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Verifying aircraft stealthiness

With the many missions flown already by stealth aircraft such as the F-117A, pilots have to remain confident that their airplanes' stealth characteristics remain in good condition. Engineers at the Department of Energy's Pacific Northwest National Laboratory have developed a prototype holographic, three-dimensional radar camera capable of verifying the condition of an aircraft's stealth characteristics. This handheld, zone-imaging device will help the Air Force determine the condition of radar-absorbing material on F-117A Nighthawks.

Pacific Northwest National Laboratory developed a holographic, three-dimensional radar camera capable of determining the condition of a stealth aircraft's radar-absorbing material.

The 3-D radar camera works much like a videotape camcorder by recording parts of an aircraft's radar reflection and translating that information into an image showing where radar-absorbing material is creating a larger reflection than desired. As the aircraft's radar reflection increases, so do its chances of being detected by enemy radar. Pre- and post-repair inspections are supported by the system to ensure that radar-absorbing material is performing as expected, particularly in cases when the aircraft has been damaged, even slightly, during flight.

Pacific Northwest engineers have already built a Ku-Band radar camera that operates at 12 to 18 GHz and are building a second, X-band camera that will operate at 8 to 12 GHz. It is important to be able to measure across a range of frequencies because longer-range search and surveillance radar generally operate at lower frequencies while shorter-range radar, such as those used by missile and artillery targeting systems, operate at higher frequencies. Using both cameras, the Air Force will be able to measure and characterize any defects in an aircraft's stealth material.

The camera is operated by positioning it about two feet from the area to be inspected, "shooting" the aircraft with low-power electromagnetic waves. An antenna array receives the reflected energy and sends it to a computer for processing. Software algorithms translate the level of reflection into a radar image, which is then projected into head-mounted virtual vision glasses. Each snapshot covers an area of 1 ft².

Through the glasses, the operator sees an image depicting the brightness of the aircraft's radar reflection, or signature. The image displays the radar signature in green, yellow, or red to denote pass, assess, or fail, respectively.

X-35 moves through testing and manufacture

Left: Predictions using Lockheed Martin's analytical simulation tool. Center: Photo of actual damage. Right: LaserUT scan of wing-skin delaminations.

Demonstrating the Joint Strike Fighter's combat survivability, Lockheed Martin has subjected the X-35 wing to ballistic testing. The testing confirmed the accuracy of advanced analytical simulations performed to predict the structural response of the wing during the ballistic event. The predictions were sent to U.S. Air Force Research Laboratory survivability engineers.

Lockheed Martin's Laser Ultrasonic Test (Laser UT) system was used to assess the wing structure damage during post-test analysis. This production inspection system required no hard tooling and had a total setup time of less than 10 minutes. A complete ultrasonic scan and analysis of the wing structure was completed in less than an hour and a half, an inspection process that generally requires 36 hours or more throughout the industry.

The ballistic test structure was designed and manufactured as part of the JSF Airframe Affordability Demonstration program, performed by the company to refine and demonstrate affordability in design, manufacture, and assembly.

Runner-up technologies

Technology	Issue published
Raptor completes limit load testing	December 1999
Birdstrikes remain a concern for pilots	March 2000
Concepts selected for NASA aeronautics project	November 1999
All set for more wings	June 1999
A3XX development	September 1999
Robotic aircraft used to study global warming	July 1999
UCAV work continues at Boeing	July 1999

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