The International Air Transport Association (IATA) has asserted that the aviation industry will be entirely carbon neutral by 2050.
Sustainable aviation fuel (SAF) is one part of the solution. Existing fossil fuels release carbon into the atmosphere from crude oil deposits accumulated over aeons. Instead SAF relies on plants extracting carbon already in the atmosphere, converting the resulting biomass into fuel which then returns the captured carbon back into the atmosphere in engine exhaust gases.
SAF is unlikely to be entire solution. I wrote about the potential for new airframe designs, including blended wings, to reduce carbon emissions in this column last year
The Lufthansa Group has been taking an entirely innovative approach to reducing emissions and fuel consumption in its existing fleet of commercial airliners, retrofitting a new technology to them which mimics how ocean sharks are able to swim fast.
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German palaeontologist and biologist Wolf-Ernst Reif first observed miniature grooves in the scales of sharks in the late 1960s. Together with Dietrich Bechert from the German national aerospace centre, a specialist in fluid mechanics, the pair found that the prevailing doctrine that the fastest surfaces need to be entirely smooth was in fact incorrect. Micro-grooves can reduce frictional resistance in fluids, as compared to smooth surfaces, by between 8 and 11 per cent.
In 2011, Lufthansa Technik in Hamburg started investigating whether sharkskin-like grooves could reduce air resistance in commercial airliners, and thus improve fuel efficiency. However, achieving this would be extremely challenging. High-speed air particles in-flight could degrade any grooving, as could extensive exposure to strong UV radiation at altitudes as well as just plain dirt. Any new surface would be exposed to temperatures of minus-60 degrees at flight cruise at high altitudes, and to ground temperatures of 45 degrees at some airports. Icing safeguards and flame resistance would also need to be verified. Naturally, regulatory approval would need to be given by the appropriate aviation safety authorities.
At first a sharkskin-like adhesive film was trialled as small test patches applied to aircraft surfaces, but had poor results. The team switched to painting on test patches, in which grooves were induced into the paint surface as it dried. A robotic application system was built, and part of a wing segment of an Airbus A330 tested under real in-service conditions. However, the approach was abandoned.
Then in 2015 Dr Kai-Christoph Pfingsten, a senior manager at Lufthansa Technik, discovered that the Red Bull air race team in Graz were successfully using thin-film sharkskin technology developed by a start-up, Bionic Surface Technologies, and an Austrian research institute, Joanneum Research. Sceptical at first, Dr Pfingsten mused about trying adhesive films once again, by adapting the more advanced technique identified by Bionic Surfaces. He approached BASF (a large chemical producer) to collaborate on scaling up the approach from small racing aircraft to full-size commercial airliners.
[ Decarbonising aviation will be a challengeOpens in new window ]
In 2017 the first tests of the new BASF shark film, now dubbed AeroShark, were made on a Boeing B747 at about 100 points using 15cm by 15cm patches. Then in October 2019 the entire lower fuselage of in-service B747 was covered with 500sq m of the film, requiring about 1,000 panels of film to be individually and carefully applied, almost as jigsaw pieces. The observed fuel savings were just under 1 per cent, considered an encouraging result.
To achieve the optimal orientation and positioning of the film patches, highly detailed computational fluid dynamic (CFD) models were built. Parked aircraft on the ground were digitally scanned by laser, and then augmented by photogrammetric captures of the flexing of wings in flight. The thin film patches require careful arrangement, avoiding areas susceptible to ice aggregation or foreign object damage, and avoiding maintenance and other panels. The CFD models, once available for a particular aircraft type, identify regions of the aircraft surface where the sharkskin film is likely to have the most benefit.
In 2021 and based on the results from the B747 with only its lower fuselage covered, Lufthansa Cargo and Swiss Air jointly decided to adopt AeroShark for the entire fuselages on many of their Boeing B777s, requiring about 800 to 950sq m for each specific aircraft. It took about a year for the European Union Aviation Safety Authority to certify the new technology as safe for commercial aviation.
The emissions reductions now being obtained are well over 1 per cent for each long-haul flight, equating on average to about 1,200 metric tonnes of carbon annually per aircraft. The fuel savings provide a return on investment in the AeroShark technology in about 18 months.
Currently 17 aircraft are equipped with AeroShark, including 12 B777s from Swiss Air and four from Lufthansa Cargo. Austrian Airlines have recently decided to retrofit most of their B777 fleet with AeroShark from next December. All three organisations are within the Lufthansa Group. Lufthansa Technik has said that multiple airlines are now in negotiations to adopt the technology.
It is interesting that nature is helping illustrate solutions to reduce carbon emissions in aviation.
Dr Pfingsten, and colleague Oliver Oeser, tell the story to date in detail here and here
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