For Release: Oct. 8, 1996
Headquarters, Washington, D.C.
Dryden Flight Research Center, Edwards, Calif.
Langley Research Center, Hampton, Va.
Flight Experiment Smoothes Flow Over Supersonic Wings
In a series of flight tests, NASA engineers have smoothed the flow over the surface of an F-16XL wing flying at supersonic speeds (faster than sound), bringing to a successful conclusion a historic achievement in high-speed aerodynamics.
"Supersonic laminar flow control has been called the "holy grail" of aerodynamics, because it's the last frontier that can offer significant drag reductions and save airlines, and eventually the flying public, a great amount of money," said Jeffrey Lavell, project manager of the F-16XL Supersonic Laminar Flow Control (SLFC) experiment at NASA Langley Research Center, Hampton, Va.
As an aircraft flies, the friction between the air and the wing creates drag, or resistance, called skin friction drag. Skin friction drag accounts for about half of the total drag on an aircraft. When airflow over the wing becomes turbulent and separates from the wing, skin friction drag increases. Laminar flow, a condition where the airflow over the wings remains smooth and close to the wing, greatly reduces skin friction drag. Smooth, or laminar, flow over a wing can reduce drag and contribute to reduced operating costs by improving fuel consumption and lowering aircraft weight.
The objective of the flight tests, part of NASA's High-Speed Research (HSR) program, was to demonstrate that laminar flow could be achieved over a significant portion of a supersonic wing. "We've had terrific results," Lavell said. "We've obtained a large amount of data that can be used to refine our design codes and provide the US aircraft industry with the means to design SLFC wings."
Lavell said that the project's objectives were met, although exact details of the amount of laminar flow achieved and with what amount of suction is restricted information. The US aircraft manufacturers may compete with aircraft manufacturers from other countries someday, and SLFC technology could create a considerable competitive advantage.
This successful method of maintaining laminar flow could be incorporated into the design of a future High-Speed Civil Transport (HSCT), a conceptual supersonic airliner of the future that would carry 300 passengers at 2.4 times the speed of sound.
Flights with the SLFC experiment at NASA Dryden Flight Research Center, Edwards, Calif., used an F-16XL, which has a large delta wing. The wing's shape is similar to the design that likely will be used on the HSCT, making the F-16XL an excellent testbed for the laminar flow research project.
A large, titanium panel, perforated with more than 10 million laser-cut holes, was attached to the upper surface of the F-16XL's left wing. Natural aerodynamic drag on an aircraft wing is caused by the friction of a thin turbulent layer of air moving across the wing's surface. During research flights, a suction system pulled a portion of that thin layer of air through the glove's porous surface to keep the airflow over the wing from becoming turbulent.
Without any means of control, the flow over a highly-swept supersonic wing is laminar for only a few inches. By perforating the skin of the glove and providing suction through the perforations, the airflow can remain stable and laminar flow can be extended over most of the wing.
NASA flew approximately 40 flights over a twelve-month time span, and achieved "a significant amount of laminar flow," according to Lavell. Most of the research flights were at speeds of Mach 2 (approximately 1,400 mph) and altitudes of 35,000 to 55,000 feet, which is close to the proposed range for the future HSCT.
The HSR SLFC experiment represents a collaborative effort between NASA and the US aerospace industry. A team composed of Boeing, Rockwell and McDonnell Douglas designed the wing panel and suction system. The panel was assembled at a Boeing facility in Seattle, Wash., while the suction system was fabricated by McDonnell Douglas in Long Beach, Calif.
NOTE TO EDITORS: A laminar flow fact sheet, a graphic of the SLFC concept and video b-roll are available by calling NASA Langley Research Center at (757) 864-6122. Photos of the F-16XL aircraft are available by calling NASA Dryden Flight Research Center at (805) 258-2665.
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