Flapping Flight

Description of Flapping Flight

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II. Flapping Flight

A. Description of Flapping Flight

Four degrees of freedom in each wing are used to achieve flight in nature: 

flapping, 

lagging, 

feathering, 

and spanning. 

This requires a universal joint similar the shoulder in a human. 

        Flapping is an angular movement about an axis in the direction of flight. 

(Up and down)

        Lagging is an angular movement about a vertical axis which effectively moves the wing forward and backward parallel to the vehicle body. (Back and forth)

        Feathering is an angular movement about an axis in the center of the wing which tilts the wing to change its angle of attack. 

(Pitching)

        Spanning is an expanding and contracting of the wingspan.

Not all flying animals implement all of these motions. Unlike birds, most insects do not use the spanning technique. Insects with low wing beat frequencies (17-25 Hz) generally have very restricted lagging capabilities (Brodsky3, 1994). Insects such as alderflies and mayflies, have fixed stroke planes with respect to their bodies, and the only way these insects can alter the stroke plan with respect to gravity is to change their body angle (Brodsky3, 1994). Thus, flapping flight is possible with only two degrees of freedom: flapping and feathering.

Using only these two degrees of freedom, there are 3 important variables with respect to wing kinematics: wing beat frequency, wing beat amplitude, and wing feathering as a function of wing position. When coordinated, these motions can provide lift not only on the down stroke, but also on the up stroke. The ability to generate lift on both strokes results from a change in the angle of attack of the wing whose tip which inscribes an ellipse when considered relative to a body-referenced point. The ability to generate lift on both the up- and down-stroke leads to the potential for hovering flight in entomopters and ornithopters.