טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentKariv Daniel Haim
SubjectDynamic Response of an Elastic Aircraft to Store Ejection
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Daniella Raveh


Abstract

This study presents a novel approach for the analysis of single and ripple ejections in the frequency domain, accounting for the time-variation of the inertial properties of the configuration. The major advantage of the method is that it does not rely on an approximation of the unsteady aerodynamic forces, as required for time-domain analyses. The test case of the study is a subsonic, elastic, generic unmanned aircraft carrying up to six stores on each wing. Using the newly developed simulation tool and advanced signal processing tools, the study investigates how the different load sources (jettison, inertial, and aerodynamic forces) affect the total load, which structural modes are involved in each response, and how the time interval between ripple ejections affects the resulting loads. It is shown that the jettison and inertial forces are the largest contributors to the structural loads. Although the aerodynamic load is insignificant compared with the other loads, it critically affects the dynamic response by adding a damping force, which is dependent on the flight dynamic pressure. Study of the ripple time-interval between consecutive ejections effect on the maximal load, showed that a larger time interval does not necessarily lead to lower loads.

Ripple ejections were simulated using several optional variations of the numerical analysis in the frequency domain. It was concluded that the most accurate and robust method is to solve the nominal system response in the modal approach and then to use the same mode set for the modal solution of the new system, following the ejection. It is also shown that a relatively small number of natural modes, about 30 for the studied test case, is sufficient to accurately compute the load.

The study also includes a parametric investigation of the effect of several physical and numerical parameters on the results. These include the number of modes used for the analysis, the analysis time step, the structural damping, the dynamic pressure, the ejected store mass, and the ejection force. All those parameters have a direct effect on the resulting loads and hence have to be considered in a practical ejection case.