Parker Variable Wing

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The Parker Variable Wing is a wing configuration in biplane or triplane aircraft designed by H.F. Parker in 1920^[1]. His design allows a supplement in lift while landing or taking-off. The system is depicted in the figure. The figure shows the biplane configuration. The lower airfoil is rigid. The upper airfoil is flexible. At high angle of attack the flow over the lower airfoil will cause the airflow to bend up and create an upward force at the lower surface of the upper airfoil. This upward force will cause the flexible section to be pushed upward. The flexible wing section is held at points A and B. The trailing edge is rigid and can rotate about point B. Due to this effect the camber of the airfoil is increased. And hence the lift it creates is increased.

[edit] Principle

The first biplane series, with the variable wing for the upper plane and with the negative stagger, shows excessive stability. The vector diagram (see second picture) was obtained by assuming a center of pressure travel by plotting a curve through the appropriate points. Up to 2½° te variabel plane is stream line, at 4½° is assumed to be one-third lifting, at 8° to be two-thirds lifting and 12° fully lifting. In lift-drag diagrams the full potential of the wing can be evaluated. The combination with the stream line plane is most efficient at the small values of the lift coefficient appropriate to very high speeds. Maximum lift/drag is obtained at high but not top speeds. The variable camber wing has a maximum lift coefficient of 0.76 (absolute) and a mimimum drag of 0.0070. It has a stable travel of the center of pressure of 0.035 of the chord. Within the biplane, the lift over drag is doubled at speeds in excess of 2.1 times the landing speed, and trebled at three times the landing speed. Similar results obtained for the triplane.

[edit] References

1. ^ The Parker variable wing, naca-report-77, 1920