Learning from biodiversity's flying machines

Challenge: better aircraft design

Natural inspiration: seeds, birds and fliesWright brothers © US Federal GovernmentRAF Typhoon F1 jet fighter plane, © http://www.military-aircraft.org.uk/

 

 

 

Humans have dreamed of flying since very early in history.  Although the famous flight by the Wright brothers was in 1903, the first hot air balloon went up 120 years before, and art works recovered by archaeologists show that people imagined flying machines centuries earlier. 1  Today, flying is an integral part of the world's economy and culture.  In 2008, there were 77 million aircraft flights worldwide, including passenger flights, freight, military and general aviation. 2  In 2007, the global air freight sector facilitating worldwide trade had a value of 93.6 billion US dollars: it is  predicted to rise to $129.1 billion by 2012. 3  Flight technology has advanced to a level that would have been barely imaginable to the early inventors, with military aircraft in particular able to perform such feats as taking off vertically, travelling faster than sound, and becoming nearly invisible to radar. 4

 

 

 

 

Biodiversity, of course, invented flight much earlier than humans.  Many plants have seeds that are shaped for gliding, to increase the distance they can disperse.     However, gliding is not true flying. Insects were the first to evolve true powered flight, about 330 million years ago 5.  Flying evolved independently and later on in birds and bats. 6  Being able to fly gives various advantages, for example escaping from predators, catching prey or expanding to new habitats.

 

Maple seeds © Derek Ramsey Inventors working on flying machines have always looked to biodiversity for inspiration.  Igo Etrich in 1904 built a glider based on the winged seed of the Javan cucumber (Alsomitra macrocarpa). 7  Alsomitra seeds have continued to attract interest.  A study in 1987 showed that the falling seeds achieve a descent angle of just 12°, allowing them to travel a long way from the parent tree. 8  Other seeds that have inspired designers over the years include the maple, one of the well-known seeds that spins as it falls from the tree.  The latest maple-inspired design, unveiled in 2009, is a small remote-controlled device that can take off from the ground, perform controlled flight and hover. The design is directly based on the aerodynamic and geometric properties of the maple seed. This sort of device would be ideal for surveillance: for example it could search for earthquake survivors under collapsed structures, or transmit images of an unexploded bomb so that the bomb disposal experts could study it from a safe distance.swift in flight © Thomas Böder

 

 

Birds are an inspiring example of biodiversity's flying machines, and some of the most accomplished fliers are the swifts.  The common swift Apus apus is an extremely agile flier, swooping and diving at high altitudes to catch insects in flight.  These birds spend most of their lives in the air, only coming down to lay eggs: they even sleep on the wing. 10  Swifts spend the winter in Africa and visit Europe to breed. 10  Because of their wide geographic range and large population, swifts are not currently of global conservation concern. 11 However, within the UK they have recently been moved from 'green' to 'amber' conservation status because their breeding population is declining. 12 

 

 

NASA morphing aircraft (artist's impression) http://www.dfrc.nasa.gov/Gallery/Photo/index.htmlSwifts have taught designers a lot about efficient flying.  Part of the secret of swifts’ agility is their ability to change the shape of their wings while in the air.  Different wing shapes are best for different tasks.  For example, swifts extend their wings for slow glides to get more lift, but sweep them back for high-speed manoeuvres, enabling them to turn three times faster without breaking their bones. 13  This concept of ‘morphing’ is of great interest to the aviation industry.  In 2007, researchers built a micro airplane called the RoboSwift with shape-shifting wings inspired by swifts.  The device was able to keep up with a group of real swifts for 20 minutes (limited by its battery life): when mounted with a camera it could enable in-depth studies of swift biology. 14 Like the maple seed-inspired device above, it could also be used for ground-level surveillance.  Both NASA 15 and DARPA (the USA’s Defence Advanced Research Projects Agency) 16, among others, have invested in research programmes to explore the possibility of military aircraft that could change shape during a mission.  Currently, aircraft can be designed to be fast, agile, or fuel efficient, but there is always a trade-off between the different qualities.  A morphing aircraft could change its wing shape to suit the task at hand, whether it is taking off, dashing in a straight line, dodging or hovering.  Other advantages might include less noise and a smoother flight for passengers.  NASA carried out test flights of their ‘twist wing jet’ in 2003.  Morphing aircraft are still in the early design stages, using hinges and heavy, rigid materials.  State-of-the art lightweight materials and miniaturised computer technology will be needed before man-made aircraft can begin to rival the agility of the swift.  17

 

 

Dragonfly midair © Fir0002/Flagstaffotos http://commons.wikimedia.org/wiki/File:Dragonfly_midair.jpgAlong with birds, flying insects have always fascinated engineers.  Flight is believed to have evolved in insects only once 5, but since that first flying organism an incredibly diverse array of flight mechanisms has arisen. 18 Stoneflies simply raise their wings when they feel a breeze to sail across the surface of water.  19 Dragonflies, in contrast, can perform a wide variety of manoeuvres, as anyone knows who has watched them catching smaller insects.  As well as dashing and darting, they can hover and fly backwards, and are strong enough fliers to cross oceans. 20  Like most insects, dragonflies have two pairs of wings. They are able to move all four wings independently in a co-ordinated fashion, and like swifts their wings change shape in response to aerodynamic forces. 20  Dragonflies can out-manoeuvre modern helicopters. 21

 

 

fly and raindrops © Ellie CraneTrue flies (Diptera) have only one pair of functional wings.  The group includes many familiar insects, such as mosquitoes and house flies, and is found everywhere in the world except Antarctica. 22  Many researchers have investigated the mechanisms of flight in true flies over the years, using methods ranging from photographing tethered flies in wind tunnels, through to building and testing robots and computer models.  These studies have revealed a very complex picture of how flies fly, including a specialised movement of the wings called ‘clap and fling’ 23.  Scientists still do not fully understand how flies fly so well, and sophisticated studies are being carried out using computer modelling of the movements of the wings and the air around them. 24  Knowledge has advanced to the point where engineers can build ‘robot flies’ that perform in a similar way to the real thing.  In 2009, engineers built a micro-robot that combined the shape of a fly wing with the motion of a helicopter.  They found that by whirling the wing round rather than flapping it, they could use 50% less energy.  However, as the designers were quick to point out, the robot’s motor and energy storage are still nothing like as efficient as a real fly’s. 25, 26  Hang glider © Sam Segar, www.sxc.hu

 

 

 

Aviation science still has a lot to learn from biodiversity, but it seems certain that the dream of flight will continue to inspire scientists and engineers into the future.

 

 

 

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References

 

  1. History of human flight, FirstFlight website. Accessed April 2010.
  2. Airports Council International.  Accessed April 2010.
  3. Air Freight: Global Industry Guide.  Report Linker, November 2008.  Accessed April 2010.
  4. US Military aircraft.  Global Security website. Accessed April 2010.
  5. Evolution of flight website and references therein.  Accessed April 2010.
  6. Vertebrate flight exhibit, University of California Museum of Paleontology.  Accessed April 2010.
  7. Early flying wings (1870 - 1920) by E.T. Woodridge.  On Century of Flight website.  Accessed April 2010.
  8. Azuma, A. et al. (1987) Flight of a samara, Alsomitra macrocarpa.   Journal of Theoretical Biology 129: 263-274
  9. Spiraling flight of maple tree seeds inspires new surveillance technology. A. James Clark School of Engineering,  October 2009.  Accessed April 2010.
  10. Swift fact sheet, Royal Society for the Protection of Birds.  Accessed April 2010. 
  11. Swift fact sheet, Birdlife International.  Accessed April 2010.  
  12. Swift fact sheet, British Trust for Ornithology.  Accessed April 2010.   
  13. Lentink, D. et al. (2007) How swifts control their glide performance with morphing wings.  Nature 446, 1082-1085
  14. Bird sized airplane to fly like a swift.  PhysOrg, July 2007.  Accessed April 2010.
  15. Morphing Aircraft Developments underway for eventual modern marvel of flight.  Dryden Flight Research Center, December 2003.  Accessed April 2010.
  16. Morphing Aircraft Stuctures, Defense Sciences Office.  Accessed April 2010.
  17. NASA's twist-wing jet explores a radical future, NASA June 2003.
  18. Srygley, R.B. et al. (2002) Unconventional lift-generating mechanisms in free-flying butterflies.  Nature 420: 660-664
  19. Marden, J.H. et al. (1995) Locomotor performance of insects with rudimentary wings. Nature 377: 332 - 334
  20. Dragonfly flight, by Richard J. Rowe (2004).  Tree of Life web project.  Accessed April 2010.  
  21. Janine M. Benyus. Biomimicry: Innovation Inspired by Nature.  Perennial, 2002.
  22. Diptera.  Tree of Life web project. Accessed April 2010.  
  23. Lentink, D. (2008) Exploring the Biofluiddynamics of Swimming and Flight. Wageningen University. 
  24. Lentink, D et al. (2009) Rotational accelerations stabilize leading edge vortices on revolving fly wings. Journal of Experimental Biology 212: 2705-2719
  25. Micro flying robots can fly more effectively than flies.  Science Daily, August 2009.  Accessed April 2010.