Patent Application
20080210821
1. Field of the Invention
This invention relates generally to the field of aircraft structural systems and more particularly to a rib structure and attachment system for composite wing panels.
2. Description of the Related Art
In aircraft structures, wing panels, which consist of skins and stringers, react wing bending loads. These loads and the resulting deflections produce upper wing compression buckling and a crushing load on ribs supporting the wing panels. The compression buckling capability for the panel is driven by geometry, rib spacing and stringer spacing. The boundary conditions for the panel are determined by the method of support the rib gives the skin/stringer.
Traditional aluminum panel design as shown in
Further, if this rib bolt design is applied to a composite wing structure, it creates interlaminar tension problems in the stringer radius. This is a poor load path for composite structure which may require reinforcement methods for the stringer radius adding more cost. The composite wing also needs disbond arrestment fasteners common to the stringer and skin in addition to the rib to stringer attachment.
It is therefore desirable to provide structural elements that provides improved load path for rib support of wing panels. It is further desirable that the structure not require drilling of holes inside an enclosed wing box.
The present invention provides an innovative structure for the ribs to support the panels without an attachment between the rib and the stringer free flange or the web. The support is provided by rib shear ties installed directly to the stringer skin flange. The rib incorporates a cut away to allow the stringer to pass through the rib. The composite stringer is an ‘I’ section and is designed to be stable under compression, not requiring mechanical methods to prevent rolling over.
This design provides further benefit in that all drilling can be done from outside the wing box facilitating automation, allowing fabrication which is much easier, less costly, and less prone to rework.
The wing skin attachment structure of the present invention provides a rib having shear ties at a surface profile and a plurality of cut aways proximate the shear ties. A plurality of stringers have skin flanges which are engaged by the shear ties and free flanges received through the cut aways. A plurality of fasteners attach the skin flanges to the shear ties. The ribs employed in the present invention further incorporate gussets extending from the shear ties adjacent the cut aways to transfer loads to the rib. In an exemplary embodiment, the fasteners engage a wing skin, the skin flange and the shear tie, the skin flanges incorporate tab outs proximate the shear ties and the free flanges incorporate tab outs proximate the cut aways.
These and other features and advantages of the present invention will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
As shown in
The ribs are stiffened from the lower wing surface to the upper wing surface. To react tension load pull off created by the stringer attachment to the shear ties at the ribs, the ribs have gussets 36 surrounding stringer cut aways 38 to help transfer skin panel attachment loads into the web 40 of the ribs and rib stiffeners 41 while providing pass through of the stringers 42. These gussets act in concert with the rib stiffeners for structural integrity of the ribs in conjunction with reacting the pull off loads. For the embodiment shown in the drawings, the ribs are machined to provide the gussets and cutouts. In alternative embodiments the rib features are created by stamping, casting or forging.
The stringers skin flanges are wide with a profile incorporating some local tab outs 43 at the ribs to accommodate the shear ties as shown in
The wing skin panel is well supported at the rib so the critical location for buckling is between ribs. The profile of the stringer free flange is tabbed out, as necessary, between the ribs to provide the column stability as shown in
Having now described the invention in detail as required by the patent statutes, those skilled in the art will recognize modifications and substitutions to the specific embodiments disclosed herein. Such modifications are within the scope and intent of the present invention as defined in the following claims.
