Ground Vibration Testing of the World’s Longest Wingspan Aircraft—Stratolaunch

Abstract

The record-setting Stratolaunch (Roc) carrier aircraft first took to the skies on April 13, 2019, staying aloft for 149 minutes before successfully landing back in Mojave, California. Since 2012, Stratolaunch Systems Corporation, a space transportation venture created in part by Scaled Composites, has been designing, building, and testing the world’s largest composite aircraft. The goal of this mobile launch system is to make orbital access to space more convenient, reliable, and routine. To achieve the first successful flight of Roc, several ground vibration tests (GVTs) were necessary to characterize the modal properties of the composite aircraft and its subassemblies. ATA Engineering, Inc., (ATA) completed two partial GVTs and a full-scale GVT to help Stratolaunch Systems Corporation engineers achieve their successful first flight. The results of the GVTs were used to update the finite element models (FEMs) used for flutter and dynamic stability predictions. Testing an aircraft of this size imposed a number of challenges not encountered in most GVT programs; to efficiently conduct the tests, a distributed data acquisition system approach was used, and seismic accelerometers characterized the aircraft’s low-frequency rigid body modes. The distribution of shakers and sensors around the aircraft was addressed by the implementation of a new sensor cable system and the adaptation of multishaker excitation methods using temporary support structures.