Thierry Miquel

Non-Linear Control Structures for Rotorcraft Positioning

The purpose of this communication is to apply and compare three different non-linear control approaches to the design of control structures with control laws allowing autonomous positioning and orientation for a four-rotor aircraft. Realistic rotorcraft flight dynamics are established and analyzed so that a reference three-layers control structure is defined. Then are introduced different non-linear control approaches: non-linear inverse control, backstepping control and differential flat control. The compatibility of these control approaches with the three-layer control structure is assessed and adaptations are .proposed so that they can cope with the guidance of the rotorcraft. The corresponding control laws are detailed and their expected performances are discussed. The simplification of these control laws around equilibrium conditions produces close quasi-linear proportional derivative controllers. A careful tuning of one of them provides a reference to evaluate the improvements resulting from the use of full non-linear control laws, when applied to the positioning and orientation problem. This evaluation is performed by simulation and numerical results are displayed for analysis.

Path Stretching and Tracking for Time-Based Aircraft Spacing at Meter Fix

The delegation to the flight crew of some tasks currently performed by air traffic controllers provides new perspectives potentially to increase air traffic control efficiency. More specifically, the task of establishing properly spaced landing sequences is very demanding in heavy traffic conditions for the air traffic controllers in charge of the terminal maneuvering area. Automatic merging operations could relieve air traffic controllers of providing time-consuming radar-vectoring instructions and could provide more optimal flight profiles to the aircraft. With these new tasks being transferred to the flight crew some automation in order to limit the workload is required. The outcomes of this paper are twofold: firstly it presents a technique to generate path stretching with length and endpoint constraints and secondly it provides a nonlinear control law to track the reference trajectory. The reference trajectory is used to stretch the path of a trailing aircraft in order to delay its arrival on a meter fix. The purpose of the nonlinear control law based on feedback linearization is to enable the trailing aircraft to follow the reference trajectory. This communication treats level flight, but wind is considered. The design is followed by two illustrative examples which show the effectiveness of the proposed approach.

A Simplified Backstepping Design for 3D Time-based Aircraft Relative Guidance

The delegation to the flight crew of some tasks currently performed by air traffic controllers provides new perspectives to potentially increase air traffic control capacity. The objective of this communication is to provide technical insight into the airborne devices and algorithms which may be used to automatically perform merging and station keeping operations. Indeed, these maneuvers in the field of civil aviation seem difficult to be performed manually and may result in this case in an increase of the flight crew workload. Nevertheless new automated functions onboard aircraft could help to overcome this limitation. This paper investigates the design of a new autopilot mode dedicated to merging and station keeping maneuvers behind a leading aircraft. The proposed relative guidance law considers a 3 -D relative motion, including constant wind and lateral, longitudinal and vertical control. It is based on vectorial backstepping and takes advantage of the skewsymmetric matrix which appears in the relative motion equations. An alternative ‘simplified’ design based on a matrix form of the Young’s inequality is also presented in order to simplify the computation of the guidance law. Then, an illustrative example is discussed and conclusions are raised.

Design of a robust controller/observer for TCP/AQM network: First application to intrusion detection systems for drone fleet

This paper proposes a robust controller/observer for UAVs network anomaly estimation which is based on both Lyapunov Krasovkii functional and dynamic behavior of TCP (Transmission Control Protocol). Several research works on network anomaly estimation have been led using automatic control techniques and provide methods for designing both observer and command laws dedicated to time delay problem while estimating the anomaly or intrusion in the system. The observer design is based on a linearized fluid-flow model of the TCP behavior and must be associated to an AQM (Active Queue Management) to perform its diagnosis. The developed robust controller/observer in this paper has to be tuned by considering the time delay linear state-space representation of TCP model. As a first result, the designed controller/observer system has been successfully applied to some relevant practical problems such as topology network for aerial vehicles and the effectiveness is illustrated by using real traffic traces including Denial of Service attacks. Our first results show promising perspectives for Intrusion Detection System (IDS) in a fleet of UAVs.

Modified Bezier curve for 4D reference trajectory definition under flight profile constraint

The task of establishing properly spaced landing sequences is quite demanding for air traffic controllers in heavy traffic conditions. Indeed, air traffic controllers combine two or more streams into a single stream before landing by means of radar vectoring and speed instructions. This high level task of sequencing aircraft is not currently communicated to the pilot. Instead, controller translate it into clearances to the pilot, typically radar vectoring and speed instructions. In this paper, the task of merging an aircraft over a specified meter fix is addressed through a novel ?Set Reference Path? procedure in which the air traffic controller may clear an aircraft to merge at a specified meter fix at a given time. This paper focuses on the definition of a reference path for time-based operations at meter fix. It includes path stretching operations, which occur when the aircraft is predicted to overfly too early a meter fix with respect to other traffic flow constraints. This paper presents a new approach to generate a reference path with length and endpoint constraints based on modified Bezier curves. Compared to reference trajectories based on straight lines and circle arcs, which are usual in the aviation community, the proposed approach allows for smooth control cues and avoids the scheduling between straight lines and circle arcs segments. The proposed design is followed by illustrative examples which show the effectiveness of the proposed approach.

Design of a supervised flight control system for aircraft relative guidance

In this paper, the automation of the relative guidance is performed thanks to the recursive non-linear control technique, namely backstepping according to M. Krstic et al. (1995). This is quite new design methodology for construction of both feedback control laws and associated Lyapunov functions in a systematic manner. In order to tackle safety and passenger comfort aspects, which are crucial points for commercial aircraft, the controller is supervised: the purpose of this device is to handle on-line the gain of the controller, taking into account the current value of the state in order to satisfy some limitations in commercial aircraft maneuvering capabilities.

A Feedback Linearizing Controller for Relative Guidance Between Commercial Aircraft

During the last few years, several concepts concerning the delegation to commercial aircraft flight crew of some tasks currently performed by the air traffic controllers have emerged [3]. Among these new ideas, relative guidance has appeared to be of some interest to contribute to the enhancement of air traffic capacity [1] though it rises hard technical challenges. Indeed, this kind of maneuver appears difficult to perform manually, and may induce an excessive increase of the flight crew workload, thus requiring a new on-board automated function, as suggested in [7]. This paper investigates the design of an autopilot mode dedicated to the trailing aircraft for merging and maintaining station keeping behind a leading aircraft. The investigated approach is based on feedback linearization control. We use a new form of relative position error which results in a singularity free stabilizing controller. Moreover, we take explicitly into account the separation between the two aircraft in order to safely manage the maneuver. Some properties of such a controller are also discussed on the basis of a case study including wind.

Suboptimal longitudinal reference trajectory computation for time based continuous descent operations

This paper addresses a specific aspect of air traffic control services, namely the achievement of an orderly and expeditious flow of air traffic under time constrained continuous descent approach. More specifically, a futuristic 4D trajectory application where the air traffic controller will ask an aircraft to overfly a meter fix at a specific time is addressed. The main benefit expected from this application is to improve flight efficiency by more precise maneuvering resulting from on-board capabilities as well as noise abatement and fuel saving. More precise maneuvers are also expected to increase sector capacity. Indeed moving from radar vectoring to monitoring precomputed trajectories would contribute to decrease controllers workload and therefore to increase sector capacity. This paper presents a new methodology to compute a reference trajectory for time based continuous descent operations and focuses on aircraft longitudinal motion including known wind. As far as time constrained operations are assumed, final time as well as final altitude and along track distance to be flown are imposed. We propose a new methodology to compute a reference calibrated airspeed (CAS) and a reference vertical speed to achieve imposed final position and altitude at a prescribed time which solve the Two-point Boundary Value Problem (TPBVP) where initial and final constraints are coupled with the set of ordinary differential equations associated with the aircraft motion. The aircraft is considered as a point mass model. The optimal control problem consists in minimizing fuel consumption while ensuring that the maximum longitudinal and normal accelerations remain lower than the acceptable level for civil flights. The computed trajectory is a time parametrized trajectory which will be used as a reference trajectory by some envisioned tracking controller installed on board the aircraft. Nevertheless the design of the tracking controller is out of the scope of this paper. Numerical simulations using Bada 3.11 9 are provided to illustrate the suboptimal trajectory generation method and achieved results.

A Simple Altitude Capture Avoiding TCAS Resolution Advisories During Level-Off Situations

TCAS resolution advisories generation process during level-off situation is overviewed and illustrated on a real situation captured through mode S radar with RA downlink service. It underlines that one common type of resolution advisories is that which is issued when aircraft are expected to level-off 1000 feet apart, and are converging at the same time. These resolution advisories, often subsequently classed as ?operationally unnecessary? from an air traffic control standpoint, can be perceived as disturbing by controllers and by pilots. This issue has been tackled in this paper by proposing a method to prevent RA triggering during level off situation. This method is based on the setting of the altitude at which the autopilot switches towards the altitude capture mode and on an intrinsic parameter of the autopilot altitude capture mode, namely its natural frequency. It is shown that applying the proposed method to the illustrative example prevents the issuance of resolution advisories when aircraft are expected to level-off 1000 feet apart. The method which is presented is one of the simplest options, and allows altitude capture without triggering resolution advisories for vertical speeds up to 3000 feet/min. Nevertheless, the time needed by the aircraft to capture the cleared flight level is increased. Consequently, future work will focus on improving the time needed to capture the cleared flight level under the constraint to keep positive the distance between the autopilot altitude capture dynamic and the boundary of the RA zone.

GENERIC 4D FLIGHT GUIDANCE BASED ON DIFFERENTIAL FLATNESS

With the increase of traffic density, it appears of interest to design more versatile guidance systems for civil transportation aircraft. In this paper, a new approach is proposed to design a guidance system able to achieve 4D trajectory tracking. Flight guidance dynamics are shown to be implicit differentially flat with respect to the inertial position of an aircraft. To overcome the numerical difficulty implied by this implicit property, artificial neural networks are introduced to capture the differential relationship between guidance parameters and attitude control inputs. A corrective term is also introduced to take into account the effects of model approximation, neural network errors and disturbances.