AIAA 99 McClinton

Significant advancements in hypersonic airbreathing vehicle technology have been made in the country’s research centers and industry over the past 40 years. Some of that technology is being validated with the X-43 flight tests. This paper presents an overview of hypersonic airbreathing technology status within the US, and a hypersonic technology development plan. This plan builds on the nation’s large investment in hypersonics. This affordable, incremental plan focuses technology development on hypersonic systems, which could be operating by the 2020’s. Copyright © 1999 by the American Institute of Aeronautics and Astronautics, Inc. No copyright is asserted in the United States under Title 17, U.S. Code. The U.S. Government has a royalty-free license to exercise all rights under the copyright claimed herein for Governmental purposes. All other rights are reserved by the copyright owner. experimental methods required for this complex multidisciplinary problem. The smaller ART program focus is on RBCC wind tunnel testing of alternate airframe integrated scramjet flowpath concepts. Likewise, within the DOD several hypersonic programs are emerging. The USAF AFRL Hypersonic Technology (HyTech) program, the Defense Advanced Research Projects Agency (DARPA) Affordable Rapid Response Missile Demonstrator (ARRMD) Program, The USN Rapid Response Missile Program and the Army Scramjet Technology Development Program. In addition, the USAF Aeronautical Systems Center, in collaboration with the Air Combat Command, is conducting a Future Strike study, which focuses on hypersonic aircraft. With this renewed interest in hypersonic vehicles, requirements are being developed which can only be met with hypersonics systems. These include the USAF CONUS-based Expeditionary Aerospace Force concepts, and reduced cost to orbit. This paper discusses the potential of hypersonic airbreathing technology for endoor exo-atmospheric vehicles (airplanes and space planes). The status of hypersonic technology, the significance of the X-43 flights to technology advancements, and a method of filtering vehicle proponents’ claims are also discussed. Finally, a plan to efficiently demonstrate hypersonic technology is presented. HYPERSONIC TECHNOLOGY STATUS This section discusses the status of hypersonic technology—with the goal of showing significant advancement; thus, justification for continuing to push hypersonic technology development to flight. System Analysis and Conceptual Designs The key to any hypersonic vehicle development or technology program is a credible preliminary system analysis to identify the technical requirements and guide technology development. The X-30 program provided an excellent training ground for system design, analysis and development of hypersonic technology. The complexity of the hypersonic airbreathing system and the small thrust margin dictate that a thorough system analysis be performed before any focused technology development is started. Over the past 40 years, many bright individuals and companies brought forward vehicle, engine or structural concepts, which at first blush appeared to be an excellent solution. However, due to the highly integrated nature of this class of vehicles, an excellent component solution is not always beneficial to the overall system. The impact on the overall system is the only adequate measure of goodness. An example of this is the development of a combustor performance index, namely thrust potential (ref. 1). This parameter was developed during the 1990’s, as scramjet engine designers realized that combustion efficiency was not an adequate measure of the combustor design. A method of quantifying the combustor impact on overall engine performance was required, and exergy, as applied in the literature, did not provide an optimum design. Formal system analysis procedures are required for vehicle design and performance analysis. The LaRC design process is illustrated in figure 1. Engine and aerodynamic performance, structural requirements, weights, and flight vehicle performance (mission or trajectory) are evaluated, always “closing” on take off gross weight for the specified mission. This design process can be executed using four basic levels of analysis. The lowest level, designated “0” in Table 1, does not require a physical geometry. The level zero analysis utilizes ideal engine cycle performance, historical L/D and Cd values for aerodynamic performance, design tables (or weight fractions) for structure and components weight, “rocket equation” for flight trajectory, and estimates for packaging. This analysis does not require a specified vehicle, engine flowpath or systems definition. All higher levels of analysis require a vehicle, engine flowpath shape and operating modes, system definition, etc. The next level of system analysis, referred to herein as Level 1, utilizes uncertified cycle performance and/or CFD, impact theory, unit or uncertified finite element model (FEM) weights, single equation packaging relations, and energy state vehicle performance. (Certification is discussed in the next paragraph). This level of analysis does not capture operability limits, and thus has large uncertainties. Level 2 analysis utilizes “certified,” methods; i.e., the user has sufficient relevant experience. This level uses the same methods for propulsion, aerodynamics, structure and weights (but certified), trimmed 3-DOF (degree of freedom) vehicle performance analysis and multiple equation, linear or non-linear packaging relations. Certification is only achieved by demonstration that the methods used work on the class of problems simulated (this relates to the method, as well as the operator applying that method). For example, at level 2 analytical models utilize corrections for known errors, such as inlet mass spillage, relevant empirical fuel mixing models (ref. 2), shear and heat flux models (ref. 3), etc. This empirical approach is based on experimental (wind tunnel tests, 2 American Institute of Aeronautics and Astronautics AIAA 99-4978