About

Craig Woolsey is a professor in the Kevin T. Crofton Department of Aerospace and Ocean Engineering at Virginia Tech. He earned his Ph.D. in Mechanical and Aerospace Engineering from Princeton University in 2001, his M.A. from Princeton in 1997, and his B.M.E. from Georgia Institute of Technology in 1995. His research interests focus on the nonlinear dynamics and control of ocean and atmospheric vehicles, with a particular emphasis on energy-based nonlinear guidance and control methods that enable effective vehicle operation over a broader performance envelope than conventional linear methods. Woolsey's disciplinary expertise includes Lyapunov-based nonlinear control, nonlinear guidance, path and motion planning, vision-based control, biomimetic locomotion, multi-body dynamics, and autonomous system reliability. His application areas encompass fixed-wing and multi-rotor aircraft, ocean surface vessels, and subsurface ocean vessels at various scales, as well as vehicle autonomy for unmanned aircraft, surface vessels, and underwater vehicles, along with in-situ sensing of ocean and atmospheric phenomena. Woolsey is actively involved in professional service, holding leadership roles such as Chair of the Atmospheric Flight Mechanics Technical Committee of the AIAA and serving on various IEEE and oceanic engineering societies. He has received numerous honors, including the Virginia Tech College of Engineering Dean’s Award for Excellence in Research and the NSF CAREER Award, and is recognized as an Associate Fellow of AIAA and a Senior Member of IEEE.

Research topics

• Computer Science
• Physics
• Engineering
• Aerospace engineering
• Applied mathematics
• Mathematical optimization
• Simulation
• Environmental science
• Mathematics
• Meteorology
• Mathematical analysis

Selected publications

• Aircraft System Identification Approach for Control Surface Fault Diagnosis

  2026-01-08

  articleSenior author

  Modern fault detection and diagnosis (FDD) methods are critical to maintaining flight vehicle safety. This paper presents a model-based FDD approach for identifying control-surface loss of effectiveness on a small, fixed-wing research aircraft. The work considers several real-time system identification methods to estimate changes in control effectiveness and provide fault information to a fault-tolerant control allocation framework. A baseline aero-propulsive model for an experimental aircraft was developed from flight-test data to establish nominal control-effectiveness parameters used to compare fault diagnosis methods. Five real-time estimation methods were formulated and evaluated: exponentially weighted recursive least squares in the time- and frequency-domain, two Lyapunov-based adaptive parameter estimation methods with exponential or finite-time convergence guarantees under a persistence of excitation condition, and an augmented-state extended Kalman filter. These methods were applied to flight data containing an artificially injected stuck left-aileron fault, implemented through a custom maneuver injection capability, with multisine excitation inputs applied to the control effectors. The estimated control-effectiveness parameters associated with the faulted surface displayed an immediate response to the failure and a clear trend towards zero, while the parameters corresponding to healthy effectors remained near nominal values. The resulting estimates were used to construct a time-varying health matrix that scales the nominal control-effectiveness matrix, producing a fault-weighted representation suitable for control allocation and supporting the objective of fault hiding. Overall, this work advances in-flight fault diagnosis by providing real-time parameter estimation for fault-tolerant control allocation, enabling redistribution of control authority to support safety-critical flight operations.

  PublisherDOI

• Practical Universal Tracking With Pivoted Unidirectional Actuation

  arXiv (Cornell University) · 2026-04-07

  preprintOpen accessSenior author

  This paper addresses the problem of tracking control for robotic vehicles equipped with pivoted unidirectional actuators. Starting from a baseline robust controller that assumes unconstrained inputs, we redesign the control law to be compatible with the pivoted actuator. This is accomplished by driving the output of the pivoted actuator to a ball centered at the target input value. The guarantees for the baseline controller are recovered in a practical sense. The theory is illustrated with simulation examples.

  PublisherDOI

• An Evaluation of Fault-Tolerant Control Allocation Strategies for eVTOL Aircraft

  2026-01-08

  articleSenior author

  Electric vertical takeoff and landing (eVTOL) aircraft typically have more control effectors than controlled axes, offering an opportunity to improve flight safety through recovery from control effector failures. Realizing this potential depends on control allocation strategies that intelligently redistribute virtual force and moment commands among redundant effectors under saturation and fault constraints. However, eVTOL aircraft pose unique challenges for control allocation because of varying control effectiveness across the transition flight envelope. This paper presents a geometric evaluation approach to understand the force and moment generation capability of an aircraft using the attainable force and moment set (AFMS)--a convex set in the six-dimensional space of generalized force and moment control inputs that is defined by saturation and fault constraints. Several classical pseudoinverse-based and optimization-based linear allocation methods are evaluated using the NASA Lift Plus Cruise eVTOL aircraft model in static and dynamic simulations. Their performance is benchmarked by their ability to reproduce the AFMS volume in nominal and faulted conditions, while also evaluating control effort and computational burden. Results show that the direct allocation and mixed L1 optimization algorithms consistently realize the full AFMS volume across hover, transition, and cruise regimes, demonstrating robust reconfiguration capability, while pseudoinverse formulations exhibit significant shortfalls. The dynamic simulation demonstrates zero allocation error, improved trajectory tracking, and successful fault hiding while using the direct allocation algorithm. Beyond specific results for the NASA Lift Plus Cruise aircraft, this study establishes a scalable, aircraft-agnostic method for comparing fault-tolerant control allocation algorithms for real-time implementation in overactuated eVTOL flight control systems.

  PublisherDOI

• Side Forces in Gliding Flight of Draco Lizards

  2026-01-08

  article

  Gliding {\it Draco} lizards generate subtle but non-negligible lateral aerodynamic forces through coordinated modulation of body pose (e.g., wing dihedral, tail shape) and wind–relative attitude (e.g., sideslip angle, angle of attack). Using high–fidelity motion–capture data from 24 voluntary glides, we isolated the wind–frame side force and quantified its influence on three–dimensional trajectories. Although modest in magnitude—about 5\% of the total aerodynamic force—the resulting lateral displacement exceeded 10\% of glide distance, underscoring its biomechanical relevance. To explain this force, we applied an equation–error system–identification framework to the nondimensional side–force coefficient. Two linear model structures were compared: an angle–based formulation using instantaneous posture variables, and an angular–rate–based formulation incorporating sideslip rate and tail pitch/yaw rates. Eighteen glides were used for model identification and six were held out for validation. Across the identification set, the angular–rate–based model consistently yielded lower prediction errors than the angle–based model. Drop–term tests further showed that removing the sideslip–rate regressor $(\dot{\beta})$ substantially degraded performance, suggesting a key role for sideslip dynamics in shaping lateral force during gliding {\it Draco}.

  PublisherDOI

• Practical Universal Tracking With Pivoted Unidirectional Actuation

  arXiv (Cornell University) · 2026-04-07

  articleOpen accessSenior author

  This paper addresses the problem of tracking control for robotic vehicles equipped with pivoted unidirectional actuators. Starting from a baseline robust controller that assumes unconstrained inputs, we redesign the control law to be compatible with the pivoted actuator. This is accomplished by driving the output of the pivoted actuator to a ball centered at the target input value. The guarantees for the baseline controller are recovered in a practical sense. The theory is illustrated with simulation examples.

  PublisherOA PDF

• Symmetry-Preserving Reduced-Order Wind Observers with Flight Test Results

  Journal of Guidance Control and Dynamics · 2026-05-06

  articleSenior author

  Inferring wind velocity from aircraft motion is an enabling technology with applications in synthetic air data systems, path planning, safety monitoring, and atmospheric science. A reduced-order nonlinear state observer is developed to estimate wind velocity from aircraft motion. The observer is constructed by leveraging the symmetry of aircraft dynamics under the action of a Lie group to achieve global exponential convergence of the wind estimates to their true value. By only estimating the unmeasured wind and air-relative velocity, this reduced-order observer reduces computational complexity and simplifies nonlinear stability analysis. This approach eliminates the need for a small-perturbation assumption on the nonlinear dynamics yet casts the nonlinear wind estimation problem as the design of a linear, time-varying observer. Simulations and flight test results for a fixed-wing aircraft demonstrate the observer’s performance and robustness to unmodeled turbulence, aerodynamic modeling error, and measurement noise, highlighting its practical applicability and potential to ensure safe operation of future aircraft systems.

  PublisherDOI

• Wind Estimate Uncertainty Quantification and Sensitivity Analysis Using Generalized Polynomial Chaos

  Journal of Guidance Control and Dynamics · 2026-02-18

  articleSenior author

  Indirect wind estimation onboard unmanned aerial systems (UASs) can be accomplished using existing onboard sensors along with a dynamic model of the UAS augmented with additional wind-related states. Although many indirect estimation approaches achieve desirable accuracy under the assumption of known system parameters, the effect of parametric uncertainty on wind estimate precision is important and has not been thoroughly investigated. This paper describes the theory and process for using generalized polynomial chaos (gPC) to recast the dynamics of a system with nondeterministic parameters as a deterministic system. The concepts are applied to the problem of wind estimation and to characterizing the precision of wind estimates over time due to known parametric uncertainties. In the multivariate case, gPC exhibits a computational advantage over Monte Carlo sampling-based methods and produces a deterministic system upon which control and estimation methods can be applied.

  PublisherDOI

• Adaptive control with magnitude and rate limited observer-based disturbance rejection

  Systems & Control Letters · 2025-09-17

  articleOpen accessSenior author
  PublisherDOI

• Depth dependent added mass computations using impulse motion simulations for shallowly submerged vehicles, Part 2: Accelerating from steady forward velocity

  Applied Ocean Research · 2025-06-26

  articleOpen accessSenior author

  Simulations of impulsive motion have previously been shown to accurately calculate depth dependent added mass at zero forward speed for underwater vehicles that are shallowly submerged. The simulation procedure, using high-fidelity CFD, produces added mass values at the infinite frequency limit while minimizing modeling assumptions that are present in lower-fidelity methods. The use of impulse-like simulations during parameter calculation results in shorter simulation times while simultaneously allowing for frequency independent parameters to be identified separately from memory effects. The present study extends the application of impulsive motion computations to cases that involve vehicle motions from an initial steady forward speed. Although they are independent of acceleration, calculated added mass values are shown to depend on both steady forward velocity and depth of submergence. Changes in the free surface elevation due to the creation of a Kelvin wave pattern alter the local submergence depth of the vehicle thereby affecting the added mass. The inclusion of viscosity and the presence of a viscous boundary layer is captured using steady-state simulations but is shown to have little influence on the added mass during a transient impulse-like maneuver. This viscosity independence is explained by the relatively small change in velocity from the nominal steady forward velocity and the focus on inertial effects by using small time scale simulations. • A computational procedure is implemented to simulate impulsive motions from steady forward velocities. • Forward speed effects on the calculation of added mass are most significant when the vehicle is shallowly submerged. • Changes in the free surface wave elevation due to the creation of a Kelvin wave pattern affect added mass.

  PublisherDOI

• A Noise-to-State Stable Symmetry-Preserving Reduced-Order Observer for Wind Estimation

  2025-01-03 · 2 citations

  articleSenior author

  Inferring wind velocity from aircraft motion is an enabling technology that can be used for synthetic air data systems, path planning, safety monitoring, and atmospheric science. This paper presents a reduced-order nonlinear wind observer applicable to uncertain aircraft models in turbulent wind. The aircraft dynamics are formulated as a stochastic differential equation that is invariant under the action of a Lie group. The proposed observer leverages this symmetry to achieve linear error dynamics that are shown to be noise-to-state stable in probability. A Monte-Carlo simulation of a nonlinear multirotor aircraft model is conducted to demonstrate the probabilistic guarantees and evaluate their conservatism.

  PublisherDOI

Recent grants

• I/UCRC: Center for Unmanned Aircraft Systems Phase II Site: Virginia Tech

  NSF · $1.6M · 2017–2022

• CAREER: Internal Shape Control for Ocean and Atmospheric Vehicles

  NSF · $381k · 2002–2007

• Analysis and Optimal Design of Aquatic and Atmospheric Vehicles That Use Biologically Inspired Propulsion and Control Methods

  NSF · $350k · 2014–2017

• Collaborative Research: Unsteady Hydrodynamics and Geometric Control of Pisciform Locomotion

  NSF · $286k · 2016–2020

• Structure-preserving Numerical Methods for Engineering Applications

  NSF · $236k · 2018–2021

Frequent coauthors

• Laszlo Techy

  Hood Technology (United States)

  15 shared

• Jeremy W. Hopwood

  15 shared

• James L. Gresham

  Virginia Tech

  15 shared

• Artur Wolek

  12 shared

• Benjamin M. Simmons

  12 shared

• Muhammad R. Hajj

  Stevens Institute of Technology

  12 shared

• Sevak Tahmasian

  Virginia Tech

  11 shared

• Francis Valentinis

  RMIT University

  11 shared

Labs

• Nonlinear Systems LaboratoryPI

Awards & honors

• Virginia Tech College of Engineering Dean’s Award for Excell…
• Virginia Tech Student Engineers Council Undergraduate Resear…
• SAE Ralph R. Teetor Educational Award (2008)
• NSF Faculty Early Career Development (CAREER) Award (2002)
• ONR Young Investigator Program Award (2002)