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Inner Journeys, LLC Group

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Christopher Garcia
Christopher Garcia

Flight Of The Inner Bird.

The discovery of wing-warping was one of the Wrights' truly original contributions to aeronautics. The principle was discovered by Wilbur one day in 1899 as he idly twisted an empty bicycle inner-tube box. If he twisted one side, the other side would twist in the opposite direction. He and Orville soon realized that by rigging a double-deck kite with wires looped through pulleys to the wingtips, they could warp the wings just as they had seen birds doing as a means of control.

Flight of the Inner Bird.

Because both brothers would be busy trying to get their machine off the ground, Orville set the camera on a tripod, focused on the spot where the machine would take off and showed John Daniels how to snap the shutter. Because of a coin toss, Orville is the one at the controls. Wilbur is to the side having steadied the machine as it went down the runway track and just released the upright strut. This first flight lasted 12 seconds and covered 120 feet. Each of the next three flights was longer than the last.

Distant view of the Wright airplane just after landing. . . . This flight, the fourth and final of December 17, 1903, was the longest: 852 feet covered in 59 seconds. Copyprint. Prints and Photographs Division, Library of Congress (77)

All of the photographs in this album were taken by the Wrights themselves. This opening contains images from Kitty Hawk during October 1902. Besides the excellent photos of their 1902 glider in flight, the brothers included a close-up of the new larder or storeroom they had just built and an image of the proud men of the Kills Devil Hills Lifesaving Station, who had befriended them. This album was produced after 1913, when many of the glass-plate negatives were damaged in a flood while stored in the Wrights' house.

In his pocket diary, Orville provides a characteristically matter-of-fact account packed with details of the first four flights. His retelling of the day's events contains not a hint of emotion. The only suggestion of drama is when Orville describes how the wind-tossed machine nearly killed John Daniels, who became tangled in its engine and chains.

First flight for Katharine Wright, seated in plane with Wilbur; Orville standing to left, in Pau France, 1909. Photograph. Mabel Beck Collection, Prints and Photographs Division, Library of Congress (96)

Following his celebrity tour of Europe, Wilbur was invited to fly at New York's Hudson-Fulton Celebration honoring the centennial of Robert Fulton's steamboat and the 300th anniversary of Henry Hudson's entry into New York Harbor. In the Wrights' first flight over American waters, Wilbur took off from Governor's Island with a canoe strapped underneath his machine and flew around the Statue of Liberty as hundreds of ships tooted in the harbor.

Strong, rigid vanes are especially important for flight. The trailing, inner wing feathers, the secondaries, provide lift, while the trailing, outer wing feathers, the primaries, provide thrust. Most species have large tail feathers. They function like a rudder when flying and like brakes when landing.

Smaller contour feathers cover the body and leading edges of the wings. On the wings, the feathers help form the airfoil shape that is necessary for flight. On the body, they contribute color, which is important in courtship and for camouflage, and they form a sleek outer covering, providing an aerodynamic tear-drop shape that assists flight. From songbirds to swans, the neck is narrow and the breast muscles are massive. Where the body parts meet, contour feathers create a gradual slope.

The other three feather types are quite specialized. Two, filoplumes and bristles, are hairlike. Filoplumes consist of a calamus and rachis but have only a few small barbs, near the tip. The feathers are found around contour feathers, especially on the wings. Filoplumes are associated with sensory receptors in the skin, and are thought to provide information about wind, air pressure, and feather movements that birds use to maintain efficient flight.

According to a new study, the shape of the inner ear offers reliable signs as to whether an animal soared gracefully through the air, flew only fitfully, walked on the ground, or sometimes went swimming. In some cases, the inner ear even indicates whether a species did its parenting by listening to the high-pitched cries of its babies.

Power is measured at three different levels pertinent to flapping flight. The first level is metabolic power input (Pmet) to the muscles, directly of interest to a flying, foraging bird, and generally a realm of study for respiratory, thermal and chemical physiologists. Pmet is the rate the bird expends chemical energy to supply the flight muscles, and it may be measured using double-labeled water(Nudds and Bryant, 2000; Ward et al., 2004; Engel et al., 2006), labeled bicarbonate (Hambly et al.,2002), oxygen consumption and carbon dioxide production(Ward et al., 2001; Ward et al., 2004; Bundle et al., 2007). Pmet equals the sum of mechanical power output from the muscles (Pmus) and the rate of heat loss from the muscles. Thus, Pmet may also be modeled using measures of heat transfer (Ward et al.,2004).

To introduce the biomechanics of bird flight, I will first summarize current understanding about the functional morphology of the avian wing with implications for Pmus. Then, I will evaluate how Paero varies with flight speed and explore some of the wingbeat kinematics, flight modes and styles that covary with Paero. Other variables besides work and power are of great importance to the biology of flying birds, including the ability to maneuver(Warrick et al., 2002) as well as be stable (Thomas and Taylor,2001; Taylor and Thomas,2002; Taylor and Thomas,2003). Compared with the amount of empirical data describing steady hovering and forward flight, less is known about the biomechanics of maneuvering and stability, and these subjects represent a new frontier of study. Thus, I will include a synopsis of current data from maneuvering flight before concluding with reflections on promising avenues for future research.

The pectoralis, the primary depressor and pronator of the wing, is the largest muscle of the wing (Fig. 1A), and the supracoracoideus, the primary elevator and supinator(Poore et al., 1997), is second in mass. Both muscles insert upon the humerus and decelerate and reaccelerate the wing across the transitions between upstroke and downstroke(Dial, 1992a). Because of its size, the pectoralis is perceived to be the `motor' that accounts for the bulk of Pmus for bird flight(Dial and Biewener, 1993). Birds can take-off and fly without use of their supracoracoideus(Sokoloff et al., 2001), which indicates that other flight muscles may contribute to wing elevation. Likewise, birds can fly steadily, but not take-off or land in a controlled manner, without the use of their distal wing muscles(Dial, 1992b). Distal muscles of the wing are activated primarily during non-level modes of flight(Dial, 1992a), and bird species that regularly engage in non-steady modes of flight, including maneuvering, have proportionally bowed forearms. This outward bowing of the radius and ulna is hypothesized to be due to the need to accommodate more muscle mass with an enhanced role of distal wing muscles in these species. The forearm muscles supinate, pronate, flex and extend the distal wing(Dial, 1992b). With the exception of the supracoracoideus (Poore et al., 1997; Tobalske and Biewener, 2007), the mechanical contribution the other muscles of the wing has not yet been measured. Power output in the supracoracoideus closely matches estimated Piner for upstroke (Tobalske and Biewener, in press).

Birds may use a variety of methods to modulate Pmus. Among flight speeds, cockatiels Nymphicus hollandicus primarily modulate Pmus by varying the proportion of motor units recruited in the pectoralis and, thereby, varying force(Hedrick et al., 2003). Likewise, pigeons Columba livia vary motor-unit recruitment and pectoralis force among flight modes (Dial,1992a; Dial and Biewener,1993). Other factors may permit modulation in Pmus, including the shortening fraction, trajectory, and timing of muscle activation and deactivation(Askew and Marsh, 1997; Askew and Marsh, 2001). It was formerly hypothesized that small birds were constrained by their muscle physiology to use a narrow range of contractile velocity in their pectoralis(Rayner, 1985), but sonomicrometry and electromyography reveal that they use the same mechanisms as larger birds, the timing and magnitude of neuromuscular activation as well as the contractile velocity of the muscle, for modulating Pmus (Tobalske et al., 2005; Tobalske and Biewener, in press; Askew and Ellerby, 2007). Many birds also regularly use non-flapping phases (brief, extended-wing glides or flexed-wing bounds) to modulate power during intermittent flight (see`Intermittent flight', below).

A variety of mathematical models may be used to estimate the effects of flight speed upon components of Paero(Norberg, 1990). Models that are mostly widely employed are those of Pennycuick(Pennycuick, 1975; Pennycuick, 1989) and Rayner(Rayner, 1979a) for forward flight and, for hovering, those of Rayner(Rayner, 1979b) and Ellington(Ellington, 1984). Regardless of which model is used, the general prediction that always emerges is that Paero should vary with flight speed according to a U-shaped curve, with greater Paero required during hovering and fast flight and less required during flight at intermediate speeds (Norberg, 1990)(Fig. 2A). As a function of forward flight velocity, the cost of producing lift, Pind,decreases, while power needed to overcome drag on the wings and body, Ppro and Ppar, respectively,increases.

The U-shaped curve for Paero features a characteristic minimum power speed (Vmp) and a maximum range speed(Vmr; Fig. 2A). These characteristic speeds represent one of the most obvious ways in which the biomechanics of flight may be integrated with behavioral ecology. Often, a starting premise for ecological studies of flight is that birds should select Vmp for aerial foraging or searching and select Vmr for long-distance flight such as migration,although specific predictions change when optimal foraging factors such as rate of energy intake or prey-delivery rates are incorporated into the models(Hedenström and Alerstam,1995; Houston,2006). 041b061a72


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