Aircraft OML Reverse Engineering Enables Complex CFD Analysis

A case study featuring Texas A&M University’s Flight Research Laboratory

Published: Monday, May 24, 2010 - 13:50

There are many reasons why firms need to model the exterior contour of existing aircraft outer mold lines (OML). Most aircraft flying today were not designed in a modern 3-D CAD system. Even with a current 3-D digital design, the actual as-built contour deviates from the intended shape, at least on some level.

In 2009, Direct Dimensions Inc. of Owings Mills, Maryland, was approached by Texas A&M University’s Flight Research Laboratory (FRL) with a challenging yet typical 3-D problem. The FRL, while primarily an active teaching facility, also offers both flight and wind-tunnel test services. This particular project was for a customer who had contracted the FRL to perform feasibility and conceptual design studies for a flight-test program using a business-jet-class aircraft.

This type of “virtual” aerodynamic testing, called “computation fluid dynamics” (CFD) analysis, requires a dimensionally accurate “as built” 3-D CAD model of this specific Gulfstream airplane. The FRL would also need additional 3-D models showing the plane in various configurations, such as with and without the engine and with and without the vortex generators.

Given the complexity of these specifications, the FRL contracted Direct Dimensions, a reverse-engineering company with 15 years of expertise in 3-D metrology technologies, specifically within the aerospace industry. The company’s extensive experience in creating accurate 3-D models for CFD analysis made Direct Dimensions uniquely suited to work on the team’s project.

During the course of three days, Direct Dimensions engineers worked on-site at NASA’s Forward Operating Location in El Paso, Texas, to scan the entire OML of the designated Gulfstream II. The airplane surfaces were captured using the uniquely accurate Surphaser HSX 3-D laser scanner. This scanner captured the shape to an accuracy of less than 1/4 of a millimeter, with extremely high data resolution. The ease of use and portability of the Surphaser allowed the large plane to be scanned from multiple positions to rapidly obtain all the data for the final CAD modeling process.

With the raw point-cloud data gathered during scanning, Direct Dimensions engineers then reverse engineered 3-D CAD models using PolyWorks, Imageware, and SolidWorks. These digital models allowed FRL to then “virtually” test the aircraft and design modifications in its CFD program and evaluate the suitability of the Gulfstream II for the test program.

Read more about the test program in this Aviation Week (March 2010) article, “NASA to Conduct Adaptive-Wing Trials,” by Guy Norris.

About The Author

Michael Raphael

Michael Raphael is founder and president of Direct Dimensions Inc., a Baltimore-based company offering a full range of 3-D imaging services including reverse engineering, dimensional inspection, and 3-D scanning. Direct Dimensions has been providing solutions for a wide range of fields from manufacturing, engineering, and design to art, sculpture, and architecture for nearly 15 years.