Hypersonics is considered a critical field for national defense, and the Arnold Engineering Development Complex at Arnold AFB, Tenn., is critical to the success of the Department of Defense in that field.
“Effective test and evaluation is key to the rapid fielding of hypersonic systems,” said Col. Jeffrey Geraghty, AEDC commander. “It provides knowledge to reduce the probability of in-flight failures and performance shortfalls, while delivering large cost and schedule risk reductions for acquisition programs.”
AEDC engineers and scientists conduct test and evaluation of hypersonic systems and system components in the areas of aerodynamics, aerothermal, propulsion, weather effects and flight testing.
“It is difficult to produce the extreme conditions of a representative hypersonic environment in ground test,” said Ed Tucker, AEDC senior technical director. “Because there is no single test cell that can fully duplicate all the key parameters of hypersonic flight simultaneously, AEDC has various types of test facilities which are optimized to provide insight into a specific aspect of hypersonic flight.”
The complex has three wind tunnels capable of aerodynamic testing of models at hypersonic speeds. At Arnold Air Force Base, Tunnel B can achieve speeds of Mach 6 and 8, while Tunnel C can generate Mach speeds of 8 and 10. AEDC Hypervelocity Wind Tunnel 9 in White Oak, Maryland, has nozzles that allow for Mach speeds of 6.7, 8, 10, 14 and 18.
“The Mach 18 nozzle is a recent addition to the capabilities of Tunnel 9, extending the tunnel’s operational envelope from Mach number 14 to 18 provides greater insight into a vehicle’s performance across a wider portion of mission trajectory,” said John Lafferty, Tunnel 9 technical advisor.
This nozzle was the result of advanced-technology nozzle material development and state-of-the-art nozzle design tools.
“Following the calibration conducted from May to July 2020, the new capability will be used extensively for current and future programs,” Lafferty said.
The characterization for hypersonic system Thermal Protection System (TPS) materials is conducted in three AEDC arc heater facilities.
“Mid-Pressure Arc Heater technologies developed by Arnold AFB engineers have resulted in a world-unique capability that allows for high-enthalpy flows, pressures and mission durations which are representative of typical boost glide vehicle trajectories,” Tucker said.
The increased activity in hypersonic systems has resulted in a very high test tempo for these test capabilities.
The J-5 Phoenix test facility, currently under construction at Arnold AFB, will expand the aerothermal and advanced high speed propulsion testing capabilities of AEDC. J-5 will provide true temperature, clean air testing at speeds in excess of Mach 7 for mission-length run times. Plans also call for a variable Mach number nozzle to provide accurate flight trajectory simulations.
Currently, AEDC conducts advanced propulsion testing of hypersonic systems in the Aerodynamic Propulsion Test Unit (APTU). Last year, the AEDC Hypersonic Systems Test Branch ground test team conducted testing in APTU, which set a record for the highest thrust produced by an air-breathing hypersonic engine.
“Both the APTU and J-5 test capabilities will play a critical role in the nation’s development of future hypersonic systems,” said Sean Smith, Hypersonic Systems Test Branch Ground Test technical advisor.
“The APTU team has been working hard for the past several years with AFRL (Air Force Research Laboratory) to test some of the largest and most complex hypersonic engines we’ve ever tested in this country.
“This team has overcome many challenges along the way and that includes learning how to operate with the disruptions imposed by COVID-19. This will be the same innovative team that will ultimately lead the execution of test programs in the J-5 facility. J-5 will be the most advanced hypersonic propulsion test facility in the U.S. when it comes online, and its unique capabilities will enable the team to accomplish even greater things in the future.”
AEDC also is capable of subjecting hypersonic systems to weather that may be encountered in flight.
“A key element of evolving from a hypersonic demonstration concept vehicle to an operational weapon is to test and evaluate how the system will perform when operating in weather that it may encounter during a mission,” Tucker said.
Hypervelocity Ballistic Range G at Arnold AFB allows for soft-launch at speeds in excess of Mach 20. The range can be configured to simulate a projectile encountering dust, rain, snow and ice.
“The weather encounter test techniques being developed will allow for highly controlled testing of hypersonic materials being developed for future systems,” said Jonathan Carroll, capability manager for Hypervelocity Flyout, Impact and Lethality Ground Test and Evaluation. “These capabilities ensure systems are survivable, reliable and well-characterized in any operational environment. The ground test data generated will validate modeling and simulation (M&S) tools that will be used across multiple hypersonic development programs. The combination of this ground test data and M&S tools will serve as a risk reduction and generate cost savings as we prepare for future flight tests.”
While Range G provides lethality capability ground testing at smaller scales, at the AEDC Holloman High Speed Test Track (HHSTT) at Holloman Air Force Base in New Mexico customers can test models ranging in size up to full-scale at speeds up to Mach 8. In many cases, the test articles can be recovered. The HHSTT is a rocket sled track operated by the 846th Test Squadron. The Squadron provides customers relevant test data to verify lethality effects, impact survivability, aerothermal and weather effects, separation dynamics, guidance system performance, sensor performance and other key performance metrics.
“The HHSTT provides customers affordable risk reduction by producing operationally-relevant hypersonic weapon lethality characteristics for our program offices, characteristics that will allow our warfighters to develop strategy and tactics for these weapons,” said Lt. Col. Paul Dolce, commander of the 846th TS.
Recently, the 846th TS, in conjunction with the Hypersonic Test and Evaluation Investment Portfolio, upgraded the HHSTT’s rainfield to improve weather effects testing. Additionally, the 846 TS has been studying natural rainfall in order to improve the simulation capabilities of the rainfield.
The HHSTT is currently studying recovered hypersonic monorail testing, a capability unique to only the HHSTT. While the 846 TS has proven this capability in the past, the Squadron is refining design methods to make the sleds more survivable at the higher speeds expected in future testing.
The AEDC Hypersonic Systems Test Branch integrates ground testing and flight testing within the same branch. The Ground Test Team of the branch operates APTU. The Flight Test Team, located at Edwards Air Force Base in California, provides capabilities such as trajectory analysis and optimization, simulation, test and safety planning, and project management support. Together, the branch’s teams coordinate early involvement and support from essential test resources within or outside the Air Force Test Center.
“Rapidly providing hypersonic capabilities to the warfighter requires a united effort from organizations across AFTC and the Department of Defense,” said Maj. John Wilder, Hypersonic Flight Test Team director. “Bringing those experts together as a team to plan and execute test programs and shape the future of hypersonic testing is a top priority for us.”
Due to the surge in hypersonic flight test requirements, additional flight test support assets for data collection are required to meet the capacity and capability requirements of the DOD. In response to this need, AEDC is developing, with support from the Test Resource Management Center (TRMC), a High Altitude Long Endurance (HALE) Unmanned-Aerial-Vehicle (UAV)-based flight test support capability, called SkyRange, to supplement or replace traditional data collection assets, such as ships that are used for hypersonic flight testing.
SkyRange will use UAVs with new or improved sensors to support hypersonic flight tests. The UAVs utilized by SkyRange are RQ-4 Global Hawks and MQ-9 Reapers. Initial sensor capabilities include telemetry, an airborne telescope to characterize vehicle surface conditions and a system to measure atmospheric conditions. Additional test support applications and sensors are being considered.
“SkyRange represents a novel approach to addressing our nation’s need to conduct high-fidelity hypersonic flight tests by increasing flight test capacity and operational flexibility, while improving the quality of data collected during flight,” said Tyler Neale, executing agent for High Speed Systems Test Technology program.
The combination of facilities and personnel available within AEDC enables the execution of the hypersonic mission.
“AEDC has an outstanding team of technical experts developing and operating a unique suite of hypersonic test and evaluation capabilities,” Tucker said. “They serve a vitally important role in gaining the knowledge needed to successfully field effective hypersonic systems.”