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Thesis (M.S.)--Air Force Institute of Technology, 2000. / "AFIT/GOA/ENS/00M-3." Includes bibliographical references (p. 130-131).

This study outlines the requirement for a company to be able to manage its intellectual capital. On the basis of this requirement this study presents a new design methodology based around the requirements of the military aircraft industry. It tackles the difficult management problem of capturing, storing and re-using valuable company product knowledge. The detailed research documented in this thesis focuses on the conceptual design area of this methodology. Work in this area has resulted in the development of a further methodology for the conceptual design arena. This methodology is called the intelligent conceptual engineering system (ICES). The ICES methodology embraces the artificial intelligence disciplines of knowledge-based systems and case-based reasoning. Through the evolutionary development of the ICES methodology a significant contribution to knowledge has been made in three areas. Firstly, this study introduces a new method of assigning justifiable numerical weights to design drivers acting on the design process. Secondly, the work introduces the novel concept of using secondary rules in the knowledge-based system so a 'best structure' can be derived from the manufacturing and structures perspectives. Finally, this work adds a new concept to case-based reasoning called the 'jury technique'. These concepts, developed to support the ICES methodology have been placed in a prototype design decision support tool.

Polycarbonate is commonly used in windshield-canopy structures for military aircraft since it is transparent and possesses excellent toughness characteristics at temperatures well below its glass transition region. It is believed that ultraviolet radiation present in sunlight causes polycarbonate to degrade. This is a serious problem since the majority of the military aircraft in the United States spend their entire service lives outdoors. This study was conducted in connection with the United States Air Force to analyze the photodegradation of polycarbonate caused by ultraviolet radiation. First, aircraft-grade polycarbonate plates were exposed to continuous ultraviolet light in a QUV laboratory weathering chamber for durations of three, seven, ten, and twenty weeks. The material changes were then characterized by several mechanical, viscoelastic, and chemical experiments. The feasibility and sensitivity of each test method was determined, and the amount of polymer degradation was measured. The results from uniaxial tension and dynamic mechanical (DMA) tests indicated a significant reduction in strength and ductility and an increase in stiffness. Polycarbonate also experienced a decrease in impact resistance of approximately 42% at intermediate exposure levels followed by a slight increase for the longest exposure durations. Micro-indentation experiments showed about a 27% increase in hardness for surfaces directly exposed to ultraviolet light while the hardness of the surfaces indirectly exposed was insensitive to ultraviolet exposure. A 30% weight loss was also seen after only seven weeks of exposure. A few conclusions were made about the causes of photodegradation along with recommendations for future work in the area of ultraviolet exposure of thermoplastic materials. / Master of Science

Doctor of Philosophy / Department of History / Donald J. Mrozek / In the late 20th and early 21st centuries, military aviation technology grew expensive and politically divisive, and this is not without precedent. In the 1960s and 1970s, the F-15 Eagle and F-16 Falcon represented a controversial shift both in the cost of development and in tactical doctrine for the United States Air Force (USAF), yet the motivating factors that influenced their design are not fully understood. Most of the literature either has focused on a teleological exploration of technical evolution or has held to a “genius inventor” paradigm, lionizing individual engineers and planners. Other works have focused on these aircraft as factors that changed the Air Force's tactical approach to warfighting or have simply evaluated their combat performance. Although these approaches are valuable, they do not account for the effect that institutional culture and historical memory had on the F-15 and F-16 programs. This dissertation argues that the culture of the fighter pilot community was based on a constructed memory of World War I fighter combat, idealizing a heroic, romanticized image of “Knights of the Air.” This fighter pilot community attempted to influence the F-15 and F-16 programs to conform to their vision of an idealized past. Furthermore, a smaller group of these pilots, calling themselves the “Fighter Mafia” (and later the “Reformers”) radicalized these ideas, rejecting the Eagle and Falcon as not representative of their ideal vision. Through public and political activism, this group affected the discourse of military technology from the mid-1970s to the present. Drawing on David Nye’s work on the connections between technology and cultural historical narratives and identity, this work will demonstrate that culture and institutional historical memory can be important factors in driving the development of military technology.

This material is based on research sponsored by Air Force Research Laboratory under agreement number FA8650-09-2-3938. The U.S. Government is authorized to reproduce and distribute reprints for Governmental purposes notwithstanding any copyright notation thereon. The views and conclusions contained herein are those of the authors and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Air Force Research Laboratory or the U.S. Government. / This work seeks to develop multidisciplinary design optimization (MDO) methods to find the optimal design of a particular aircraft called an Efficient Supersonic Air Vehicle (ESAV). This is a long-range military bomber type of aircraft that is to be designed for high speed (supersonic) flight and survivability. The design metric used to differentiate designs is minimization of the take-off gross weight. The usefulness of MDO tools, rather than compartmentalized design practices, in the early stages of the design process is shown. These tools must be able to adequately analyze all pertinent physics, simultaneously and collectively, that are important to the aircraft of interest. Low-fidelity and higher-fidelity ESAV MDO frameworks have been constructed. The analysis codes in the higher-fidelity framework were validated by comparison with the legacy B-58 supersonic bomber aircraft. The low-fidelity framework used a computationally expensive process that utilized a large design of computer experiments study to explore its design space. This resulted in identifying an optimal ESAV with an arrow wing planform. Specific challenges to designing an ESAV not addressed with the low-fidelity framework were addressed with the higher-fidelity framework. Specifically, models to characterize the effects of the low-observable ESAV characteristics were required. For example, the embedded engines necessitated a higher-fidelity propulsion model and engine exhaust-washed structures discipline. Low-observability requirements necessitated adding a radar cross section discipline. A relatively less costly computational process utilizing successive NSGA-II optimization runs was used for the higher-fidelity MDO. This resulted in an optimal ESAV with a trapezoidal wing planform. The NSGA-II optimizer considered arrow wing planforms in early generations during the process, but these were later discarded in favor of the trapezoidal planform. Sensitivities around this optimal design were computed using the well-known ANOVA method to characterize the surrounding design space. The lower and higher fidelity frameworks could not be combined in a mixed-fidelity optimization process because the low-fidelity was not faithful enough to the higher-fidelity analysis results. The low-fidelity optimum was found to be infeasible according to the higher-fidelity framework and vice versa. Therefore, the low-fidelity framework was not capable of guiding the higher-fidelity framework to the eventual trapezoidal planform optimum. / Air Force Research Laboratory / Ph. D.

The sound produced by military aircraft is dominated by noise generated by the turbulent mixing of the jetted exhaust with the ambient air. This jet noise has the potential to annoy the community and pose a hearing loss risk for military personnel. The goal of this dissertation is to characterize spatiospectral features in the field produced by full-scale military aircraft that are not traditionally seen at the laboratory scale and identify potential noise mechanisms for these features. Measurements of two military aircraft jet noise fields are found to be best described as a superposition of spatiospectral lobes, whose relative amplitudes dictate the overall directivity at each engine power. Near-field acoustical holography techniques are applied to one of the military aircraft measurements to characterize the behavior of the lobes as a function of engine power. The simulated jet noise of a highly heated laboratory-scale jet is then analyzed to compare with the military aircraft measurement and is found to only partially contain the spatiospectral lobe phenomenon. Application of near to far field coherence tracing and near-field acoustical holography to the simulations provides validation of the methods used on the military aircraft and illuminate potential source mechanisms that may explain the presence of the spatiospectral lobes.

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