Wave drag

Lift.

Generally for flat wing , where - the non-linear additive existed only at a subsonic leading edge. It can be estimated by the formula

At (supersonic edge) . There are schedules constructed in a generalized form for definition of the derivative , as dependence on parameters of similarity: .

Approximately it is possible to consider, that the taper practically does not influence onto lift coefficient. For each wing the function is various. However, as it was mentioned above, at we receive for all wings . Practically this dependence can be used at .

Fig. 6.14.

The general view of dependence is shown in a Fig. 6.14. It is characteristic for it - the presence of fractures at changing of flow modes about edges:

In a point - the trailing edge passes from subsonic to supersonic flow mode;

In a point - the leading edge passes from subsonic to supersonic flow mode.

In experiment these fractures are smoothed out.

Generally . At irrespectively of the wing plan form we shall have - the characteristic of an airfoil. Practically this formula can be used at . It is necessary to note weak influence of taper onto wave drag. The presence of fractures on a curve (Fig. 6.15). is characteristics for general dependence on reduced aspect ratio.

Fig. 6.15.   Fig. 6.16.

The fracture in a point - wing trailing edge passes from a subsonic flow mode to supersonic; in a point - transition of the maximum thickness line from subsonic to supersonic flow; in a point - the leading edge passes from subsonic to supersonic flow mode. These fractures are not present in experimental dependencies, they are smoothed out.

The maximums of curves are observed in the are of transition of the maximum thickness line () from a subsonic flow mode to supersonic (point ). For a sound line of maximum thickness . It is necessary to pay attention that at subsonic lines of maximum thickness the wave drag of swept wings is less than drag of unswept wing. Thus the longer wing aspect ratio (at ), sweep (at ) or parameter , then the larger profit is received in drag. On the contrary, at a supersonic line of maximum thickness the wave drag of swept wing is more than of unswept one (Fig. 6.16).

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