Aviation continues in its inexorable search for fuel efficiency and emissions reduction, and a fascinating development from Lufthansa Technik, based on how sharks move at speed through the water, is offering savings of a full percent-plus aboard Boeing 777 aircraft. It’s called AeroSHARK, it’s a film with tiny protrusions 0.05mm high, and the scientists behind it think that, applied across more of the aircraft, it could save up to three percent of fuel — and emissions. We sat down with Jens-Uwe Mueller, project manager, commercial for AeroSHARK at Lufthansa Technik, to wind back the clock nearly fifty years from the story from discovery to implementation.
“AeroSHARK is a surface technology developed jointly by Lufthansa Technik and German chemical giant BASF,” Mueller tells us. “It consists of an adhesive film that is applied to the outer skin of an aircraft. The film features microscopic ribs around 50 micrometers in size — known as riblets. These riblets specifically imitate the properties of sharkskin, which is known to have particularly favourable flow characteristics, and thus optimises aerodynamics in relevant areas on the aircraft skin. As a result, friction and thus aerodynamic drag is reduced, less fuel is consumed and emissions are lowered.”
The fluid mechanics science — air is, scientifically, a fluid — behind this dates to a 1982 paper on the scale pattern in fast swimming sharks by German scientist Wolf-Ernst Reif using then-groundbreaking electron microscopes. Discovering tiny microstructures within the skin, Reif and other scientists, including Dietrich Bechert, developed their work in conjunction with the German Aerospace Center, the DLR. At the same time, independently, NASA scientist Michael Walsh was experimenting with using microscopic longitudinal grooves, now called riblets, in the direction of flow to reduce skin friction.
Fast-forward to 2011 and Lufthansa Technik entered a partnership with Fraunhofer IFAM and Airbus to research the effect of riblets on aircraft, followed by a research project funded by the German federal government on application via coating, and “the FAMOS project that aimed at ‘embossing’ the riblet structure into an additional painted surface,” Mueller outlines.
To start with, he notes, “we concentrated solely on materials and durability testing with small patches of several square centimeters. The major breakthrough came when we moved from the pure materials testing to real-world savings evaluation, for which significant parts of the aircraft skin need to be modified.”
As part of that research and development, Mueller says, “we tested around half a dozen different riblet film materials before we finally came up with the current state-of-the-art product. The challenge is: Not everything that works in a lab does also work in real-life operating conditions. Thus, we also performed extensive flight test campaigns with various material specimen over several years.”
The first minimum viable product (MVP1) for the film applied some 500 square metres of riblet film to the lower fuselage of a Lufthansa Boeing 747-400. The second minimum viable product (MVP2) is for the Boeing 777, and is currently applied on two variants: Lufthansa Cargo’s 777F (some 800 square metres on this shorter variant based on the 777-200LR, but without the need to avoid the cabin windows) and Swiss’ passenger 777-300ER (some 950 square metres thanks to its longer fuselage).
“The actual savings estimation for the MVP2-modified 777s is calculated to be around 1 percent for the 777F and 1.1 percent for the longer 777-300ER. For the latter, this translates into annual savings of around 400 metric tons of jet fuel and more than 1,200 metric tons of carbon dioxide, just for a single aircraft,” Mueller explains. “The first AeroSHARK-modified SWISS aircraft is currently used to validate these figures under real operating conditions in daily operations. Once the more than 20 Boeing 777s at Lufthansa Cargo and SWISS have all received their AeroSHARK modification, they are projected to reduce the Lufthansa Group’s carbon footprint by more than 25,000 tons annually.”
In an industry where reducing fuel burn and emissions by a percentage point is big news, it’s notable that this saving comes from covering less than half of these 777s’ surface in the riblet film. While some surfaces will inherently be unsuitable for modification, Lufthansa Technik estimates that riblets across almost the entire aircraft could reach some 2.5–3 percent savings if furhter development and certification efforts are successful.
“It is our intention to systematically develop this new technology further,” Mueller says. “One focus of future developments will be laid on extending the square meter size and aircraft skin percentage of the AeroSHARK modification in order to maximise its savings potential on the aircraft level. In addition, we want to design and certify riblet modifications for many more commercial aircraft types to assist airlines even better in reaching their sustainability goals and make maximum use of the technology’s savings potential on a global fleet level. Certification, however, is far from trivial, and it has to be performed for every aircraft type separately.”
Lufthansa Technik uses a variety of digital tools and methodologies to support the further development and certification, including extensive computational fluid dynamics calculations, computer-aided design, finite-element method simulations, layover planning tools and fuel saving validation software. The validation process includes real fuel flow data from Swiss and Lufthansa Cargo, via the AVIATAR digital technical operations platform from Lufthansa Technik. This platform, and the data that flows through it, help to eliminate coincidences or factors like weather, piloting and other externalities from the final efficiency figures.
Obtaining a supplemental type certificate in December 2022 from EASA, the European Union Aviation Safety Agency, the full rollout across the Lufthansa Group’s 777 fleet — the Cargo 777Fs and Swiss 777-300ERs — is now in full swing.
“Once the MVP2 savings are validated with the launch customers’ aircraft, our plan is to offer AeroSHARK to any interested 777F or 777-300ER operator in the world,” Mueller notes. “However, in our view, the current approach with adhesive films is by far the most promising technology for the desired large-scale modifications, at least in the mid-term.”
“The current AeroSHARK product is designed as a retrofit solution that can be applied during the usual heavy maintenance layovers of commercial aircraft — that is, a C-check,” Mueller concludes. “However, I see no reason why it could not be applied on factory-fresh aircraft as well. Thus, we are in active discussions with several aircraft OEMs [original equipment manufacturers] regarding further opportunities and perspectives for this fascinating technology.”
Author: John Walton
Published 21st February 2023
Image source – SWISS. Photographer -Reto Hoffmann
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