Wing and fin motions share universal principles

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Most animals that fly or swim bend their wings or fins in similar geometrical proportions and by similar angles, a study says. The seemingly universal principle, which applies to creatures as diverse as moths and sharks, holds lessons for researchers designing devices that propel themselves through air or water. The work is published today in Nature Communications.

The quest to develop flying machines based on the aerodynamics of flapping wings is hampered by a lack of information about how birds achieve stability and control. So even though the earliest dreams of human flight, from the story of Icarus to the designs of Leonardo da Vinci, attempted to emulate birds, practical designs from the Wright brothers onwards have focused on the stationary aerofoil wing. Working flapping-wing devices have been built only very recently.

Scientific opinion has varied on whether the fact that animal wings are flexible, rather than rigid like the wings of an airplane, helps or hinders the production of thrust. John Costello, a biologist at Providence College in Rhode Island, and his colleagues thought that the flexibility might be key to natural fight, so they decided to look at just how real animal wings deform.

Feathers and fins
They suspected that similar bending effects would be evident in wings and in fins and flukes used for propulsion in water. In fact, they were initially motivated by their work on a project for the US Office of Naval Research to develop a biologically inspired “jellyfish vehicle”. That work, says Costello, showed that “the addition of a simple passive flap to an otherwise fairly rigid bending surface resulted in orders of magnitude increases in propulsive performance”.

Written By: Philip Ball
continue to source article at scientificamerican.com

25 COMMENTS

  1. @OP – Most animals that fly or swim bend their wings or fins in similar geometrical proportions and by similar angles, a study says. The seemingly universal principle, which applies to creatures as diverse as moths and sharks, holds lessons for researchers designing devices that propel themselves through air or water.

    Who better to explain this than David Attenborough!

    BBC Life – Flying Fish – http://www.youtube.com/watch?v=9uFjmeWnFZ4

      • In reply to #5 by Light Wave:

        In reply to #2 by aquilacane:

        I would expect flexibility is the key to absorbing and creating energy whereas rigid is rigid.

        That notion seems to contradict the first law of thermodynamics…

        Absorbing and releasing energy then?

  2. One major difference is that fins operate in an incompressible medium, water, and wings operate in a compressible medium, the atmosphere. This does create design and operational differences.

    • In reply to #7 by Paris Price:

      Being a plane pilot, sailor and boat builder… duh

      To illustrate the difference, and you are obviously qualified to do so, consider a sailing yacht, which may be thought of as a very strange aeroplane, that flies sideways, with one wing in the water, and one wing in the air. The chord section and area of the wing in the air can be altered to suit conditions, and the wing in the water is fixed, although it may be pivoted (rudder) in the yaw axis to control direction.

      Their interrelationship, an ongoing fascination for all yotties, shows more and more about their differences than their similarities.

      • In reply to #14 by Sheepdog:

        In reply to #8 by Paris Price:

        Bernoulli’s Law of 1738 is old news.

        Strictly speaking, it’s a principle, not a law, and anyway, 1738, were you there to see it? 😉

        See what? That Bernoulli wrote his book, or the Wright Brothers using wing warping to steer their plane.

        Best

        • In reply to #18 by Paris Price:

          In reply to #14 by Sheepdog:

          In reply to #8 by Paris Price:

          Bernoulli’s Law of 1738 is old news.

          Strictly speaking, it’s a principle, not a law, and anyway, 1738, were you there to see it? 😉

          See what? That Bernoulli wrote his book, or the Wright Brothers using wing warping to steer their pla…

          Sorry, maybe I was being a bit obscure. “Were you there to see it?” is Ken Ham’s favorite line whenever he can come up with nothing better.

      • In reply to #14 by Sheepdog:

        In reply to #8 by Paris Price:

        Bernoulli’s Law of 1738 is old news.

        Strictly speaking, it’s a principle, not a law, and anyway, 1738, were you there to see it? 😉

        Yes it is a principle not a law. I also like to call Gravity a law, because judge, jury and executioner are always swiftly at hand. 😉

        Best

  3. I applaud any further reseach into flight in animals. However I consider the idea of flapping aircraft frankly silly. Flapping clearly works very well in birds but imagine flying in an aircraft with flapping wings. Turblence already makes flight in fixed wings unbearable in rough weather or hot days (rotorcraft use flapping hinges -invented for autogiros) which automatically compensate for differences around the rotor disk so are far less nausiating in rough conditions. But imagine adding flapping to the process then the stresses and fatigue issues. No a nice natually flexable spar and an electric motor or jet will be the ultimate in travel experience in the air for us – rotorcraft at slow speed and fixed wings at higher speeds. No, the invention of the bearing is a much nicer idea.

  4. “the addition of a simple passive flap to an otherwise fairly rigid bending surface resulted in orders of magnitude increases in propulsive performance”.. . .this reminds me of the effect of wearing fins to ones feet while swimming, snorkelling or scuba diving, though obviously most of the advantage comes from increased surface area.

  5. OP

    …thought that the flexibility might be key to natural fight

    Fanciful rubbish.

    Adaptability was the key to natural flight, whereas revolutionary propulsion systems will be the key to more efficient mechanical flight. This is mere science fiction from a biologist with insufficient grounding in fluid dynamics and who has likely never heard of a Reynolds Number (Re).

    Reckless Monkey is being reasonable to predict a flying wing or blended body device using revolutionary powerplants as the probable next generation of flight, although decades away yet. Bearing research will be more productive than mining nature for novel solutions.

    The applied science of aerodynamics is already mature and unlikely to benefit from biomimickry, save for miniaturised bots or tiny recreational models. Nature used what’s available to modify for purpose but has never evolved flight for animals weighing many tons. No clues there, not even for the marvelous Janine Benyus. Sheepdog could probably design a whale’s shape to be more hydrodynamically efficient than nature has managed to do.

    If any substantial, aerodynamically advantageous improvement remained available to be discovered then either Airbus or Red Bull’s Adrian Newey would have already applied it. Material sciences (better bearings) will improve planes incrementally for decades before novel replacement designs will replace them.

    The best aircraft designs have been explored and deployed. Airliners resemble each other because of design imperatives to realize maximum efficiency. Military fighters were fully mature when the Russians produced the Su-35 and the British their Harrier. Subsequent “Generations” of military aircraft suffer from inferior performance due to the incorporation of an imaginary quality, invented by marketing, called Stealth, which is merely a euphemism for camouflage.

    • In reply to #16 by Len Walsh:

      OP

      …thought that the flexibility might be key to natural fight

      Fanciful rubbish.

      Adaptability was the key to natural flight, whereas revolutionary propulsion systems will be the key to more efficient mechanical flight. This is mere science fiction from a biologist with insufficient grounding in…

      I agree. I don’t even know what “natural flight” is. Everything is natural. There are only things that are common.

      Best

    • In reply to #16 by Len Walsh:

      Sheepdog could probably design a whale’s shape to be more hydrodynamically efficient than nature has managed to do.

      Thanks for the compliment, but when I look at a Killer Whale, I think I know my limits. Apart from pure hydrodynamics, add the apparent pressure pulsing of the skin, that effectively removes any static boundary layer, and therefore a large drag component, the sophistication of the body shape gets even better.

      Then add the ancillary systems, fuel range, diving depth, guidance system, and relatively small size, and the final clincher, they make themselves. They don’t even need a shipyard. Nor before the YEC’s chime in, do they need God. And something for the YEC’s to ponder, there is no benefit really to horizontal tail flukes for propulsion over vertical. Sharks do just fine with a vertical tail fin. It is an indication, as if we needed another, that whales returned to the water from land, and evolved from a new starting point. Their horizontal tale flukes may be just that, a “fluke” (sorry) of evolution that flowed from the muscular structure of a land animal. Were intelligent design involved, what is intelligent about changing the perfectly workable and proven existing arrangement in sharks?

      And in response to another post that said that evolution could not produce a flying animal that weighed in the order of tons, please bear in mind that whales and fish and seals do fly, they just do it water, not air, and whales in particular are very heavy when out of the water. It is just that mass law, and Reynolds numbers limit the size of airborne animals. It is not so much weight that is the limit as the ratio of body mass to the mass and viscosity of the supporting atmosphere, liquid compared to gas.

      It is also interesting the extent to which the latest “Astute” class of British submarines, and the “Trafagar” class before them even more so, mimic the fore body shape of a sperm whale.

      • In reply to #24 by Sheepdog:

        In reply to #16 by Len Walsh:

        Thanks for the compliment, but when I look at a Killer Whale, I think I know my limits. Apart from pure hydrodynamics, add the apparent pressure pulsing of the skin, that effectively removes any static boundary layer, and therefore a large drag component, the sophistication of the body shape gets even better.

        There is also an interesting feature where the underwater “flight” of penguins gains a boost in speed by releasing bubbles from their feathers to reduce drag.

        Penguins fly underwater like supercavitating rocket torpedoes

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