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

In the process of developing a master plan and strategy for the next 20 to 30 years, Arnold Engineering Development Center (AEDC) requested that the National Research Council (NRC) Aeronautics and Space Engineering Board (ASEB) assemble an ad hoc committee to assist in facility and strategy planning for both the near- and long-term future.

Created shortly after World War II, AEDC resulted from the recognition that the United States needed the basic developmental tools that would allow it to reach out to the horizons of technology in developing its modern military air systems. In the years since that time, significant test facility additions have been made that have kept AEDC one of the premier aerospace ground testing facilities in the world. These capabilities have been and will continue to be a key ingredient in the development of the U.S. Air Force (USAF), the most advanced air force in the world.

Today, despite the easing of international tensions and the inevitable pressure on the defense budget, the need and the responsibility of AEDC remain the same, that is, to help provide the United States with the kind of military aerospace systems that can protect against a wide range of threats that could materialize during the next 20 to 30 years by providing state-of-the-art ground test facilities.

Accomplishing this task requires a process similar to the one that originally led to the development of AEDC. However, many factors must be folded into a strategy that meets 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 maintained, efficiently operated, and broadly utilized;

• the requirement to be very selective in the identification of new test facilities by developing comprehensive, gated roadmaps¹ to ensure that the proper role of any new facility as a tool for aerospace systems 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 for facility procurement.

The committee believes that this report and its recommendations provide guidance in meeting AEDC facility and strategy planning requirements. The following material summarizes the full report and includes all of the principal recommendations that appear therein.

Comprehensive and continuing long-range planning is required for AEDC to fulfill its role in the development of advanced new Air Force systems.

The Air Force Systems Command has had effective planning activities related to specific new aerospace systems development. However, in looking toward the sophisticated technology of the future, pre-systems planning adequate to define new facilities and other key resources that will be vital to the selection and specification of our future aerospace systems is required. As the new Air Force Materiel Command (AFMC) integrates its various new systems-planning functions into a consolidated organization, it is important that a strong, structured planning function be dedicated to the identification of, and provision for, the testing and development tools required for advanced systems. AEDC should be strongly represented in those planning activities that involve advanced aerospace ground test facilities.

The development tools include ground test facilities, computational fluid dynamics (CFD), flight test beds, and experimental flight vehicles. The relative roles of these development tools, which will vary with the system and the technology involved, must be determined and the specific facilities and aircraft that represent the physical parts of the tools must be identified.

An AFMC Long-Range Planning Team (LRPT) should be responsible for planning development tool acquisition. Testing technology and necessary facility research will be important elements. As the research and technology of new tools progress, it may be found that some major planning must be revised. This carefully structured planning activity should provide for feedback of information and a possible redefinition of plans.

The principal planning activity should be supported by permanent staff and representatives from all concerned USAF laboratories and test centers. Invited outside participation in focused study efforts should be much the same as it is now on ad hoc committees, including other military services, the National Aeronautics and Space Administration (NASA), industry, and academia.

The committee recommends that the AFMC augment present system-planning activities by creating a Long-Range Planning Team to be responsible for a structured preplanning process that contributes to the broader planning leading to new Air Force aerospace systems. The LRPT should examine all options and alternatives under consideration and concern itself with system technology requirements, test capabilities required, and the roles of the various developmental tools for those options. Strong participation in the LRPT by AEDC and the earliest possible identification of required development ground test facilities and their funding plans are critical.

For ease in discussion, the facility requirements in this report are divided into the following categories: subsonic and supersonic airplane systems, turbopropulsion systems, hypersonic cruise and transatmospheric systems, and launch and space systems. In general, the committee describes needs in which technology is a driving factor and certain system developments appear to be highly probable. Although comments are offered on priorities, the committee believes that comprehensive future studies of priorities should be handled by the structured AFMC planning activity described above.

Subsonic and supersonic aircraft configuration testing generally takes place in AEDC wind tunnels 16T (transonic) and 16S (supersonic). Wind tunnel 16T is in great demand, whereas 16S is lightly loaded. Tunnels 16T and 16S share the same drive system. The drive system is worn and may need to be replaced in the near future.

Because of the importance of 16T and 16S, the current demands on 16T, and the high cost of replacing the drive system (currently estimated by AEDC at several hundred million dollars for a complete replacement), the committee recommends that AEDC develop a 16T and 16S replacement main drive design, funding plan, and implementation strategy to ensure the continuing availability of these facilities. Also, a means of closely monitoring the integrity of the present drive system should be incorporated to minimize the risk of catastrophic failure.

The technology of transonic wing design has progressed to the point where few, if any, existing transonic wind tunnels such as 16T can adequately serve as development and validation tools. Although today 's tunnels still can generate much useful design data for airplane development as a whole, the technology of advanced supercritical wing design requires much higher-test Reynolds numbers with an order of magnitude reduction in flow disturbance. Quiet tunnel research has been ongoing at NASA for several years and is now ready for use in a developmental facility. Although the NASA Langley Research Center cryogenic National Transonic Facility is designed to match full-scale Reynolds number, the facility was not intended as a day-to-day developmental facility. The new European Transonic Wind Tunnel scheduled to become operational in 1993 will provide the higher Reynolds number capability with some improvement in productivity.

The possible requirement for transonic cruise laminar flow control (LFC) also points to the desirability of a high-Reynolds-number transonic capability. Although the general complexity and projected cost of such systems have, to date, inhibited their use on production aircraft, each LFC research program seems to result in performance equal to or better than expected. These positive results and their implications for fuel-efficient aircraft create a continuing interest in LFC development tool capability.

The committee recommends that AEDC, with the close cooperation and support of NASA and industry, develop alternative strategies for providing the ability to ground test cost-effectively at transonic speeds at near-flight Reynolds number. The alternative strategies should include estimates of costs, benefits, timing, and anticipated utilization. In formulating a recommendation for consideration by the AFMC, the LRPT should consider the alternatives presented by AEDC, other facilities that may be coming on line, and alternative development tools (other than ground testing) for obtaining the required higher-Reynolds-number data for Air Force development programs.

As in the case of transonic cruise wing development, the technology of low-speed airplane design has advanced to the stage where the design validation for high-lift wing design, high angle-of-attack fighter maneuvering capability, and low-speed structural loads should be accomplished at Reynolds numbers representative of full-scale flight. AEDC has never had a facility dedicated to low-speed work. The only facility generally available for such high-Reynolds-number development work has been the 12-foot low-speed pressure tunnel at the NASA Ames Research Center. That facility has been undergoing reconstruction for several years and will be ready for use in 1994. In recent years, U.S. industry, needing this capability for certain critical low-speed tests, has had to resort to European facilities.

The committee recommends that AEDC, with the close cooperation and support of NASA and industry, develop alternative strategies for providing the ability to ground test cost-effectively at low speed at near-flight Reynolds number. The alternative strategies should include estimates of costs, benefits, timing, and anticipated utilization. In formulating a recommendation for consideration by the AFMC, the LRPT should consider the alternatives presented by AEDC, other facilities that may be coming on line, and alternative development tools (other than ground testing) for obtaining the required higher-Reynolds-number data for Air Force development programs.

The supersonic cruise technology being pursued by NASA and industry is likely, in the judgment of the committee, to result in a commercially viable supersonic transport. This could easily, in the opinion of the committee, lead to an international competition in which the commercial airplane leadership of the United States could be challenged by Europe and Japan. Such supersonic cruise aircraft would also have military applications. The committee observes that, although 16S is not highly utilized today, this could change in the future. Modernization and plans for operating this facility as efficiently and at as low a cost as possible should be part of the AEDC near- term plan. Modernization includes at least the ability to run powered models that simulate the influence of engine flows, improved tunnel airflow (including low turbulence

and noise), and accommodations for supersonic laminar flow testing. The large test section size in 16S is very attractive in providing an ability to simulate detailed geometry.

The committee recommends that AEDC develop an upgrade and funding plan for wind tunnel 16S in anticipation of increased demand for the development of supersonic cruise vehicles.

The Integrated High Performance Turbine Engine Technology (IHPTET) program is the U.S. government-wide initiative for the development of advanced turbopropulsion systems. Significant performance gains will be achieved in all flight regimes by improved performance of the engine core. Specific core power (core horsepower per core airflow) can be expected to improve by a factor of 2.5, with accompanying increases in thermal efficiency, in the next 20 years. For subsonic applications, continuing to increase the diameters of very high bypass ratios of both ducted and unducted propulsors will provide a continuing improvement in propulsive efficiency.

The current AEDC Aero-Propulsion Systems Test Facility (ASTF) is adequate for projected supersonic engine developments and for the core developments of both supersonic and subsonic engines. Also, ASTF is capable of handling complete subsonic engines up to approximately 100,000 pounds of thrust. However, a 40 percent increase in flow capacity is required to handle altitude testing of ultrahigh-bypass-ratio engines in the next decade. The diameters of the fans and propulsors of such high-bypass-ratio engines will exceed the capabilities of present test cells.

The committee recommends that the LRPT (with strong support from AEDC) develop options for meeting the projected large propulsor airflow and diameter requirements of the next decade. These options should include, for example, increasing the current facility capabilities, testing the propulsor separately, testing engines with shortened (or clipped) versions of the propulsor, and using flight testbeds.

Programs involving hypersonic cruise or transatmospheric technology have requirements for developmental tools that are among the most difficult to define. The relative roles of various developmental tools (such as ground test facilities, CFD, flight testbeds, and flight research vehicles) are difficult to assign without extensive preliminary facility research and testing technology programs.

The National Aero-Space Plane, the X-30, is projected to be a major flight research vehicle. It has single-stage-to-orbit and aircraft-like operation design objectives. The X-30, if carried to flight test, could greatly enhance understanding of the hypersonic flight environment and the performance of the integrated components and systems that comprise that particular vehicle design. However, in order to develop any single system in a wide variety of possible operational hypersonic vehicles for the future (ranging potentially from weapons to cruise

aircraft to orbital vehicles that have vasty different design and performance requirements) a structured, lower-risk process for development, test, and evaluation of major vehicle components and systems is needed. In this regard, it is important that the LRPT develop a plan that defines the relative roles of the various developmental tools.

Options for the ground test facility portion of the plan are discussed in Chapter 3. Briefly, a two-phased approach is suggested. Phase One would include the development of a state-of-the-art, moderate-size (about 5-foot-diameter test section), high quality, clean air, quiet facility to use as a comparison standard to study the simulation qualities of other facility design approaches (e.g., arc heaters, combustion heaters, liquid air arc heaters) that may be needed to achieve higher enthalpies. Such a Phase One facility could use an improved AEDC Aerodynamic and Propulsion Test Unit (APTU) ceramic heater that is qualified to generate stagnation pressure and temperature at Mach 8 for 1 to 120 seconds. Also in Phase One would be parallel research programs aimed at studying the technology of obtaining high-quality flow with a minimum of contamination from conditions of very high stagnation temperature. Since it may not be possible to obtain high stagnation temperature test streams without freezing excited gas states (e.g., dissociation), additional programs must address partial simulation of flight conditions that relates to the incorrect chemical state of the test gas. Phase Two would then be the design and development of the selected hypersonic systems test facility (or facilities) identified from the work in Phase One.

The committee recommends that, within the LRPT structured planning activity, a roadmap be created for the development of ground test facilities for transatmospheric and hypersonic cruise systems. A two-phase program is recommended. Phase One would consist of the development of a high-quality, state-of-the-art, Mach 8 facility, accompanied by parallel research programs aimed at critical hypersonic test facility issues. Based on the results of Phase One, Phase Two could entail the design and construction of the selected major development facility resulting from the Phase One program. Because of the uniqueness and responsibility of operation of the hypersonic development ground test facilities and the possible use of extensive present air and vacuum capability, it is recommended that Phase One be a primary responsibility of AEDC.

The testing of major launch vehicle components, including liquid propellant and solid propellant rocket engines under simulated vacuum exhaust conditions, is a very significant and unique capability at AEDC. In addition to the development and performance assessment of major rocket systems, AEDC has the capability of performing ground test simulations of anomalies at high-altitude flight. The committee supports the AEDC plan to reconfigure Rocket Development Test Cell J-4 to test liquid rockets. Test Cell J-6, a new facility capable of testing 500,000-pound-thrust engines at altitudes up to 100,000 feet, is currently under construction at AEDC. The committee believes that the capability to test launch systems at AEDC will be well in hand if the present course of upgrading J-4 and completing J-6 continues.

The committee recommends that AEDC continue to give high priority to providing state-of-the-art capability as a national resource for liquid and solid propellant rocket testing.

AEDC also conducts tests of spacecraft in simulated space environments. Although a significant amount of environmental space testing is conducted at contractor facilities, AEDC has developed new capabilities in evaluating focal plane arrays and has used those capabilities to support a variety of programs. An expanded capability for scene generation and spectral analysis is being planned.

The committee recommends that AEDC continue to provide unique capabilities as a national resource for simulated space environmental testing.

As in most advanced technical facilities, the computer plays a multifaceted role in the operation of AEDC. The role of the computer is generally well understood in its use in test design, test control, and data reduction and analysis. Understanding the internal flow in the facilities through computational fluid dynamics and, consequently, the improvement of that flow and the design of new facilities is also a well-accepted use of computational analysis. As test objectives become more demanding, it is important to understand the predicted flow over the model, especially for the purpose of instrumentation design and location. Chemically reacting flows, due to combustion and high stagnation temperature dissociation, are very complex and require a sophisticated analysis capability to evaluate the test data.

The first priority in satisfying requirements for computational capabilities is in the area of data reduction (including test corrections), facility design (facility flow analysis), instrumentation, and load analysis. AEDC currently has a plan called the Advanced Scientific Computing Enhancement Project to upgrade the in-house computer facility. Briefly, the strategy is to provide four computers, one for each of four major test areas, to ensure availability upon demand in each of those test areas. The committee agrees that this new capability would easily satisfy the demands listed above as first priority requirements.

The second priority involves data prediction and analysis, data interpolation and extrapolation, and tasks requiring complex CFD representation of flow parameters. The committee believes that the advanced scientific computing enhancement upgrade is not adequate to properly handle these requirements. Such applications require access to a large computer with at least 128 million words (MW) of central memory and a minimum central processing unit (CPU) performance of 160 MFLOP on the 100 by 100 all-FORTRAN LINPACK Benchmark.

The committee recommends that AEDC continue the implementation of computer enhancements required to ensure state-of-the-art capabilities in tunnel control, data reduction and analysis, instrumentation, and facility flow analysis.

The committee recommends that AEDC plan to acquire a supercomputer with at least 128 MW and a minimum CPU performance of 160 MFLOP on the 100 by 100

all-FORTRAN LINPACK Benchmark in order to support a full three-dimensional CFD applications capability.

The committee recommends that key personnel be added to the AEDC staff to enhance the understanding and application of turbulence models and chemically reacting flow CFD models.

Currently, for Department of Defense (DoD) and DoD-sponsored tests, direct costs are reimbursed, including for power and civilian personnel. For purely commercial testing, charges would include both direct and indirect costs as well as amortization of facilities. In addition to the normal budget pressures, AEDC has been experiencing a declining business base due to several factors. Some programs from which AEDC was expecting business have recently been canceled. Also, under a recent policy change, Air Force programs that are in development may now do testing at non-AEDC facilities, provided the program manager deems it cost effective for his program to do so. It is difficult to argue against such cost-saving measures, even though they may create some inefficiency at AEDC because of underutilized facilities. To compensate for this, the committee believes it is in the national interest for AEDC to perform testing on nongovernmental programs for which the facilities are ideally and uniquely suited. Also, practices should be implemented to lower costs and to provide incentive for Air Force program managers to use the center to the maximum possible extent, both to more fully utilize the AEDC facilities and to enable more testing on future systems at affordable rates.

One of AEDC's marketing strengths is the uniqueness of its facilities. Ensuring that the customer understands AEDC's capabilities and how the facilities may solve the customer's problems is key to maintaining a strong business base.

In addition, being flexible in offering partial test support services may help keep a customer's test program costs down. In the past, AEDC generally has only provided testing with full test support at the attendant high charges that one might expect.

AEDC has had essentially no pure commercial program testing because of the high commercial rate structure. (Commercial testing has been conducted at government rates in cases where a military program specifically sponsors the test). Commercial testing is consistent with the genesis of AEDC under P.L. 415-766, the Unitary Wind Tunnel Plan Act of 1949, and the Federal Technology Transfer Act. It is in the national interest that the facilities be used. USAF policy should be adjusted to specifically state that commercial testing at AEDC is encouraged when it is to the net national advantage. The LRPT, with the support of AEDC, should undertke a study of measures to encourage such testing, including delegating to the commander of AEDC the authority to approve application of the government rate structure to commercial programs without the necessity of a separate DoD sponsor. Additional productive use of AEDC facilities can be made by providing limited institutional funding for research in AEDC facilities by other government users such as NASA and the Wright Laboratories.

AEDC is to be commended for working diligently on these issues during the last year.

The committee recommends that AEDC place representatives at customer sites to provide good communication links and customer support to ensure that potential business converts to actual business.

The committee recommends that AEDC develop practices wherein the customer has the option of negotiating for partial test support services for only the services specifically wanted and needed, thereby minimizing customer test program costs.

The committee recommends that DoD policy state that commercial testing at AEDC is encouraged when such testing works to the net national advantage. The LRPT, with the support of AEDC, should undertake a study of measures that would encourage such testing, including delegating to the AEDC commander the authority to approve rates for commercial testing that are comparable with rates for DoD testing. Consideration should be given to the criteria that the AEDC commander should apply to determine at which facilities and under what circumstances such rates are justified in the net national interest.

The committee recommends that a separate institutionally-funded research and development account be provided specifically for a limited amount of research in AEDC facilities by such users as the Wright Laboratories and NASA.

Upgrades ensure the continued utility of facilities already in place. The long-term plan for facility improvements and upgrades is dependent on the limited resources available and the need for those facilities to match the requirements of near-term new systems developments, the special data requirements requested, and complex simulations of advanced model configurations. In order to accomplish significant changes in capability, upgrades are frequently associated with major new initiatives. For example, substantial upgrades typically involve expenditures of $50 million or more, whereas the AEDC annual budget for generic improvements and modernization on a lesser scale is $3 million.

The committee recommends that the backlog of approved facility upgrade projects be reexamined on a continuing basis and that plans to address the backlog be developed, along with a recommended funding policy. Modest support also should be allocated for research into advanced facility concepts.

AEDC suffers from a situation common to many operators of major government facilities--insufficient allocations for a minimum level of maintenance and repair. This low level of support risks expensive unplanned downtime due to equipment failures, especially when the age of many of the principal facilities is considered. The NRC Building Research Board has recommended that agencies allocate for maintenance and repair of public buildings, such as schools and office buildings, exclusive of major infrastructure such as roads, water systems, and sewers, a minimum of 2 to 4 percent of replacement value. This compares to a 1.1 percent allocation in AEDC planning for fiscal year 1992. The committee believes that in the case of sophisticated facilities with large, complex machinery such as that at AEDC, it is likely that at least that percentage could prudently be applied toward maintenance. Furthermore, of the $41 million that this represents, only $8 million is a line item, Real Property Maintenance. The remainder ($33 million) must be funded from the general operating funds provided in the Direct Budget Authority account.

The AEDC facilities are very similar in sophistication and age to those at several of the NASA centers. A concern at NASA relative to increases in breakdowns and operational difficulties led to a series of studies on the subject, including one by the National Research Council in 1988 and one by the General Accounting Office in 1990. These studies resulted in recommendations of higher maintenance and repair allocations and actual NASA budget changes, which amounted to about 2 percent of capital replacement value at the Ames, Langley, and Lewis Research Centers.

The committee recommends that annual funding of $8 million (and actual expenditures of $41 million amounting to 1.1 percent of current capital replacement value) for maintenance and repair of AEDC facilities be increased to a funding (and expenditure) level of $72.8 million (2 percent of current capital replacement value). Also, a plan should be developed for dealing with the $86 million backlog for normal maintenance and repair items and $180 million for the special high- value projects.

The committee endorses the AEDC processes to review and evaluate the status of test facilities and their workload in future years. This includes designating facilities as being on active, modification, stand-by, or mothball status, as well as decisions to close inactive facilities for which no requirement is foreseen.

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.