The proof of an aircraft’s structural integrity and safety is typically provided by analysis and supported by structural test evidence. The experimental test of a wingbox, which is the main structural component of a wing, can provide useful data on assessment of its structural performance in an actual airplane for the design objectives. To this end, a testing fixture was designed and manufactured to introduce a prescribed shear force and bending moment at one end of a variable stiffness thermoplastic composite wingbox and react the load at the other end. We report experimental results and compare them with detailed finite element data.