The imitation of sharkskin on aircraft surfaces can lead to a significant reduction in friction and, consequently, an increase in efficiency.
As we all know, nature is a source of reference and inspiration to find solutions to technological problems we are confronted with on a daily basis.
Can you imagine a shark with wings? Obviously it is something far from reality, but what is certain is that the skin of the king of the oceans could be key in aeronautics for reduce aircraft fuel consumption thanks to increased efficiency.
But before going into the details of how this idea would be possible, it is necessary to understand what is special about a shark for its rapid movement in the aquatic environment.
The first thing that catches the eye is their streamlined shape, common with all other fish, which allows them to move very quickly with a minimum expenditure of energy. But in their case, the secret to being the fastest is also in their skin. It is not for nothing that the world's fastest aquatic species is the mako shark, which can travel up to 124 kilometres per hour.
I'm sure you've seen many sharks through photos or videos, but to understand how their skin helps them to be so fast you have to put it under the lens of a microscope. Paradoxically, the same skin that helps it to be faster when moving through fluid turns out to be very rough to the touch. It's very similar to the sensation you would get if you were stroking sandpaper. This is because they are not scales like the conventional scales you would see on any other fish, but rather they are tooth-shaped plates.
The "placoid" scales of sharks have a striking feature: fine raised ridges, or "ribs", along the length of each scale. These ribs are aligned in such a way that they form small ridges that run lengthwise along the shark's body. Although the ridges are only a few micrometres long, it has been demonstrated that reduce friction when the shark swims, being able to swim faster using the same amount of energy.
In the same vein, it has been shown that sharks that swim more slowly due to the needs of the environment in which they live have fewer ridges on their elongated, pointed scales.
The study of shark skin was initiated in 1970 by the German palaeontologist and evolutionary biologist Wolf-Ernst Reif, who emphasised the reduced flow resistance produced by shark scales. Finally, after almost half a century, a promising new development has begun with the application of this technology in aeronautics.
The path has not been easy, prototypes have been tested with different materials and positioning of the denticles, and 3D printers have been of great help in helping the project to reach reliable conclusions.
In the most recent studies, laboratory reproduction of shark skin has yielded very clear data: friction with the surrounding fluid is reduced very significantly.
In an experiment at Harvard University, researchers concluded that such a structure can achieve a speed increase of up to 6.6% while reducing the energy required to achieve it.
To reach this conclusion, they glued samples of an artificial shark skin to both sides of a flexible sheet. The idea was that the sample could stand still in a flow of water or simulate the movement of a shark. They then measured the forces exerted alternately on the still and moving film.
The result was that the sharkskin imitation reduced friction by 8.7% when the water flowed at low velocity. At higher flow velocity, the sharkskin produced 15% more drag than a smooth membrane. However, when the sheet was moved to simulate the movement of a fish as it moved, the performance of the shark skin improved significantly, increasing speed by 6.6% with a reduction in energy expended of 5.9%..
It could be said that it decreases the resistance to the advance of your body to the make it difficult for the surrounding fluid to adhere to it on the surface of their skin due to the space between each denticle.
For this reason, the initial studies on this animal created so many expectations in relation to the applications it could have. Its main characteristics became clearer following studies at Harvard University (Cambridge) and Emory University (Atlanta), which were:
- Reduction of friction,
- Increased speed,
- Reduction of energy costs.
The first relevant applications of designs emulating sharkskin were in swimming costumes used by professional swimmers. Such were the spectacular results obtained during the 2008 and subsequent Olympic Games that they led to the banning of certain types of fabrics in these competitions.
But its evolution did not stop there, as the enormous possibilities offered by this technology for the naval and aeronautical industries were realised from the very beginning.
And focusing on the latter, the German airline Lufthansa was the first to make a serious commitment to this technology.
In 2019, the first tests were carried out on a part of the fuselage of a Boeing 747-400 of this company, resulting in a reduction of friction on the aircraft of up to 0.8%.
It might not seem very relevant, almost imperceptible. But if we take into account the number of hours an aircraft is in operation, the calculations indicate a annual savings of many tonnes of fuel. This would not only have a positive impact on the economics of any airline, but also on the reduction of the carbon footprint, an essential subject for the coming decades in aeronautics as in all other industries.
After the hiatus of the coronavirus pandemic, research is continuing to expand this technology to other parts of the aircraft and other aircraft models. The world's major manufacturers also have open projects in this direction.
If it is feasible to extend this technology to the entire aviation fleet, it would save a large amount of fuel, a further step towards the milestone of reducing the aviation carbon footprint to zero by 2050.
Although there is still a long way to go in developing this research, the results are optimistic for the future, where airlines could improve their economics while advancing the decarbonisation of the aviation industry. It could be called a total "win to win".
A few months ago Lufthansa Technik shared a video explaining some of the features and advantages of this proposal to improve aircraft efficiency. You can watch it by clicking click here.
