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 bo th 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 c hatter reduction.
Representative maneuvers are flown to evaluate the control allocator’s ability to perform
during realistic tasks. An inve stigation 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 y et 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 s olved it, and for this
and his ceaseless tutelage I am deeply indebted to him. To the remaining members of m y
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 po licies or endorsements, either expressed or implied, of Naval Air Warfare Center or
any other agency of the U.S. Government.
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Contents
Abstract......................................... ii
Acknowledgments.................................... iii
TableofContents.................................... v
ListofFigures...................................... ix
ListofTables ...................................... xiv
Nomenclature...................................... xv
1 Introduction 1
1.1 Background .................................... 1
1.2 ResearchObjectives................................ 3
1.3 SuggestionstotheReader ............................ 5
2 F-15 ACTIVE 6
2.1 Introduction.................................... 6
2.2 ACTIVEObjectives ............................... 6
2.3 Hardware ..................................... 7
2.4 ControlLaw.................................... 8
2.4.1 Objectives................................. 8
2.4.2 DynamicInversionFormat........................ 9
v
