Study of the effects of tooth geometry on characteristics of contact In the aeronautic field even the smallest aspect can results determining in term of performance and competitiveness. There is a continuous request for lighter product to minimize weights and costs. In this context vibrations have a very important role. They are source of noise and could bring at unexpected resonances, therefore represents a critical aspect to analyze paying extreme attention. Even if this kind of investigations would be referred to a system, it it not possible yet to neglect the sub-systems analysis. For this reason, this thesis is focused on static and dynamic aspects of gears, in particular way on spur gears.