STRUCTURES, DESIGN
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 General Dynamics is using a compute-based mockup technique to eliminate "hard" mockups.New computer-aided design approaches are enhancing both the design engineering process and the role of the engineer who carries it out. The use of three-dimensional digital modeling, for example, represents a fundamental change in the way aerospace hardware is developed. Traditionally, engineering defines the product by creating two-dimensional drawings. Physical mockups are then built to develop harness and tubing routing, perform maintainability studies, or tryout ideas before the design is committed IO production. Today, companies find that they can accomplish all of these goals and more by developing a three-dimensional digital model of the product. This approach saves the high cost of building mockups and allows problems to be identified and resolved much earlier in the product definition process. General Dynamics Space Systems Division has been successfully using these computer-based mockups since 1988 to support its Atlas launch vehicle program. Since then the division has used them to replace over a dozen "hard" mockups, including all those required for the numerous Atlas I, II, IIA, and IIAS payload adapters and payload fairings. The group is currently integrating these same computer techniques into its overall concurrent engineering product development team approach. Rockwell International's Space Systems Division used CAD modeling in its work on the NASA Advanced Manned Launch System contract. A configuration CAD model of the NASA HL-20 lifting body, a candidate for the Personnel Launch System, was generated. The concept maximizes maintenance access to subsystems located between the cylindrical crew cabin and the complex outer mold-line. The CAD model was used to package subsystems without interferences and to calculate vehicle mass properties that met aerodynamic requirements. |
The design was particularly challenging since the crew cabin
vehicle's shape was driven by its function as a pressure vessel; moreover, the volume in
the subsystem bays had to be carefully allocated to the subsystems to assure
accessibility. The CAD database was further used with "desktop prototype"
equipment to create several 1/50 and l/lOO scale models for the HL-20 concept. These
models were used in management support and in customer briefings. Martin Marietta's Manned Space Systems Division is using the digital mockup approach in the development of future heavy-lift launch vehicles. The approach uses a common database configured so that it can be accessed and utilized by the product development team personnel. Models are built and overlaid to check interferences as the design matures. Small bore tubing is defined in the mockup, and the resulting digital data drive numerical control tube bending machines, where tubes are fabricated without the need for templates. Tooling and access platforms are developed from the common database, allowing early identification of problems that would normally be found during fabrication. As problems are found, human factor and maintainability assessments are performed, and the design is revised. Analysis models can be built from this common database and the results fed back, so that deflections and motions can be checked to ensure clearances, for example. The use of the common database with advanced visualizer software permits the real-time animation of selected critical conditions. Such innovations are creating basic changes in the way design engineers are educated, trained, and used. An added benefit of these new approaches is that the digital database provides a focal point for product definition data, thus contributing significantly to the successful implementation of concurrent engineering.
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