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774 HONG AND COLLOPY disks, beginning with Inconel 718 and progressing to powdered met- allurgy turbine disks; 3) investment cast nickel alloy turbine blades, with cast-in cooling passages, resulting in production engine tur- bine rotor inlet temperatures of 2450◦F; 4) turbofan architecture; 5) thermodynamic cycle modeling, to a level that was useful for performance prediction and control design; and 6) control strate- gies to deal with interacting components and manage compressor stall margin. For example, the CF6 achieved 2455◦ F (1345◦ C) in 1970. According to James Williams, 24 years later, the state of the art GE90 exceeded this by only 145◦F (80◦C). Since 1975, the only comparable advances have been digital con- trols (an adaptation of technology from another industry) and higher turbine temperatures, in spite of billions of dollars expended on air- craft engine development. At the same time, engine development has slowed from two new engine models per year in the 1960s, ac- cording to Donohue, to a the point where, in the 1990s, Pratt and Whitney produced no all new large engines and GE only produced one. Explaining this precipitous dropoff in research productivity is key to understanding aircraft engine science and technology in the period. Three forces can be observed as contributing to the slow- down, without speculating on their relative importance: 1) The aircraft engine is a “mature product” (D. Edmunds) or a “commodity” (J. Fischer). This concept of maturity follows from the notion that technologies can be ranked by the ratio of payoff to development cost. The high-payoff low-development-cost tech- nologies were developed first. By 1975, the only technologies left to discover were low payoff with high development cost. Technology investment has reached a point of diminishing returns. The com- modity argument is similar: The performance of competing product lines have converged and airframes have matured so that compe- tition is focused today on price and reliability. Therefore, product improvement is concentrated on making engines more rugged and less expensive. These improvements are best achieved by modifi- cations to production engines rather than new models, so that they are seldom tracked as research or development. Both arguments presume that the array of potential technology improvements to en- gines is more or less fixed and has been known since 1960. The really good ideas for performance improvement are already taken, and so the opportunities are exhausted. 2) Complexity theory offers a more sophisticated view of the same phenomenon.8 Early in the development of a complex product fam- ily, various architectures are explored. Design effort focuses on the most promising architectures, and they are refined into higher value products. Exploration of new architectures is reduced because, when a new architecture is compared with the current, refined architecture, it invariably comes up short, if only because it lacks the decades of incremental improvements that benefit the status quo. Furthermore, adopting a radical change entails substantial investment in the in- frastructure that has been built up around the status quo design. Thus, to adopt a new and different architecture, the new concept in its unrefined state must be significantly superior to the refined status quo. This is unlikely to happen, even if the new architecture is very superior to status quo architecture, when compensation is made for the refinements. Thus, complex products tend to lock into particular architectures over time and radical technologies that entail major changes to the product become less and less attractive. 3) The third theory is organizational. Like Lockheed Skunkworks projects, the engines of the 1960s were developed by small, highly motivated teams of engineers and machinists with flat organizational structures, operating with a minimum of reviews and oversight. See, for example, the description of the development of the GOL1590, the demonstrator that led to the J79, by Neumann.9 A great deal of responsibility was entrusted in a small number of people, so that if engineers wanted to incorporate a radical technology, they often had the latitude to do so without obtaining consent from many others. This could be an essential element of achieving radical improve- ments. Early on, the promise of radical technologies is not clear and seldom quantifiable. Support is often a matter of faith as much as reason. Such designs cannot survive multiple layers of top level reviews, but instead depend on champions and trust. When man- agement funds a tight knit team and depends on trust rather than reviews and tollgates, there is a significant risk that, at the end of the day, there will be little to show for the investment. However, when layers of oversight and reviews are used, there is almost no chance of successful radical innovation. There are too many oppor- tunities for someone to say no. Another advantage of small, tight knit teams with little supervision is their ability to develop tech- nology rapidly and inexpensively so that a much higher failure rate becomes tolerable. Numerous examples of Skunkworks-type programs exist in both industry and government. What is more interesting is that more structured research programs, such as the IR&D program in the 1980s and IHPTET of the late 1980s and 1990s, have featured bu- reaucracies on the industry and government sides who conduct sys- tematic layered reviews of technology programs. These programs have notably failed to produce radical innovations that have tran- sitioned to products in service as promised. They have succeeded in introducing many incremental technological improvements, par- ticularly in raising cycle temperature limits. On the other hand, IR&D, IHPTET, and other government-funded programs have in- vested decades of research into programs such as ceramic matrix composites, metal matrix composites, analytical sensor redundancy, and performance seeking controls, many of which have so far failed to transition into full-scale production in a meaningful way, or at least to anticipated levels. Many veterans of the period reinforced these points: Past experience dictates that the planning process be balanced, so that meticulous planning does not become incompatible with more radical innovative potential, and may require that some sep- aration between the two activities could be warranted. (Richard Weiss) Bureaucracies grew up in the lab and in the industry to man- age IR&D in meticulous detail, which may have detracted from its effectiveness. Although IR&D was supposedly contractor con- trolled, there was still Air Force oversight and review. IR&D was, in many cases, not effective. Research programs under IR&D were not often transitioned into products. (Thomas Donohue) The government has spent considerable funds and resources to introduce first low and then high temperature advanced compos- ite materials to replace metals. The gas turbine engineers were not successful in applying these materials into many engine com- ponents due to their inherent lack of ductility. The government WPAFB materials personnel persisted in expending resources for Fig. 4 Key technology advances; highest impact technologies in bold.PDF Image | Technology for Jet Engines: A Case Study in Science and Technology Development
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