2.2 THE IMPORTANCE OF DESIGN QUALITY

Even today many people still regard the design of technical objects as not much more than the act of putting pencil lines on large pieces of paper. Of course, the general concept of design is much broader. Many a designer may not even occupy a drawing board, since he may be completely devoted to the creation of basic ideas and solutions, to the numerical checking of their validity, or to the planning, direction, and integration of a design team. By contrast, many of the most successful designers always retain their board, their most valuable tool of creation, however advanced their position in the organization may be.

It is a commonplace to state that a technical project will stand or fall with the quality of its design. Obviously, no device can be built, tested, or used until and unless it has been specified first how to build, test, and operate it. With this in mind, a completed design can be considered a set of instructions for shop actions to follow. For instance, final drawings are only the end product of an extensive, diversified effort which preceded their release. All this is well known, yet sometimes forgotten in the daily grind of a project. May it suffice to state that the design and the designer are principal links of the chain in a project.

This book attempts to supply some of the necessary special tools required to arrive at a detailed "set of instructions" to the shop foreman, from which an engine could be actually built and prepared for test. The following chapters are devoted to the necessary technical detail, based on the latest state of the art in the field of liquid propellant rocket engines.

There are numerous areas which the designer should consider early and keep in mind at all times, for overall increase of quality and reliability, and for reduction of cost. Among these are: (1) Experience, reliability, and reputation of subcontractors and their products (2) Adequate receiving inspection (3) Clear and complete instructions for inspection and quality control (4) Full use of the experience of others: in-plant and out-of-plant (5) Use of suitable existing designs, from small parts to subsystems (6) Availability and application of an effective failure analysis and correction system (7) Last, but not least, the experience. knowledge, analytical capabilities, and judgment of the designer himself. A number of time-proven tools are available to the designer to optimize his design and the end product it describes. Among these are:

Design checkoff sheets.-Checkoff sheets force the designer to check his design systematically from all imaginable angles, before release. See sample sheet on next page.

Design change checkoff sheets.-Used for systematic evaluation of design changes for effects on all potentially affected systems, including the user and the vehicle. A sample sheet is shown below.

Failure reports.-The feedback to the designer of failures of his product in the field, for immediate corrective action.

Change control.-A projectwide effort to scrutinize and minimize proposed changes; and to establish and monitor implementation by engine serial number, if the change must be made.

Specifications.-Detailed specifications, often based on applicable Government specifications, to establish the exact execution of all manufacturing processes, materials used, parts purchased, tests to be performed, and so on.