High score: the detailed action of birds flying

Birds have perfect flying organs-wings and tails, and the structure and function of their bodies are fully prepared for flying. So, how do birds soar in the sky and the blue sky?

The structure of bird wings conforms to the aerodynamic principle. It is not only streamlined, with little resistance when passing through the air, but also its cross section is curved, which can generate lift and keep it from falling in the air. When the air flows over the leading edge and convex surface of the airfoil, it will increase the speed. Bernoulli's law in physics tells us that the pressure at the highest speed in liquid flow is the smallest, which leads to the pressure drop above the wing; At this time, the air pressure at the bottom of the concave wing remains normal. Because of the pressure difference between the upper wing and the lower wing, lift is generated. Just like airplanes, slots and flaps on the wings can be used to increase or decrease the lift. There are many different types of birds' wings, which reflect their adaptation results in different environments. For example, seagulls living in a vast space have evolved their wings to be light and narrow, so that they can be lifted by the wind in the airflow; On the contrary, the pigeon's living environment is relatively narrow, so it can't slide and float by this airflow, so it has a pair of muscular short wings, making it a flier flapping its wings by itself.

The surface area of birds' wings is in direct proportion to the rising force. The surface area of wings varies with different kinds of birds, and it is also related to the extent to which wings are unfolded or folded. When the air speed increases, the lift also increases, and the lift is proportional to the square of the air speed. When the bird is flying slowly, or taking off or landing, in order to enhance the lift, another method can be used to achieve the goal. For example, tilting the wing will raise the leading edge and increase the windward angle, thus increasing its lift. But at the same time, the wing surface also increases the rising disturbance airflow. At this time, the feathers on the wings separate to form many wing grooves, which makes the airflow flow quickly, thus making the disturbed airflow disappear, thus forming a great lift. Some birds often spread their tail feathers and bend down when landing, which is used to gain extra lift and act as a brake. The movement of the tail is very important for the bird's body to rise and fall and the direction of flight. When the tail is raised, the bird's head and trunk will also rise due to the reaction of air. On the contrary, the tail feather descends, and so does the head and trunk. According to the principle of air action, birds change their flight direction by swinging their tail feathers.

Birds are very clever in flying skills. They can use different flying skills in different environments to adapt to changing natural conditions. To sum up, birds can be roughly divided into three flight postures. These three flying postures are constantly changing and using, which makes birds fly freely in the air and become the pride of the blue sky.

Gliding flight This may be the earliest way for birds to fly. Primitive ancient birds, such as Archaeopteryx, thought that they climbed to rocks or trees first, and then spread their wings and swooped down. Other animals can fly like this, such as flying fish, flying frogs and flying squirrels, but they are "incomplete fliers", that is to say, they can only fly like this, and birds can master other ways of flying besides gliding. In normal times, we can often see the gliding flight of birds, such as a gliding flight of chickens before landing, waterfowl skimming over the water, swallows flying low and so on. , are common gliding flight.

When gliding, the bird's wings produce a little lift. As a result of gliding in the air, the result of gliding will be lower and lower. At this time, if the wings of the bird are slightly changed, the flying height can remain the same or rise higher. Terrestrial birds, such as vultures, hover in suspended rocks near warm updraft or inclined airflow, which is called "static gliding" Although their wings are short and wide and have enough surface area to generate lift, they are more suitable for the changeable airflow to complete the ascending movement. They fly very slowly, and the rising force comes from the wing slot (especially near the end).

Seabirds use the airflow above the sea surface to glide dynamically with the increase of height. Due to friction, the sea surface is the place where the air velocity is the smallest. Birds quickly descend from the sky with the wind, hover in the wind when approaching the sea surface, maintain their height by using the inertia of gliding, increase their lift by gradually accelerating airflow, and then return to their original height. All these birds have long narrow wings. Although gliding can save energy, you must flap your wings after gliding for a certain distance, otherwise the bird will fall because of the influence of gravity and air.

Flapping-wing flight is the most common way of flying, and it is also a common flying posture of birds. When the drum wing flies, the two wings move up and down, and the movements are very coordinated, so that the maximum speed can be achieved with the minimum energy.

The flight of drum wings is closely related to the configuration of flight feathers. The outer headland of the flight feather is narrower, while the inner headland is wider. When the wings are spread out, the outer headland only covers the edge of the inner headland adjacent to the flight feathers. Because of the arrangement of the flight feathers and the slight rotation of each flight feather, when the bird's wings rise, air can freely pass through the gaps between the flight feathers, which greatly reduces the resistance without forcing the bird to descend; When the bird's wings descend, the flight feathers form an interconnected surface, and the gas cannot pass through the wing surface, thus causing considerable resistance. In this way, birds can be suspended in the air without falling.

Birds flap their wings to fly horizontally and flap their wings up and down. If its wings move down, what works at this time is lift and tension. When the wing is lifted upwards, its movement route is inclined upwards. At this time, lift and frontal resistance do work, so the flight slows down. If the lift and weight are equal, the bird will keep flying horizontally. If the lift exceeds the weight, the bird will rise. If the lift is less than the weight, the bird will slowly descend. At this time, it is necessary to increase the number of flapping wings and speed up the flight speed, thus enhancing the lift.

As mentioned earlier, the lift is related to the wing area and also to the flight speed. Therefore, birds with smaller wings fly slower than their weight; Birds with big wings fly faster. The smaller the bird is, the more times it flaps its wings. For example, seagulls have smaller wings than cranes, so seagulls flap their wings more times per second than cranes. The former is 3 ~ 4 times per second; The latter is enough once a second.

Birds need a lot of energy to flap their wings. Birds are muscular and can flap their wings frequently to fly. Big birds have less muscles than small birds, so they have less power to flap their wings. Therefore, medium-sized birds and large birds use a relatively economical and energy-saving flight mode-semi-soaring flight. Compared with birds, it only needs 2/3 of muscle energy, and sometimes only needs 1/3. For example, when seagulls fly, they gently put down their wings, so that the leading edges of phalanges and metacarpals with primary flying feathers droop, resulting in forward pulling force. Because the wing has a protruding surface, the airflow is accelerated, thus increasing the lift. When seagulls raise their wings slightly, the air blows them up, and at the same time, they bring the bird's body together, so that the effect of wings is almost without consuming muscle strength. When doing such a flight, the number of flapping wings is less, the wings are not raised much, and the wings are not lowered very low, so it is more labor-saving. The muscle tissue of birds that often make such flights is extremely underdeveloped. The weight of muscles below the clavicle when seagull wings are raised is 12 times different from that when wings are lowered, which is only equal to 1. 1% of the whole body weight. Pheasants frequently stir their wings when flying, so the muscles below the clavicle are very developed, only three times different from the pectoral muscles, which account for about 5% of the whole body weight.

Soaring flight is a special way of flying. Contrary to flapping-wing flight, it uses the airflow in the air to fly. As we know, the land is colder than the ocean in winter, so the cold wind from the mainland blows all the way to the southeast sea, and from the sea to the land in summer. In addition, mountains and rivers, sandy lakes, downtown wilderness, farmland forests and other different environments have different degrees of air cooling and heating, which is caused by airflow movement between different environments. Birds use the airflow that often exists in nature as the power of flight. Sometimes, before a thunderstorm, we can see seagulls flying in the sky and dark clouds hanging over the sea. At this time, they are using the updraft before the thunderstorm to fly.

However, this aerodynamic condition suitable for birds to soar is not available at any time and place. Only when the rising airflow can support the weight of the bird can the bird soar, so we can only see the kite flying freely in the open area of the forest, but not over the forest.

Soaring is a special flying skill. This kind of flight can effectively use the updraft without flapping its wings for a long time. In Eagle Mountain, Pennsylvania, USA, hundreds of people often come to watch eagles perform in the wind on autumn weekends. If the northwest wind blows, there is a strong upward airflow on the windward slope, and birds will fly straight along the ridge. The observer timed them at two places where the distance was measured. They saw an osprey soaring along the wind ridge at the speed of 129 km per hour in the wind without flapping its wings. On a sunny and warm day, when warm air rises from the hot ground, resulting in "helicopter wind", observers can see wonderful performances that really soar in the wind-red-tailed vultures, vultures and other eagles will gracefully circle on the rising air column like gliders.

The air flow over the mainland is completely different from the air flow over the ocean. Over the mainland, it is mainly a relatively stable thermal updraft. Above the ocean, there is a dynamic updraft. Because of this, birds on the mainland are different from those on the sea in flight nature and flight organ structure. Wings of vultures, eagles, kites, etc. They are spacious and powerful, suitable for soaring in the quiet thermal updraft, but unable to adapt to the rapid and changeable airflow power. Albatrosses have long and narrow wings and a small area, and can be handy for the changeable airflow of the ocean, but they can't adapt to the quiet updraft.

The flight of birds, in terms of adaptability, is indeed very complicated. The bird's body has a complex lever system, which can be adjusted freely with great precision and flexibility to adapt to the flight movement of various air currents. The ability of birds to fly is hereditary. When the young birds have just left their nests, they can already make a preliminary flight.

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