enhancements, resulting in the improved-performance engines that powered the F-15E and the later sections of the F-16 engine.

If materials development is to continue to play its historically demonstrated role in advancing engine performance, some enhanced investment will likely be needed. However, it is important to understand where this investment might best be placed, and this in turn depends on an understanding of the process that a new materials development goes through from concept to insertion.

2.4
THE NOTIONAL DEVELOPMENT PROCESS FOR PROPULSION MATERIALS FROM IDEA TO INSERTION

As discussed in Section 2.5, below, the introduction of new materials into a new or demonstration engine rarely follows the specified model. But regardless of whether or not the model is followed, it is important to discuss it because it is clear that funding plans are made under the assumption that this notional development plan will be followed. The time period from the point of the introduction of a new material idea to the point at which it is seriously considered for insertion into an engine involves a long-term process that can exceed 20 years. But rather than specifying time in years, it is easier here to describe a notional process with a “timeline” in TRLs. The notional timeline given in Figure 2.5 indicates a continuous maturation of a single material from a large number of initial candidates being nurtured at the 6.1, TRL 1 level of funding and readiness. In general, funding requirements at the lowest TRL level, even for a large number of good ideas, are small compared to the costs of insertion in the final stages of development of, by then, a single material. The funding requirements are also notionally described in Figure 2.6 as a companion to Figure 2.5. As one or a few of the ideas progress into further development, during which coupons are actually produced and property information is beginning to be obtained, the cost increases above the levels provided for all of the basic-concept materials. As larger scale-up occurs, representative geometries are reduced and spin tests and other tests are run on even fewer ideas, the costs escalate again, eventually rising to a level of risk that allows a single material to be matched against a conceptual design in pre-Milestone A, TRL 4 to 5 (see the discussion of milestones, above). Finally a Milestone B point is reached, and full-scale development begins.

It is difficult to ascribe actual years along the timeline axis in Figures 2.5 and 2.6, but Table 2.2 is helpful in this regard. Table 2.2 describes the nominal number of years required to bring a new material to the maturity level needed for insertion, depending on the level at which the material development starts. It is probably possible to match the “Development Phase” description in the table with a TRL level; however, for the purpose of this description, it is assumed that the TRL for the shortest development time is approximately TRL 5 or 6. At the longest devel-



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