Maximum lift coefficient

The maximum lift coefficient is connected to occurrence and development of flow stalling from the upper wing surface near the trailing edge and depends on many factors, first of all, from the characteristics of an airfoil (, nose section shape), wing plan form (, ), Reynolds number . The value practically does not influence onto for wings of large aspect ratio (Fig. 4.9), at that with decreasing increases.

The influence of has an effect as follows for wings of small aspect ratio: grows with growing from 0 up to ; and then decreases - with increasing of . Small values of ()and large values of () (fig. 4.10) are characteristic for wings with . A flow stalling delay in the latter case caused by influence of vortex structures formed on the upper wing surface.

Fig. 4.9. Dependence for wings of large aspect ratio .

Fig. 4.10. Dependence for wings of small aspect ratio

The properties behaviour of curve in area depends on the nose section shape. The presence of low values is characteristic for a wing with the pointed airfoil nose section which do not depend on Reynolds numbers (Fig. 4.11). The increasing of (up to certain values) is characteristic for a wing with a rounded airfoil nose section nose at increase of Reynolds numbers (Fig. 4.12).

Approximately, value of large aspect ratio wing () can be determined by the formula

,

where - the maximum value of an airfoil lift coefficient;
for symmetrical airfoil at Reynolds numbers and at .

Fig. 4.11. Dependence for wings with a sharp leading edge

Fig. 4.12. Dependence for wings with a classical airfoil

Number - kinematic factor of similarity describing the ratio of inertial and viscous forces:

, (4.8)

Where - characteristic speed; - characteristic length; - kinematic factor of viscosity.

Дата добавления: 2014-12-16