Fabrizio Giulietti

Autonomous formation flight

This article describes an approach to close-formation flight of autonomous aircraft. A standard LQ-based structure was synthesized for each vehicle and for formation position error control using linearized equations of motion and a lifting line model of the aircraft wake. We also consider the definition of a formation management structure, capable of dealing with a variety of generic transmission and communication failures among aircraft. The procedure was developed using a decentralized approach and relies on the Dijkstra algorithm. The algorithm provides optimal path information sequencing in the nominal case, as well as the redundancy needed to accommodate failures in data transmission and reception. Several simulations were carried out, and some of the results are presented. The overall scheme appears to be a valuable starting point for further research, especially specialization to situations representing more detailed and operational failures.

Maximum Range for Battery-Powered Aircraft

T HE interest in electrically-driven propeller airplanes has been steadily increasing over the last 15 years with applications ranging from small electric remotely piloted vehicles [1] up to large high-altitude/long-endurance aircraft [2], passing through general aviation size airplanes powered by means of hydrogen fuel cells [3]. The art and science of preliminary sizing of conventional aircraft has been the subject of many textbooks over the years [4,5] and, in this framework, reasonably accurate range and endurance prediction against design performance requirements plays quite obviously a crucial role. Unfortunately, the extension of the results valid for conventional configurations to electrically powered aircraft is not always straightforward. In a recent paper, [6] the equations for the evaluation of range and endurance of battery operated electrical aircraft are derived, keeping into account the effects of Peukert’s law on the battery discharge process [7]. Wilhelm Peukert performed tests on lead–acid batteries and discharging them with a constant current. His analysis proved that the discharge time Δt and the discharge current i satisfy the law [7]

Magnetic Detumbling of a Rigid Spacecraft

DOI: 10.2514/1.53074 In this paper, a control law that detumbles a spacecraft with magnetic actuators only is developed. A rigorous mathematical proof of global asymptotic convergence from arbitrary initial tumbling conditions to zero angular velocity in a time-varying magnetic field is derived. Furthermore, a simple criterion for determining a reasonable value of the control gain is developed. The selected gain results in a quasi-minimum time detumbling for different initialconditions,inthepresenceofmagneticcoilsaturation.Performanceoftheproposeddetumblingcontrollawis demonstrated by numerical simulations on a large set of test cases using a Monte Carlo approach.

Management of Communication Failures in Formation Flight

This paper addresses the problem of the management of unmanned air vehicles flying in formation, in the presence of failures in the communication system or aircraft loss. The problem is solved representing the formation as an oriented graph, and a procedure based on shortest path theory provides the optimal solution for the information flow within the formation. When a failure occurs, the procedure runs again providing a sub-optimal solution, and formation geometry is changed according to pre-set reconfiguration maps. Formal definitions, such as the novel definition of Virtual Leader, and simulation results validate the methodology.

Dynamics and control of different aircraft formation structures

The problem of aircraft formation dynamics and control is investigated from the viewpoint of formation architecture. Three different formation structures, leader-wingman, virtual leader and behavioural approaches are introduced. A comparative study is made using a unified approach through a suitable control law. The formation systems are analyzed on a quantitative basis and objective results are made available for the designer. The trade-off between system performance and complexity is indicated. A complete nonlinear simulation involving a flight-path change and a heading change manoeuvre is discussed. Results show the superiority of a behavioural approach to maintain close formations of vehicles. Language: en

Unified Algebraic Approach to Approximation of Lateral-Directional Modes and Departure Criteria

Introduction L ITERAL expressions involving aerodynamic derivatives and inertial data provide physical insight into the behavior of the aircraft motion. For instance, they are well suited for the optimization of flight control systems, both for the setup of nominal system design and for the prediction of motion characteristics in off-nominal problems.1 In fact, such literal expressions show the direct connection between the transfer function poles and zeros as a function of the relative values of certain key derivatives and give valuable insight into the nature of the associated control problem. More precisely, they show the detailed effect of particular stability derivatives on aircraft characteristics. Also, they are of fundamental importance in obtaining stability derivatives from flight data and in developing analytical departure criteria to be used in the design process of new aircraft configurations.2 However, it is difficult to find exact closed-form solutions, especially to the aircraft modes, because both the longitudinal and the lateral aircraft eigenvalues come from fourth-order characteristic equations. Therefore, an approximation is required to arrive at reasonably compact and usable expressions that delineate the dominant effects. In many cases this process of approximation is useful for the designer. Indeed, the omission of certain terms, which are relatively unimportant, allows such important simplifications to be made that the relation between cause and effect becomes apparent. Very often such effects vary among vehicle types, so that literal approximate factors, which apply to all vehicles for all flight conditions, are quite difficult to obtain. This conclusion is particularly apparent when aircraft lateral–directional modes are considered. In particular, an accurate expression for the Dutch-roll damping is traditionally known to be a difficult task, although relatively satisfactory approximations for the spiral, roll, and Dutch-roll natural frequency are available, for example, see McRuer et al.,3 pp. 367–377. This is a serious difficulty when analytical approximations to aircraft departure criteria are sought. In fact, a natural approach to this problem is to set to zero the Dutch-roll damping expression to predict its instability. However, this is impractical as long as the Dutch-roll damping approximation is inaccurate. The main reason for this difficulty comes primarily from the physical behavior of lateral–directional motion. In fact, the easiest way to obtain accurate simplified models is to resort to a timescale analysis of the problem, separating slow from fast modes. However, when applied to the lateral–directional motion, this approach is not fully satisfactory because the complete

Acquisition of a Desired Pure-Spin Condition for a Magnetically Actuated Spacecraft

b = geomagnetic-field vector expressed in FB e1, e2, e3 = spacecraft principal axes of inertia FB = body-fixed frame FI = inertially fixed frame FO = local–vertical/local–horizontal orbit frame h = angular momentum vector i = orbit inclination I3 = 3 × 3 identity matrix J diag J1; J2; J3 = spacecraft inertia matrix kh = control gain M = external torque acting on the spacecraft m = magnetic dipole moment vector rc = orbit radius Torb = orbit period TBI = coordinate transformation matrix between FI and FB TBO = coordinate transformation matrix between FO and FB tF = convergence time to the desired spinning motion α = angle between ei and b Γ = plane containing ei and b δ = elevation of e with respect to Γ e = e1; e2; e3 T , error between desired and actual angular momentum vectors χ = angle between the projection of e on Γ and ei Ω = orbit rate ω = ω1;ω2;ω3 T , absolute angular velocity vector Subscripts

Spacecraft Attitude Control Using Magnetic and Mechanical Actuation

The aim of this paper is the analysis of simultaneous attitude control and momentum-wheel management of a spacecraft by means of magnetic actuators only. A proof of almost global asymptotic stability is derived for control laws that drive a rigid satellite toward attitude stabilization in the orbit frame when the momentum wheel is aligned with one of the principal axes of inertia. Performance of the proposed control laws is demonstrated by numerical simulations under actuator saturation. Robustness to external disturbances and model uncertainties is also evaluated.

Preliminary Design Analysis Methodology for Electric Multirotor

Abstract Unmanned platforms with a conventional fixed wing configuration can be designed according to well assessed aircraft sizing techniques. Conversely, the design of multi-rotor vehicles is still based mainly on scale-model enthusiastic experience. At present there has been a limited effort by the community in developing a systematic approach for sizing this unconventional class of flying vehicles. This paper proposes a revised version of a classical aircraft sizing methodology, based on statistical data available in the literature, with the objective of preliminary sizing an electric multi-rotor configuration, taking into account mission profile and a few performance requirements.

Modeling and Simulation of a Quad-Tilt Rotor Aircraft

Abstract Multi-rotor autonomous aerial vehicles have been proposed for several missions where the capability of controlled flight in small areas is required. Unfortunately, small-size electrically powered rotary wings UAVs have usually very short endurance, because of inherent limitation in battery energy density and constraints on maximum weight of the battery pack. At the same time, maneuverability can be improved by a variation of rotor thrust orientation. This paper presents a novel quad—rotor configuration where the use of a combustion engine and variable pitch propeller will allow for increasing endurance performance, whereas tilting of rotor disks improves maneuverability. A preliminary design of simple control laws is also discussed for this particular configuration, tested on a few basic maneuvers.