is either NC milling tapes or DNC (direct numerical control) data stored on disc. Figure 4 shows a wind-tunnel wing model that has been partially completed using this program. One of the areas of system improvements being addressed by our loft department is the conversion of the various mathematical formats of all our graphic programs into a common mathematical database. For example, in the past, the loft department has provided computer-stored lofted surface definitions with cubic surfaces: When the design department wanted a cross-section of a surface, the cut was represented by a series of points, reconnected with a series of conic curves and then displayed on the CRT. This curve-to-point-to-curve conversion provides an extremely close approximation of the actual lofted surface and more than adequately satisfies the engineering and manufacturing needs; however, it does mean that dual
computer-aided design
Figure 3. Advanced design loft surface definitions
mathematical definitions of the same geometry exist. Providing a single mathematical definition of a surface will result in a more efficient use of computer resources.
Computer graphics design applications CADD is being used for a wide range of design applications a few of which are • Geometry studies and layouts • Composite materials • Machined parts • Sheet metal flat pattern • Assemblies and installations • Hydraulic tubing design • Mechanism design One prime reason for using CADD for these applications is its unique 3-D capability which provides rapid and accurate solutions to complex spatial geometry problems, direct readout of all spatial relationships, natural part depiction, efficient utilization of computer resources and the provision of defining geometry in an unambiguous manner. Ambiguity of conventional two-dimensional orthographic projections results from the fact that each of the x, y, z coordinates must be defined twice to properly describe part geometry. In the case of the part being defined as a single three-dimensional model, each point of the model is defined with a single x, y, z coordinate, thus eliminating ambiguity. Figure 5 shows a comparison of these two methods of part definition. Another example of CADD's ability to solve spatial geometry problems is depicted in Figure 6. The geometry of McDonnell's MACS III flight simulator installation was recreated via CADD and stored in our central computer. Included in the computerized definition of this installation are all the target projection cameras, missile and horizon projectors, and all the support and base structure of the in-
volume 9 number 4 october 1977
Figure 4. 8% VTOL WTM variable sweeplwing (right-hand side) y
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stallation. With these data stored in the computer, the cockpit of any aircraft can be recreated with CADD, stored in the computer, merged with the simulator definition and viewed from the pilot's eye position to determine if the projectors and support structure are out of view from the pilot, as shown in Figure 7. This may all be done before building a simulator cockpit and provides early information to determine whether cameras and equipment will have to be relocated to keep them out of the pilot's view. Volumetric studies are also readily accomplished with CADD. Figure 8 shows an example of a fuel-tank volume study where the tank has been defined with surfaces. By lightpen detection of all the surfaces, and utilizing the geometric properties key on the function keyboard, all of the properties shown are immediately displayed. The TFP (triangulated flat pattern) routine in CADD is particularly useful in the application of composite material design. On the F-15 fighter aircraft, the composite speed
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brake (Figure 9) is comprised of both machined hardware and a series of 0.0054in (0.13716mm) thick graphite composite plies that are preimpregnated with epoxy. There are 76 plies at one section of the speed brake, each of which is mould-line related. In the past, it was necessary for the designer to describe each ply in the installed configuration, but he was unable to define the flat-pattern dimensions required by manufacturing to cut out the plies from raw stock. Personnel from master layout section of the loft department would have to manually lay out each ply, which was costly and time consuming. With the TFP routine in the CADD system, our designers now define the installed, curved configuration of each ply, then instruct the computer to unroll them into a flat pattern. In an instant, the flat pattern of the ply is displayed on the CRT screen. Each of the flat patterned plies are then hardcopied at full scale and input to manufacturing as a template for cutting out the material. Thus, manual-layout errors are
computer-aideddesign
eliminated and the design/fabricate cycle time is reduced. Figure 10 shows a typical example of a curved flat pattern that has been rolled out from its curved installation position. Figure 11 shows a hardcopy of a: ply as it appears in the released drawing format, depicting type, ply number, dash number, the filament direction and a reference outline of the overall speed brake. With a dramatic increase in the number of machined parts on modernday aircraft cut with 5-axis milling machines, it has become prudent for us to devise a new method of defining parts in the computer and to establish a more automated means of creating drawings having the necessary data to interpret its definition. Figure 12 depicts a canard rib defined with surfaces, each of which has been uniquely labelled. Although this model is mathematically defined in three dimensions and stored in the computer, additional information is required for interpretation to facilitate its analysis and for manufacturing planning purposes. As a result, we are looking at methods of creating a batch-operated automatic drafting package and a batchoperated automated dimensioning package. This would eliminate the designer having to model each section-cut and view of the part (duplication of effort and computer
Figure 10 Triangulated flat pattern Figure 8. Fuel volume studies
Figure 9. Composite speed broke
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9 number 4 october 1977
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storage) and would eliminate the tedium of manually keying in dimensional data. Figure 13 shows a hardcopy of the sections of the part. All surfaces are automatically and uniquely labelled to assist the parts programmer in planning the machine cutting of the part. The only dimensions shown are the dimensions deemed critical for analysis and inspection of the part. Large-part definitions such as an F-15 fuselage bulkhead (Figure 14) have presented problems to both engineering and manufacturing personnel due to the 48 kbyte limit on model size. Figure 15 shows how the bulkhead must be modelled in segments with as many as 40 models required for a complete definition of the bulkhead. Even though these models are merged during the hardcopy process to provide a drawing of the complete part, accessing specific portions of the part definition from the computer might require retrieving segments from several models and merging them at the console, which is time consuming. An approach to solving this problem is currently being worked on, which we call Schematic File/Retrieval. This would require the creation of a simplified two-dimensional sketch of the part where each pocket or specified area of the sketch would be labelled and programmed to 'point' to the model stored in the computer, when lightpen detected, and retrieve and display the desired segments of each of the models. Thus, only the desired elements from several models would be displayed in a region less than 48kbytes in size. Another method of handling the problem of large-part definitions which is currently being addressed is data compression. This technique allows the designer to design
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by rules, where only a minimum of geometric details would be modelled and the remainder of the parametric design details would be implied. For example, the pocket of the part shown in Figure 16 would have the bottom surface modelled, a depth keyed in and the corner and fillet radii implied, resulting in an implied surfaced model without actually having the entire pocket modelled and stored in the computer. This will provide the data compression necessary to define much larger models than we can currently display.
CGSA (computer graphics structural analysis) CGSA is a module that has been developed to aid structural analysis and design. CGSA is used to provide internal loads, stresses and strains for structural sizing, and documentation of structural integrity. This system functions in conjunction with the CADD system. CGSA is used to prepare three-dimensional finite-element model input data for either the CASD or NASTRAN structural analysis programs. CASD, an acronym for computer-aided structural design, is a structural analysis program developed by Douglas Aircraft Company before the development of NASTRAN by NASA. Basic geometry is developed from loft data, conventional engineering drawings or the three-dimensional geometry of the vehicle constructed and filed in the computer by the designer. This results in a point-line model (which is converted to a finiteelement model by defining bar/panel/membrane element properties, applied loads and external boundary condition). The model can be viewed, checked and edited at the console for verification of the input data. Hardcopies are produced displaying input properties and element labels and the model is then stored in the CADD drawing files for future retrieval. The CASD or NASTRAN input card images are automatically created on a disc data set for submittal to the structural analysis program. The utilization of CGSA for model generation eliminates the need for manually creating the models, input sheets and punched cards. Upon completion of the CASD or NASTRAN structural analysis program (which performs a minimum strain energy solution), the results are stored with the model in the CADD drawing file and are also output in the more usual manner on an alphanumeric printer. The answers can be displayed at the console and hardcopied for all structural
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Figure 12. Surfaced canard rio
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elements. The display options include magnitudes of bar load, bar stress, panel shear flow, panel shear stress, membrane stress, membrane strain and membrane running loads. Bar loads, bending moments and deflected shapes can also be plotted. The displays and hardcopies in the form sheets are used by engineering supervisors to gain an overall feel for the structural analysis, and also by the detail stress analyst as inputs for his computations. This type of graphic presentation eliminates the need to manually prepare loads sheets. This was previously done by reading the printed output data and associating it with the pictures of the structural idealization. CGSA is also used to transmit, within the computer, structural flexibility influence coefficients or a reduced stiffness matrix to the loads and structural dynamics departments. Additional geometric data are passed to the loads department who then generate panel point loads which are transmitted back to the CGSA module. CGSA is effective when used in both advanced design and project environments. The advanced design department requires smaller models, quick turnaround and good visibility, and it adds to the technical credibility of technical proposals. In a project environment, it is effective in handling large quantities of data (the F-15 wing model has 10000 card images) and in providing the design and strength department personnel with essential data when responding to design changes and updates.
Some of our current activities integrate several of the structures technology disciplines' computer programs with the CADD package. These include aerodynamics, loads, weights, strength, materials and process, and structural dynamics. This integration will yield the interactive flow of technical data necessary to provide rapid convergence to a proper design resulting from the iteration process.
CADD-GNC/APT interfaces Once a part definition has been created and stored in the computer, manufacturing can access the 8eometry from the computer files and, using the GNC (graphic numeric control) module, automatically generate APT source statements
Figure 14. Large drawing file requirements
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This method of part programming is more rapid than methods previously used. In addition to creating the part program for machining the part, the part programmer must also add lugs to the part to hold the part to the cutter bed during the machining operation. The lugs are then machined off after the rest of the part has been completed. After all the part programming has been completed, the programmer can usually review the path of the cutter at the console (Figure 18) to assure that he has no errors in his program.
CAQA (computer-aided quality assurance) Upon completion of the machining operation, inspection of the part is necessary to determine if it accurately represents the design definition. A copy of the part definition that was defined by the designer is retrieved by the quality assurance programmer. Using the lightpen, he generates points on the surface of the part that the DNC inspection machine is to probe (Figure 19). Vectors are displayed (Figure 20) on the part at the points which the probe is to make contact
Figure 15. Large drawing file capability at the console. These source statements are used as instructions to drive the machine tools for cutting the parts. The key to the success of this interface is the automatic labelling of the surfaces when they are created by the designer. Figure 17 exemplifies how the part source program is generated. The pocket of the part is completely defined with uniquely labelled surfaces. The part programmer need not know what the geometric definitions of these surfaces are, only what the label names are. In this example, the programmer would identify the part number of the machining and that it would be cut on a 3-spindle, 5axis milling machine. He would then identify the set point location from which the cutting tool would move to position (1) where the first plunge of the cutter would be made. This position is defined by the intersection of the three labelled surfaces: RSO001, PLO005 and RS0033. The next instruction would be for the cutter to move along surface RSO001 to position (2), then along surface RSO002 to position (3), where surface RSO003 starts, and so on.
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computer-aideddesign
/--RSO001 ~RS0033
Figure 17. CADD lobe/- APT source program Port 68A 123#56 33PNL5 From/SP I Go/R$O001, PLO005, R50033 2 Go forword/R$O001 3 Go forword/R$O002 to R50003
Finish Figure 19. DNC inspection mochlne probing points on surfoce of pert
Figure 18. Review of cutter poth
Figure 20. 'Blasting'points on surface of port when probe is to make contact
and APT statements, which will guide the probe to these points on the actual part, are created as vectors appear. He next reviews the program, using data set edit if required and then, as in the case of the cutter path plot, it is visually verified (Figure 21), edited if required and finally sent to an IBM 1800 computer for the inspection operation. During the actual inspection operation, the inspection probe is driven by DNC to each of the preprogrammed inspection points until contact of the part is made. When contact is made, the probe stops and the actual surface coordinates, the programmed surface coordinates, the allowed tolerances and out of tolerance conditions are automatically printed out on a high-speed line printer. This process eliminates many hours of inspection setup time and the human error that can result from more conventional inspection methods. This inspection method is primarily used for first article
F/gum 21. Plotting the peth the probe treversesend the points of contact
volume 9 number 4 october 1977
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inspections, for checking out modified GNC programs or for checking parts to determine the effects of cutter-tool wear. For inspecting subsequent parts after a first-article inspection, a F I A T (film inspection apply template) is sometimes used. It is made of clear polyester plastic (Mylar) sheet 0.19mm thick. When a FIAT is required, a console operator in the loft department will call up a copy of the engineering drawing, display it on the CRT and input a request to the computer for a scribecoat hardcopy. When the hardcopy is completed, a photo-sensitive sheet of Mylar is overlaid on the hardcopy, exposed and run through a development processor. Within a matter of minutes, an inspection template made of a dimensionally stable base material is ready for use. These templates are used by the quality assurance department to check a finished machined part for proper machining of flanges, webs and caps by overlaying the FIAT on the machined part. Any deviation from the intended configuration is readily detectable.
SUMMARY The use of CADD, CGSA, GNC, CALL, CAQA, ICADE and all the other programs and systems comprising computeraided technology at MCAIR, has effected many changes in traditional work methods of our various interfacing disciplines. We have streamlined our tasks by utilizing the various cost/time saving techniques afforded by these systems and plan additional development efforts which will further improve it. One might argue whether these activities are evolutionary or revolutionary, but in either case, it must be recognized that there is never an 'optimum' method of operation in the design/manufacture cycle. We are never satisfied with the tools for accomplishing the required tasks and are always seeking improvements. Our final objectives or goals cannot accurately be defined since they are in a constant state of change, but we are confident that the enhancements afforded by computeraided technology will continue to provide increased productivity in the years to come.
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by John Paterson, Department of Construction Management, University of Reading. Fragmentation of the construction industry has caused problems of communication for all the participants in the design and construction of buildings. Furthermore, concepts of data and information are changing more rapidly than the processes are being changed. These and other aspects of information methods are examined and discussed and positive proposals made which range from simple manual systems to complex computer systems which may precipitate dramatic changes in the structure of the industry. Contents: Introduction; Man: Designer and User; Data;
Information Flow; Design; Communication: Design and Cost; Construction; Maintenance; Policy; The Machine: The Future; Appendixes; References; Name Index; Subject Index. About the Author: John Paterson has been a principal in private practice, consultant and lecturer in Construction Management at the University o f Reading since leaving West Sussex County Council where he was Deputy County Architect until Local Government Reorganization. Whilst he was in West Sussex he achieved an international reputation for his pioneering work in computer aided architectural design and energy conservation in building. He has served on many committees relating to these subjects and is at present a member o f the Transport and Civil Engineering Committee o f the Science Research Council and its building sub-committee. As an articled pupil before the war and a student at the Architectural Association School o f Architecture after the war, he has seen both types o f architectural training which has been a continued influence on his approach to design and construction.
0471 99449 9
254
208 pages
April 1977
$15.001£7.95
computer-aided design