Finite element simulation of a full-scale crash test of a composite helicopter

A finite element model of the Sikorsky Advanced Composite Airframe Program (ACAP) helicopter was developed using the nonlinear, explicit transient dynamic code, MSC.Dytran. Analytical predictions were correlated with experimental data obtained from a full-scale crash test of the Sikorsky ACAP helicopter flight test article that was conducted at the Impact Dynamics Research Facility of NASA Langley Research Center. The helicopter was impacted at 38 ft/s vertical and 32.5 ft/s forward velocity with an attitude of 6.25 nose-up pitch and 3.5 left-down roll. The objective of the crash simulation was to evaluate the capabilities of a commercially available transient dynamic analysis code in predicting the response of a composite airframe subjected to impact loading. The model was developed from an existing MSC.Nastran modal-vibration model of the helicopter. Considerable modifications were made in converting the original modal-vibration model to a model for crash simulation. Following conversion of the model, a two-stage modeling approach was used to generate analytical predictions. Because of the relatively long pulse duration, a rigid structural model containing a fairly complex landing gear model was executed from initial contact through landing gear stroke. Prior to fuselage contact, the nodal displacements and velocities were output to a file. Then, a flexible structural model was executed with the nodal displacements and velocities used as initial conditions. This paper describes the development of the finite element crash model, the two-stage modeling approach, and the correlation of the analytical predictions with the experimental data from the full-scale crash test of the ACAP helicopter.