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An aircraft
or hydrofoil wing behaves as a cantilever beam from a structural viewpoint.
Structures of this sort have a "flexural center" associated
with them. If they are loaded at the flexural center their deformation will
be pure bending, otherwise both bend and twisting will occur. The top diagram
illustrates the effect of loading a wing away from the flexural center. The
twisting causes the angle of attack (angle to the mean airflow) to increase
towards the wingtip. In general this will increase the lift force, increase
the twisting, and in light structures may lead to wing failure.
The
lower diagram shows the lift distribution over a typical airfoil in steady state.
The center of pressure is seen to be towards the front of the wing at about
the quarter chord location. To avoid torsional effects, the flexural center
must also be located at the quarter chord position. |
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