Flutter Analysis Methodology for Military Aircraft with External Stores – IAR-99 HAWK

The new Finite Elements Model (FEM) allows the visualization of the results and the study of the behavior of the structure at the local level (frames stringers; spars; frame-body, shell-body and longeron-body interaction) in the case of global dynamical phenomena. After creating FEM of the aircraft IAR-99 HAWK in the empty equipped configuration using special elements, the team decided to extend the study of flutter to aircraft in different external stores configurations. The results of the theoretical free-free vibrations obtained for the IAR-99 HAWK in different external stores configurations are presented and compared to those obtained from ground tests, thus confirming the accuracy of the new Finite Element Model (FEM). The aerodynamic idealization of the IAR-99 HAWK in external stores configurations aircraft was made using the Doublet Lattice Method (DLM) for subsonic flow, also considering the load-bearing wing/fuselage/pylon/store interference and aims to determine the generalized aerodynamic forces. The flutter calculation for the IAR-99 HAWK in external stores configurations aircraft, was made using the p-K methodology presented in the MSC. Nastran program, using the vibration modes obtained on the basis of the new finite element model and the matrix of generalized aerodynamic forces in subsonic flow. The V-g curves drawn lead us to flutter speeds outside the safety margin related to the maneuvering diagram, according to the regulations in force, both in the case of the plane in smooth configuration and the plane in the selected external storers variants.