Aerospace applications call for suitable mathematical description of components like wings, fu­selages, empennages, pylons and nacelles, to mention just the main parts which will have to he studied by parameter variation. Three-view geometries of wings and bodies are defined by plan – forms. crown lines and some other basic curves, while sections or cross sections require addi­tional parameters to place surfaces fitting within these planforms and crown lines. Figure 54 shows a surface clement defined by suitable curves (generatrices) in planes of 3D space, it can be seen that the strong control which has been established for curve definition, is maintained here for surface slopes and curvature.

Подпись: Surface definition by cross sections c in plane (xlt Xj) determined by generatrices (ксу|), along x2 and defined in planes (x,f x2) and (x2, Xj).

Figure 55

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