Numerical simulation of the system “engine-mounting-airframe” according to experimental data results

The introduction of high by-pass ratio engines has caused re-distribution of noise sources, broadening of the spectrum of power plant vibration impact and increase of structure-borne noise contribution to the acoustic field of the pressurized cabin. Facilities for reduction engine vibration intensity and vibration transfer along structure come first by selecting of vibration protection for pressurized cabin and integration vibration protection units into engine mounting attachments seems to us the most effective. But whatever vibration protection means (active or passive) are used to select parameters of vibration isolation units, calculated model is required which is based on real dynamic characteristics of engines and airframe in mounting points. The long-term investigations directed to dynamical characteristics definition for bodies of several engines (with different by-pass ratio) and airframe constructions of main-line aircraft allow to significantly specify calculation models of modern aircraft constructions in engine's rotor frequency range. And it allows to define tendency of engine's dynamical characteristics variation with by-pass ratio increasing. Analysis of obtained data makes it possible to divide the frequency range of investigation into three sub-ranges characterized by certain dynamic behavior of the engine and consequently each of said ranges can be provided with its special mathematical model – simple and clear enough.