Development of a Graphite Horizontal Stabilizer

The analysis, repair, and further static testing of the previously failed graphite horizontal stabilizer are described. The design, analysis, and development testing of redesign concepts to correct the understrength condition at the main pivot fitting joint are discussed. Finite element analyses of the joint region were conducted to quantify the interlaminar shears and bending moments induced in the laminated skin panel by secondary bending effects. The calculated interlaminar shear and tensile stresses were of the order of 5 to 10 percent of allowable stresses determined in quality control specimens. The failed static test article was repaired with bolted and bonded steel splice plates and additional static tests were conducted to verify the strengths of the three elevator hinge brackets and supporting structures. These tests successfully demonstrated the design integrity of the hinge brackets since loads in excess of design ultimate load (150 percent design limit load) were sustained in each case. Joint specimens were tested to evaluate two redesign concepts (i.e., bonded external scarf and internal stepped-lap titanium doublers) to correct the understrength condition at the pivot fitting joint. The latter concept was selected for further development because it eliminated design reliance on laminate properties in the immediate vicinity of the major bolted joint. (Author Modified Abstract)