The Parker Variable Wing is a wing configuration in biplane

Biplane

A biplane is a fixed-wing aircraft with two superimposed main wings. The Wright brothers' Wright Flyer used a biplane design, as did most aircraft in the early years of aviation. While a biplane wing structure has a structural advantage, it produces more drag than a similar monoplane wing...

 or triplane

Triplane

A triplane is a fixed-wing aircraft equipped with three vertically-stacked wing planes. Tailplanes and canard foreplanes are not normally included in this count, although they may occasionally be.-Design principles:...

 aircraft designed by H.F. Parker in 1920. 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

Airfoil

An airfoil or aerofoil is the shape of a wing or blade or sail as seen in cross-section....

 is rigid. The upper airfoil is flexible. At high angle of attack

Angle of attack

Angle of attack is a term used in fluid dynamics to describe the angle between a reference line on a lifting body and the vector representing the relative motion between the lifting body and the fluid through which it is moving...

 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

Trailing edge

The trailing edge of an aerodynamic surface such as a wing is its rear edge, where the airflow separated by the leading edge rejoins. Essential control surfaces are attached here to redirect the air flow and exert a controlling force by changing its momentum...

 is rigid and can rotate about point B. Due to this effect the camber

Camber (aerodynamics)

Camber, in aeronautics and aeronautical engineering, is the asymmetry between the top and the bottom surfaces of an aerofoil. An aerofoil that is not cambered is called a symmetric aerofoil...

of the airfoil is increased, and hence the lift it creates is increased.