System Identification and Modal Extraction from Response Data

ABSTRACT: To address the needs of the Air Force regarding improved flight control room tools, Systems Technology, Inc. (STI) proposes the development of a software toolbox suite for real-time aeroelastic aircraft system identification and modal extraction using flight test data. Modal extraction includes accurate identification of system modal frequencies, damping ratios, and aeroelastic mode shapes. Since high-performance aeroelastic aircraft are significantly driven by unmeasured atmospheric turbulence, a primary goal of the suite is identification of modal properties using only measured output data assuming no measured inputs. STI will leverage extensive experience in the field of aircraft system identification that utilize both the time and frequency domains to produce robust algorithms specialized for high-performance aeroelastic aircraft. These methods will exploit modern system identification approaches including subspace-based time domain identification and frequency domain decomposition that take direct advantage of data from distributed aircraft sensors. In addition to the core algorithm development, STI proposes a prototype visualization interface to aid flight test engineers in the control room. The visualization interface will include the ability to track in real-time system modal frequencies, damping ratios, and mode shapes with the ability to compare results directly with known analytical models in a clear and straightforward manner. BENEFIT: The capability and technology resulting from this research will specifically address the needs of the US Air Force Flight Test Center and similar DoD labs. The algorithms developed from this work will provide enhanced capability to the flight test engineer for use in the control room. Specifically, the analyst will have to ability to monitor, in real-time, the aeroelastic modal properties of a test vehicle in flight. Tracking modal frequencies, damping ratios and real-time mode shapes will allow on-the-fly assessment of the aircraft aeroelastic properties at flight condition including the impact on flying qualities and the proximity to the flutter boundary. The proposed visualization interface will allow the analyst to directly compare the flight test vehicle modal properties to existing models, presenting the information in a complete, clear and straightforward manner for efficiency and allowing for improved model validation and confident decision making for safety. Following a successful test, data can be used with the algorithms and visualization tools in off-line mode to update and enhance existing analytical models. Outside of the government, the proposed toolset can be utilized for aeroelastic certification and clearance by commercial aircraft manufacturers as both an on-line control room tool and an off-line analysis tool.