Carlos E. S. Cesnik

University of Michigan | U-M · Department of Aerospace Engineering

High-aspect-ratio (AR) wings are the prominent feature of very flexible aircraft, and greater AR designs are being explored for enhanced flight efficiency in civil aviation. However, the impact of higher flexibility on the aeroelastic behavior of fixed-wing aircraft still needs to be fully understood. This paper assesses the effects of aerodynamic...

This paper compares aeroelastic models for gust response prediction in very flexible wings. The investigations focus on the Pazy wing benchmark developed at Delft University of Technology for gust response experiments in low-speed flow. The comparisons consider two geometrically nonlinear aeroelastic models of the wing, which comprise an equivalent...

Ground vibration testing is typically conducted on an aircraft where the structure is supported using a suspension setup that emulates the free-flying aircraft. When the structure is very flexible, it is challenging to find a suspension system that can support the structure without influencing its dynamic response. This study investigates the compu...

This paper investigates inflow model effects on propeller whirl flutter focusing on a propeller-nacelle test case from classical whirl flutter theory. The model is implemented into the Rotorcraft Comprehensive Analysis System framework considering two approaches to capture the inflow on the propeller disk: a uniform inflow model and the viscous vor...

This paper addresses the aerodynamic interaction effects between a wing and a propeller on the whirl flutter boundary. A wing-pylon model with a propeller is defined and modeled in the Rotorcraft Comprehensive Analysis System, considering both a flexible and rigid wing. The aerodynamic interaction effects on the whirl flutter boundary between the w...

This paper investigates inflow model effects on propeller whirl flutter focusing on a propeller-nacelle test case from classical whirl flutter theory. The model is implemented into the Rotorcraft Comprehensive Analysis System framework considering two approaches to capture the inflow on the propeller disk: a uniform inflow model and the viscous vor...

This paper investigates roll maneuvers of a very flexible, transonic high-aspect-ratio-wing aircraft with flared folding wingtips representing a potential future commercial transport configuration. The computational study leverages a fully coupled nonlinear aeroelastic-flight dynamics framework for simulating roll maneuvers commanded by deflecting...

In this paper, collaborative aeroelastic analyses of the Pazy Wing are presented, which support the activities of the Large Deflection Working Group, a subgroup of the 3rd Aeroelastic Prediction Workshop (AePW3). The Pazy Wing is a benchmark for the investigation of nonlinear aeroelastic effects at very large structural deflections. Tip deformation...

Flexible aircraft designs with high-aspect-ratio wings and lightweight structures are increasingly adopted to achieve improved fuel efficiency. To design a controller for a flexible aircraft, a low-order model of its dynamics that captures the aeroelastic behavior is needed. One approach to establishing such a low-order model is to extend the six-d...

Explore the connections among aeroelasticity, flight dynamics, and control with an up-to-date multidisciplinary approach. New insights into the interaction between these fields, which is a distinctive feature of many modern aircraft designed for very high aerodynamic efficiency, are fully illustrated in this one-of-a-kind book. Presenting basic con...

Explore the connections among aeroelasticity, flight dynamics, and control with an up-to-date multidisciplinary approach. New insights into the interaction between these fields, which is a distinctive feature of many modern aircraft designed for very high aerodynamic efficiency, are fully illustrated in this one-of-a-kind book. Presenting basic con...

The classical theory of atmospheric flight mechanics is introduced. The kinematic description of a rigid aircraft is first described using Euler angles. This is followed by the derivation of the Newton-Euler equations describing the aircraft dynamics, with a discussion on the external forces appearing on the vehicle. Steady-state flight conditions...

Explore the connections among aeroelasticity, flight dynamics, and control with an up-to-date multidisciplinary approach. New insights into the interaction between these fields, which is a distinctive feature of many modern aircraft designed for very high aerodynamic efficiency, are fully illustrated in this one-of-a-kind book. Presenting basic con...

Explore the connections among aeroelasticity, flight dynamics, and control with an up-to-date multidisciplinary approach. New insights into the interaction between these fields, which is a distinctive feature of many modern aircraft designed for very high aerodynamic efficiency, are fully illustrated in this one-of-a-kind book. Presenting basic con...

Geometrically-nonlinear composite beam solutions are discussed as structural models for airframes with slender subcomponents. As this is intended for aircraft applications, the beam equations of motion are written with respect to a moving reference frame, which is rigidly-attached to a fixed point on the aircraft. Three different solution methods a...

A generalization of the classical theory of flight dynamics is presented that includes quasi-steady aeroelastic effects using residualization approach. This is then used to investigate static stability of the aircraft, which may result in torsional divergence, as well as its controllability, which results in a metric for control effectiveness and p...

Vortex-lattice solutions for unsteady aerodynamics on lifting surfaces are introduced. They provide a general description for aeroelastic applications with low-speed aircraft undergoing large wing deformations. The basic solution process is first outlined for 2-D problems, using a discrete vortex model for the fluid, and then extended to 3-D models...

Explore the connections among aeroelasticity, flight dynamics, and control with an up-to-date multidisciplinary approach. New insights into the interaction between these fields, which is a distinctive feature of many modern aircraft designed for very high aerodynamic efficiency, are fully illustrated in this one-of-a-kind book. Presenting basic con...

The basic control architecture for flexible aircraft is introduced. Both linear and nonlinear optimal control methods are considered in a sequential manner. First, the theory of linear-quadratic regulators is described, and applied to simple aeroelastic problems. A linear estimator is then introduced thus resulting in linear quadratic Gaussian (LQG...

A modelling strategy based on geometrically-nonlinear composite beams and unsteady vortex-lattice aerodynamics is introduce for the computer simulation of very flexible aircraft dynamics. The key challenges of this approach are discussed, including spatial coupling of structural and aerodynamic models and time integration schemes. This is then exem...

Explore the connections among aeroelasticity, flight dynamics, and control with an up-to-date multidisciplinary approach. New insights into the interaction between these fields, which is a distinctive feature of many modern aircraft designed for very high aerodynamic efficiency, are fully illustrated in this one-of-a-kind book. Presenting basic con...

Explore the connections among aeroelasticity, flight dynamics, and control with an up-to-date multidisciplinary approach. New insights into the interaction between these fields, which is a distinctive feature of many modern aircraft designed for very high aerodynamic efficiency, are fully illustrated in this one-of-a-kind book. Presenting basic con...

Explore the connections among aeroelasticity, flight dynamics, and control with an up-to-date multidisciplinary approach. New insights into the interaction between these fields, which is a distinctive feature of many modern aircraft designed for very high aerodynamic efficiency, are fully illustrated in this one-of-a-kind book. Presenting basic con...

The dynamic interactions between aeroelasticity and flight dynamics are discussed, under the assumption of small-amplitude vibrations of the elastic aircraft. Firstly, the equations of the dynamics of a flexible aircraft are described using quasi-coordinates. Linear normal modes are then defined, and used to project the dynamics of the flexible air...

Lightweight, high-aspect-ratio wings make aircraft more energy efficient thanks to their lower induced drag. Because such wings exhibit large deflections, design optimization based on linear flutter analysis of the wing undeformed shape is inadequate. To address this issue, we develop a framework for integrating a geometrically nonlinear flutter co...

This paper investigates geometrically nonlinear effects due to nonlinear kinematics and follower aerodynamics in the aeroelastic dynamics of a very flexible wing. The test case is the Pazy wing, a benchmark model for geometrically nonlinear aeroelastic studies involving large deflections in low-speed flow. The work builds on a low-order model of th...

When designing aircraft, avoiding dynamic aeroelastic instabilities such as flutter is a key requirement. One way to meet this requirement is to use a multidisciplinary design optimization subject to a flutter constraint. Flutter-constrained design optimizations have used geometrically linear detailed models, which do not accurately predict flutter...

This paper introduces a new metric to constrain post-flutter responses of aeroelastic systems in design optimization. The new metric aggregates the recovery rate to equilibrium for a range of operating conditions, modes, and amplitudes, resulting in a scalar constraint that does not involve the bifurcation diagram. By generalizing damping-based flu...

Even in multidisciplinary aircraft design, most aspects of nonlinear controllability are only considered in later design phases. Hence, control considerations are not used to inform the overall design of the airframe. This paper presents a control-aware, controller-agnostic design optimization framework that integrates nonlinear controllability con...

This paper investigates the ability of low-order structural and aerodynamic models to predict geometrically nonlinear aeroelastic behaviors associated with large wing deflections. The study considers the Pazy wing, a very flexible wing developed at the Technion—Israel Institute of Technology for geometrically nonlinear aeroelastic benchmark studies...

This paper investigates geometrically nonlinear effects associated with nonlinear kinematics and follower aerodynamics in the aeroelastic behavior of a very flexible wing in low-speed flow. The test case is the Pazy wing, a benchmark model for geometrically nonlinear studies developed under the Third Aeroelastic Prediction Workshop Large Deflection...

This paper studies roll maneuvers of a very flexible, high-aspect-ratio-wing transport aircraft with free flared folding wingtips. The maneuvers are commanded by different control surfaces inboard or outboard of the hinge. The computational study is conducted using a fully coupled nonlinear aeroelastic-flight dynamics framework-the University of Mi...

This paper presents a constraint aggregation approach for Nonlinear Model Predictive Control (NMPC). Constraint aggregation functions provide an approximation of the feasible region with a reduced number of nonlinear constraints. The effect of the aggregation on the closed-loop system performance and stability is studied using tools from sensitivit...

As aircraft wings become more flexible as a result of searching for more fuel efficient and higher performance solutions, structural nonlinearities become more apparent. Geometric nonlinearities make the structure’s modal parameters a function of the deformed shape and therefore of the loading condition. Modal characterization of very flexible stru...

In the past few decades, modal testing has become a major technology for determining , improving and optimizing dynamic characteristics of engineering structures in different fields, with emphasys (but not limited to) mechanical, civil, and aero-nautical/aerospace engineering. One of the great advantages of using modal tests is related to their exp...

Slides from my presentation at the 2022 International Forum on Aeroelasticity and Structural Dynamics (IFASD) in Madrid. The corresponding journal paper is available at the link below: https://www.researchgate.net/publication/370061901_High-Fidelity_Aerostructural_Optimization_with_a_Geometrically_Nonlinear_Flutter_Constraint

Please see the peer-reviewed version of this paper published in the AIAA Journal, available at: https://www.researchgate.net/publication/370061901_High-Fidelity_Aerostructural_Optimization_with_a_Geometrically_Nonlinear_Flutter_Constraint

Ride qualities measure passenger and/or pilot comfort while aircraft experience vibrations and accelerations during flight. Assessing ride qualities is critical to ensure aircraft meet operational requirements. This paper studies the ride qualities of a transonic high-aspect-ratio-wing aircraft representative of a potential future civil transport c...

The Third Aeroelastic Prediction Workshop Large Deflection Working Group (AePW3-LDWG) revolves around the Pazy wing, a geometrically nonlinear benchmark model for aeroelastic tests in low-speed flow. Previous work by the authors assessed a low-order model of the Pazy wing against higher-order numerical solutions and experimental data. This paper le...

A wind-tunnel experiment is developed to validate maneuver load alleviation (MLA) systems based on model predictive control (MPC). An MPC architecture is implemented in real time to coordinate trailing-edge control surfaces on the wing and tail of an aircraft model to perform a longitudinal maneuver while reducing the out-of-plane bending moment at...

This paper presents the design of an active maneuver load alleviation (MLA) system for very flexible aircraft (VFA) using a linear parameter varying reduced-order model (ROM) referred to as the top-to-bottom ROM (T2B-ROM). This model is obtained by constructing a piecewise-linear model as a function of the altitude and Mach number, and then reducin...

This paper describes the basic characterization and experimental results performed on a 3D-printed wing designed for aeroelastic studies. This effort is part of a collaborative project to exercise the methods and solutions to evaluate the flutter behavior of tail-sitter, swept-wing unmanned aerial vehicle configurations. The structural vibration ch...

This paper introduces a method for estimating flutter bifurcation diagrams of systems described by time-domain state-space models. The method estimates the bifurcation diagram by quantifying changes in the recovery rate in the pre-flutter regime. The recovery rate is approximated from the state velocity, overcoming the need for transient output dat...

This paper presents a new control co-design optimization (CCDO) framework to integrate controller-agnostic, nonlinear viability constraints informed by the solutions to optimal control problems into the multidisciplinary design process. To implement the optimization, procedures to evaluate the sensitivity of the controllability constraint to variat...

This paper presents a methodology based on optimal control to characterize the ability of a supersonic aircraft to reject atmospheric disturbances during its final approach to land. A longitudinal flight dynamics model is considered for which a set of rejectable disturbances is defined based on the values of three proposed barrier functionals. The...

View Video Presentation: https://doi.org/10.2514/6.2022-1185.vid As aircraft wings become more flexible as a result of searching for more fuel efficient and higher performance solutions, structural nonlinearities become more apparent. Geometric nonlinearities make the structure’s modal parameters a function of the deformed shape and, therefore, of...

This paper has been superseded by our peer-reviewed journal paper, which can be found at: https://www.researchgate.net/publication/371071869_High-Fidelity_Gradient-Based_Wing_Structural_Optimization_Including_Geometrically_Nonlinear_Flutter_Constraint

Civil transport aircraft typically use trailing-edge control surfaces for gust and maneuver load alleviation. However, wash-out effects due to wing flexibility reduce the effectiveness of these devices and may even result in control reversal. Future aircraft configurations with very flexible, high-aspect-ratio wings may use novel load alleviation s...

The development of a new generation of flying supersonic vehicles is a complex endeavor. Among the challenges, aeroelastic effects are known to be critical at high-speed flight. However, aeroelastic effects can also impact handling qualities and control during low-speed, high angle-of-attack maneuvers associated with the initial climb and final des...

The Third Aeroelastic Prediction Workshop Large Deflection Working Group is dealing with the analysis and experimentation of the Pazy wing, a very flexible wing developed for benchmark studies at the Technion-Israel Institute of Technology. This work leverages the Pazy wing as the test case to study the ability of low-order structural and aerodynam...

The challenges of modeling flexible aircraft include appropriate fidelity capturing and validation with experimental data. In fact, the validation of formulations and models for the flexible flight dynamics is indispensable to ensure that all the important phenomena are correctly captured. With this objective, two high-aspect-ratio flexible aircraf...

Control surfaces nonlinearities can lead to aeroelastic systems with limit cycle oscillations (LCO). Several methods have been proposed to predict LCO, as Harmonic Balance-based methods (HB). Describing function (DF) is a particular case of HB with a single harmonic motion assumed, and the approach can be combined with a classical eigenvalue stabil...

In this paper, the accuracy and practical capabilities of three different reduced-order models (ROMs) are explored: an enhanced implicit condensation and expansion (EnICE) model, a finite element beam model, and a finite volume beam model are compared for their capability to accurately predict the nonlinear structural response of geometrically nonl...

View Video Presentation: https://doi.org/10.2514/6.2021-2531.vid The design optimization of a supersonic transport aircraft should account for low speed flight considerations as a part of the constraints to be satisfied. In particular, the initial climbing and final descent should be protected from violating angle-of-attack limits in the presence o...

Considering flutter as a constraint in aircraft design optimization has the potential to enable energy-efficient vehicle designs with high-aspect-ratio wings while meeting flutter requirements early in the design cycle. However, nonlinear aeroelastic effects in high-aspect-ratio wings may cause self-sustained oscillations to arise even before flutt...

This paper demonstrates an adaptive approach for solving fluid–structure interaction problems using high-fidelity numerical methods along with a detailed analysis of mesh-motion errors. A high-order partitioned approach is applied to couple the fluid and the structural subsystems, where the fluid subsystem is discretized using a discontinuous Galer...

This paper describes the aeroelastic analyses intended and the ones performed on the Active Aeroelastic Aircraft Testbed (A3TB), a low-cost design, flexible platform for aeroelastic research and technology demonstration developed at Technion Israel Institute of Technology. The aircraft is a 3D-printed, flying-wing configuration designed to be a mod...

This paper introduces an adaptive mesh refinement approach for solving fluid-structure interaction problems. A high-order partitioned approach is applied to couple the fluid and the structural subsystems, where the fluid subsystem is discretized using a discontinuous Galerkin finite-element method, while the structures solver uses a continuous Gale...

This paper presents a maneuver load alleviation (MLA) system based on model predictive control (MPC) capable of enforcing constraints on a flexible commercial aircraft subject to different mass configurations. The unknown mass parameters are handled by considering multiple pre-computed scenarios in the design of the MPC problem. The computational b...

A low-order model for control design of very flexible aircraft (VFA) that accounts for geometrical nonlinearities under large deformations is derived in this work. The low-order model uses strain-based modal amplitudes as the flexible states and body-fixed frame linear and angular velocities for the basic flight dynamics. The model is informed by a...

With the pursuit of operating cost and emission reductions, modern transport aircraft increasingly adopt designs with high-aspect-ratio wings and lightweight structures. Accordingly, to avoid structural failure, the flight control system of very flexible aircraft is expected to alleviate the structural loads besides its standard function of rigid-b...

Advanced large-wing-span aircraft result in more structural flexibility and the potential for instability or poor handling qualities. These shortcomings call for stability augmentation systems that entail active structural control. Consequently, the in-flight estimation of wing shape is beneficial for the control of very flexible aircraft. This pap...

High-performance flutter and post-flutter predictions are critical in the design of a vast range of nonlinear fluid-structural systems. However, these predictions are often unfeasible due to their high computational cost. Moreover, traditional methods for flutter and post-flutter predictions are model intrusive and limited to one varying parameter...

The Third Aeroelastic Prediction Workshop Large Deflection Group is invested in validating computational models to analyze geometrically nonlinear wings. The effort is based on the Pazy wing, a wind-tunnel aeroelastic benchmark developed at the Technion-Israel Institute of Technology. To consolidate the techniques for testing the Pazy wing, the Tec...

In this research, a loop-separation concept (LSC) is applied to a very flexible aircraft. Appealing features of this control architecture include decoupled control logic and the use of high-order models for controller design, thus not requiring model order reduction. The LSC consists of two control loops. The inner loop employs a linear quadratic r...

The need for improving fuel efficiency of civil transport aircraft is leading to design high-aspect-ratio-wing configurations that have high aerodynamic performance. However, these configurations exhibit higher structural flexibility, which degrades aileron effectiveness and roll maneuverability. This paper investigates the influence of aileron spa...

Ensuring adequate flutter margins is a critical step in aircraft design. However, in the presence of nonlinear effects, subcritical limit-cycle oscillations can arise even before flutter occurs. When nonlinear effects are anticipated, post-flutter analyses have to be integrated into aircraft design in addition to flutter computations for preventing...

This work investigates the propeller’s influence on the stability of High Altitude Long Endurance aircraft, incorporating all resultant loads at the propeller hub, propeller slipstream, and gyroscopic loads. Such effects are usually neglected in the aeroelastic simulation of HALE aircraft. For that goal, a previously developed framework, which coup...

The numerical investigation of the stochastic aeroelastic characteristics of conventional and tow-steered composite laminates subjected to random uncertainties affecting the laminate fiber volume is addressed in the present paper. A computationally efficient stochastic model is constructed combining the semi-analytical Rayleigh–Ritz approach with t...