蜂鸟曰常飞行时，羽翼大约每秒拍打十八到八十次，视鸟的大小而定。

In normal flight a hummer 's wings beat about18-80times per second depending on the size of the bird.

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它们飞行能力不强，常贴近地面飞行。

Also, they fly weakly and not far from the ground.

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就简化的非定常气动力数学模型提出了分析气动弹性时飞行器稳定性的影响的方法。

With simplified unsteady aerodynamic force mathematical model, method of analysis for the effects of aeroelasticity on the dynamic stability of elastic vehicles is established.

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