Damage tolerant wing-fuselage integration structural design applicable to future BWB transport aircraft

Abstract

Wing joint design is one of the most critical areas in aircraft structures. Efficient and damage tolerant wing-fuselage integration structure, applicable to the next generation of transport aircraft, will facilitate the realisation of the benefits offered by new aircraft concepts. The Blended Wing Body (BWB) aircraft concept represents a potential revolution in subsonic transport efficiency for large airplanes. Studies have shown the BWB to be superior to conventional airframes in all key measures. Apart from the aerodynamic advantages, the BWB aircraft also provides a platform for wing-fuselage design changes. The main objective of this research is to design a damage tolerant wing-fuselage joint with a novel bird’s mouth termination for a BWB aircraft that has a similar payload range to the B767 aircraft. The damage tolerance analysis of the proposed BWB wing/fuselage integration structure includes assessments of fatigue crack growth life, residual strength and inspection capability. The proposed structure includes a bird’s mouth termination of the spars that facilitates smooth transfer of loading from the spar web into the root rib and the upper and lower skins and is novel in its application to the blended wing body configuration. A finite element analysis was required to determine local stresses for the prediction of fatigue crack growth life, residual strength and inspection capability and to identify weak spots in the proposed structure. The project aircraft wing comprises of three spars (front, centre and rear) and a false rear spar thus defining a four cell wing box. Wing root shear, bending moment and torque loads were derived and applied to a thin-walled three box idealisation of the proposed structure. The challenges experienced in replicating the loads obtained from the three box idealisation were addressed by modification of the boundary conditions. Checks for compression and shear buckling were also undertaken that confirmed that the applied loads were below the limits of the proposed structure. The finite element analysis showed very clearly that the stresses in the novel bird’s mouth spar termination were significantly lower than in the skin and that the skin remained the more critical damage tolerant component at the wing root when the structure was subjected to ultimate design stresses. The spar web at the bird’s mouth termination was shown to have a larger crack growth life compared to the skin. The thickness of the skin requires further investigation as a significant amount of local bending was experienced due to the applied pressure. The skin will sustain a two-bay crack at the design limit load thus proving the proposed wing fuselage integration structure to be damage tolerant. In conclusion, the main objective of the thesis has been achieved. An integrated wingfuselage joint with novel bird’s mouth spar termination and surrounding structure have been designed and substantiated (evaluated) by damage tolerance requirements.