Future Aerospace Ground Test Facility Requirements for the Arnold Engineering Development Center (1992)

This report was prepared by a committee of the National Research Council (NRC) Aeronautics and Space Engineering Board (ASEB) at the request of the United States Air Force (USAF) Arnold Engineering Development Center (AEDC).

The committee was asked to perform the following tasks:

• Provide guidance for planning and modernizing AEDC facilities for the development and testing of future classes of military aerospace systems.

• Identify anticipated facility needs based on current and future Air Force systems requirements.

• Assess how well AEDC can satisfy future needs.

The scope of the investigation covers aerodynamic and aerothermal, propulsion (air breathing, rocket, and space), space environmental, computational, and technical support facility requirements. (See Appendix A for a complete statement of task). For purposes of discussion, the facility requirements in this report are divided into the following categories: subsonic and supersonic airplane systems, turbopropulsion systems, hypersonic and transatmospheric systems, and launch and space systems.

The successful aircraft and space systems in service today are visible evidence of a disciplined development process that is founded on decades of experience and designed to ensure that the final products meet national needs. One of the most important steps in this development process is the captive ground testing of entire systems (e.g., a space satellite) or their major subsystems (e.g., an aircraft engine). The aim of ground testing is to permit highly instrumented articles to be precisely evaluated under carefully controlled and realistic conditions until they are

proven to be ready for flight. This allows performance, reliability, and durability to be compared with requirements and, where necessary, improvements to be made or unexpected problems solved.

AEDC is one of the premier aerospace development ground test facilities in the world. It has provided the highest quality ground testing capabilities to government and commercial systems development programs for more than 35 years and has a direct, positive, and enduring impact on the security and prosperity of the nation. Examples of significant contributions by AEDC include

• identifying the sources of a serious discrepancy in predictions for stability and control of the Space Shuttle orbiter;

• discovering a nozzle instability during testing of the YF120 engine for the YF22 Advanced Tactical Fighter; and

• identifying the cause of a failed nozzle extended exit cone on the Peacekeeper Stage III.

AEDC as we know it today is primarily the legacy of the extraordinary vision of General Henry A. (Hap) Arnold, the first Chief of Staff of the U.S. Air Force, and Dr. Theodore von Karman, his principal scientific advisor. Reflecting on the recent experiences of World War II and projecting to the more peaceful times ahead, they concluded that technological supremacy in air power would be essential to the maintenance of U.S. global leadership. A crucial corollary to their finding was that comprehensive ground testing would be an indispensable ingredient of the system development process. Their vision was embodied in the Unitary Wind Tunnel Plan of 1949, which authorized the USAF an initial $100 million toward constructing, installing, and equipping the wind tunnels that were destined to usher in the supersonic era and beyond. This initiated development of AEDC, which led to activation of the first facility in 1954. This was followed by further activations in the 1950s and 1960s. By about 1970, all but a few of the facilities currently at AEDC were activated. This buildup of testing capability is illustrated in Figure 1-1.

Although the vast majority of present AEDC facilities were completed by the mid-1960s, a few facilities have been added recently, particularly in the area of propulsion testing.

AEDC is an Air Force-managed, contractor-operated complex. Its principal missions are to test and evaluate aircraft, missile and space systems and subsystems at simulated flight conditions; to conduct in-house technology programs that develop advanced test techniques along with the necessary instrumentation; and to acquire, maintain, and modernize the appropriate test facilities. AEDC is comprised of some 53 aerodynamic and propulsion wind tunnels, rocket and turbine engine test cells, space environmental chambers, arc heaters, ballistic ranges, and other specialized units. Of these, 25 have capabilities unmatched in the United States, and many are unmatched in the world. The various facilities can simulate flight conditions from sea level to altitudes around 1,000 miles and from subsonic velocities to over Mach 20.

FIGURE 1-1 Cumulative number of primary AEDC ground test facilities entering service by date. (For more information on AEDC facilities, see Appendix B).

The principal testing units at AEDC are grouped into three major categories:

1. The Engine Test Facility. This facility includes the 11 turbine engine and rocket motor test cells devoted to testing liquid- and solid-fueled propulsion systems for advanced aircraft, missile, satellite, and space launch vehicles. These facilities include the world's two largest high-altitude simulation test cells along with the newest addition to the Center's engine testing, the Aero-Propulsion Systems Test Facility (ASTF). ASTF provides the capability for full mission simulation--from take-off, through climb, to descent and landing--accommodating multispeed combat maneuvering requirements. Its two test cells are large enough for major portions of propulsion systems and, in some cases, the complete propulsion system.

2. The von Karman Gas Dynamics Facility. This facility is comprised of four high-speed wind tunnels, four ballistic and impact ranges, two arc heaters and four space chambers. In these

facilities, the effect of airflow on relatively large-scale models of high-speed aircraft and missiles can be tested at flight conditions from Mach 1.5 to 10 and at pressures from sea level to 240,000 feet. Snow, rain, and dust, at velocities up to 30,000 feet per second can be simulated to determine the erosion effects. The ranges can be used to study the effects of natural or man-made debris on space vehicles and satellites. Arc heaters simulate re-entry pressures and temperatures and are used to study ablation and erosion effects on re-entry vehicles. Another range is used to determine the effects of bird strikes on aircraft components. Vacuum chambers simulate launch trajectory pressures, solar radiation, vehicle vibration, and the effects of vacuum, cold, and altitude conditions.

3. The Propulsion Wind Tunnel Facility. This facility is comprised of one supersonic and three transonic wind tunnels. In these tunnels, airflow can be distorted to simulate conditions found in actual flight maneuvers to test the aerodynamic performance of full-scale engines, large aircraft models, large-and full-scale missiles, or store capabilities.

AEDC facilities are generally very large scale, sophisticated and expensive, and contain extensive and comprehensive data-taking capabilities. They are designed for the development and production of aerospace components and systems and focus on operational and durability capabilities, as well as performance. In addition, full-spectrum test support includes formulating and implementing test plans; acquiring, processing, and analyzing test data and reporting test results; as well as building, repairing, and maintaining test hardware in AEDC's manufacturing facilities.

Laboratory services include a chemical laboratory to analyze fuels, gases, and other materials; a metallurgical laboratory to verify the structural integrity of critical test hardware and facility components; a photography laboratory with comprehensive still and motion picture capabilities, including high-speed photography at framing rates as fast as one million frames per second; and a precision measurement equipment laboratory to calibrate and repair instruments used to control and measure test conditions and to acquire data. AEDC's computational resources are used in all phases of testing.

More specific qualities of the facilities are identified in Appendix B. Appendix C contains information relating to AEDC expenditures and sources of funding. This record indicates that, of the total funding of $278,596,000 in 1987, $110,572,000 came from reimbursements for testing, whereas in 1992, of a total budget of $293,619,000, only $85,000,000 was received as reimbursements for testing.

The committee was briefed regarding historic and projected test workloads. In turbine test cells, the 1980s average use was over 2,500 test hours while planned usage in 1992 is 1,200 hours, and approximately 1,300 hours is projected for 1993. In the 1980s, wind tunnel work averaged around 7,000 hours. Planned usage in 1992 is less than 5000 hours, with 6,500 hours projected for 1993, attributable to the anticipated development testing of the Advanced Tactical Fighter. In the mid-1980s, rocket test firings ranged from 25 to 33 yearly--more than twice the current and projected workload. Utilization of the ranges, now running about 100 tests a year, was more than twice as great in the 1980s.

As discussed in the report, projections in the out years are optimistic for use of space chambers, now running less than 8,000 hours annually, largely because of anticipated new

facilities. There is little change in projected and historic usage of the arc heaters, primarly utilized for re-entry measurements, mainly because of projected National Aero-Space Plane tests--which appear likely to be postponed. The facilities that bring in the most revenues for testing are the turbine test cells, wind tunnels, rocket test cells, and ranges. Wind tunnel usage is down from the 1980s by 10 to 15 percent, while the others are down roughly by a factor of two.

As AEDC contemplates the development of a master plan for ground test and computational facilities over the next 20 to 30 years, many factors must be folded into a strategy that can still meet the basic objectives of a premier development center:

• a general recognition that budgets are very tight and will not be significantly eased in the foreseeable future;

• the necessity to identify the existing facilities that can contribute significantly to future developments so they can be properly improved and maintained, efficiently operated, and broadly utilized;

• the need to be selective in the addition of new test facilities by developing comprehensive, gated roadmaps * to ensure that the proper role of any new facility as a tool for aerospace system development is well understood before significant outlays are committed for design and construction; and

• the need for the key testing technology and facility research required to implement the roadmap strategy and provide the basis for major developmental facility procurement.

There is a growing realization that test facility planning must be proactive (as opposed to reactive) because of the long lead times to operational readiness. Moreover, the role of computational fluid dynamics (CFD) is increasing in both the research and developmental phases of aerospace systems, and it has a complex interdependent relationship with both ground and flight testing. A further consideration that needs to be addressed is the direction and focus of AEDC's fiscal policy as it attempts to optimize its resource allocation and achieve maximum utilization of this national asset.

The main part of this report consists of seven chapters including data analyses and recommendations. Chapter 2 provides a guide for structured long-range planning and an integrated perspective for the entire report. Chapter 3 discusses ground test facility requirements and covers a wide spectrum of promising future aerospace systems. Chapter 4 identifies computational requirements. Chapter 5 discusses the AEDC charging policy and commercial

marketing. Chapter 6 addresses the issue of facilities upgrades, while Chapter 7 focuses on maintenance, repair, and closure issues.

Cost analyses were not performed. The level of detail required to make credible estimates was not available to the committee for many of the areas studied. The committee believes AEDC should make detailed cost estimates of the various facility options and improvements under consideration as part of the planning activities that have been recommended. This will represent an important input to the Long-Range Planning Team and provide Air Force management with information necessary to make implementation decisions.