AFRL-Developed Simulation Tool Improves Aircraft-Stores Carriage Certification Process Published Aug. 29, 2007 By Air Vehicles Directorate AFRL/VA WRIGHT-PATTERSON AIR FORCE BASE, Ohio -- AFRL researchers delivered the Medium-Fidelity Flutter Analysis Tool (MEDFFAT) to the Air Force SEEK EAGLE office (AFSEO). The first of three tools designed to enhance AFSEO's simulation and modeling capabilities, MEDFFAT improves the limited, linear capacity of current commercial off-the-shelf (COTS) software by allowing users to more accurately assess the stability of aircraft carrying stores during transonic flight, which occurs in a highly nonlinear aeroelastic environment. A team of researchers from AFRL, Lockheed Martin Aerodynamics, and ZONA Technology worked with collaborators from the National Aeronautics and Space Administration (NASA) to develop the MEDFFAT software, OVERCAP™. This streamlined aircraftstores clearance product will improve AFSEO's process for certifying stores carriage safety, ultimately enabling the Air Force to field new weapons more quickly and confidently. During transonic flight, the interaction between airflow and an aircraft loaded with stores often produces unstable or limited-amplitude, time-periodic wing deformations, which can lead to pilot disorientation, loss of wing fatigue life, or even catastrophic wing failure. Therefore, for each new missile, bomb, or external fuel tank, AFSEO researchers must verify safe carriage (1) at nine different stations along the wingspan, (2) for a large permutation of carriage configuration combinations, and (3) under many different flight conditions and maneuvers. The linear capability of current COTS software cannot model nonlinear transonic physics or accommodate multibody stores aerodynamics. OVERCAP overcomes these limitations by automatically generating transonic computational grids for the aircraft and its stores based on a single linear panel model, solving the nonlinear aeroelastic equations, and interpolating the solutions between the aircraft and stores grids. The core of the OVERCAP tool is a highly modified version of the NASA Langley Research Center's computational aeroelasticity algorithm for inviscid and viscous flow, known as CAPTSDv. The team's modifications to CAPTSDv include implementation of an overset grid methodology and new boundary conditions. These improvements enable the influence of stores aerodynamics to be modeled. In the MEDFFAT process, OVERCAP first generates a nonlinear steady-state result for a given flight condition. This is followed by several dynamic nonlinear aeroelastic analyses for flight test maneuvers at the steadystate flight condition. The results are then processed to provide information used for assessing safe carriage of the configuration.