Real-Time Mode Shape and Aeroelastic System Identification Toolset for Flight Test

ABSTRACT: The ability to ascertain rapid and accurate aeroelastic system stability margin as well as the ability to extract flight test structure mode shapes for on-the-fly investigation of aero-structure interactions are some of the real challenges facing control room engineers during flight testing of aircraft. The proposed developments in this Proposal aim to meet these challenges through the application of a non-linear system identification methodology applied to uncoupled single-degree-of-freedom generalized modal coordinates (GMC) used to identify aeroelastic stability via application of the Hilbert Transformation (HT) and a Covariance-Driven Stochastic Subspace (CDSS) approach to extract flight test structure mode shapes. ZONA Technology, Inc. will extend its commercially available ZONA Aeroelastic Model Simulator (ZAMS) product under the IADS flight test display environment and build upon its framework to establish new IADS displays that will clearly address these challenges. The proposed IADS displays will provide real time display of: (1) flight test derived and analytical overlaid mode shapes, (2) aeroelastic system frequency and damping time histories, (3) an aeroelastic system damping meter, and (4) modal participation plot. Two successful proof-of-concept studies based on these methods have been conducted. Once developed, these toolsets will significantly enhance the flight test control rooms decision making capability through better gauging of aircraft stability. BENEFIT: The proposed research and development effort will enhance flight test control room personnel's capability to gauge the flight test aircraft aeroelastic stability margin and to correlate flight test mode shapes with those computed from finite element analyses. By tracking trends during flight test, this tool can help to predict the onset of large amplitude oscillation that occur during flight (e.g., Limit Cycle Oscillation). For example, tracking of the system damping meter time history during maneuvers can establish thresholds when recorded amplitudes of oscillation exceed pre-determined terminate values. These thresholds can then be used as a predictor gauge during follow-on maneuvers. The mode shape correlation display, in conjunction with the aircraft aeroelastic response displayed in the ZAMS tool, will help identify how the structure modes interact with the aerodynamics throughout all flight conditions. In addition, this tool can be used to validate the finite element analysis model, typically done through expensive Ground Vibration Testing (GVT), by correlating the extracted flight test modes during low speed flight (i.e., where aeroelastic effects on the structure are minimal). Use of the proposed tools will help to minimize aircraft fatigue thereby reducing maintenance costs as well as provide valuable insight into the aero-structure interaction phenomenon that can lead to reduced flight testing. Mode shape correlation can alleviate costs and burden associated with GVT. Users of these tools will include IADS customers, such as, Edwards AFB, Eglin AFB, Naval Air Weapons Center, Korean Aerospace, Pratt & Whitney, Israeli Air Force, Singapore Air Force, Cessna, Bell Helicopter, Northrop Grumman, Alenia/Italy, General Atomics, Boeing, Gulfstream, Holloman AFB, Raytheon, Hill AFB, and Lockheed.