Pedro Paglione

Formulation of the Flight Dynamics of Flexible Aircraft Using General Body Axes

An inertially-coupled formulation for the flight dynamics of flexible aircraft undergoing small deformations is developed. The availability of a structural-dynamic finite element model of the aircraft is presupposed. With all the coupled dynamics taken into account, an arbitrary choice of the body reference frame can be made. This frame is also allowed to be noncoincident with the frame of reference used to calculate the aerodynamic loads. In the equations of motion, the inertial coupling terms are linearized in the elastic displacements around a calculated equilibrium condition. Appropriate modes of vibration are then used in the calculation of the dynamic deformation of the structure. A simple quasi-steady incremental aerodynamic model based on the vortex-lattice method is used. The formulation is tested in the flight simulation of an idealized forward-swept-wing aircraft model. Numerical results show that, under small deformations, different body axes lead to the same overall motion of the aircraft wit...

Conceptual Flexible Aircraft Model for Modeling, Analysis and Control Studies

In this paper, we present models of conceptual flexible aircraft suitable for aerodynamic, flight mechanics and flight control studies. The aircraft is representative of a medium size civil jet transport and it is developed in three configurations of increasing flexibility. The model integrates 6 degrees of freedom rigid and structural dynamics, which are obtained via finite elements and modal decomposition (up to 9 flexible modes are considered). An incremental unsteady aerodynamic model is determined via the Doublet Lattice method. The aircraft possesses 8 aerodynamic control effectors, suitable for control of the rigid and flexible modes. A rigid body aerodynamic model is also considered. A brief numeric discussion about flutter is also presented.

Robust Flight Control Design Supported by Flying Qualities Analysis

In this work, a robust flight control law design and analysis is shown. Conventional flying qualities criteria are used to evaluate the performance of a longitudinal flight control law designed via robust control techniques. These criteria include C*, bandwidth/phase delay, Gibson frequency domain and dropback. The design in based on the C* criterion, and H1 and µ synthesis robust control techniques are applied. The conventional robust control law design structure is modified to include a feedforward path in order to attend phase requirements. For the µ synthesis design, an uncertainty model - obtained from Linear Fractional Transformations (LFTs) - is included in order to provide robustness against the variations in the aircraft response due to variations in the weight, center of gravity, inertia, airspeed and altitude. The robustness to this uncertainty is evaluated using µ analysis. The responses for some expected pilot inputs are also shown and commented.

NONLINEAR FLIGHT CONTROL USING BACKSTEPPING TECHNIQUE

A nonlinear flight control system is proposed us- ing backstepping. It is implemented a controller with an in- ternal loop controls involving the angular rates of the aircraft and an external loop which includes angle of attack, sideslip angle and bank angle. Also, it is implemented a separated controller of velocity. Finally, nonlinear simulation results for a conceptual model of a medium size jet are presented to demonstrate the effectiveness of the proposed control law.

Aircraft Control Based on Flexible Aircraft Dynamics

In this paper, the control law design for flexible aircraft is discussed. First, the traditional procedure of decoupling rigid-body and aeroelastic dynamics with low-pass and notch filters is addressed, with focus on controller performance as well as the resulting stability margin issues. A procedure based on a unified formulation of the flexible aircraft dynamics for flight control law design is proposed. In this procedure, the aeroservoelastic dynamics is assessed in the loop, and the offline filtering process is avoided. The formulation is applied to the virtual aircraft generic narrow-body airliner, with improvements in closed-loop performance and stability margins.

Linear Control of Highly Flexible Aircraft based on Loop Separation

The outcome of highly flexible aircraft requires new approaches in control design. In this research, we apply the loop separation concept, which consists in two control loops. The inner loop is capable of stabilizing the plant of the flexible aircraft, while is holding shape of the trimmed structure. Once the highly flexible aircraft is artificially transformed in a slightly flexible aircraft, the second loop or outer-loop is designed according to conventional, rigid-body-based control. Three control approaches were evaluated in the inner loop: LQG/LTR, LQR with output feedback and a direct integration approach. The direct integration approach with uncoupled gains presented better performance. The outer loops for speed, heading, sideslip angle and altitude were estimated using non-smooth optimization techniques and they are capable of attaining the commanded reference with low control energy and inside the maneuver requirements, while the inner loop is capable of reducing the elastic strains of the wing.

Preliminary Attitude Control Studies for the ASTER Mission

This work discusses an attitude control study for the ASTER mission, the first Brazilian mission to the deep space. The study is part of a larger scenario that is the development of optimal trajectories to navigate in the 2001 SN263 asteroid system, together with the generation of orbit and attitude controllers for autonomous operation. The spacecraft attitude is defined from the orientation of the body reference system to the Local Vertical Local Horizontal (LVLH) of a circular orbit around the Alpha asteroid. The rotational equations of motion involve the dynamic equations, where the three angular speeds are generated from a set of three reaction wheels and the gravitational torque. The rotational kinematics is represented in the Euler angles format. The controller is developed via the linear quadratic regulator approach with output feedback. It involves the generation of a stability augmentation (SAS) loop and a tracking outer loop, with a compensator of desired structure. It was chosen the feedback of the p, q and r angular speeds in the SAS, one for each reaction wheel. In the outer loop, it was chosen a proportional integral compensator. The parameters are tuned using a numerical minimization that represents a linear quadratic cost, with weightings in the tracking error and controls. Simulations are performed with the nonlinear model. For small angle manoeuvres, the linear results with reaction wheels or thrusters are reasonable, but, for larger manoeuvres, nonlinear control techniques shall be applied, for example, the sliding mode control.

Design of Robust Static Output Feedback Flight Control Law Using Structured Singular Value Optimization

Abstract This work proposes solutions for the Robust Static Output Feedback problem using optimization. The application considered is the design of flight control laws, taking into account structured uncertainties and flying qualities criteria, written in the μ robust control framework. An analysis of the resultant cost function is presented, some methods for solution are proposed and the results are discussed.

Mathematical model of one flexible transport category aircraft

Purpose The purpose of this paper is to present a mathematical model of one very flexible transport category airplane whose structural dynamics was modeled with the strain-based formulation. This model can be used for the analysis of couplings between the flight dynamics and structural dynamics. Design/methodology/approach The model was developed with the use of Hamiltonian mechanics and strain-based formulation. Nonlinear flight dynamics, nonlinear structural dynamics and inertial couplings are considered. Findings The mathematical model allows the analysis of effects of high structural deformations on airplane flight dynamics. Research limitations/implications The mathematical model has more than 60 degrees of freedom. The computational burden is too high, if compared to the traditional rigid body flight dynamics simulations. Practical implications The mathematical model presented in this work allows a detailed analysis of the couplings between flight dynamics and structural dynamics in very flexible airplanes. The better comprehension of these couplings will contribute to the development of flexible airplanes. Originality/value This work presents the application of nonlinear flight dynamics-nonlinear structural dynamics-strain-based formulation (NFNS_s) methodology to model the flight dynamics of one very flexible transport category airplane. This paper addresses also the way as the analysis of results obtained in nonlinear simulations can be made. Comparisons of the NFNS_s and nonlinear flight dynamics-linear structural dynamics methodologies are presented in this work.

Optimal linear quadratic model following with an application to a flexible aircraft

This paper develops general theoretical results about an input–output model-following methodology for linear systems, as an optimal control problem. A control law is obtained by minimizing a quadratic index that takes into account the matching errors and the control inputs. The control is obtained from the Lagrange multiplier method and can be interpreted as an extension of the linear quadratic regulator, with finite and infinite horizon formulations. The major contribution of the paper is the development of solutions involving plant output feedback. The method is illustrated with an application to a nonlinear flexible aircraft with nonstationary aerodynamics and nine flexible modes. Simulations compare state and output feedback solutions. In the proposed example, when taking into account unmodeled flexible dynamics and parametric uncertainties, the best results are given by the proposed output feedback.