In the tilting process of the three-rotor UAV,the rotational inertia of the body along each axis direction will change as the nacelle angle of the engine changes.In order to realize the precise control of the three-rotor UAV in the tilting transitional mode,it is necessary to study the changes of the rotational inertia during the tilting process and to build a suitable mathematical model.By analyzing the changes of the position of the gravity center of the three-rotor UAV in its tilting process,the basic principle and experimental method of the torsion pendulum are used to analyze the rotational inertia of the aircraft under the condition of different nacelle angles.The relationship between the rotational inertia and the nacelle angle is obtained,which has laid a theoretical foundation for the modeling of the rotary three-rotor UAV in the tilting process.