This article presents a structural analysis of the Unmanned Aerial System UAS-S4 ETHECATL. Mass, center of gravity position and mass moment of inertia are numerically determined and experimentally attested using the pendulum method.To determine the mass moment of inertia, a bifilar torsion-type pendulum is used for the Z-axis and a simple pendulum for the X and Y axes . A nonlinear dynamic model is developed for the rotational motion about the center of gravity (Gs) of the tested system, including the effects of large-angle oscillations, aerodynamic drag, viscous damping and additional mass effects.MATLAB genetic algorithms are then used to obtain the values of mass moment of inertia that would validate the experimental data with the numerical results.The experiment used data gathered by three sensors: an accelerometer, a gyroscope and a magnetometer. Therefore, a method is used to calibrate these three sensors.For determining the accuracy of the method, the experimental results for an object of uniform density for which the moment of inertia is computed numerically from geometrical data, are presented. The experimental results obtained for the UAS-S4 ETHECATL are also presented and compared to the analytical predictions . The experimental method gives, with respect to the numerical results, an error of 4.4% for the moment of inertia around the Z-axis and of 9.5% for the moment of inertia around the X and Y axes. In addition, the experimental results of UAS-S4 inertia validate the analytical predictions  with a relative error of 6.52% on average.