Finite-Element Analysis of a Mach-8 Flight Test Article Using Nonlinear Contact Elements

A flight test article, called a glove, is required for a Mach-8 boundary-layer experiment to be conducted on a flight mission of the air-launched Pegasus® space booster. The glove is required to provide a smooth, threedimensional, structurally stable, aerodynamic surface and includes instrumentation to determine when and where boundary-layer transition occurs during the hypersonic flight trajectory. A restraint mechanism has been invented to attach the glove to the wing of the space booster. The restraint mechanism securely attaches the glove to the wing in directions normal to the wing/glove interface surface, but allows the glove to thermally expand and contract to alleviate stresses in directions parallel to the interface surface. A finite-element analysis has been performed using nonlinear contact elements to model the complex behavior of the sliding restraint mechanism. This paper provides an overview of the glove design and presents details of the analysis that were essential to demonstrate the flight worthiness of the wing-glove test article. Results show that all glove components are well within the allowable stress and deformation requirements to satisfy the objectives of the flight research experiment. INTRODUCTION Preparations are currently underway for a flight experiment that will acquire data necessary to validate boundary-layer transition prediction methods for hypersonic flight conditions. Success of the flight experiment depends on the design and development of a flight test fixture, called a glove, which can provide a smooth, threedimensional, structurally stable, aerodynamic surface from which detailed information regarding the atmospheric flight environment to a maximum of Mach 8 could be obtained. A flight test article has been designed, analyzed, manufactured, and installed on the wing of the air-launched Pegasus® (Orbital Sciences Corporation, Fairfax, Virginia) space booster. Figure 1 shows the geometry of the booster and the location of the glove for the boundary-layer experiment. The Pegasus® is a multistaged, air-launched rocket designed to place small payloads into low Earth orbit. The booster follows a predetermined trajectory designed for a particular payload requirement. For a typical mission, the booster separates from the carrier aircraft at Mach 0.8 and an altitude of approximately 13,000 m. The booster descends for 5 sec before the first stage ignites. After approximately 70 sec, the vehicle has accelerated to Mach 8 and an altitude of approximately 61,000 m. The glove experiment concludes as the first stage burns out and is jettisoned and second-stage ignition occurs. Figure 1: Plan view of Pegasus® space booster with glove. 15.2 m