InnovMetric and Berding 3D Help Lockheed Meet Tight Deadline
InnovMetric and Berding 3D help Lockheed Martin meet a tight deadline on scanning a 1950s fighter jet.
In 2005, the Lockheed Martin Missiles & Fire Control unit, whose main operations are based in Dallas and Orlando, became intrigued by the aerodynamics of a 50-year-old Swedish-built jet fighter, the Saab A-35 Draken. LM M&FC aerodynamics experts needed a very accurate data map of the aircraft that could be imported into engineering analysis tools to obtain real aerodynamic performance; the reason that they wanted this data was so that they could insure that weapons delivery systems would survive in 21st-century combat environments. Aerospace contractors such as Lockheed Martin continually search for ways to mitigate the high costs of testing. One solution is using a commercial activity instead of a military test facility, and digital rather than physical means.
Complete, accurate surface data of the entire aircraft plus high-resolution scans of weapons and gun bays were required. Lockheed Martin turned to Berding 3D (Santa Fe, NM) for scanning capabilities that would generate surfaces data to be fed into computerized flight simulations. Berding got the job because of its unique experience in long- and short-range scanning, and also because they could react right away and meet Lockheed’s deadline.
Mat Cappel, Technical Manager at Berding 3D Scanning LLC, encountered three scanning-and-digitizing challenges:
- Speed – Lockheed Martin faced 90 days of nonstop data crunching in flight simulations. Initial surfaces data was needed in a week.
- Size of the model – The Draken is over 50 feet long with a 31-foot wingspan and a rudder standing nearly 14 feet high. To minimize the file size, two types of scanners were used: a high-resolution scanner (for highly detailed areas, and a low-resolution (and faster) scanner for flat areas.
- Flexibility – Berding 3D needed a software solution that would process data obtained from both high- and low- resolution scanners.
Solution
Cappel and a scanner
operator were on a plane to Los Angeles three days after receiving
Lockheed’s call. The scanning took place at Inyokern, in California's
Mojave Desert where six of the remaining Drakens are refurbished and
flown, and was completed in two days.
In the Draken project, Berding needed to speedily process several gigabytes of point-cloud data in wildly differing resolutions – as much as 10,000x or five orders of magnitude – into a single CAD model. In the high-resolution work, Berding gathered 266 point clouds averaging 250,000 points apiece. This was close-in, short-range work capturing images about two feet square, using a Minolta Vivid 910 scanner.
The low-resolution scans were done with a Cyra2500 from Leica Geosystems. For these scans, the technicians gathered about 20 million points. "This was sufficiently precise for even the smallest aerodynamic shapes but not so high in resolution to capture unneeded data such as rivet heads and hinge points," Cappel said. "The low-resolution work was more like a surveying application for us."
After all the scanning and digitizing – about 250 high- and low-resolution scans aggregating 4.6 gigabytes of data – Berding's final deliverable file to Lockheed Martin was a relatively small 200 megabytes (MB), uncompressed.
Scan Alignment
The
PolyWorks IMAlign module was used to align the 260 scans into a single
model. The PolyWorks alignment technique does not require the use of
targets or markers on the part. Instead, it uses the geometrical shape
of the scans themselves to align them to each other. "Not having to use
targets on the plane dramatically improved the scanning process,"
declared Cappel.
After the scans were aligned, the resulting point cloud model was transformed in the PolyWorks IMMerge module into a polygonal model in the Stereolithography Tessellation Language (STL) format. PolyWorks creates a polygonal mesh (triangles) adapted to the surface curvature, preserving high resolution across edges and fillets while creating larger triangles in flat areas. Some simulation software packages can process STL files, however, the system used by Lockheed Martin M&FC did not support them. A CAD-usable file was needed.
Creating a CAD-Usable File
To
create a CAD-usable model, PolyWorks computed a mathematical
representation of the surfaces called NURBS (non-uniform rational
B-splines) on the polygonal model. Prior to computing the NURBS
surfaces, a curve network was built on the polygonal model to determine
where the surfaces were to be fitted. PolyWorks provides both automatic
and manual tools to create the curve network. Feature curves can be
extracted in one click of the mouse using PolyWorks' extracting
algorithms, and the curve network can be refined manually with
techniques that require only a couple of clicks by the user. NURBS
surfaces were then automatically fitted on the curve network. These
surfaces were exported as IGES or STEP files to Lockheed Martin’s
analysis system. The final deliverables met Lockheed Martin's
requirements in terms of accuracy, file size and number of patches.
Outcome
Not only
did Lockheed experience dramatic cost savings from computer-based
simulation instead of physical testing in wind tunnels, but they also
saved from the speed that Berding and Polyworks were able to work. From
scanning to final deliverables, Berding took two and a half weeks to
capture, edit and format the huge amount of Saab A-35 scanned data to
Lockheed Martin's requirements. Every external surface of the entire
aircraft was scanned and digitized in just two days by two people.
Other methods would have taken two to four times longer, so there was a
67 to 80 percent savings in data acquisition time. "For a job in the
multiple gigabyte range, this is a very fast turnaround," said Mat
Cappel.
PolyWorks was also essential to the project as it was able to accurately handle four gigabytes of data. Otherwise, the file would have had to be split into several pieces, requiring additional merging steps and data assembly, doubling and possibly tripling the processing time. PolyWorks saved an estimated two weeks over less efficient software.
Conclusion:
Thanks
to Berding and InnovMetric, Lockheed Martin now has all the aerodynamic
details in its flight-simulation systems—quickly and at very low cost.
For more information on Berding 3D Scanning visit >www.b3dscan.com
For more information on InnovMetric call (418) 688-2061. And for more information on Lockheed-Martin visit >www.lockheedmartin.com
