AH-64 Composite Aft Fuselage Ground Test Load Derivation, Execution, and Results Correlation

As part of the aircraft modernization effort, The Boeing Company has designed, tooled, and built a prototype composite tailboom (CTB) and, in partnership with the Aviation Missile Research & Development Engineering Center (AMRDEC) Manufacturing Science & Technology Division, a composite vertical stabilizer (CVS) for the AH-64 Apache helicopter. The resulting composite aft fuselage (CAF) utilizes X-CorTM fiber-reinforced core sandwich panels with carbon/epoxy facesheets. The CTB and CVS are designed to carry increased flight loads while reducing weight and manufacturing cost, and improving maintainability and aircraft performance. Successful proof load testing is necessary in order to clear prototype aircraft structure for instrumented flight test. The CAF ground proof test was designed to show strength and structural stability under static load, evaluate the dynamic characteristics, validate analytical predictions, and clear the CAF for safe risk reduction instrumented flight test. Test loads were derived with the objective of enveloping all flight and landing loads on the tailboom and vertical stabilizer with a minimum number of loadcases and without excessive conservatism. External loads were obtained from landing and flight simulation (with an improved tail rotor) and were used to develop fuselage shear and moment diagrams. Test loads; applied at the tail rotor, horizontal stabilator, and landing gear; were regressively derived to envelope the moment diagrams. The results were checked against all available flight test data to ensure that no conditions were missed. The tested structure was analyzed for response to the test loads to ensure failure would not occur and to provide data for post test correlation. The CAF was mounted in the ground test fixture. Loads were applied with numerically controlled hydraulic actuators. In addition to recording applied loads, deflections were measured sufficient to determine both CAF flexure and rigid body motion. The CTB and CVS were instrumented with strain gages to 1) capture strains at critical locations, 2) check for eminent buckling behavior, 3) record data for post test correlation, and 4) provide calibration data for flight test instrumentation. The CAF was dynamically evaluated by execution of a response analysis pulse (RAP) test and a sine sweep test using a dynamic shaker in order to determine the fundamental frequencies and mode shapes in bending and torsion. Accelerometers were used to monitor the response of the CTB and CVS during dynamic testing and to compare against analytical predictions. Successful completion of the CAF ground proof test is defined by demonstration of strength and structural stability without evidence of failure or yielding under the applied loads. Weight, strength, and dynamic performance goals of the CAF were achieved through linear and non-linear Finite Element Analysis (FEA). These analytical models, used for design structural substantiation, are validated by comparison to strain, deflection, and acceleration data recorded during testing. Pending United States Government (USG) approval, the demonstrated structural capability supports clearance of the composite aft fuselage for instrumented flight test.