Ways of eco-flight

　　　They are to make use of the inertia as much as possible, to beat with the
　　natural frequency of the wing system and the irreducible minimum amplitude
　　of a demand, and to avoid the occurrence of negative thrust or negative lift
　　which might appear on the flapping up run.

　　　They make use of a thermal ascending current, a climbing current along
　　a slope, or a current in atmospheric boundary layer. (They acquire a
　　potential energy from those currents and exchange to the kinetic energy by
　　the gravity in spite of beating or non-beating flight.)

　　　It rides on a fair wind. (It increases the velocity relative to the earth
　　(the flight velocity).) For example, if a bird rides on the fair wind of
　　velocity 10m/s, the velocity of 36km/h will be supplemented.)

　　　It make use of the surface effect by skimming the surface of the water or
　　the ground. (The flow around the bird changes under the influence of the
　　surface of the water or the ground, the lift and the thrust should increase.)

　　　Large-size, that keep somewhat of lift in the flapping up run, fly in
　　formation, and then the opposte rotating vortices running out from both
　　tips of wing are canceled out and as a result the induce drag should be
　　reduced.

　　　Small-size birds, that have small weight and powerful muscle, makes use
　　of the bounding flight and the inertia in maximum.

　　　The ways of bird's eco-flight are similar to our eco-drive in car and bicycle.
　　They should run with the velocity that make maximum the value of the
　　distance covered/the spent fuel. The inertia should be utilized maximum.
　　The brake uses at irreducible minimum of a demand. A downward slope
　　should be utilized maximum.

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