Aeroelastic Stability of a Transport Aircraft With Wing Mounted Store Suspension: Part II — Flight Test

This study outlines the work performed for the flight test verification of the aeroelastic stability of a transport aircraft modified with the installation of an external store to the outer wing. The purpose of the flight test phase was to demonstrate that the aircraft with wing mounted external store suspension was free from flutter within the flight envelope up to the dive speed of the aircraft. Based on the flutter analysis results of the previous study, the most critical two mass configurations were selected for the flutter flight test. The impact of sound flutter analyses on the reduction of the number of flights, and the selection criteria of the flight test configurations of the aircraft was highlighted. After the final evaluation of the flutter analysis results, a six sorty of flight test was planned to be executed with an instrumented aircraft for flutter testing of the modified aircraft for two different mass and CG configurations, and envelope expansion is achieved up to the dive speed of the basic aircraft. Analysis of the damping data of the flight test phase indicate that overall damping of the wing vibration modes stay above the minimum 3% aerodynamic plus structural damping, required by the flutter regulation MIL-A-8870C, for the wing structure modes up to about 10 Hz which is a typical frequency range that can be excited by control surface kicks. The lowest damping values were identified to be associated with the external store-wing structural interface and improvement recommendations for the store-wing interface were given.