The paper deals with a special case of identifying the operation mode of an unmanned aircraft (UAV) engine by an acoustic signal (provided that a known type of propellers is used), the main frequency extraction from the signal, and a numerical experiment. A full-scale experiment was performed with the recording of the acoustic signal of a real quadrocopter. The signal is analyzed by the method of frequency filters and Fourier transform. A numerical experiment was performed on a scanned model of a UAV propeller, rotating at a frequency obtained from an acoustic signal. The experiment involved a hybrid finite-volume method on the mesh of the finite element method of the ANSYS CFX simulation environment. The correspondence of the required lifting force with the permissible error is revealed, and as a result, the ability to identify the engine operating mode by an acoustic signal is shown. The field measurements of the acoustic signal are compared with the values recovered from a numerical experiment. A significant amount of data has been obtained suitable for use in the inverse problem and semi-analytic methods.