A Comparison of Control Allocation Methods for the F-15 ACTIVE Research Aircraft Utilizing Real-Time Piloted Simulations
Kevin R. Scalera
Thesis submitted to the Faculty of the Virginia Polytechnic Institute and State University in partial fulfillment of the requirements for the degree of
Master of Science in Aerospace Engineering
Dr. Wayne Durham - chair Dr. Mark Anderson Dr. Frederick Lutze
July 1999 Blacksburg, Virginia
Keywords: Control Allocation, Aircraft Dynamics, ACTIVE, Reconfiguration Copyright 1999, Kevin R. Scalera A Comparison of Control Allocation Methods for the F-15 ACTIVE Research Aircraft Utilizing Real-Time Piloted Simulations
Kevin R. Scalera
(ABSTRACT)
A comparison of two control allocation methods is performed utilizing the F-15 ACTIVE research vehicle. The control allocator currently implemented on the aircraft is replaced in the simulation with a control allocator that accounts for both control effector positions and rates. Validation of the performance of this Moment Rate Allocation scheme through real-time piloted simulations is desired for an aircraft with a high fidelity control law and a larger control effector suite.
A more computationally efficient search algorithm that alleviates the timing concerns as- sociated with the early work in Direct Allocation is presented. This new search algorithm, deemed the Bisecting, Edge-Search Algorithm, utilizes concepts derived from pure geometry to efficiently determine the intersection of a line with a convex faceted surface.
Control restoring methods, designed to drive control effectors towards a “desired” configu- ration with the control power that remains after the satisfaction of the desired moments, are discussed. Minimum-sideforce restoring is presented. In addition, the concept of variable step size restoring algorithms is introduced and shown to yield the best tradeoff between restoring convergence speed and control chatter reduction.
Representative maneuvers are flown to evaluate the control allocator’s ability to perform during realistic tasks. An investigation is performed into the capability of the control allo- cators to reconfigure the control effectors in the event of an identified control failure. More specifically, once the control allocator has been forced to reconfigure the controls, an inves- tigation is undertaken into possible performance degradation to determine whether or not the aircraft will still demonstrate acceptable flying qualities.
A direct comparison of the performance of each of the two control allocators in a reduced global position limits configuration is investigated. Due to the highly redundant control effector suite of the F-15 ACTIVE, the aircraft, utilizing Moment Rate Allocation, still ex- hibits satisfactory performance in this configuration. The ability of Moment Rate Allocation to utilize the full moment generating capabilities of a suite of controls is demonstrated. Acknowledgments
I would like to extend my most sincere gratitude to my parents for their support and en- couragement over the years. They have inspired me to make the most of myself and to live each day to the fullest. It is because of their guidance and direction that I find myself conti- nously striving towards the top with aspirations of overcoming any obstacle along the way. To my brothers Steve and Jon between whom I have been fortunate enough to have grown up. With Steve’s endless effort to lead the way, blazing new trails and setting benchmarks at each step, and with Jon’s relentless desire to never stay in the shadow of Steve and I, it has thus far been an exhausting yet rewarding quest through academia and life.
I must thank my advisor Dr. Wayne Durham for his persistence and patience with me. He took me under his wing and pushed me to discover new things and really question and ponder what had already been found. He always challenged me to try to figure out the solution to a problem on my own before seeing how somebody else solved it, and for this and his ceaseless tutelage I am deeply indebted to him. To the remaining members of my committee, Dr. Fred Lutze and Dr. Mark Anderson, thank you for helping to guide me through my education and for sharing your seemingly endless knowledge with me.
I would also like to acknowledge the help and support that Keith Balderson and his group at Manned Flight Simulator have given in support of making the Flight Simulation Lab the facility it is today. To Jim Buckley and John Bolling at Boeing Phantom Works, thank you for offering debugging hints as well as other necessary data crucial to the implementation of the F-15 ACTIVE model and the completion of my research.
I must thank my friends that have helped to make my stay at Virginia Tech so enjoyable. To Drew Robbins, Greg Stagg, Bill Oetjens, Dan Lluch, Roger Beck, Mike Phillips, Michelle Glaze, Jeff Leedy, Josh Durham, Abhishek Kumar and Mark Nelson, thank you for creating a work environment in the Simlab that was second to none. To the rest of the Aerospace crew,
iii especially Cindy Whitfield, John Prebola, Alex Remington, Samantha Magill, Matt Long, Troy Jones and Mike Goody, thanks for two years of nonstop fun, innumerous memories and for sharing so much time and so many experiences with me outside of work. Finally, I would like to thank my friends from back home who have offered me support and encouragement from hundreds of miles away and kept true to their promise to never lose touch.
Financial support for this research project was provided by the Naval Air Warfare Center, Aircraft Division under Contract N00178-98-D-3017. The views and conclusions contained herein are those of the author and should not be interpreted as necessarily representing the official policies or endorsements, either expressed or implied, of Naval Air Warfare Center or any other agency of the U.S. Government.
iv Contents
Abstract...... ii
Acknowledgments...... iii
TableofContents...... v
ListofFigures...... ix
ListofTables...... xiv
Nomenclature...... xv
1 Introduction 1
1.1Background...... 1
1.2ResearchObjectives...... 3
1.3SuggestionstotheReader...... 5
2 F-15 ACTIVE 6
2.1Introduction...... 6
2.2ACTIVEObjectives...... 6
2.3Hardware...... 7
2.4ControlLaw...... 8
2.4.1 Objectives...... 8
2.4.2 DynamicInversionFormat...... 9
v 2.4.3 DetermingDesiredMoments...... 12
2.5SimulationCodeandEnvironment...... 14
2.5.1 EvaluationPilots...... 15
2.5.2 HandlingQualitiesEvaluationUsingReal-TimeSimulation...... 16
2.6CodeVerification...... 17
3 Control Allocation Theory 19
3.1AllocationMethods...... 19
3.2Frame-wiseControlAllocation...... 20
3.3DirectAllocationSolution...... 22
4 Bisecting, Edge-Searching Algorithm 24
4.1Background...... 24
4.2Two-DimensionalProblem...... 25
4.3Three-DimensionalProblem...... 31
4.4TimingAnalysis...... 36
4.4.1 AllocationMethodsInvestigated...... 36
4.4.2 RequiredFloatingPointOperations...... 37
4.4.3 ErrorAnalysis...... 39
4.4.4 TimingConclusions...... 41
5 Restoring Methods 43
5.1Background...... 43
5.2RestoringtoaKnownSolution...... 45
5.2.1 Minimum-NormRestoring:KnownSolution...... 46
5.3RestoringtoanUnknownSolution...... 47
vi 5.4Minimum-SideforceRestoring...... 48
5.4.1 VariableStepSizeRestoring...... 49
6 Representative Maneuvers 52
6.1 Canned Input: Lateral Stick Doublet ...... 52
6.2AirCombatManeuvering:HighYo-Yo...... 61
6.2.1 HighYo-Yo:Description...... 61
6.2.2 HighYo-Yo:SimulatorImplementation...... 63
6.2.3 HighYo-Yo:TaskDesiredPerformance...... 64
6.2.4 HighYo-Yo:Results...... 65
6.2.5 HighYo-Yo:Minimum-SideforceRestoring...... 72
6.3TerrainFollowing...... 73
6.3.1 TerrainFollowing:Description...... 73
6.3.2 TerrainFollowing:TaskDesiredPerformance...... 74
6.3.3 TerrainFollowing:Results...... 76
7 Control Reconfiguration 83
7.1Background...... 83
7.2Implementation...... 84
7.3Examples...... 86
7.3.1 LateralStickDoublet:AileronFailure...... 87
7.3.2 HighYo-Yo:AileronFailure...... 88
7.3.3 HighYo-Yo:DoubleHorizontalTailFailure...... 96
7.3.4 TerrainFollowing:DoubleHorizontalTailFailure...... 103
7.4 Viability of MRA for Control Reconfiguration ...... 111
vii 8 Performance Comparison 113
8.1EuclideanNormComparison...... 113
8.2ReducedGlobalPositionLimits...... 116
8.2.1 LateralStickDoublet:ReducedControlsConfiguration...... 119
9 Summary and Conclusions 124
Bibliography 128
A F-15 ACTIVE Specifications 131
B Control Effectiveness Extraction Code 137
B.1 Subroutine Bgetter.c ...... 137
B.1.1Description...... 137
B.1.2Code...... 138
B.2 Subroutine Jacob.f ...... 151
B.2.1Description...... 151
B.2.2Code...... 152
B.3 Function Ydu.f ...... 158
B.3.1Description...... 158
B.3.2Code...... 158
Vita 166
viii List of Figures
2.1F-15ACTIVEhardwarecomponents...... 7
2.2 Affine control effectiveness data (∂Cl/∂δAILL) as a function of Mach number for the F-15 ACTIVE at 10,000 ft...... 11
2.3Generalformatofcontrollaw-controlallocatorframework...... 12
2.4 Standard stability-axis system...... 13
4.1 Two-dimensional AMS for the F-15 ACTIVE. Small dots represent the vertices of the AMS. x and y axes correspond to non-dimensional pitching and yawing momentcoefficients,respectively...... 26
4.2 Identification of yx,Max ...... 27