NASA tests laminar flow wing design that boosts fuel efficiency

Researchers at NASA have tested a wing design that aims to increase laminar flow on swept wings at transonic speeds this month.

The test at Armstrong Flight Research Centre attached a 3ft (1m) scaled model of the wing vertically under the belly of an F-15 testbed jet, which then reached a speed of 144mph (230km/h) during taxiing.

The wing is a concept NASA calls Crossflow Attenuated Natural Laminar Flow (CATNLF), which aims to increase laminar flow on swept wings at transonic speeds. Reducing laminar flow reduces wind resistance, saving fuel and money when operating commercial aircraft.

Laminar flow

During flight, a thin cover of air known as the boundary layer forms very near an aircraft’s surface. In this area, most aircraft experience increasing friction, also known as turbulent flow, where air abruptly changes direction.

These abrupt changes increase drag and fuel consumption. CATNLF increases laminar flow, or the smooth motion of air, within the boundary layer. The result is more efficient aerodynamics, reduced friction, and less fuel burn.

NASA’s Cross Flow Attenuated Natural Laminar Flow test article is mounted beneath the agency’s F-15 research aircraft (NASA/Christopher LC Clark)

NASA research done between 2014 and 2017 estimates that applying a CATNLF wing design to a large, long-range aircraft like the Boeing 777 increases laminar flow and could achieve annual fuel savings of up to 10%. Although quantifying the exact savings this technology could achieve is difficult, the study indicates it could approach millions of dollars per aircraft each year.

“Even small improvements in efficiency can add up to significant reductions in fuel burn and emissions for commercial airlines,” said Mike Frederick, principal investigator for CATNLF at NASA’s Armstrong Flight Research Center in Edwards, California.

Subsonic commercial aircraft applications

The CATNLF concept of was first developed by NASA’s Advanced Air Transport Technology project, and in 2019, NASA Armstrong researchers developed the initial shape and parameters of the model.

“Laminar flow technology has been studied and used on airplanes to reduce drag for many decades now, but laminar flow has historically been limited in application,” said Michelle Banchy, Langley principal investigator for CATNLF.

This limitation is due to crossflow, an aerodynamic phenomenon on angled surfaces that can prematurely end laminar flow. While large, swept wings like those found on most commercial aircraft provide aerodynamic efficiencies, crossflow tendencies remain.

In a 2018 wind tunnel test at Langley, researchers confirmed that the CATNLF design successfully achieved prolonged laminar flow.

“After the positive results in the wind tunnel test, NASA saw enough promise in the technology to progress to flight testing,” Banchy said. “Flight testing allows us to increase the size of the model and fly in air that has less turbulence than a wind tunnel environment, which are great things for studying laminar flow.”

CATNLF currently focuses on commercial aviation, which has steadily increased over the past 20 years, with passenger numbers expected to double in the next 20, according to the International Civil Aviation Organization. Commercial passenger aircraft fly at subsonic speeds, or slower than the speed of sound.

“Most of us fly subsonic, so that’s where this technology would have the greatest impact right now,” Frederick said. NASA’s previous computational studies also confirmed that technology like CATNLF could be adapted for supersonic application.

NASA ground crew prepares the agency’s F-15 research aircraft and Cross Flow Attenuated Natural Laminar Flow (CATNLF) test article ahead of its first high-speed taxi test (NASA/Christopher LC Clark)

CATNLF is being flight tested as part of the current program at Armstrong to evaluate the design’s performance and capabilities in flight.

In the future, NASA’s work on CATNLF could lay the groundwork for more efficient commercial air travel and might one day extend similar capabilities to supersonic flight, improving fuel efficiency at even higher speeds.

“The CATNLF flight test at NASA Armstrong will bring laminar technology one step closer to being implemented on next-generation aircraft,” Banchy said.

This article was originally published by NASA.