Flow stalling

D ifferent values of along wing span are the reason of flow stalling in one of cross-sections in which the local value is reached. For example, the flow stalling on a flat rectangular wing occurs at increasing of angles of attack in central cross-section. Ii is evidently shown in fig. 4.24., that the true angle of attack in central cross-section of a rectangular wing is more than at the tip , therefore flow stalling will begin in that place, where the true angle of attack comes nearer to critical.

Fig. 4.24.

In general the position of flow stalling spanwise on a tapered unswept wing can be determined by the formula , for swept tapered wing the position of stalling spanwise is determined by the following dependence , .

For improvement of wing aerodynamics at high angles of attack it is necessary to create a condition of simultaneous flow stalling spanwise, i.e. uniform distribution of loading spanwise It can be achieved by geometrical twist application. It is necessary to apply washin to rectangular wing for the purpose of increasing loading in tip cross-sections, washout is used for unswept wing, in this case tip cross-sections are unload. (It has be noticed, that for a wing with the elliptical law of chords distribution spanwise without geometrical twist all cross-sections have an identical , because and true angles of attack are identical for such wing spanwise).

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