An Orion Crew Exploration Vehicle heat shield material sample model undergoes preproduction aerothermal testing in Arnold Engineering Development Center's H2 test facility as part of a facility validation and calibration run. More testing is slated to occur in December. (Photo by Rick Goodfriend)
The High-Enthalpy Arc-Heated Facilities at Arnold Engineering Development Center provide aerothermal ground test simulations of hypersonic flight over a wide range of velocities and pressure altitudes in support of materials and structures development by the Department of Defense and the commercial aerospace industry.
The facilities are the sole DoD arc facilities in operation in the world. They can provide high-enthalpy test conditions that simulate aeroheating environments at velocities from 5,000 feet per second up to and exceeding 20,000 feet per second.
Arc facilities are unique in their ability to reproduce thermal environments simulating flight from Mach 8 to 20 for the long exposure periods required to validate thermostructural performance and survivability of materials and components. Arc heaters have found widespread usage in the development of high-speed vehicles, including hypersonic missiles, re-entry vehicles, high-speed transports, military/civil space transportation and space access vehicles, and ordnance and munitions systems.
AEDC's arc-heated test facilities include two high-pressure segmented arc heaters (HEAT-H1 and H3) and one Huels arcs-heated tunnel (H2). The facilities utilize a high-voltage, d-c electric arc discharge to heat air to temperatures up to 13,000 degrees Rankine. High-pressure test flows are achieved by confining the electrical arc discharge to a water-cooled plenum section capable of withstanding high chamber pressures above 100 atm.
The combination of high-enthalpy test gas and high plenum pressure makes possible heat flux simulations representative of flight at speeds in excess of Mach 20 at high dynamic pressures (i.e. low altitude flight simulation).
HEAT-H1. The HEAT-H1 Test Unit is an advanced performance arc-heated facility providing high-pressure, high-enthalpy test conditions for qualification of thermal protection materials, nosetips, and electromagnetic apertures and structures for hypersonic missiles, space access systems, and re-entry vehicles.
The test unit utilizes a segmented arc heater with 200 electrically isolated segments which form the heater plenum. The unique segmented construction, with the anode and cathode at opposite ends of the plenum, allows the arc to be held at a fixed length to optimize heater efficiency, total enthalpy at high pressure, and flow uniformity. Normal operating conditions for the heater are about 20,000 volts and 1,200 amps, providing heater chamber pressures up to 120 atm at high stagnation enthalpies.
The H1 test cell is equipped with a multiple-strut, programmable rotary model injection system capable of positioning one to seven test models sequentially into the test free jet for preset dwell times. Transient calibration probes of various configurations are available to define heat flux and pressure conditions inside the test jet.
HEAT-H2. The HEAT-H2 Test Unit is an arc-heated aerothermal tunnel providing high-enthalpy flow at high Mach numbers and dynamic pressures simulating hypersonic flight at pressure altitudes up to 120 atm. H2 utilitzes an N-4 Huels-type arc heater to generate high-temperature, high-pressure air for expansion through a hypersonic nozzle into the evacuated test cell.
The combination of the arc heater driver, various nozzle/throat combinations, the evacuated test cell, and exhauster makes possible high-enthalpy flows at Mach numbers from 5 to 9. Direction and distribution of the injected air can be selected to optimize the enthalpy distribution across the flow to match specific test requirements. Run times of 20 minutes or longer are available in HEAT-H2 for selected operating conditions.
HEAT-H3. The HEAT-H3 Test Unit was developed to provide a large, high-pressure arc facility with sufficient size and performance for testing of full- and large-scale missile and re-entry samples and structures. H3 is a 12-module, 50-percent geometric scale-up of H1. The test unit is designated to operate at over twice the available power level and mass flow of H1, with operational pressure up to 150 atm.
AEDC ARC-HEATED TEST FACILITIES
Atm. Exhaust (Freejet)
Atm. Exhaust (Freejet)
Maximum Run Time (minute)
Nozzle Mach Number
1.8 to 3.5
3.4 to 8.3
1.8 to 3.5
Nozzle Exit Diamater (inches)
0.75 to 3.0
5.0 to 24.0
1.2 to 4.5
Stagnation Pressure (atm)
Up to 100
Up to 12
Up to 115
Stagnation Enthalpy* (Btu/lbm)
Mass Flow Rate (lbm/sec)
Facility Power (NW)
Up to 30
Up to 45
Up to 70
*Stagnation enthalpy inferred from stagnation heat flux and pressure measurements by the Fay-Ridell method.