ASME 2017 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference IDETC 2017 August 6-9, 2017, Cleveland, Ohio IDETC2017-67886 A CASE STUDY OF EVOLVABILITY AND EXCESS ON THE B-52 STRATOFORTRESS AND F/A-18 HORNET Daniel Long Dr. Scott Ferguson1 Graduate Research Assistant Associate Professor North Carolina State University North Carolina State University Raleigh, NC, USA Raleigh, NC, USA [email protected] [email protected] ABSTRACT operate for 60 years, yet there is speculation that they The moment a system is put into service it begins to lose value ultimately could operate for eighty to one hundred years [2]. as technological and societal changes accrue while the system The total cost of building a replacement unit in 2009 was is frozen in the state it was constructed. System decision estimated at $7 billion per unit excluding transmission [3], makers are faced with the choice of accepting a decline in which was a nontrivial fraction of the then $53.5 billion market performance, updating the design, or retiring the system. Each cap for Duke Energy, the largest utility in the US [4]. time a decision maker faces these alternatives, the value of the A variety of methods for increasing CES lifecycle value available options must be evaluated to determine the preferred have been explored in literature. Design for: adaptability [5], course of action. A design that can adapt to changes with flexibility [6,7], changeability [8,9], and reconfigurability [10] minimal cost should provide more value over a longer period all provide system designers with heuristics and tools to design than a system that is initially less costly, but less adaptable. an adaptable CES. The general focus of these studies has been This is especially desirable for systems that have large initial on product architecture; with the optimization of system costs and/or a lengthy development cycle. The purpose of this modularity and design of interfaces [11] as tools to reduce the paper is to evaluate the United States Air Force (USAF) B-52 time and cost, or generically “effort”, for modifying a system. Stratofortress and the United States Navy (USN) F/A-18 These approaches have generally not explored the Hornet to characterize the changes in desired capabilities and capability of the system to support the components being what system attributes allowed them to either successfully modified or replaced. Upgraded or substantially changed adapt or prevented them from adapting. These observations components are likely to require system resources in quantities allow the development of heuristics that designers can use that differ from the original component. Even when no design during system design to enhance system lifetime value. change is required it is possible that the original component has become obsolete and unobtainable. This requires the 1.0 INTRODUCTION qualification of a replacement [12] that might need different Large scale Complex Engineered Systems (CES) are resources. This type of system attribute has been labeled integral to modern life but are challenging to develop due to the “excess”, and research has begun to explore what excess is and complex interactions of numerous sub-systems, lengthy what it’s properties are [13–16]. In this paper excess is defined development time, extended in-service time, and potential for as a modified version of that found in Allen [16] and Tackett unanticipated emergent behavior [1]. Society benefits from [15] to be the quantity of usable surplus of a system resource these systems every time someone turns on a light with power that is likely to be prohibitively expensive to increase with in- from a nuclear power plant, travels internationally on a service design changes. A prohibitive cost would be one for commercial airliner, or watches a movie transmitted from a which the system decision maker would prefer performance satellite. Some of these systems provide capabilities that cannot degradation or retirement to configuration change. be cost effectively obtained any other way. This line of inquiry is important to CES design because it The design effort and costs required to develop CES often addresses one of the aspects of system design that may limit its leads to lengthy in-service periods. For example, the age of the lifetime. One example cited in literature is that of a nuclear average U. S. nuclear power reactor in 2009 was over thirty powered aircraft carrier [16]. The electrical power generated by years. Many of these reactors had been licensed by the NRC to the carrier is a limiting factor for the addition or modification of 1Corresponding Author 1 Copyright © 2017 by ASME systems. An upgrade requiring electrical power supply that is system designers faced when making decisions. The majority of greater than remaining useable surplus will be far more likely selected systems had insufficient public information available to result in either degradation of system performance or the to properly study evolutionary trajectory. The search was system’s retirement. Conversely, the inclusion of too much therefore limited to military aircraft due to the availability of capacity can result in unnecessary system cost or suboptimal historic records, government documents, and a plethora of performance [17]. accounts written by aviation enthusiasts. Previous research on excess generally focuses on either The final two systems selected for study were the B-52 non-complex systems or applies the proposed methodology to a Stratofortress and the F/A-18 Hornet. The B-52 was selected complex system in the context of future or hypothetical changes because of its lengthy operational history and proven ability to to the system. Little work has been done to examine the adapt to technological challenges for 65 years, with another 20 evolutionary path that existing complex systems have taken in planned. The F/A-18 was selected because it was unable to response to changes in their environment or desired evolve to meet new operational requirements. A public debate capabilities. Knowledge, of what changes have occurred and between the U.S. Navy and the U.S. Government what the changes were in response to, can help inform the Accountability Office (GAO) provides public record of the design of both systems and the methodologies used in their design discussion which ultimately resulted in a redesign as the development. Similar examinations of historical systems for Super Hornet leaving only 15% commonality with the original lessons in design have successfully been conducted [18]. airframe [19]. This paper contributes to the field by assessing the The research objectives were as follows. First, explore the evolutionary trajectory of existing CES and what system environment in which the system was designed to capture attributes most affect that system’s evolvability. Evolvability assumptions and initial design decisions. Second, identify refers to a systems ability to physically transform from one drivers of change for each system during its operations. configuration to a more desirable configuration [15] after being Understanding what challenges drove certain adaptations, placed in service at a cost which isn’t prohibitive. especially unforeseen challenges, could provide guidance for The following section outlines the method by which the what to consider during initial design. Finally, identify and research and analysis was conducted to find appropriate CES categorize the kinds of adaptations the systems experienced to and track their evolutionary trajectory in this paper. After the overcome challenges with special attention payed to the types method, discussion of each system begins with the of components and the system resources required to support circumstances surrounding its design and desired initial them. capabilities. For the B-52, challenges to the system’s These objectives provide knowledge useful to academics operational capability are discussed and the compensatory and system designers for military aerospace systems but also design changes analyzed including the new/modified system provide more general guidance for CES research and design. capabilities and what physical or operational changes were Since understanding the context in which each system operated required to support those capabilities. After the B-52 section, is critical to understanding the motivation for design changes the F/A-18 has a more comprehensive developmental history each adaptation described is preceded with the historical driver and discussion of system evolutions with an examination of for that change. Each objective is explored in the following what symptoms were exhibited when excess was depleted. The sections beginning with the B-52. paper concludes with a distillation of the lessons learned from the evolutionary trajectory of each system. 3.0 THE B-52 At the close of World War 2, and the opening of the Cold 2.0 METHOD War, the United States found itself in need of a bomber that This assessment qualitatively examines existing systems’ could deliver an atomic bomb to targets far from United States abilities to meet unforeseen needs and identify what Air Force (USAF) bases. Initially only propeller aircraft like relationships exist between design excess decisions and in- the B-36 could provide the desired range, but they were service evolutionary capabilities. The systems chosen share significantly slower than newer jet bombers like the B-47. Jet characteristics associated with complex systems [1], have bombers were capable of faster speeds, but suffered from a sufficient public information available to perform a qualitative smaller payload capacity and reduced range [20]. Between analysis, and provide noteworthy examples of how a system’s 1945 and 1948 the Air Force released increasingly challenging architecture impacts its evolvability. specifications for the new bomber and Boeing iterated through A wide variety of systems were selected for preliminary many different configurations. Finally, the USAF established study including commercial aircraft, military aircraft, space requirements for a bomber with a range of 8,000 miles and a systems, nuclear power plants, and large infrastructure systems.