Using bionics to reduce noise levels – silent flight inspired by owls
Bionics is an important area of research in order to optimise components especially in the aerospace industry. Owls’ wings have already attracted scientific attention and their analysis may make it possible to create planes and helicopters for the future that will fly virtually silently. Initial findings in relation to aerodynamics and noise emissions have already been implemented by the aviation industry.
One of the founders of bionic research in the 1960s was Professor Werner Nachtigall from Saarbrücken in Germany, who made the topic popularly accessible. The professor’s research focused on the way birds and insects fly, drawing conclusions for the use of natural “templates” for modern technology. Since then, many qualities that have evolved in nature have been implemented using technology, such as winglets – upright wingtips on passenger aircrafts – which are derived from the shape of storks’ wings. Or, what about the aerodynamic qualities of sharks’ skin, which serves as the inspiration for coatings on aircraft?
Currently, another animal has attracted the attention of scientists, even though it is rarely encountered face-to-face. Owls, and their unusually quiet and efficient flight, are the subject of scientific curiosity as, during an era of constantly increasing air traffic, a vitally important goal is a drastic reduction in noise levels. One thing is clear: to ensure that all flights are dispatched according to schedule in future, night flights (and takeoffs and landings in particular) cannot be avoided. However, these will only be possible if flights are quiet enough. While modern aircraft engines already play a role in minimising noise emissions, air turbulence around the wings continues to generate a level of noise that should not be underestimated.
Drawing inspiration from the silent flight of owls, it may soon be possible to reduce aircraft noise emissions
This is a concern that could be solved by adopting characteristics found in owls’ wings. When owls are observed hunting for prey, one particular thing strikes the observer: the beating of their wings is almost impossible to hear. While this fascinates us as human observers, it represents a significant biological advantage for owls, as they blend into background noise for their prey, meaning that the birds can hunt efficiently and, above all, successfully. Owls’ wings have at least three characteristics that contribute towards the silence of their flight. As such, their wings feature a ridge of extremely stiff feathers on the front, flexible fringes on the opposite side of the wing, and an extremely soft, almost downy layer on the upper surface of the wing.
Fascinating aspects of owls’ wings
In respect of owls’ wings the scientific field of bionics is still undertaking basic research. Even though a variety of teams are working intensively to research the characteristics of these silent, nocturnal hunters, there are no imminent breakthroughs that could lead to practical applications in the short term. However, theoretical research demonstrates that the fine, thoroughly flexible structure on the tips of owls’ wings have a significant impact in terms of reducing noise levels during flight. Owls’ wing tips are formed by many small, ultra-fine and densely placed feathers; however, we do not yet know the exact influence of these wing tips on noise levels. The assumption is that these feathers reduce noise emissions from collisions between air currents created by the upper and lower surfaces of the wings.
The upper surfaces of owls’ velvety wings are also being examined by scientists. This structure – which can be likened to that of a carpet – is currently the least-researched aspect of the wing and researchers suspect that this structure eliminates noise in a hitherto completely unknown manner, quite different from that of other noise-reducing materials. The stiff ridge of feathers on the leading edge of the wing is also being researched intensively, with current opinions suggesting that this ridge works in conjunction with the velvety soft upper surface to create micro-turbulence that improves the adhesion of air currents.
The unique characteristics of an owl’s wings cause them to flap almost silently
Current scientific opinion suggests that it will take more than 20 years until these discoveries can be put into practice in the aircraft industry. The reason: the so-called Reynolds number. In fluid dynamics, this measures the ratio of inertial forces to viscous forces of specific objects. It would only be straightforward to apply the findings of bionic research into to the aircraft industry if owls and aircraft had the same Reynolds number. However, the Reynolds number of an owl's wing is smaller than that of an aircraft wing.
On the other hand, some findings from research into owls’ wings are already being used in everyday life. One turbine manufacturer is using owls’ wings as a model for particularly silent products, inspired by the ridge on the front edge of wings, and applying the findings to fan blades in turbines, successfully reducing operational noise levels as a result.
A quiet axial turbine inspired by owls’ wings
It is also conceivable that the principles behind owls’ wings could be applied on a larger scale in the near future. Wind turbines and their rotor blades could be developed using natural principles in a few years’ time, resulting in even quieter operational performance. Once the principles of reducing turbulence in the wing surfaces of owls are fully understood, it is possible that this could be applied to the surfaces of cars or trucks. One thing is certain: the research and development departments of all major aircraft, car, truck, and ship manufacturers are showing great interest in the wider field of bionics and its findings, as well as ways in which these could be applied to technology.
What the future holds
People have been learning from nature since the dawn of time. Whereas we once learned to develop fundamental items from the natural environment (such as the wheel, which was derived from observations of rocks rolling downhill), modern science is concerned with making existing technology even more efficient, even quieter, and even better than ever by using natural influences. People, however, have one decisive disadvantage compared to nature: time. Whereas nature had millions of years to create optimal conditions through trial and error, we must repeat this achievement over the course of just a few decades.
Nevertheless (and all researchers agree on this point) we will be able to translate the advantages that owls’ wings offer to our everyday life within the next few decades. The aerospace industry has an interest in low-noise, high-efficiency aircraft – and is providing appropriate financial resources for research. The automotive industry is also seeking noise-reducing surface structures – as these provide a significant distinguishing factor and a decisive competitive advantage.
ARTS is also looking for committed team members who can contribute to the evolution of the aviation and aerospace industries, and who can work with our customers to develop a decisive competitive advantage. ARTS’ organisational alignment allows it to act as a partner to the aerospace industry and actively works to build the future. If you are interested in a dream job in research and development (with the possibility of being involved in breakthrough research into owls’ wings), one of our job offers may be of interest to you.