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The AeroShark film can currently cover 40% of the surface of a Boeing 777, and Lufthansa Technik hopes to increase that to 80%.
In the early 1970s, German biologist Wolf-Ernst Reif was studying sharkskin fossils when newly available scanning electron microscopes enabled him to discover small longitudinal grooves. He then found the same microstructures in the skins of contemporary fast-swimming sharks. When Reif spoke with Dietrich Wolfgang Bechert, a scientist working on turbulence at German aerospace center DLR, they understood the purpose of those microstructures, now known as riblets: They reduce friction drag by limiting contact between vortices in the turbulent boundary layer to the sharp tips of the microns-high grooves.
Fast-forward to November 2019. After three years of testing an adhesive film mimicking sharkskin, Lufthansa Technik (LHT) obtained the first supplemental type certificate (STC) to use it on the Boeing 747-400. Australian startup MicroTau began testing a competing riblet film two years later.
- Lufthansa Technik and MicroTau riblets reduce drag
- Older-generation widebodies can save 1% of fuel over a 10-hr. flight
As more aircraft types gain STCs, they may welcome a 1% or greater increase in fuel efficiency. Such enhancements during an aircraft’s service life usually come from engine upgrades. Many operators need to keep older aircraft in service longer due to new-build delivery delays, and they may appreciate a new way to cut their fuel bill.
LHT’s AeroShark is in service on 27 aircraft—mostly Boeing 777-300ERs and 777Fs, as well as four 777-200ERs and one 747-400. The film consists of prism-shaped 50-micron riblets. Installing the adhesive film involves placing the riblets at various angles to follow the airflow. As AeroShark is designed for the cruise phase, it is more suitable for long-haul flights than short hops, LHT engineers say.
Starting at Door 1, the film covers the entire aircraft length. Viewed from the front, the film covers three-quarters of the fuselage, as well as the nacelles, leaving the crown area free. On a 777-300ER, the film covers more than 900 m2 (9,700 ft.2), including 50 m2 for each nacelle, says Jens-Uwe Mueller, product sales lead for Aeroshark.
The crown area is trickier, Mueller explains. “Because of the aircraft’s slightly nose-up attitude in cruise flight, the film would have less influence in the area,” he says. “Moreover, we would have to certify the fact the film does not negatively impact the airflow on the stabilizer. And it is even harder to install on the crown.” The film currently covers 40% of the surface of a 777, and Mueller hopes to increase that proportion to 80%.
AeroShark adds some 150 kg (330 lb.) to the 777. LHT estimates it provides 1% in fuel savings on a 10-hr. flight. The return on investment comes after 2-3 years, depending on aircraft utilization, fuel price and installation costs, which themselves vary with labor costs at the modification center, Mueller says.
LHT is now designing a version for the Airbus A330. The A321XLR also could be an interesting target for future developments, as an AeroShark modification could squeeze out extra range, Mueller says.
The company has received more than 50 orders since product launch, the 27th and 28th of which are undergoing modification. The first installation is approaching six years of use and shows little to no deterioration, an LHT spokesperson points out.
Meanwhile, MicroTau is working toward obtaining STCs for its Riblet Modification Package on commercial aircraft, beginning with the Airbus A320 and Boeing 767. The startup plans flight testing and certification on the A320 in cooperation with JetStar Airways within the next 12 months, founder and CEO Henry Bilinsky says. The 767 is to fly with riblets next year, and MicroTau has partnered with Delta Air Lines to obtain FAA certification.
MicroTau flight-tested its package on a U.S. Air Force Lockheed Martin C-130J airlifter in December with funding from the Pentagon’s Defense Innovation Unit. In 2021, the first trials with a riblet film applied on the wing of a Zivko Edge 540 aerobatic aircraft showed a speed improvement equating to a 1-2% reduction in drag throughout the flight profile. MicroTau is planning on a fuel-burn reduction of up to 4% on commercial aircraft.
MicroTau’s manufacturing process allows for fabrication of more complex riblet patterns, Bilinsky says. The company can produce 3D riblets with a continuously variable cross-section or print multiple concurrent riblet geometries on a single film substrate, enabling it to conform to local airflow streamlines.
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