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  • 1
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    Design and test of three active flutter suppression controllers (1991)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: Three flutter suppression control law design techniques are presented. Each uses multiple control surfaces and/or sensors. The first uses linear combinations of several accelerometer signals together with dynamic compensation to synthesize the modal rate of the critical mode for feedback to distributed control surfaces. The second uses traditional tools (pole/zero loci and Nyquist diagrams) to develop a good understanding of the flutter mechanism and produce a controller with minimal complexity and good robustness to plant uncertainty. The third starts with a minimum energy Linear Quadratic Gaussian controller, applies controller order reduction, and then modifies weight and noise covariance matrices to improve multi-variable robustness. The resulting designs were implemented digitally and tested subsonically on the Active Flexible Wing (AFW) wind tunnel model. Test results presented here include plant characteristics, maximum attained closed-loop dynamic pressure, and Root Mean Square control surface activity. A key result is that simultaneous symmetric and antisymmetric flutter suppression was achieved by the second control law, with a 24 percent increase in attainable dynamic pressure.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: Fourth NASA Workshop on Computational Control of Flexible Aerospace Systems, Part 2; p 535-56
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 2
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    A methodology for computing uncertainty bounds of multivariable systems based on sector stability theory concepts (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The application of a sector-based stability theory approach to the formulation of useful uncertainty descriptions for linear, time-invariant, multivariable systems is explored. A review of basic sector properties and sector-based approach are presented first. The sector-based approach is then applied to several general forms of parameter uncertainty to investigate its advantages and limitations. The results indicate that the sector uncertainty bound can be used effectively to evaluate the impact of parameter uncertainties on the frequency response of the design model. Inherent conservatism is a potential limitation of the sector-based approach, especially for highly dependent uncertain parameters. In addition, the representation of the system dynamics can affect the amount of conservatism reflected in the sector bound. Careful application of the model can help to reduce this conservatism, however, and the solution approach has some degrees of freedom that may be further exploited to reduce the conservatism.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-TP-3166 , L-16846 , NAS 1.60:3166
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 3
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    Design, test, and evaluation of three active flutter suppression controllers (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Three control law design techniques for flutter suppression are presented. Each technique uses multiple control surfaces and/or sensors. The first method uses traditional tools (such as pole/zero loci and Nyquist diagrams) for producing a controller that has minimal complexity and which is sufficiently robust to handle plant uncertainty. The second procedure uses linear combinations of several accelerometer signals and dynamic compensation to synthesize the model rate of the critical mode for feedback to the distributed control surfaces. The third technique starts with a minimum-energy linear quadratic Gaussian controller, iteratively modifies intensity matrices corresponding to input and output noise, and applies controller order reduction to achieve a low-order, robust controller. The resulting designs were implemented digitally and tested subsonically on the active flexible wing wind-tunnel model in the Langley Transonic Dynamics Tunnel. Only the traditional pole/zero loci design was sufficiently robust to errors in the nominal plant to successfully suppress flutter during the test. The traditional pole/zero loci design provided simultaneous suppression of symmetric and antisymmetric flutter with a 24-percent increase in attainable dynamic pressure. Posttest analyses are shown which illustrate the problems encountered with the other laws.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-TM-4338 , L-17041 , NAS 1.15:4338
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Modeling and model simplification of aeroelastic vehicles: An overview (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The rigid-body degrees of freedom and elastic degrees of freedom of aeroelastic vehicles are typically treated separately in dynamic analysis. Such a decoupling, however, is not always justified and modeling assumptions that imply decoupling must be used with caution. The frequency separation between the rigid-body and elastic degrees of freedom for advanced aircraft may no longer be sufficient to permit the typical treatment of the vehicle dynamics. Integrated, elastic vehicle models must be developed initially and simplified in a manner appropriate to and consistent with the intended application. This paper summarizes key results from past research aimed at developing and implementing integrated aeroelastic vehicle models for flight controls analysis and design. Three major areas will be addressed: (1) the accurate representation of the dynamics of aeroelastic vehicles, (2) properties of several model simplification methods, and (3) the importance of understanding the physics of the system being modeled and of having a model which exposes the underlying physical causes for critical dynamic characteristics.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-TM-107691 , NAS 1.15:107691
    Format: application/pdf
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  • 5
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    Active flutter suppression using dipole filters (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: By using traditional control concepts of gain root locus, the active suppression of a flutter mode of a flexible wing is examined. It is shown that the attraction of the unstable mode towards a critical system zero determines the degree to which the flutter mode can be stabilized. For control situations where the critical zero is adversely placed in the complex plane, a novel compensation scheme called a 'Dipole' filter is proposed. This filter ensures that the flutter mode is stabilized with acceptable control energy. The control strategy is illustrated by designing flutter suppression laws for an active flexible wing (AFW) wind-tunnel model, where minimal control effort solutions are mandated by control rate saturation problems caused by wind-tunnel turbulence.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-TM-107594 , NAS 1.15:107594
    Format: application/pdf
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  • 6
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    Design and experimental validation of a flutter suppression controller for the active flexible wing (1992)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The synthesis and experimental validation of an active flutter suppression controller for the Active Flexible Wing wind tunnel model is presented. The design is accomplished with traditional root locus and Nyquist methods using interactive computer graphics tools and extensive simulation based analysis. The design approach uses a fundamental understanding of the flutter mechanism to formulate a simple controller structure to meet stringent design specifications. Experimentally, the flutter suppression controller succeeded in simultaneous suppression of two flutter modes, significantly increasing the flutter dynamic pressure despite modeling errors in predicted flutter dynamic pressure and flutter frequency. The flutter suppression controller was also successfully operated in combination with another controller to perform flutter suppression during rapid rolling maneuvers.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-TM-4381 , L-16977 , NAS 1.15:4381
    Format: application/pdf
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  • 7
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    Design of an active flutter suppression system for the Active Flexible Wing (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The design of an active flutter suppression controller and wind tunnel validation test results are presented. This controller, designed using Nyquist methods and traditional root locus, is applied to the Active Flexible Wing (AFW) wind tunnel model. Wind tunnel tests were conducted to validate the design and demonstrate flutter suppression at a fixed altitude while performing aggressive rolling maneuvers representative of high-performance military aircraft. The controller succeeded in simultaneous suppression of two distinct flutter modes by significantly increasing the flutter dynamic pressure in spite of errors in the mathematical model.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 91-3111
    Format: text
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  • 8
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    Modeling and model simplification of aeroelastic vehicles (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: The rigid-body degrees of freedom and elastic degrees of freedom of aeroelastic vehicles are typically treated separately in dynamic analysis. Such a decoupling, however, is not always justified and modeling assumptions that imply decoupling must be used with caution. The frequency separation between the rigid-body and elastic degrees of freedom for advanced aircraft may no longer be sufficient to permit the typical treatment of the vehicle dynamics. Integrated, elastic vehicle models must be developed initially and simplified in a manner appropriate to and consistent with the intended application. This paper summarizes key results from the research aimed at developing and implementing integrated aeroelastic vehicle models for flight controls analysis and design. Three major areas will be addressed: (1) the accurate representation of the dynamics of aeroelastic vehicles, (2) properties of several model simplification methods, and (3) the importance of understanding the physics of the system being modeled and of having a model which exposes the underlying physical causes for critical dynamic characteristics.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: ICAS Congress; Sept. 9-14, 1990; Stockholm; Sweden
    Format: text
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  • 9
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    A simulation study of the flight dynamics of elastic aircraft. Volume 2: Data (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The simulation experiment described addresses the effects of structural flexibility on the dynamic characteristics of a generic family of aircraft. The simulation was performed using the NASA Langley VMS simulation facility. The vehicle models were obtained as part of this research project. The simulation results include complete response data and subjective pilot ratings and comments and so allow a variety of analyses. The subjective ratings and analysis of the time histories indicate that increased flexibility can lead to increased tracking errors, degraded handling qualities, and changes in the frequency content of the pilot inputs. These results, furthermore, are significantly affected by the visual cues available to the pilot.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-CR-4102-VOL-2 , NAS 1.26:4102-VOL-2
    Format: application/pdf
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  • 10
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    A simulation study of the flight dynamics of elastic aircraft. Volume 1: Experiment, results and analysis (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The simulation experiment described addresses the effects of structural flexibility on the dynamic characteristics of a generic family of aircraft. The simulation was performed using the NASA Langley VMS simulation facility. The vehicle models were obtained as part of this research. The simulation results include complete response data and subjective pilot ratings and comments and so allow a variety of analyses. The subjective ratings and analysis of the time histories indicate that increased flexibility can lead to increased tracking errors, degraded handling qualities, and changes in the frequency content of the pilot inputs. These results, furthermore, are significantly affected by the visual cues available to the pilot.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-CR-4102 , NAS 1.26:4102
    Format: application/pdf
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