Mechanisms of locomotion of Flight in BirdsAbout 400 million years ago, the earth was populated by plants and tress; the air was moist, and the ground was covered with decaying leaves; and the insects began to appear (quoted in Fung 1990).
Birds came on the scene later, about 150 million years ago; the wing of birds and insects not only differ in size and structure, but also, in basic articulation mechanism. As stated by Fung (1990), the bone structure of a bird does not differ too much from that of a human arm; the bird moves its wings by muscle, so its flying muscles are big and strong. Powered flight has been evolved only by insects, birds, bats, and apparently the extinct pterosaurs (McNeill 2003).The aerial performance of flying animals is remarkable and has inspired human myth and experimentation over much of our history (Biewener 2003).
According to Biewener (2003), for comparison with the manmade flying machines that they inspired, the flight of a housefly at 3 m/s represents a speed of 430 body lengths/s; when normalized for size in this way, a fly achieves a speed that is more than 12 times greater than the speed of a high performance fighter jet and 80 times greater than the speed of a propeller-driven airplane. In addition to such spectacular performance, flight has proven a highly successful mode of life for a wide range of taxa, having contributed to the enormous success of insects, birds, and bats, which constitute the highest group of mammals; although more expensive than swimming, flight is a cheaper means of transport over a given distance than when moving on the ground particularly when changes in elevation must be negotiated (Biewener 2003). According to Biewener (2003), flight enables animals to migrate and forage over large distances, avoid harsh environmental conditions and thereby reach otherwise inaccessible forage sites, and also provides an exceptional means of predator defense as well as excellent access to prey and other food resources.For birds and larger insects in fast forward flight, the lift principle is similar to that of the airplane.
According to Fung (1990), many birds can also utilize the natural air currents to soar and to glide over long distances; the albatross can even take advantage of the wind shear over the ocean to spiral and soar with a little expenditure of energy. To understand the mechanism of flight, it is useful to compare birds and insects with helicopters and airplanes. Birds uses flapping motion for propulsion, hence their aerodynamics is predominantly unsteady; to understand their aerodynamic lift, thrust, moment and induced drag, we must think of the vortices shed into the airstream at the trailing edge of the wing, as well as the oscillatory horseshoe vortices which are bounded to the wing in the spanwise direction and shed into the wake in the streamwise direction (Fung 1990).Forward Flight of BirdsThe motion of the head wings is coordinated with that of the forewings; the forewing motion exhibits a phase lag behind that of the hind-wings.
This phase lag is characteristic of four-winged insects in general. Birds have been trained to fly along a 60m long to a cage as he photographed them with a high speed camera halfway along the passage; from these studies, it was found that pigeons can fly at a speed of about 10m/sec, wing beat frequency of about 5Hz (Fung 1990).The bird’s lift is probably acquired mainly on the down-stroke when the primary feathers are spread out, and the wing area is increased. Compared with insects, birds have a high power requirement per unit mass with an estimated power requirement for sustained pigeon flight of 20 W/kg, amounting to over 96% of the total metabolic rate and an oxygen consumption of over 130ml/min to sustain flight, in contrast to a resting metabolic requirement of only 5ml/min; thus the bird needs along that can handle a large variation in ventilation to meet the enormous variation in its energy requirement in life.
Aerodynamics of Wing assisted Incline Running in BirdsWing-assisted inclined running (WAIR) is a type of escape behavior in birds that consists of flapping the wing during climbing which is commonly used by ground dwelling species like Galliformes when they have access to slope terrain, and may also be common among nestlings of a diverse array of bird species (quoted in Tobalske 2007). As gravity controls the ‘force balance’ total lift in ‘steady-flapping flight’ is leaning mainly upward; on the contrary, in ‘WAIR’ it’s theorized that lift from the wing mainly as ‘thrust’ that accelerate body in the direction of the substrate surface being ascended, thus rising ‘friction’ and helping the feet to gain purchase.According to Tobalske (2007), even though ‘WAIR’ is an interesting ‘escape-behavior’ on mature birds, it appears as an intriguing action when consequences of ‘flap running’ are taken into consideration compare to the ‘ontogeny’, and probably the flight evolution. Bird species’ majorities are ‘altricial’ in their maturity, so juveniles depart the nest and soar for the first-time by means of ‘flight-feathers’ which are almost the same in the grown-ups.
In the study conducted by Tobalske and Dial (2007), they have noticed that Alectoris chukar utilized its wings to create ‘lift’ in ‘WAIR’ and the ‘impulse’ from ‘down stroke’ is adjusted so to speed up the animal’s body both toward and upward the ‘substrate’ it is ‘climbing’. Coupled with data from kinematic studies, their results revealed a wake dominated by the effects of lift production as in flapping flight in birds rather than a drag-based wake such as might be produced by a paddling motion. According to Tobalske and Dial (2007), an case of factor of fast ‘wake decay’ seems destabilized by current findings, that enough ‘circulation’ is can be seen in the ‘wake’ of flying-birds to explain for ‘weight-support’; conversely, in WAIR, it is probable that closeness of the ‘substrate’ influenced ‘wake-dynamics’ & might have amplified ‘vortex instability’ in methods that are ‘straight forward’ to approximate provided that ramps they utilized in ‘WAIR experiments’ were comparatively ‘narrow’ and wing parts constantly expanded on the substrate edge.Effects of Body Size on Take-off flight PerformanceIt is observed that flight ability declines with increasing body size in birds and other flying animals, and it is genetically expected that these trends will explain aspects of the ecology and evolution of flight (Tobalske & Dial 2000).
As Tobalske and Dial (2000) quoted, maximum ‘acceleration’ during ‘take off’ are reported to ‘go down’ as the body mass increases in ‘aerial-insectivores’, and pigeons and doves.One explanation why aspects of animal design can explain these trends is that the maximum mechanical power available from the flight muscles may be limited by wingbeat frequency. According to Tobalske & Dial (2000), the ‘mass specific power’ needed for ‘flight’ is anticipated to the range of between mass m0 and m0.16, resulting in a ‘predicted-adverse-scaling’ of available power in relation to the needed power that possibly reports for a ‘flight-ability’ decline as ‘species’ become bigger.
The max-load that a ‘flying-animal’ can raise during ‘take off’ has been seen to be relative to ‘body-mass’ over a wide variety of ‘body-sizes’ so it means that the ‘mass-specific lifting-ability’ goes up as the body mass increases. In this experiment, ‘direct-measurements’ of ‘mechanical-power output’ hasn’t been acquired; rather , mechanical power cost were estimated using aerodynamic theory and from such estimates, it appears that the maximum mass-specific power available from the flight muscles scales positively with mass, but less lift is produced per unit power output. Among bird species, the percentage of larger diameter, more glycolytic fibers in the pectoralis scales positively with increasing body mass in woodpeckers but not in doves, so this explanation may be appropriate for some group of birds but not for others; similarly, other factors that may shape the maximum power available from a cyclically contracting muscle include the proportion of the cycle time spent shortening and the time of muscle activation and deactivation (quoted in Tobalske & Dial 2000).Aerodynamics and Energetics of Intermittent Flight in Birds‘Intermittent flight’ is the trait ‘flight-pattern’ of most birds; in some cases these flight patterns are adaptive responses which are a result of evolutionary adaptation and optimize some aspect of flight performance (Rayner et al.
2001). According to Rayner et al. in others, as for example in bird that is mainly ‘gliding’ but do occasional ‘wing-flaps’ to balance for ‘local air currents’ or for control, ‘intermittent-flight actions’ represent a ‘proximal-behavior response’ in the ‘adaptive-envelope’ which bird has ‘evolved’.Flight has been an enormously successful mode of movement, witnessed by the impressive diversity of insects, birds and bats.
Relative to human engineered aircraft, the flight of animals is impressive. Similar fluid mechanical principles underly both swimming and flying; in contrast with swimming, weight support is key to successful flight performance because of much lower density of air compared with water (Biewener 2003). According to Biewener, the capacity for flight based on the mechanical power derived from striated muscle is impressive, particularly given the remarkable maneuvering ability of most flying animals. The design and contractile performance of flight muscles are now being linked to the aerodynamic performance of the wing (Biewener 2003).
Because flying animals can manipulate the shape and orientation of their wings, they have the ability to utilize unsteady aerodynamic mechanisms to generate lift providing them with enhance performance which exceeds that predicted by analyses of fixed-wing aircraft (Biewener 2003). According to Biewener (2003), however, this also provides greater challenges for biologist and aerodynamicist interested in understanding the design, control, and performance of flapping airfoils. New experimental techniques now provide complementary approaches to aerodynamic modeling analyses that are likely to provide new insights in the beauty and complexity of animal flight. Although much work has been carried out to understand the basic features of steady forward flight and aerodynamic principles that underlie its capability, future work will seek to unravel the mechanisms by which animals maneuver in flight and how the neuromuscular system function to achieve the impressive array of aerial acrobatics of which both small and large flying animals are capable (Biewener 2003).
ReferencesBiewener, A. 2003. Animal Locomotion. Oxford: Oxford University Press.
Fung, Y. 1990. Biomechanics: Motion, Flow, Stress, and Growth. New York: Springer.
McNeill, R. 2003. Principles of Animal Locomotion. Princeton: Princeton University Press.
Rayner, J., P. Viscardi, S. Ward & J.
Speakman. 2001. Aerodynamics and Energetics of Intermittent Flight in Birds. American Zoologist:188-204.
Tobalske, B. & K. Dial. 2000.
Effects of Body Size on Take-off Flight Performance in the Phasianidae (aves). The Journal of Experimental Biology: 3319-3332.Tobalske, B. & K.
Dial. 2007. Aerodynamics of wing-assisted incline running in birds. The Journal of Experimental Biology: 1742-1751.