Thursday, March 02, 2006

Scientist Uses Dragonflies To Better Understand Flight

Another older article from my backlog, with my comments bold and in square brackets.

Scientist Uses Dragonflies To Better Understand Flight, ScienceDaily/Cornell University, February 21, 2006 If mastering flight is your goal, you can't do better than to emulate a dragonfly. With four wings instead of the standard two and an unusual pitching stroke that allows the bug to hover and even shift into reverse, the slender, elegant insect is a marvel of engineering. [What did she say, "a marvel of engineering"? By a Cornell professor at an AAAS seminar? Call the thought-police! Tell her that the DC (Darwinistically correct) terminology is "apparent engineering. Strike one!]

Z. Jane Wang, professor of theoretical and applied mechanics at Cornell University, presented her research on flying systems and fluid dynamics today (Feb. 19) at the annual meeting of the American Association for the Advancement of Science. In a seminar "Falling Paper, Dragonfly Flight and Making a Virtual Insect," she said the best way to learn about flight is by first looking at what happens naturally. … Conventional wisdom holds that airplanes (airfoils) are more efficient because they travel from point to point with no wasted up-and-down motion. … "Of all these paths, are any better than a straight line? Some are -- that's what I found." The insight came from dragonflies. "Dragonflies have a very odd stroke. It's an up-and-down stroke instead of a back-and-forth stroke," she said. "Dragonflies are one of the most maneuverable insects, so if they're doing that they're probably doing it for a reason. [Strike two! "A reason"? What "reason" could there be if dragonflies evolved by a mindless, `blind watchmaker' process, hundreds of millions of years before reason itself evolved in man? ]

But what's strange about this is the fact that they're actually pushing down first in the lift. "An airfoil uses aerodynamic lift to carry its weight. But the dragonfly uses a lot of aerodynamic drag to carry its weight. That is weird, because with airplanes you always think about minimizing drag. You never think about using drag." The next question, she said, is whether engineers can use these ideas to build a flapping machine as efficient as a fixed-wing aircraft. Questions of size and feasibility remain. "To hover well or to fly for a long time is hard, especially at slow speeds," she said. "Power is limited. So finding these efficient motions is very important." Still, Wang's work moves researchers a step closer to building such a machine. "I want to build insects on a computer as a way of learning why almost all things that move in fluid use a flapping motion," said Wang. "Whether it's a fish which flips its fins or a bird, they're actually using the same principle. "The way paper or leaves fall, and how insects fly, may give us some ideas about why animals use these methods at all," she said. ... [Strike three and out! There is no "why animals use these methods." (That is teleological, i.e. end, design, purpose). They just do!]

Seriously, insect flight is just as (if not more) marvellous than bird or bat flight and just as (if not more) difficult to imagine how it ever began. Here is another quote from my zoology textebook (in the context it is only talking about insects at that stage):

"Wings and the Flight Mechanism. Insects share the power of flight with birds and flying mammals. However, their wings have evolved in a different manner from that of the limb buds of birds and mammals and are not homologous with them. Insect wings are formed by outgrowth from the body wall of the mesothoracic and metathoracic segments and are composed of cuticle. Most insects have two pairs of wings, but the Diptera (true flies) have only one pair, the hindwings being represented by a pair of small halteres (balancers) that vibrate and are responsible for equilibrium during flight. Males in the order Strepsiptera have only the hind pair of wings and an anterior pair of halteres. The males of scale insects also have one pair of wings but no halteres. Some insects are wingless. Ants and termites, for example, have wings only on males, and on females during certain periods; workers are always wingless. Lice and fleas are always wingless. Wings may be thin and membranous, as in flies and many others; thick and horny, as in the forewings of beetles; parchment-like, as in the forewings of grasshoppers; covered with fine scales, as in butterflies and moths; or with hairs, as in caddis flies. Wing movements are controlled by a complex of muscles in the thorax. Direct flight muscles are attached to a part of the wing itself. Indirect flight muscles are not attached to the wing and cause wing movement by altering the shape of the thorax. The wing is hinged at the thoracic tergum. and also slightly laterally on a pleural process, which acts as a fulcrum, In all insects, the upstroke of the wing is effected by contracting indirect muscles that pull the tergum down toward the sternum. Dragonflies and cockroaches accomplish the downstroke by contracting direct muscles attached to the wings lateral to the pleural fulcrum. In Hymenoptera and Diptera all flight muscles are indirect. The downstroke occurs when the sternotergal muscles relax and longitudinal muscles of the thorax arch the tergum, pulling the tergal articulations upward relative to the pleura. The downstroke in beetles and grasshoppers involves both direct and indirect muscles. Contraction of flight muscles has two basic types of neural control: synchronous and asynchronous. Larger insects such as dragonflies and butterflies have synchronous muscles, in which a single volley of nerve impulses stimulates a muscle contraction and thus one wing stroke. Asynchronous muscles are found in the more specialized insects. Their mechanism of action is complex and depends on the storage of potential energy in resilient parts of the thoracic cuticle. As one set of muscles contracts (moving the wing in one direction), they stretch the antagonistic set of muscles, causing them to contract (and move the wing in the other direction). Because the muscle contractions are not phase-related to nervous stimulation, only occasional nerve impulses are necessary to keep the muscles responsive to alternating stretch activation. Thus extremely rapid wing beats are possible. For example, butterflies (with synchronous muscles) may beat as few as four times per second. Insects with asynchronous muscles, such as flies and bees, may vibrate at 100 beats per second or more. The fruit fly Drosophila ... can fly at 300 beats per second, and midges have been clocked at more than 1000 beats per second! Obviously flying entails more than a simple flapping of wings; a forward thrust is necessary. As the indirect flight muscles alternate rhythmically to raise and lower the wings, the direct flight muscles alter the angle of the wings so that they act as lifting airfoils during both the upstroke and the downstroke, twisting the leading edge of the wings downward during the downstroke and upward during the upstroke. This modulation produces a figure-eight movement that aids in spilling air from the trailing edges of the wings. The quality of the forward thrust depends, of course, on several factors, such as variations in wing venation, how much the wings are tilted, and how they are feathered. Flight speeds vary. The fastest flyers usually have narrow, fast-moving wings with a strong tilt and a strong figure-eight component. Sphinx moths and horse flies are said to achieve approximately 48 km (30 miles) per hour and dragonflies approximately 40 km (25 miles) per hour. Some insects are capable of long continuous flights. The migrating monarch butterfly Danaus plexippus ... travels south for hundreds of miles in the fall, flying at a speed of approximately 10 km (6 miles) per hour." (Hickman C.P., Jr., Roberts L.S. & Larson A., "Animal Diversity," [1995], McGraw-Hill: Boston MA, Second Edition, 2000, pp.216-218. References removed. Emphasis original)

Which reminds me of Dawkins' `explanation' of "How did wings get their start?" His `just-so' story was about a "small animal" species which leaped "from bough to bough" with some falling to the ground, and natural selection favouring "slight, prototype wingflaps" to "break the fall":

"What use is half a wing? How did wings get their start? Many animals leap from bough to bough, and sometimes fall to the ground. Especially in a small animal, the whole body surface catches the air and assists the leap, or breaks the fall, by acting as a crude aerofoil. Any tendency to increase the ratio of surface area to weight would help, for example flaps of skin growing out in the angles of joints. From here, there is a continuous series of gradations to gliding wings, and hence to flapping wings. Obviously there are distances that could not have been jumped by the earliest animals with proto-wings. Equally obviously, for any degree of smallness or crudeness of ancestral air-catching surfaces, there must be some distance, however short, which can be jumped with the flap and which cannot be jumped without the flap. Or, if prototype wingflaps worked to break the animal's fall, you cannot say 'Below a certain size the flaps would have been of no use at all'. Once again, it doesn't matter how small and un-winglike the first wingflaps were. There must be some height, call it h, such that an animal would just break its neck if it fell from that height, but would just survive if it fell from a slightly lower height. In this critical zone, any improvement in the body surface's ability to catch the air and break the fall, however slight that improvement, can make the difference between life and death. Natural selection will then favour slight, prototype wingflaps. When these small wingflaps have become the norm, the critical height h will become slightly greater. Now a slight further increase in the wingflaps will make the difference between life and death. And so on, until we have proper wings." (Dawkins R., "The Blind Watchmaker," 1986, pp.89-90)

Well, since Dawkins is a zoologist, he must know that wings got their start with insects and being so light they would never have had a problem of falling from trees and being killed.

And Dawkins is also obviously wrong with his unsubstantiated claim that "there is a continuous series of gradations to gliding wings, and hence to flapping wings." Just consider in the quote above the muscular and neural controls necessary for powered flight. And just consider the Wright Brothers. Their first powered flight was not a mere slight incremental advance on gliding. Powered flight required a major, discontinuous increase in complexity over gliding. ]

Stephen E. Jones, BSc (Biol).
"Problems of Evolution"

No comments: