Guido De Matteis

Bifurcation Analysis of a Highly Augmented Aircraft Model

The bifurcation theory is applied to analyze the dynamics of an F-16 fighter aircraft model, which includes a full-authority flight control system. One of the objectives of the study is to determine the practical worth of this technique in situations where the behavior of statically unstable or marginally stable aircraft is tailored by the control system, according to different mission tasks. A numerical continuation method is used to trace the steady states of the system as the control force is varied. Significant bifurcation diagrams are presented and discussed for the different modes of operation of the flight control system. (Author)

Solution of aircraft inverse problems by local optimization

A feedforward control technique is presented for the determination of the input/output map associated to the inverse problem of the simulated motion of an aircraft. The procedure is particularly suitable in the redundant cases, which are reduced to nominal ones by imposing physically reasonable constraints on the state variables through a local optimization algorithm. Comparisons with already available solutions are shown together with some significant applications.

Full-Envelope Robust Control of a Shrouded-Fan Unmanned Vehicle

The development is described of a rate-command system for the control of a novel unmanned vehicle, the baseline model of which is highly nonlinear and presents fast and unstable open-loop modes. Structured singular-value design methodology is used to achieve the desired command response characteristics under specified uncertainties taking into consideration typical problems of small-size helicopters and ducted-fan vehicles such as rate-limited servos and significant time delays. Two robust linear controllers are designed for the low- and high-speed subsets of the operating envelope, and full-envelope flight control is achieved by switching between controllers as the threshold airspeed is traversed. Following an analysis of scaling effects, controller performance is evaluated against rotorcraft handling-qualities specifications. Flight control system development is assessed by piloted, hardware-in-the-loop simulation in the full range of operating conditions, with the controller implemented in the flight computer and pilot commands transmitted to the vehicle via radio link. Simulation testing also shows that the control system has good turbulence pust rejection performance and is robust to significant variations of c.g. position.

Performance and Stability of Ducted-Fan Uninhabited Aerial Vehicle Model

The nonlinear model of a novel ducted-fan uninhabited aerial vehicle is presented, where the aerodynamic coefficients are determined by numerical analysis of the flowfield about the airframe. The model is used to investigate performance and stability characteristics and to gain a sound physical understanding of dynamic behavior of this unconventional design. Finally, the influence of uncertainty in the aerodynamic derivatives on the open-loop dynamics is discussed as a result of significant approximations in the aerodynamic analysis

Analysis of Aircraft Agility on Maximum Performance Maneuvers

We present an analysis of aircraft agility as an inverse simulation problem. The analytical framework is based on the differential geometry of the trajectory and on the complete set of motion equations for a rigid airframe. A local optimization method is adopted and the solution is obtained in terms of the trajectory properties subjected to assigned constraints. Three applications are presented, namely a rapid deceleration maneuver, a maximum performance turn, and a reverse turn. The results show that the method is flexible enough to deal with the maximization of the agility components, for some assigned characteristics of the trajectory, and to determine the control actions for maneuvers that are usually proposed for evaluating the aircraft agility

Bifurcation Analysis of Attitude Dynamics in Rigid Spacecraft with Switching Control Logics

A numerical continuation method is used for bifurcation analysis of the complex behavior that appears in the attitudedynamics of rigid spacecraftasa resultof switching logicsin control system elements.Becausethestability analysisoflimitcyclesiscarriedoutinmostcircumstances,theapplicationofthecontinuationmethodraisesanumberofissueswhensuchaspectsasnonlinearitiesthatcannotbeapproximatedbydifferentiablefunctionsandnoninvertibleinput ‐outputrelationsaretaken intoconsideration.An approachbasedonthecontinuation ofequilibrium

Dynamics of hang-gliders

In this paper, a general formulation for the analysis and simulation of the hang glider dynamics and control is presented. The hang glider is modeled as a compound system made of wing and pilot. Static stability criteria are reviewed for a typical, indicative configuration. The small-perturbation dynamic stability is investigated in the fixed and free control cases in analogy with the conventional aircraft. Unsteady aerodynamic effects are shown to play a role in the stability of the system. A b C CD CL Nomenclature = aspect ratio == b2/S = wing span = Theodorsen function = drag coefficient - lift coefficient , Cm, Cn = aerodynamic moment coefficients Cw = weight coefficient c = reference chord F = control force FA = aerodynamic force FI = longitudinal control force, normal to S-P Fn = lateral control force g = acceleration of gravity hd = deformation component of the momentum

Dynamics of a tethered satellite in elliptical, non-equatorial orbits

The effects of the orbit eccentricity and of the inclination to the equatorial plane on the stability of a tethered subsatellite are examined. For circular orbits, the eccentricity is seen to cause a reduction of the divergent time constant of the system in cases where the liiear stability analysis predicts the insurgence of a parametric resonance. The orbit inclination appears to be responsible for a forced resonance phenomenon involving energy transfer from the in-plane to the out-of-plane modes.

A DISCRETIZED MODEL FOR THE DYNAMICS OF A TETHERED SATELLITE SYSTEM AND APPLICATIONS

This paper deals with a simulation of a tethered satellite system where a discretized model of the cable is considered. The characteristics of a few space discretization procedures are compared while investigating the dynamics of two physically relevant models, namely the Space Pendulum and the Space String. The study of these limit problems provides a reference line for a better understanding of other more complex dynamic situations.

Stability of a tethered satellite subjected to stochastic forces

Abstract This paper considers the problem of the relative equilibrium and stability of a tethered subsatellite (TSS), when the aerodynamic forces can be only probabilistically evaluated. The location in the space of the TSS is thus a stochastic process. The range of possible stationary states of the system is determined and a procedure is adopted for giving the evolution in time of the probability density of that location and the range of possible trajectories.