Editing Grumman X-29 (section)

===Aeroelastic considerations===
[[File:X-29 at High Angle of Attack with Smoke Generators.jpg|thumb|left|X-29 with aft control surfaces deflected]]

In a forward swept wing configuration, the aerodynamic lift produces a twisting force which rotates the wing leading edge upward. This results in a higher angle of attack, which increases lift, twisting the wing further. This [[Aeroelasticity#Divergence|aeroelastic divergence]] can quickly lead to structural failure. With conventional metallic construction, a torsionally very stiff wing would be required to resist twisting; stiffening the wing adds weight, which may make the design unfeasible.{{sfn|Pamadi|2004}}

The X-29 design made use of the [[isotropic|anisotropic]] elastic coupling between bending and twisting of the carbon fiber composite material to address this aeroelastic effect. Rather than using a very stiff wing, which would carry a weight penalty even with the relatively light-weight composite, the X-29 used a laminate which produced coupling between bending and torsion. As lift increases, bending loads force the wing tips to bend upward. Torsion loads attempt to twist the wing to higher angles of attack, but the coupling resists the loads, twisting the leading edge downward reducing wing angle of attack and lift. With lift reduced, the loads are reduced and divergence is avoided.{{sfn|Pamadi|2004}}