Book•
Survey of Applications of Active Control Technology for Gust Alleviation and New Challenges for Lighter-Weight Aircraft
28 Jun 2013-
TL;DR: In this paper, the authors provide a historical survey and assessment of the state of the art in the modeling and application of active control to aircraft encountering atmospheric disturbances in flight, with particular emphasis on applications that enable weight reduction in aircraft by mitigating the effects of atmospheric disturbances.
Abstract: This report provides a historical survey and assessment of the state of the art in the modeling and application of active control to aircraft encountering atmospheric disturbances in flight. Particular emphasis is placed on applications of active control technologies that enable weight reduction in aircraft by mitigating the effects of atmospheric disturbances. Based on what has been learned to date, recommendations are made for addressing gust alleviation on as the trend for more structurally efficient aircraft yields both lighter and more flexible aircraft. These lighter more flexible aircraft face two significant challenges reduced separation between rigid body and flexible modes, and increased sensitivity to gust encounters due to increased wing loading and improved lift to drag ratios. The primary audience of this paper is engineering professionals new to the area of gust load alleviation and interested in tackling the multifaceted challenges that lie ahead for lighter-weight aircraft.
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TL;DR: Active flutter suppression, which is a part of the group of flight vehicle technologies known as active controls, is an important contributor to the effective solution of aeroelastic instability.
Abstract: Active flutter suppression, which is a part of the group of flight vehicle technologies known as active controls, is an important contributor to the effective solution of aeroelastic instability pr...
129 citations
TL;DR: In this article, a symmetric, active, gust load alleviation system for a regional transport aircraft, based on a static output feedback with a constrained structure, is presented, which is carried out on a comprehensive finite state aeroservoelastic model, including sensor units and actuator transfer functions.
Abstract: The paper presents the design of a symmetric, active, gust load alleviation system for a regional transport aircraft, based on a static output feedback with a constrained structure. The design is carried out on a comprehensive finite state aeroservoelastic model, including sensor units and actuator transfer functions, and verified by taking into account saturated control positions, rates, and hinge moments. The controller is designed within a quadratic optimal framework, through a second-order Hessian-based optimization algorithm, exploiting block diagonal Schur transformations of the closed-loop state equations and performance weightings. An accurately chosen worst discrete gust and a reference flight condition provide a baseline design, which is significantly effective in alleviating continuous turbulence loads. Such a reference design proves itself robust enough to alleviate atmospheric loads over the complete flight envelope and is eventually further improved and robustified through a simple bilinear ...
43 citations
TL;DR: In this article, an adaptive feed-forward controller that uses the preview information of the gust sensed by an onboard alpha probe is designed to operate the ailerons symmetrically to alleviate the wing-root bending moment induced by the gust.
Abstract: This study develops an active control technology to reduce the incremental dynamic loads of a large four-engine transport airplane flying through a gust field The mathematical model of the proposed gust-alleviation system features composite structural motions (for example, rigid-body motions, elastic vibrations, and deflections of control surfaces) and unsteady aerodynamic forces induced by the structural motions and the gusts A clear outline of the procedure is first provided to determine the aeroservoelastic equation of the system Then, an adaptive feedforward controller that uses the preview information of the gust sensed by an onboard alpha probe is designed to operate the ailerons symmetrically to alleviate the wing-root bending moment induced by the gust The rigid-body motions due to travelling gusts are also compensated for using symmetrical deflections of the elevators To solve the problems of weight drift and weight bias that are commonly encountered in adaptive control, the circular leaky l
32 citations
05 Jun 2017
TL;DR: A combined feedback and feedforward active load alleviation system and its associated design and tuning methodology that remains very easy to use and tune, thanks to a limited number of parameters that can easily be interpreted physically and that exhibit only very little and very predictable couplings.
Abstract: This paper presents a combined feedback and feedforward active load alleviation system and its associated design and tuning methodology The feedback part is strongly structured and its robust performance across the flight envelope is ensured by the use of a multi-model and multi-objective controller design approach The feedforward function is based on a Doppler LIDAR sensor and the processing of the measurements as well as their physical interpretation combines various ideas from the system identification, the signal processing, and the control design domains The proposed solution remains very easy to use and tune, thanks to a limited number of parameters that can easily be interpreted physically and that exhibit only very little and very predictable couplings The performance and behavior of the active load alleviation functions is shown extensively based on a representative flexible long range aircraft model (based on the Airbus XRF1 configuration)
31 citations
TL;DR: This paper presents a systematic and comprehensive overview of important concepts and applications of gust loads on aircraft, and recommends to learn from previous experiences to avoid aviation accidents due to flight through atmospheric gusts and turbulence.
Abstract: An important prerequisite for the design, assessment and certification of aircraft and their associated control systems is a quantitative specification of the environment in which the aircraft is intended to operate, for example, atmospheric gust. Gust loads on aircraft may induce detrimental influences such as increased aerodynamic and structural loads, structural deformation and decreased flight dynamic performance. This paper presents a systematic and comprehensive overview of important concepts and applications of gust loads on aircraft. This overview includes a brief research background, concepts, research techniques, influences and load alleviation measures of gust. Finally, we summarise some potential improvements in the future work. It is also recommended to learn from previous experiences to avoid aviation accidents due to flight through atmospheric gusts and turbulence.
27 citations
Cites methods from "Survey of Applications of Active Co..."
...In active control systems, only aerodynamic control surfaces belonging to the aircraft itself, such as flaps and ailerons, are used to generate aerodynamic forces modifying the overall forces with gusts according to a control law relating motions of the control surfaces according to the measurements made on the aircraft(183)....
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References
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15 Nov 2007TL;DR: In this paper, the authors present a MATLAB/SIMULINK program for flight/ground manoeuvres and Gust/Turbulence Encounters, with a focus on the effect of wing flexibility on lift distribution and Divergence.
Abstract: Preface. Introduction. Abbreviations. Part I: Background Material. 1. Vibration of Single Degree of Freedom Systems. 2. Vibration of Multiple Degree of Freedom Systems. 3. Vibration of Continuous Systems - Assumed Shapes Approach. 4. Vibration of Continuous Systems - Discretization Approach. 5. Introduction to Steady Aerodynamics. 6. Introduction to Loads. 7. Introduction to Control. Part II: Introduction to Aeroelasticity and Loads. 8. Static Aeroelasticity - Effect of Wing Flexibility on Lift Distribution and Divergence. 9. Static Aeroelasticity - Effect of Wing Flexibility on Control Effectiveness. 10. Introduction to Unsteady Aerodynamics. 11. Dynamic Aeroelasticity - Flutter. 12. Aeroservoelasticity. 13. Equilibrium Manoeuvres. 14. Flight Mechanics Model for Dynamic Manoeuvres. 15. Dynamic Manoeuvres. 16. Gust and turbulence Encounters. 17. Ground Manoeuvres. 18. Aircraft Internal Loads. 19. Potential Flow Aerodynamics. 20. Coupling of Structural and Aerodynamic Computational Models. Part III: Introduction to Industrial Practice. 21. Aircraft Design and Certification. 22. Aeroelasticity and Loads Models. 23. Static Aeroelasticity and Flutter. 24. Flight Manoeuvre and Gust/Turbulence Loads. 25. Ground Manoeuvre Loads. 26. Testing relevant to Aeroelasticity and Loads. Appendices. A. Aircraft Rigid Body Modes. B. Table of Longitudinal Aerodynamic Derivatives. C. Aircraft Symmetric Flexible Modes. D. Model Condensation. E. Aerodynamic Derivatives in body Fixed Axes. F. Aircraft Antisymmetric Flexible Modes. References. Index. Programs Accessible (on the Companion Website) via the Internet. G. MATLAB/SIMULINK Programs for Vibration. H. MATLAB/SIMULINK Programs for Flutter. I. MATLAB/SIMULINK Programs for Flight/Ground Manoeuvres and Gust/Turbulence Encounters.
564 citations
"Survey of Applications of Active Co..." refers background or methods in this paper
...Each form of the gust model is generally considered to be a spatial variation and invariant to both time and aircraft motion, though it is often convenient to express the gust variation as a temporal variation (Wright & Cooper, 2007)....
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...Gusts and turbulence tend to be isotropic in the real atmosphere (Hoblit, 1988) (Wright & Cooper, 2007)....
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...Two forms of continuous turbulence distributions are commonly encountered in application: Dryden and von Kármán (Hoblit, 1988) (Wright & Cooper, 2007)....
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...The 1-cosine gust 3 models the gust form as a sinusoidal application of gust velocity, and more accurately captures the form of a solitary gust (Hoblit, 1988) (Wright & Cooper, 2007)....
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...The Dryden and von Kármán distributions are both defined by a characteristic scale wavelength (typically a function of altitude) and the root-mean-square turbulence velocity (Hoblit, 1988) (Wright & Cooper, 2007)....
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Book•
17 Mar 1999
TL;DR: In this article, the authors present a model for the formation of a cyclone and a case study of cyclone formation over North America, which is based on the Second Law of Motion (SLM).
Abstract: 1. THE ATMOSPHERE Introduction / Meteorological Conventions / Thermodynamic State / Equation of State - Ideal Gas Law / Hydrostatic Equilibrium / Hypsometric Equation / Atmospheric Structure / Process Terminology / Summary / Exercises 2. RADIATION Orbital Factors / Flux / Radiation Principles / Surface Radiation Budget / Summary / Exercises 3. HEAT Sensible and Latent Heats / Lagrangian Heat Budget - Part 1: Unsaturated / Thermodynamic Diagrams - Part 1: Dry Adiabatic Processes / Eulerian Heat Budget / Surface Heat Budget / Apparent Temperatures / Summary / Exercises 4. BOUNDARY LAYERS Static Stability - A Preview / Boundary-Layer Formation / ABL Structure and Evolution / Temperature / Wind / Turbulence / Summary / Exercises 5. MOISTURE Saturation Vapor Pressure / Humidity Variables / Total Water Mixing Ratio / Lagrangian Water Budget / Thermo Diagrams - Part 2: Isohumes / Eulerian Water Budget / Lagrangian Heat Budget - Part 2: Saturated / Thermo Diagrams - Part 3: Saturated Adiabats / Summary / Exercises 6. STABILITY Thermodynamic Diagrams - Part 4: Applications / Parcels vs. Environment / Buoyancy / Static Stability / Thermo Diagrams for Boundary Layers / Brunt-Vaisala Frequency / Dynamic Stability / Summary / Exercises 7. CLOUD FORMATION Cloud Development / Cloud Sizes / Fractal Cloud Shapes / Processes Causing Saturation / Clouds and Upslope Fog / Other Fogs / Summary / Exercises 8. PRECIPITATION Nucleation of Liquid Droplets / Nucleation of Ice Crystals / Droplet Growth by Diffusion / Ice Growth by Diffusion / Collision and Collection / Precipitable Water / Rainfall Estimated by Radar / Summary / Exercises 9. DYNAMICS Newton"s Second Law of Motion / Forces / Full Equations of Motion / Height Contours on Isobaric Surfaces / Winds / Full Equations of Motion - Revisited / Mass Conservation / Summary / Exercises 10. LOCAL WINDS Scales of Motion / Wind-Speed Probability / Wind Turbines and Power Generation / Vertical Equation of Motion / Thermally Driven Circulations / Streamlines, Streaklines, and Trajectories / Bernoulli"s Equation / Mountain Waves / Foehns (again) and Chinooks / Summary / Exercises 11. GLOBAL CIRCULATION Nomenclature / Differential Heating / Thermal Wind Relationship / Jet Stream / Vorticity / Midlatitude Troughs and Ridges / Focus: Rossby Radius of Deformation and Geostrophic Adjustment - Part 1 / Three-Band General Circulation / Ekman Spiral in the Ocean / Summary / Exercises 12. AIR MASSES & FRONTS Anticyclones or Highs / Air Masses / Synoptic Weather Maps / Surface Fronts / Geostrophic Adjustment - Part 2 / Frontogenesis / Occluded Fronts and Mid-Tropospheric Fronts / Dry Lines / Summary / Exercises 13. CYCLONES Case Study of a Cyclone over North America / Cyclogenesis / Lee Cyclogenesis / Cyclone Spin-Up / Upward Motion / Sea-level Pressure Tendency / Self Development of Cyclones / Iso-surfaces and Their Utility / Case Study of a Cyclone (Continued) / Summary / Exercises 14. NUMERICAL WEATHER PREDICTION Solutions to Atmospheric Equations / Grid Points / Finite-Difference Equations / Numerical Stability / The Numerical-Forecast Process / Forecast Quality / Nonlinear Dynamics and Chaos / Useful Indicators on Weather Maps Produced By NWP / Elements of a Good Weather Briefing / Summary / Exercises 15. THUNDERSTORMS Convective Conditions / CAPE / Severe-Thunderstorm Environment / Downbursts and Gust Fronts / Lightning and Thunder / Tornadoes / Doppler Radar / Summary / Exercises 16. HURRICANES Dynamics / Thermodynamics / A Hurricane Model / Storm Surge / Surface Wind-Waves / Summary / Exercises 17. AIR POLLUTION DISPERSION Dispersion Factors / Air Quality Standards / Turbulence Statistics / Dispersion Statistics / Taylor"s Statistical Theory / Dispersion in Neutral & Stable Boundary Layers / Dispersion in Unstable Boundary Layers / Summary / Exercises 18. CLIMATE CHANGE Relative Equilibrium / Greenhouse Effect / Atmospheric Window / Water Vapor and Cloud Feedbacks / Ice-Albedo-Temperature Feedback / Daisyworld / GCMs / Sensitivity / Summary / Exercises 19. OPTICS Ray Geometry / Liquid Drop Optics / Ice-Crystal Optics / Scattering / Diffraction / Mirages / Summary / Exercises / APPENDIX A: FUNDAMENTALS OF SCIENCE / Dimensions and Units / Functions and Finite Difference / Relationships and Graphs / On Doing Science / Summary / Exercises / APPENDIX B: CONSTANTS AND CONVERSION FACTORS / Universal Constants / Earth Characteristics / Air and Water Characteristics / Conversion Factors & Combined Parameters / Other Information / APPENDIX C: NOTATION / Roman Symbols, Acronyms & Contractions / Greek Symbols / Operators / Superscripts / Subscripts / Special Symbols / APPENDIX D: ADDITIONAL READING MATERIAL / The Atmosphere / Radiation, Thermodynamics & Moisture / Cloud & Satellite Pictures / Cloud & Storm Processes / Dynamics of Atmospheres & Oceans / Boundary-Layers & Air Pollution / Synoptics / Numerical Weather Prediction & Chaos / Hurricanes / Climate Change / Optics / APPENDIX E: ANSWERS TO SELECTED EXERCISES / Answers for Chapters 1 to 6 / Answers for Chapters 6 to 13 / Answers for Chapters 13 to 19 / Answers for Appendices A & H / APPENDIX F: SYLLABUS / The Student Mix / Tests & Grading / Textbooks & Homework / Lectures & Weekly Schedule / APPENDIX G: CHAPTER CORRESPONDENCES / Ahrens" Essentials / Ahrens" Meteorology Today / Holton"s Dynamic Meteorology / Wallace and Hobbs" Atmospheric Science / APPENDIX H: TURBULENCE CLOSURE / Turbulence Closure Types / K-Theory / Transilient Turbulence Theory / Summary / Exercises / INDEX
523 citations
01 Jan 1988
TL;DR: In this paper, a presentation of the determination of gust loads on airplanes, especially continuous turbulence gust loads, is presented, emphasizing the basic concepts involved and covers relationships, definitions of terminology and nomenclature, historical perspective and explanations of calculations.
Abstract: This is a presentation of the determination of gust loads on airplanes, especially continuous turbulence gust loads. It emphasizes the basic concepts involved and covers relationships, definitions of terminology and nomenclature, historical perspective and explanations of calculations.
476 citations
"Survey of Applications of Active Co..." refers background or methods in this paper
...Gusts and turbulence tend to be isotropic in the real atmosphere (Hoblit, 1988) (Wright & Cooper, 2007)....
[...]
...Incorporation of flexible, dynamic structural response was used beginning in the mid-1950s (Hoblit, 1988)....
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...Two forms of continuous turbulence distributions are commonly encountered in application: Dryden and von Kármán (Hoblit, 1988) (Wright & Cooper, 2007)....
[...]
...The 1-cosine gust 3 models the gust form as a sinusoidal application of gust velocity, and more accurately captures the form of a solitary gust (Hoblit, 1988) (Wright & Cooper, 2007)....
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...The background on modeling gusts and co-evolution of airworthiness standards is predominantly drawn from (Hoblit, 1988)....
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TL;DR: In this paper, the authors defined the components of (W-WA) in FB or FA = components of Wm in FA and FE = velocity of airplane mass center relative to Earth relative to FA.
Abstract: = components of (W— WA) in FB or FA = components of Wm FE = velocity of airplane mass centre relative toFA = reference steady value of V = local velocity of the air relative to the Earth = mean value of W, velocity of frame FA = state vector = dX/du, etc., classical stability derivatives = wavelength, 27T/Q, = rms value of stochastic variable indicated by subscript = vector separating two points in FA = angular velocity of airplane relative to FE = local angular velocity of air relative to E = wave number vector in FA = matrix of three-dimensional spectrum functions = matrix of two-dimensional spectrum functions = matrix of one-dimensional spectrum functions = Laplace transform = transpose of matrix = ensemble average = complex conjugate Reference Frames FE:(xE,yE,zE)
198 citations