VON KARMAN GAS DYNAMICS FACILITY (VKF)
Arnold Engineering Development Center (AEDC) is the most advanced and largest complex of flight simulation test facilities in the world. The test facilities include nearly 60 aerodynamic and propulsion wind tunnels, rocket and turbine engine test cells, space environmental chambers, arc heaters, ballistic ranges and other specialized units. Twenty-seven of the test units have capabilities unmatched elsewhere. Facilities can simulate flight conditions from sea level to altitudes around 100,000 feet, and from subsonic velocities to those well over Mach 20.
The von Karman Gas Dynamics Facility (VKF) is used to test the effect of airflow over variously shaped aircraft, missiles, satellites and aerospace vehicles and their components under simulated conditions at supersonic and hypersonic speeds.
In this manner, the design, structural integrity and, in some cases, material strength of the vehicles can be evaluated and improved before they are ever flown. In addition to four aerospace chambers, the facility includes four wind tunnels, four ballistic ranges and three arc heaters of various sizes and capabilities.
The origin of VKF may be traced back to the end of World War II, when Gen. H. H. "Hap" Arnold-then Army Air Forces commander and the man for whom the center was named-sought to determine how the Germans had made such rapid progress in developing high-performance jet aircraft and rocket-powered missiles. He enlisted the help of Dr. Theodore von Karman, one of history's great aeronautical scientists, to conduct a survey of the German facilities as soon as the war was over.
Dr. von Karman's subsequent report recommended the Air Force create a center with "...wind tunnel facilities to attain speeds up to three times the velocity of sound, with large enough test sections to accommodate models of reasonable size, including jet propulsion units, and one ultrasonic wind tunnel for exploration of the upper frontier of the supersonic speed range. Ample facilities for the study of combustion and other characteristics of propulsion systems at very high altitudes should be provided..."
The decision to proceed with a gas dynamics facility was made in 1950 at a Washington, D.C., meeting by representatives of the Air Force, Navy, NACA (forerunner of NASA), the government's Research Development Board and the aircraft industry.
The actual directive to the Corps of Engineers to proceed with construction did not come until almost two years later. In 1959, two years after completion of the two large continuous-flow tunnels, the facility was renamed after Dr. von Karman, then chief scientific advisor to the Air Force and an enthusiastic participant helping Arnold Engineering Development Center.
Air is the working medium used in all VKF tunnels. The three wind tunnels are continuous-flow units. They may be operated for hours at a time using air supplied by a nine-stage compressor system that is an eighth of a mile long and is driven by electric motors totaling 92,500 horse-power. Air is stored at 4,000 psi in tow reservoirs with a combined capacity of approximately 542,000 pounds. This air is used to simulate jet flows from the models and the power ejectors in all facilities at AEDC.
Testing in two of the continuous-flow tunnels is devoted primarily to explorations of aerodynamic design. Since the early 1970s, for example, various models of the space shuttle have been tested in these tunnels to determine the aerodynamic relationship between its several parts-the orbiter, the external tanks and the two solid rocket boosters.
The third continuous-flow tunnel in the VKF facility offers and aerothermal environment for testing materials proposed for use on space vehicles and aircraft. The one-of-a-kind supersonic wind tunnel makes it possible to subject flight hardware to a combination of aerodynamic and thermodynamic-or heating-effects up to 1,440 degrees Fahrenheit so engineers can study how aerospace vehicles and materials respond to the combined effects of external heating, internal heat conduction and pressure loading.
Special photographic techniques are used in the tunnels to visualize shock waves and heating patterns.
Three arc heaters can simulate heating rates for re-entry conditions on nosecones. As many as eight nosecones can be mounted on a rotary model injection system and swept through the arc heater's high-speed, compressed airflow in a period of about one minute. Special fast-response instrumentation records data. A variety of nosecone shapes for missiles re-entering the earth's atmosphere have been tested at AEDC to determine the erosion resistance of various materials used to coat the nosetip surface, as well as to note any change in shape due to ablation. Testing is also vital to determine whether the nosetip material provides sufficient thermal protection for the payload encased behind it.
In an effort to save human lives and develop safer aircraft, tests have also been performed since 1972 in a VKF range developed exclusively to simulate the impact of birds against aircraft-especially the canopies or windshields-at speeds up to 700 mph.
Mid-air collisions between aircraft and birds have always been a serious problem for the Air Force. It has been more of a problem in recent years because of the higher operating speeds of jet aircraft and maneuvers at low altitudes. Statistics reveal that in a single year 1,072 bird strikes were reported, damaging 446 aircraft and resulting in $5.5 million in repair costs.
The tests help engineers develop transparent materials that, although light weight and optically suitable, will withstand high impact forces without breaking, shattering or excessive bending.
Another approach to satisfying hypervelocity testing requirements is used AEDC's hyperballistic ranges. This kind of testing offers exact duplication of free-stream conditions.
Instead of passing the airflow over a stationary model, as in a conventional wind tunnel, models are launched free flight inside a 1,000-foot-long, 10-foot diameter closed range, terminating in a catching device used to recover models intact.
It is, however, much more difficult to collect data on a model traveling through still air at thousands of feet per second, than on a stationary model with air flowing over it at high speeds.
Ultra-high-speed cameras with laser illumination are used to freeze frame the model, traveling at speeds up to 20,000 miles per hour, at a camera exposure equivalent to 20 billionths of a second.
The resulting photos give engineers a close look at erosion or melting of the model's nosetip surface due to high temperatures-a condition that could cause a missile to veer off its prescribed course. Weather conditions can also be made to order in the ballistic ranges, and models coated with various protective materials can be evaluated to determine their resistance to erosion caused by snow, rain or dust fields.
The ballistic technique also lends itself to investigation of hypervelocity impact phenomena that may occur in space flight due to collision with man-made or natural objects. Layered structures made of metals such as aluminum or stainless steel, which could be used for the outer skin of space vehicles, are used as targets. Launchers specifically designed for the purpose propel projectiles of various materials down a ballistic range at velocities up to 22,000 miles per hour. Since 1961, the VKF facility has been engaged in high-velocity impact studies.
In 1993, a new gun was installed permitting projectile models of 3.3-inch-diameter and weights up to nearly six pounds to be launched down the long range. In 1995, the 3.3-inch launcher was modified to accept an eight-inch-diameter launch tube. The Center now has the capability to launch projectiles weighing up to 17 pounds at around 9,000 mph.
The Aerodynamic and Propulsion Test Unit (APTU), another VKF test cell, is one of only three such facilities in the United States and the only government-owned operating cell of its type. The facility is used for testing air-breathing propulsion systems, aerodynamic systems and re-entry materials while simulating actual air temperatures and speed conditions reached at supersonic velocities. The ducted rocket, an integral rocket/ramjet propulsion system designed for tactical missile systems, has been tested in APTU. There are plans to use the facility for environmental testing of flight hardware and vehicles such as radome materials, fin drives and thermal protection systems.
Testing of full-scale satellites, space vehicles and their components is performed in VKF's four high-vacuum space chambers, where orbital environments and altitudes up to 400 miles-as well as the minus 350 degree Fahrenheit temperature of deep space-are simulated. Solar radiation is simulated by an array of powerful lamps in the top of the chamber. A full-scale Navstar Global Positioning System satellite was tested in the Mark I space environmental chambers prior to launch, as were the Intertial Upper Stage (IUS) motors, used to transfer payloads from the space shuttle and the Titan 34D to their final orbits. The separation of Payload shrouds for Titan III and IV launch vehicles and a hatch for Space Station Freedom have also been tested.
Office of Public Affairs, Arnold Engineering
Development Center (AEDC)
100 Kindell Drive, Suite B-213, Arnold AFB, TN 37389-2213
(931) 454-5586 DSN 340-5586
Cleared for Public Release
Current as of April 1998