Estimation of flight modes with Hilbert-Huang transform

Purpose - This paper aims to present a new method for identification of some flight modes, including natural and non-standard modes, and extraction of their characteristics, directly from measurements of flight parameters in the time domain. Design/methodology/approach - The Hilbert-Huang transform (HHT), as a novel prevailing tool in the signal analysis field, is used to attain the purpose. The study shows that the HHT has superior potential capabilities to improve the airplane flying quality analysis and to conquer some drawbacks of the classical method in flight dynamics. Findings - The proposed method reveals the existence of some non-standard modes with small damping ratios at non-linear flight regions and obtains their characteristics. Research limitations/implications - The paper examines only airplane longitudinal dynamics. Further research is needed regarding lateral-directional dynamic modes and coupling effects of the longitudinal and lateral modes. Practical implications - Application of the proposed method to the flight test data may result in real-time flying quality analysis, especially at the non-linear flight regions. Originality/value - First, to utilize the empirical mode decomposition (EMD) capabilities in real time, a local-online algorithm is introduced which estimates the signal trend by the Savitzky-Golay sifting process and eliminates it from the signal in the EMD algorithm. Second, based on the local-online EMD algorithm, a systematic method is proposed to identify flight modes from flight parameters in the time domain.