Non-planar wings (wings with geometrical twist)

The general form of polar equation for a non-planar wing , where profile drag and part of induced drag caused by wing geometrical twist enter into parameter , i.e. . Parameter is also determined by wing twist . The polar pull-off coefficient does not depend on wing twist.

Polar equation for a wing with geometrical twist is a square parabola with displaced peak (Fig. 4.17). It is possible to write down

, (4.15)

Where ; .

From comparison of polars for flat and non-planar wings (the Fig. 4.18) it is possible to reveal the advantages of using of a non-planar wing:

1. At twisted wing drag is less than

2. The maximum lift-to-drag ratio of a non-planar wing is higher . (The wing is staying non-planar at mechanization deflection but ).

Fig. 4.17. Polar for a wing having twist (for a non-planar wing)

Fig. 4.18. Polars for a flat and non-planar wings

In addition, due to geometrical twist it is possible to provide wing balancing without increase of induced drag (non-planar wing is self-balanced). It is easy to see, that the advantages of a non-planar wing are shown at condition of . In this case polar peak displaces upwards.

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