Baklanov V., Denisov S.

Compliance of aircraft to new noise standards defines the tendency to switch to extra-high bypass ratio engines (from 4…6 to 8…11). 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. The multi-connected model of a system 'engine - mounting - airframe' was elaborated by using generalized dynamic characteristics (such as dynamic compliance, mechanical impedance…) in attachment points. Analysis of experimental 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. Taking this into account the analytical function was found, which describe change of engine compliances frequency characteristics. The fitting parameters in calculation model based on experimental data. Within a wide range of rotor frequencies the dynamic behavior of engine body corresponds to the model of elastic-inertial system or to an elastic-dissipative element. It differs substantially from the idealized rigid-body model of aircraft gas turbine engine both by the value of dynamic compliance module and by the type of dynamic behavior. Obtained results are important for engine vibroisolation mount at the design stage