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easily integrated into a demonstrator engine that could easily be tied back to an advanced weapon system capability. One such sys- tem study that was conducted at Pratt & Whitney in 1976 was a company sponsored system study looking at the potential re- placement of the F-15. The new capability postulated for this weapon system was sustained supercruise. Individual technolo- gies were assessed as to their payoff in this weapon system and the key technologies selected to be pursued under company IR&D and government 6.2 and 6.3 [funding category] programs. What emerged from this technology planning and execution was a joint technology development effort between industry and the govern- ment that provided the technology base for the F119 and F120 engines. The science and technology advances made in gas turbine aircraft engine programs had to be physically demonstrated by some means, whether by specialized demonstrator programs or by improvements and upgrades to fielded engines. The original performance demon- strator concept was later expanded to encompass elements of struc- tural durability when durability problems in the field became dom- inant. The companies embraced this scope expansion because they could test ideas that had relevance not only to military applications but also to civilian aircraft and, hence, to their commercial busi- ness plans, according to William Heiser. A major source of research funding from the 1960s through the 1980s was independent research and development (IR&D). IR&D was nominally industry funding. However, U.S. government procurements allowed a limited amount of IR&D to be charged to contracts as allowable overhead expense, which meant that government funded a fraction of IR&D, up to the ratio of military revenue to total revenue. In the 1960s, IR&D was loosely managed and highly innovative, resulting in military turbofans, high-bypass commercial turbofans, film-cooled turbine blades, and a wide range of titanium components and manufactur- ing processes. By the 1980s, the government tied the IR&D funding limit to an annual review of IR&D programs. The government de- veloped a bureaucracy to conduct the annual reviews, and industry developed corresponding bureaucracies to internally regulate IR&D activity and prepare reviews of each technology program. These re- views eventually incorporated technology roadmaps that showed where technologies would be inserted into fielded products. These roadmaps evolved, under IHPTET, into Advanced Turbo-Propulsion Plans. Possibly as a result of the oversight of these multilayered re- views, the level of innovation declined in IR&D-funded research. In the 1990s, the government disbanded IR&D reviews, which led to industry abandoning long-range research in favor of quick payoffs.1 The review process was doomed, in any case, by shrinkage of mili- tary revenues relative to commercial business in the engine compa- nies. By the mid-1990s, government was funding a minor fraction of IR&D budgets and, thus, had no leverage to wield in determining how the research money would be spent. Transitions from Science and Technology to Fielded Engines Among the engines developed during the period before IHPTET, the Pratt F100 engine program was a noted example of extremely aggressive technology advancement and the consequent problems that could arise. Ray Standahar wrote the requirements document for this engine and observed that, before the F100, engine perfor- mance tended to limit aircraft designs. The F100 program tried to build engines to serve the most advanced airframes, capabilities, and mission attributes. However, F100 teething problems (compressor stalls and durability, with failures common at 100 h) led to extensive efforts to improve serviceability and durability.3 A major cause was that initial engine development programs did not always have suf- ficient resources to work out technical problems before the engines were put in the field, according to Ray Standahar and Richard Hill. Other sources contend that the F100 problems were caused by a lack of fundamental understanding rather than a lack of resources. In any case, the early TF30 and F100 turbofan engine designs outpaced the capabilities of materials and the execution of integration. Much of the research effort in the 1970s onward addressed engine durabil- ity problems, carried out under activities such as the Component Improvement Programs (CIPs), which were originally intended to enhance performance through field changes. James Nelson told us that CIPs were started in the 1950s, as part of continuing engineering efforts, which were managed and funded as production line items. Their role in development is similar to spiral development processes. CIPs came about because engine use in the field often did not follow original design intentions. This caused problems in the F100, particularly thermal loadings from extreme throttle transients performed by pilots who were learning to exploit the full capabilities of the F-15 airframe.3 The CIP concept was redirected in the 1980s toward safety and durability issues, although technologies that addressed durability and also enhanced performance were acceptable, according to Dean Gissendanner. The F100 difficulties also led to the creation of the Engine Model Derivative Program (EMDP), which served as the vehicle by which the U.S. Air Force and Pratt and Whitney could qualify a new low- pressure turbine and other core components created under CIP to enhance durability. The introduction of the F100-220 via EMDP reflected this type of upgrade and appears to serve as a model for such improvements. The most fruitful application of EMDP funding was the creation of GE’s F110 engine, originally designated the F101 Derivative Fighter Engine. The F101 engine, which powered the B-1 bomber, evolved from the demonstrator engine that lost the F-15 competition to the F100. EMDP developed the F110 from the F101 to replace the TF30 in the F-14 and provide an alternative powerplant to the F100 in the F-16. The F110 was also qualified for the F-15, and a dry version of the F110, the F118, was used to power the B-2 bomber and reengine the U-2 reconnaissance platform. In the 1970s through the mid-80s (leading up to the formal cre- ation of IHPTET), the technological emphasis in turbine engines for the military was durability enhancement rather than performance factors such as thrust-to weight ratio: To a significant extent, the lack of increase in thrust-to-weight ratio in the 1970–1985 period was due to the desire for an engine life substantially greater than that achieved by the F100-100 in 1973. There was a great emphasis on durability during this 15-year period, which culminated with the introduction of the F100-220 and the competing F110-100 in 1985. The most tangible result of this effort was an increase in the mean-time-between overhauls of the latter engines by a factor of about 2 over the fully developed F100 (and an even larger factor over the F100 as originally pro- duced). More specifically, data obtained in 1995 show the depot interval for the F100-100 as 450 engine flight hours (EFH), the F100-220 interval as 675 EFH, and the F110-100 interval as 950 EFH. It can also be speculated that with the introduction of produc- tion competition between the F100 and F110, the so-called “Great Engine War,” emphasis by the manufacturers was devoted to cost reduction—particularly through life improvement—as opposed to performance improvement. Since the mid-1980s, the emphasis has returned to performance improvement while maintaining a long life. For example, the depot intervals of the engines introduced in 1989, again according to 1995 data, are 1725 EFH for the F100- 229 and 1435 hours for the F110-129.4 Most of these improvements, however, did not result from advanced research programs. Initial work to address low reliability in the F100-100 was funded by CIP, which became a tool to fix produc- tion problems rather than perform research or develop new technolo- gies. The durability increases in the F110-100 and F110-129 largely arose from commercial development work because the F110 shared a common core with the CFM56, which was being produced by the thousands. The funding for this work is identified as IR&D in the government accounting structure, but is better understood as postproduction engineering improvements like military continuing engineering funding. The F110-129 and F100-229 engine devel- opments from the original F110-100 and F100-200 were funded as EMDPs, not science and technology programs. Direct contributions from U.S. government science and technology programs toward durability enhancement are not widely acknowledged within indus- try, although government direction to address durability problems through ATEGG5 certainly played a role. 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