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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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  • 2
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    Eigenvalue/eigenvector assignment using output feedback (1978)
    In:  Other Sources
    Details
    Publication Date: 2011-08-17
    Description: The problem of pole-assignment in a linear time-invariant multivariable system using output feedback is considered. New sufficient conditions are derived to assign an almost arbitrary set of min (n, m+r-1) distinct eigenvalues, where n, m, and r are the number of states, inputs, and outputs, respectively. The analysis also highlights the freedom in selection of closed-loop eigenvectors which can be used for response shaping.
    Keywords: CYBERNETICS
    Type: IEEE Transactions on Automatic Control; AC-23; Feb. 197
    Format: text
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  • 3
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    Minimal order observers for linear functions of the state vector (1978)
    In:  Other Sources
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    Publication Date: 2011-08-17
    Description: The problem of estimating linear functions of a state vector in a multi-input/output system is considered. A simple lower bound on the observer order with arbitrary eigenvalues is established. Algorithms to construct minimal-order stable (or arbitrary dynamics) observers are also outlined.
    Keywords: CYBERNETICS
    Type: Electronics Letters; 14; Apr. 27
    Format: text
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  • 4
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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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  • 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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    Eigenvalue/eigenvector assignment using output feedback (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: The problem of eigenvalue assignment in a linear time-invariant system using output feedback is considered. New sufficient conditions are derived to assign an almost arbitrary set of minimum (n,m + r - 1) distinct eigenvalues where n, m, and r are the number of states, inputs, and outputs, respectively. These conditions precisely identify the class of systems where such an assignment is impossible. The synthesis technique also highlights the freedom in selection of closed-loop eigenvectors under output feedback. The utility of eigenvalue/eigenvector assignment in transient response shaping is illustrated by the design of a controller for the lateral dynamics of an aircraft.
    Keywords: CYBERNETICS
    Type: NASA-TP-1118 , L-11869
    Format: application/pdf
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  • 8
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    Modal control theory and application to aircraft lateral handling qualities design (1978)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: A multivariable synthesis procedure based on eigenvalue/eigenvector assignment is reviewed and is employed to develop a systematic design procedure to meet the lateral handling qualities design objectives of a fighter aircraft over a wide range of flight conditions. The closed loop modal characterization developed provides significant insight into the design process and plays a pivotal role in the synthesis of robust feedback systems. The simplicity of the synthesis algorithm yields an efficient computer aided interactive design tool for flight control system synthesis.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: NASA-TP-1234 , L-12177
    Format: application/pdf
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  • 9
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    Aeroservoelastic wind-tunnel investigations using the Active Flexible Wing Model: Status and recent accomplishments (1989)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The status of the joint NASA/Rockwell Active Flexible Wing Wind-Tunnel Test Program is described. The objectives are to develop and validate the analysis, design, and test methodologies required to apply multifunction active control technology for improving aircraft performance and stability. Major tasks include designing digital multi-input/multi-output flutter-suppression and rolling-maneuver-load alleviation concepts for a flexible full-span wind-tunnel model, obtaining an experimental data base for the basic model and each control concept and providing comparisons between experimental and analytical results to validate the methodologies. The opportunity is provided to improve real-time simulation techniques and to gain practical experience with digital control law implementation procedures.
    Keywords: AIRCRAFT DESIGN, TESTING AND PERFORMANCE
    Type: NASA-TM-101570 , NAS 1.15:101570 , AIAA Structures, Structural Dynamics and Materials Conference; Apr 03, 1989 - Apr 05, 1989; Mobile, AL; United States
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  • 10
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    Flutter suppression for the Active Flexible Wing - Control system design and experimental validation (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The synthesis and experimental validation of a control law for an active flutter suppression system for the Active Flexible Wing wind-tunnel model is presented. The design was accomplished with traditional root locus and Nyquist methods using interactive computer graphics tools and with extensive use of simulation-based analysis. The design approach relied on a fundamental understanding of the flutter mechanism to formulate understanding of the flutter mechanism to formulate a simple control law structure. Experimentally, the flutter suppression controller succeeded in simultaneous suppression of two flutter modes, significantly increasing the flutter dynamic pressure despite errors in the design model. The flutter suppression controller was also successfully operated in combination with a rolling maneuver controller to perform flutter suppression during rapid rolling maneuvers.
    Keywords: AIRCRAFT STABILITY AND CONTROL
    Type: AIAA PAPER 92-2097 , AIAA Dynamics Specialists Conference; Apr 16, 1992 - Apr 17, 1992; Dallas, TX; United States
    Format: text
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