Composite Material Stub-Blade Wing Joint

A design study to determine the viability of a stub-blade wing joint for HALE (high-altitude, long-endurance) aircraft is presented. The resulting wing joint design uses advanced composite materials and is capable of carrying moderately high bending, shear, and torsional loads. The stub-blade concept is similar to the wing joint design used on sailplanes and is particularly applicable to a large-span, high-aspect-ratio, unswept wing that uses a single-cell wing box to carry spanwise loads. This wing structure and geometry are typical of many HALE aircraft. The stub-blade joint can be located at any wing station and uses “pin-in-a-socket” action to transfer loads from the outboard to inboard wing box. Justification and criteria for material selection are presented. Extensive use of graphite/epoxy, co-cured and bonded structure is made to achieve a minimum weight design. Major design drivers include minimum weight, ease of fabrication, and ease of repeated assembly and disassembly of the joint. The latter would be desirable on a large-span aircraft for which hangar or transportation limitations would require repeated removal of outer wing sections. A FORTRAN program was developed to optimize the blade length based on weight, and a NASA Structural Analysis (NASTRAN) model of the stubblade design was constructed to investigate the distribution of internal loads. The stub-blade joint presented in this paper was sized to loads generated for a representative baseline HALE vehicle. This Lockheed Baseline HALE Aircraft is an unmanned vehicle capable of reaching an altitude of 27 432 m (90 000 ft) and features a 8163-kg (18 000-lbs) gross weight and 80.5-m (264-ft) wingspan. The stub-blade wing joint design is weight competitive with the traditional tensiontype wing joint and offers attractive features such as ease of assembly and disassembly, ease of fabrication, and aerodynamic smoothness.