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  • 1
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    Testing and Validation of the Dynamic Inertia Measurement Method (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Dynamic Inertia Measurement (DIM) method uses a ground vibration test setup to determine the mass properties of an object using information from frequency response functions. Most conventional mass properties testing involves using spin tables or pendulum-based swing tests, which for large aerospace vehicles becomes increasingly difficult and time-consuming, and therefore expensive, to perform. The DIM method has been validated on small test articles but has not been successfully proven on large aerospace vehicles. In response, the National Aeronautics and Space Administration Armstrong Flight Research Center (Edwards, California) conducted mass properties testing on an "iron bird" test article that is comparable in mass and scale to a fighter-type aircraft. The simple two-I-beam design of the "iron bird" was selected to ensure accurate analytical mass properties. Traditional swing testing was also performed to compare the level of effort, amount of resources, and quality of data with the DIM method. The DIM test showed favorable results for the center of gravity and moments of inertia; however, the products of inertia showed disagreement with analytical predictions.
    Keywords: Aircraft Design, Testing and Performance; Structural Mechanics
    Type: AFRC-E-DAA-TN18039 , IMAC Conference and Exposition on Structural Dynamics; Feb 02, 2015 - Feb 05, 2015; Orlando, FL; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    Experimental Validation of the Dynamic Inertia Measurement Method to Find the Mass Properties of an Iron Bird Test Article (2015)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The mass properties of an aerospace vehicle are required by multiple disciplines in the analysis and prediction of flight behavior. Pendulum oscillation methods have been developed and employed for almost a century as a means to measure mass properties. However, these oscillation methods are costly, time consuming, and risky. The NASA Armstrong Flight Research Center has been investigating the Dynamic Inertia Measurement, or DIM method as a possible alternative to oscillation methods. The DIM method uses ground test techniques that are already applied to aerospace vehicles when conducting modal surveys. Ground vibration tests would require minimal additional instrumentation and time to apply the DIM method. The DIM method has been validated on smaller test articles, but has not yet been fully proven on large aerospace vehicles.
    Keywords: Aircraft Design, Testing and Performance; Structural Mechanics
    Type: DFRC-E-DAA-TN18038 , AIAA/ASME/ASCE/AHS/ASC Structures, Structural Dynamics, and Materials Conference; Jan 05, 2015 - Jan 09, 2015; Kissimmee, FL; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Robust Modal Filtering and Control of the X-56A Model with Simulated Fiber Optic Sensor Failures (2016)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: The X-56A aircraft is a remotely-piloted aircraft with flutter modes intentionally designed into the flight envelope. The X-56A program must demonstrate flight control while suppressing all unstable modes. A previous X-56A model study demonstrated a distributed-sensing-based active shape and active flutter suppression controller. The controller relies on an estimator which is sensitive to bias. This estimator is improved herein, and a real-time robust estimator is derived and demonstrated on 1530 fiber optic sensors. It is shown in simulation that the estimator can simultaneously reject 230 worst-case fiber optic sensor failures automatically. These sensor failures include locations with high leverage (or importance). To reduce the impact of leverage outliers, concentration based on a Mahalanobis trim criterion is introduced. A redescending M-estimator with Tukey bisquare weights is used to improve location and dispersion estimates within each concentration step in the presence of asymmetry (or leverage). A dynamic simulation is used to compare the concentrated robust estimator to a state-of-the-art real-time robust multivariate estimator. The estimators support a previously-derived mu-optimal shape controller. It is found that during the failure scenario, the concentrated modal estimator keeps the system stable.
    Keywords: Aircraft Stability and Control; Avionics and Aircraft Instrumentation
    Type: NASA/TM-2016-219430 , DFRC-E-DAA-TN36531
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Virtual Deformation Control of the X-56A Model with Simulated Fiber Optic Sensors (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-12
    Description: A robust control law design methodology is presented to stabilize the X-56A model and command its wing shape. The X-56A was purposely designed to experience flutter modes in its flight envelope. The methodology introduces three phases: the controller design phase, the modal filter design phase, and the reference signal design phase. A mu-optimal controller is designed and made robust to speed and parameter variations. A conversion technique is presented for generating sensor strain modes from sensor deformation mode shapes. The sensor modes are utilized for modal filtering and simulating fiber optic sensors for feedback to the controller. To generate appropriate virtual deformation reference signals, rigid-body corrections are introduced to the deformation mode shapes. After successful completion of the phases, virtual deformation control is demonstrated. The wing is deformed and it is shown that angle-ofattack changes occur which could potentially be used to an advantage. The X-56A program must demonstrate active flutter suppression. It is shown that the virtual deformation controller can achieve active flutter suppression on the X-56A simulation model.
    Keywords: Aircraft Stability and Control; Aircraft Design, Testing and Performance
    Type: NASA/TM-2014-216616 , DFRC-E-DAA-TN11781
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    X-56A Structural Dynamics Ground Testing Overview and Lessons Learned (2020)
    In:  CASI
    Details
    Publication Date: 2020-01-22
    Description: The X-56A Multi-Utility Technology Testbed (MUTT) is a subscale, fixed-wing aircraft designed for high-risk aeroelastic flight demonstration and research. Structural dynamics ground testing for model validation was especially important for this vehicle because the structural model was directly used in the development of a flight control system with active flutter suppression capabilities. Structural dynamics ground tests of the X-56A MUTT with coupled rigid-body and structural modes provided a unique set of challenges. An overview of the ground vibration test (GVT) and moment of inertia (MOI) test setup and execution is presented. The series of GVTs included the wing by itself attached to a strongback and complete vehicle at two mass conditions: empty and full fuel. Two boundary conditions for the complete-vehicle test were studied: on landing gear and suspended free-free. Pitch MOI tests were performed using a compound pendulum method and repeated with two different pendulum lengths for independent verification. The original soft-support test configuration for the GVT used multiple bungees, resulting in unforeseen coupling interactions between the soft-support bungees and the vehicle structural modes. To resolve this problem, the soft-support test setup underwent multiple iterations. The various GVT configurations and boundary-condition modifications are highlighted and explained. Lessons learned are captured for future consideration when performing structural dynamics testing with similar vehicles.
    Keywords: Research and Support Facilities (Air)
    Type: AFRC-E-DAA-TN73735 , AIAA SciTech Forum 2020; Jan 06, 2020 - Jan 10, 2020; Orlando, FL; United States
    Format: application/pdf
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
  • 6
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    Robust Modal Filtering and Control of the X-56A Model with Simulated Fiber Optic Sensor Failures (2014)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The X-56A aircraft is a remotely-piloted aircraft with flutter modes intentionally designed into the flight envelope. The X-56A program must demonstrate flight control while suppressing all unstable modes. A previous X-56A model study demonstrated a distributed-sensing-based active shape and active flutter suppression controller. The controller relies on an estimator which is sensitive to bias. This estimator is improved herein, and a real-time robust estimator is derived and demonstrated on 1530 fiber optic sensors. It is shown in simulation that the estimator can simultaneously reject 230 worst-case fiber optic sensor failures automatically. These sensor failures include locations with high leverage (or importance). To reduce the impact of leverage outliers, concentration based on a Mahalanobis trim criterion is introduced. A redescending M-estimator with Tukey bisquare weights is used to improve location and dispersion estimates within each concentration step in the presence of asymmetry (or leverage). A dynamic simulation is used to compare the concentrated robust estimator to a state-of-the-art real-time robust multivariate estimator. The estimators support a previously-derived mu-optimal shape controller. It is found that during the failure scenario, the concentrated modal estimator keeps the system stable.
    Keywords: Aircraft Stability and Control
    Type: DFRC-E-DAA-TN14268 , AIAA Atmospheric Flight Mechanics Conference; Jun 16, 2014 - Jun 20, 2014; Atlanta, GA; United States
    Format: application/pdf
    Location Call Number Expected Availability
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    NASA TECHNICAL REPORTS
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