**3.1.2 Analysis indexes**

The design of the wing will generate important impacts on glide efficiency and glide stability of the vehicle. The lift to drag ratio *L D* is chosen for measurement of the glide efficiency, the bigger values correspond to the more efficient gliding. The inverse of *L/D* expresses the glide slope [7, 19]. Existing oceanographic gliders are designed for static stability in steady glides, and the static stability can be measured by the non-dimensional hydrodynamic lever ' *l* α, the equations are[20~21]:

$$\mathbf{I}\_a = \mathbf{I}\_a \nmid \mathbf{I} \tag{7}$$

$$\mathcal{I}\_a = -\mathcal{M}\_a \; / \; \mathcal{L}\_a \tag{8}$$

Here, *l* is the vehicle length, *M*α is the hydrodynamic moment induced by angle of attackα , *L*α and is the Lift induced by the angle of attackα . It is static instability while ' *l* 0 α > , the moment induced by incremental angle of attack makes the angle of attack become bigger; It is neutral stability while ' *l* 0 α = ; It is called static stability while ' *l* 0 α < , the moment induced by incremental angle of attack makes the vehicle to turn to the original state.
