Flavio J. Silvestre

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...

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.

Active and Passive Control for Acceleration Reduction of an Aeroelastic Typical Wing Section

The main concern related to the flutter phenomenon is predicting and avoiding it. This paper describes the application of a flexural-torsional flutter testbed for acceleration reduction by applying active and passive model-based control. The model consists of the 2D typical section, with aerodynamic loads estimated by an unsteady time-domain formulation based on Wagner’s function. The active control architecture consists of a stability augmentation system with output feedback and gain scheduling via the linear-quadratic regulator theory and actuation by servomechanism. The passive control employs a shape-memory alloy to provide additional torsional stiffness. Experimental results show considerable reduction of oscillations at a relative low cost for both active and passive control strategies, and that the use of shape memory alloys in aeroelastic stability problems is promising.

On the Calculation of an UAV's Response to Elevator Deflection

[Abstract] UAVs are becoming more and more importan lately due to the declining costs of the electronic systems needed to guide them. This type of aircraft has many interesting applications specially substituting manned aircraft in dangerous missions such as transmission lines inspection. In the particular transmission line concerning the authors the hilss and trees along the way are of concern. To accomplish the mission the airplane has to cruise at approximately 80km/h. Thus, it is very important to gather lowReynolds number data. This is a very interesting and not fully understood flow regime. This work presents experimental data for the following aerodynamic coefficients: Lift, drag and pitching moment as a function of the angle of attack and of the horizontal tail incidence. The experimental results allowed calculations of the flight dynamics of the aircraft, and comparisons with theoretical methods to predict the aerodynamic forces for flight simulations.

Development of Robust Flight Control Laws for a Highly Flexible Aircraft in the Frequency Domain

Modern manned and unmanned aircraft designs have a lightweight and flexible structure to increase the flight performance. This trend is continuing with more flexible aircraft structures that possess a nonlinear behaviour. Typically those very flexible are equiped with a flight control system. This paper addresses trajectory control in longitudinal and lateral motion of a highly flexible aircraft with nonlinear dynamics. A new flight control design approach is introduced that is based on the classical multi-loop control law structure with specific considerations for the nonlinear structural behaviour. The inner loops of the flight control laws shall ensure stability and an optimal shape of the aircraft. The nonlinearities are summed up as uncertainties. Control design strategies in the frequency domain are used to achieve the design objectives. The outer loops are based on the classical multi-loop concept for autopilots. The design method and results in a linear and nonlinear simulation of the very flexible unmanned aerial vehicle X-HALE are presented.