Flight Testing

Vibration Analyisis: Noise Reduction

The vibration analysis is a very important part of the design and test of a new aeroplane. It gives lots of information about the behavior of the structure against the excitation of the different harmonic forces that can be found in these kinds of structures. Moreover, these analyses are useful to calculate the fatigue that the structure can withstand. In this analysis the effects of the vibrations produced by the engine have been studied, paying special attention to the noise produced in the cabin, and proposing solutions to reduce it. The engine of the aeroplane is a ROTAX 912. To make a proper analysis it has been decided to work with ANSYS software.

In order to obtain useful results, it was decided to execute a modal and harmonic response analysis. The first one can give details about the natural modes of vibration of the structure without taking into account the excitation produced by the engine or other sources. The modal analysis is also useful to evaluate the validity of the geometric model. For instance, there have been some problems doing a mesh which keeps all the elements tied together, therefore, when that happens the elements disconnected appear in the first modes with movements that only involve the element.

Next video shows the displacements produced for the mode number 100:



Regarding the harmonic response, it shows the accelerance of important points of the cabin. It has been analyzed the model for the frequencies of the engine, propeller, cylinder and some multiples. The following video shows the displacements produced by the engine excitation (83,33 Hz):



As a solution for the vibratory problem, an improvement of the engine mount through an iterative process through numerical simulations permits selecting a better solution for isolating components.


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