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International audience; In recent years, unmanned aerial vehicles applications have grown in various fields. New design configurations have emerged to address these needs. This paper focuses on the multidisciplinary design optimization of three popular concepts of drones under a common framework: multicopters, fixed-wings, and the more recent fixed-wing VTOLs. Low-fidelity but computationally efficient models for drone sizing are proposed, some of them being shared by the different concepts. The models are integrated with a design optimization approach, and an efficient sizing methodology allows for reducing the problem complexity. This approach is instrumental because of the large number of design variables and constraints involved in the multidisciplinary design process. Examples of sizing results are provided to validate the methodology for fixed wing UAVs. In addition, a study case demonstrates the benefit of a common framework for comparing the performances of different drone concepts. A key finding is that the VTOL propulsion of the fixed-wing VTOLs must be carefully optimized to avoid an undesirable mass penalty.

International audience; The number of applications that use multirotor drones has significantly increased in the past year due to their high manoeuvrability and capability to perform hovering. The main limit of such configuration is its endurance especially when batteries are used as the energy source. This paper focuses on the evaluation of the endurance of multirotor drones in forward flight using a design optimization approach. Lightweight models to represent accuratly the physics of forward flight are proposed. One significant finding is that the design optimization code enables to rapidly obtain a design for a given set of requirements and has been validated on the Parrot ANAFI USA. The end of the article illustrates the sensitivity of maximum takeoff weight to the drag of aerodynamic frame.

International audience; This paper presents a numerical and experimental investigation of the aerodynamic characteristics of a vertical take-off and landing micro air vehicle designed to fly in the Martian atmosphere. Numerical tools are validated through experimental data from the literature where Martian conditions are replicated. An innovative airfoil is designed for the specific flying conditions of the Martian MAV, i.e. compressible and ultra-low Reynolds number flows. This airfoil is evaluated in different Reynolds and Mach number conditions using unsteady compressible laminar Navier-Stokes simulations. Single rotors and coaxial configurations are designed for different thrust constraints by optimizing the chord and twist distributions using a free wake lifting line method. Rotors are firstly evaluated numerically using Navier-Stokes simulations. To validate the simulations, the optimized configurations are tested experimentally in an evacuation chamber, recreating Martian atmosphere in terms of density and gas. Thrust and torque on each rotor are measured by a two-component set-up. Tests are performed up to transonic flow conditions at blade tip. Results are extrapolated to a suggested design for a Martian MAV.

International audience; An experimental investigation on the flow topology and performance of a rotor operating at low Reynolds numbers is presented. The feasibility of laminar to turbulent transition experiments over small rotors is demonstrated. Phase-locked infrared thermography coupled with simultaneous force and torque measurements were used to study a three bladed NACA0012 rotor with a radius of 0.125 m and an angle of attack of 10 degrees. Boundary layer transition was fostered using two-dimensional (2D) and threedimensional (3D) isolated roughness elements, placed at approximately 5% and 28% of the rotor blades chord. In the smooth rotor configuration, a 3D flow topology is observed, consisting of a clear laminar region closer to the blade root and a turbulent region at the blade tip. It was found that the state of the boundary layer can significantly affect the rotor’s performance, with the forcing of laminar to turbulent transition generally resulting in a loss of performance when compared to the smooth reference rotor case.

International audience; This paper presents a numerical and experimental study of the aerodynamic characteristics of a vertical takeoff and landing (VTOL) micro air vehicle (MAV) designed to fly in Mars' atmosphere. Numerical tools are validated through experimental data from the literature where Martian conditions are replicated. Innovative airfoils are designed for the specific flying conditions of the Martian MAV, i.e. compressible and ultra-low Reynolds number flows. An optimized airfoil is evaluated in different Reynolds and Mach number conditions using unsteady laminar Navier-Stokes simulations. Rotors are designed by optimizing the chord and twist distributions using a free wake lifting line method with different geometrical and lift constraints. Rotors are numerically evaluated using two different Navier-Stokes solvers. A coaxial configuration is also defined to achieve zero total torque and double lift. To validate the simulations, experiments are performed in the ONERA's low pressure tank, recreating Martian atmosphere in terms of density and gas. Thrust and torque are measured by a two-component setup developed by ISAE-SUPAERO, with independent measures on each rotor in coaxial configuration. Tests are performed up to transonic flow conditions at blade tip.

International audience

A flight control system is configured to control the flight of a convertible fixed-wing drone (12), having two left and right wings, each supporting a propeller in front and a deflection flap at the rear edge. The control system includes an attitude regulator (154) of the drone (12) to respectively control the roll angles ϕm, pitch θ m and yaw Ψm, measured by one or more sensors on setpoint angles ϕd, pitch θ d and lace Ψd. The first attitude regulator (154) comprises a first MFC SISO device (162) for modelless control at one input-one output for regulating and controlling the pitch angle θ m measured on the pitch set angle θ d by determining a first command δn for symmetrical deflection of the left and right flaps, applied with the same sign to said left and right flaps., Un système de contrôle de vol est configuré pour contrôler le vol d'un drone convertible à voilure fixe (12), ayant deux ailes gauche et droite supportant chacune une hélice en avant et un volet de déflexion en bordure arrière. Le système de contrôle comporte un régulateur d'attitude (154) du drone (12) pour asservir respectivement les angles de roulis ϕm, tangage θ m et lacet Ψm, mesurés par un ou plusieurs capteurs sur des angles de consigne de roulis ϕd, tangage θ d et lacet Ψd. Le premier régulateur d'attitude (154) comporte un premier dispositif MFC SISO (162) de commande sans modèle à une entrée-une sortie pour réguler et asservir l'angle de tangage θ m mesuré sur l'angle de consigne de tangage θ d en déterminant une première commande δn de déflection symétrique des volets gauche et droit, appliquée avec le même signe sur lesdits volets gauche et droit.

International audience

International audience; One of the major challenges of Mini-UAV flight is unsteady interaction with turbulent environment while flying in lower levels of atmospheric boundary layer. Following inspiration from nature we expose a new system for angle of attack estimation based on pressure measurements on the wing. Such an equipment can be used for real-time estimation of the angle of attack during flight or even further building of wind velocity vector with additional equipment. Those information can find purpose in control and stabilization of the aircraft due to inequalities seen by the wing or even for various soaring strategies that rely on active control for energy extraction. In that purpose flying wing UAV has been used with totally four span-wise locations for local angle of attack estimation. In-flight angle of attack estimation of differential pressure measurements have been compared with magnetic sensor with wind vane. Difference in local angle of attack at four span-wise locations has confirmed spatial variation of turbulence. Moreover, theoretical energy dissipation of wind fluctuations described by Kaimal spectrum has shown acceptable match with measured ones.

International audience

International audience; A passive twist control is considered as an adaptive way to maximize the overall efficiency of a proprotor developed for convertible Micro Air Vehicles (MAV). Incorporated into a database of airfoil characteristics, Blade Element Momentum Theory (BEMT) is implemented to predict the performance of proprotors at low Reynolds numbers. Using this model, it is found that low twist allows for efficient hovering while high twist helps to forward flight. The Centrifugal Force Induced Twist (CFIT) concept is proposed to realize the required torsion of proprotor between hover and forward flight. Tip mass is used to provide the nose-down twisting moment by centrifugal force and stabilize the flexible blade. Classical Lamination Theory (CLT) is employed to estimate the torsion behavior of glass/epoxy laminate blade and to study the feasibility of CFIT concept. The results indicate that the predicted torsion of CFIT blade is of the same level with required deformation. The laminate blades were tested in hover and forward flight modes, with deformations measured by Laser Displacement Sensor (LDS). In rotor mode, the laminate blade can generate approximately -9◦ torsion at blade tip rotating at 1,300 RPM. By contrast, at 800 RPM and inflow velocity 8m/s, it is capable of providing around -5◦ torsion at blade tip in propeller mode.

Colloque avec actes et comité de lecture. Internationale.; International audience; L'intérêt croissant des drones voilure tournante, pour des applications militaires et civiles, a encouragé les concepteurs à considérer de nouvelles configurations miniaturisés, plus efficaces en termes d'endurance, capacité d'emport et de maniabilité. Le but de cet article est d'étudier une nouvelle configuration de rotor coaxial, dans le but de garantir la maniabilité du véhicule tout en enlevant les surfaces de contrôle inutiles qui augmentent la sensibilité aux rafales de vent. Ce papier vise à étudier une version modifiée d'un contrarotatif classique, dans lequel les rotors peuvent être inclinés de manière à créer des forces et des moments de dérive potentiellement utilisables pour la maniabilité. Lorsque les rotors rotatifs sont inclinés, ils ne sont pas coaxiaux et des effets gyroscopiques sont créés. La complexité d'un mécanisme de plateau cyclique a été remplacée par un mécanisme d'inclinaison qui est actuellement assurée par servomoteurs classiques. À l'avenir, il est prévu d'utiliser un matériau électroactif. Dans le prototype présenté, la direction de la poussée des deux rotors peut être redirigée par les une inclinaison latérale et longitudinale des rotors. Un modèle théorique du mécanisme a été mis au point sur la base d'un modèle mécanique qui comprend les forces, moments et les effets gyroscopiques induites par les pièces en rotation. En plus de l'approche théorique, un dispositif expérimental a été mis au point. Il est basé sur une balance à 5 composantes permettant de mesurer les efforts et moments résultants des différentes inclinaisons.

International audience; In the present study, a passive twist control is considered as a potential way to improve the overall flight efficiency for proprotor of Micro Air Vehicle (MAV). This paper will focus on the aerodynamic performance and deformation behaviour of a flexible laminate blade. Incorporated with adatabase of airfoil characteristics, Blade Element Momentum Theory (BEMT) is implemented for performance prediction of proprotor at low Reynolds numbers. The preliminary procedure is based on finding optimum twist distributions for hover and forward flight, but keeping a given chord distribution.A numerical model is developed using a combination of aerodynamic model based on BEMT, and structural model based on anisotropic beam finite element, in order to evaluate the coupled structural and the aerodynamic characteristics of the deformable proprotor blade. The numerical model - Fluid Structure Interaction (FSI) was then validated by means of shape reconstruction from LDS (Laser Displacement Sensor) outputs. It can be concluded that the proposedexperiment technique is capable of providing a predictive and reliable data in blade geometry and performance for rotor mode. The FSI approach is also valid as a reliable tool for designing and analyzing the MAV proprotor made of composite material.

Colloque avec actes et comité de lecture. Internationale.; International audience; Les drones des type « Tilt-Body» constitues un intérêt croissant car ils offrent une grande polyvalence dans le domaine de la reconnaissance en milieu urbain. Une question clé à résoudre pour un fonctionnement optimal est le problème qu'un rotor orientable rigide ne peut pas fonctionner de manière efficace à la fois pour le vol stationnaire et vol de croisière. Malheureusement, la plupart des grandes techniques d'adaptation d'échelle ne sont pas transférables à l'échelle des microdrones. Dans la présente étude, une commande de torsion passive est considérée comme un moyen potentiel d'améliorer l'efficacité globale de vol par rotor orientable. Ce document met l'accent sur l'évaluation des techniques de conception, à la fois pour les performances propulsives et pour les propriétés structurelles d'un rotor orientable flexible. Les modèles numériques d'ordre inférieur seront validés au moyen de mesures de performances statiques et de reconstruction de forme par laser. La procédure de conception est basée sur la recherche de conceptions optimales pour le vol stationnaire et vol de croisière, mais en gardant une distribution de corde donnée, tandis que la distribution de pas du rotor est laissée comme le seul degré de liberté pour atteindre un optimum. Un code de conception de l'hélice, FMIL, basé sur la théorie Atkins et la théorie des éléments de pale, également associés à un modèle de moteur de telle sorte que l'optimisation est obtenue sur la base de l'efficacité globale de propulsion. En termes de modèle de structure, un modèle numérique de poutre est combiné avec un modèle de section transverse BECAS avec des chargements extraits de FMIL. La procédure est en mesure de prédire la déformation pour un niveau donné de performances du rotor. Dans le but de valider les modèles numériques précédents, une procédure expérimentale a été mise au point afin d'obtenir une performance globale hélice avec mesure de la déformation lors de la rotation. Les mesures de déformations sont réalisées au moyen de deux lasers et d’un post-traitement spécifique, permettant l'extraction d'un nuage de points représentant la pale déformée. Les efforts actuels visent à mettre en place un modèle de poutre inverse, afin d'en déduire à partir des mesures, la distribution de contrainte correspondant.

International audience; This study focus on optimisation of electric propulsion system for a given mission with multiple working conditions. A program called Qpoptimizer is developed and presented which can analyse and couple numerous motors and propellers from databases for a specific mission. It can also design a custom propeller by using the motor and airfoil databases. Qpoptimizer uses Qprop and Qmil opensource propeller analyses and design programs from Mark Drela. Motor and propeller couples are simulated at each predefined working condition and given a score according to their total performance. This methodology ensures the optimisation of the selected motor and propeller couples to be valid and optimum not only for one working condition (for example: cruise condition) but for all of them (take-off,high speed,etc...). Theoretical models and experimental measurements are explained in order to generate the required databases for the existing motors, propellers and airfoils. Finally, an application of the Qpoptimizer program on a real mission is also presented where a custom propeller is optimised according to the weighted mission working conditions.

Micro Air Vehicle (MAV)s with transitioning flight capabilities, or simply Hybrid Micro Air Vehicle(HMAV)s combine the beneficial features of fixed-wing configurations in terms of endurance,with vertical take-off and landing capabilities of rotorcraft to perform five different flight phasesduring typical missions : vertical takeoff, transitioning flight, forward flight, hovering, and verticallanding. This promising MAV class has a wider flight envelope than conventional MAVs,which implies new challenges for both control community and aerodynamic designers. One ofthe major challenges of HMAVs is the fast variation of aerodynamic forces and moments duringthe transition flight phase, which is difficult to model and control accurately. In this thesis, wefocus on the development of control laws for a specific class of HMAVs, namely tail-sitters.In order to stabilize the HMAV and overcome its modeling problem, we propose a flightcontrol architecture that estimates in realtime its fast nonlinear dynamics with an intelligentfeedback controller. The proposed flight controller is designed to stabilize the HMAV attitude,velocity and position during all flight phases. By using Model-Free Control (MFC) algorithms,the proposed flight control architecture bypasses the need for a precise HMAV model that iscostly and time consuming to obtain. A comprehensive set of flight simulations covering theentire flight envelope of the HMAV is presented, with the respective analysis for each of theflight phases. Furthermore, the control performance and the limitations of the MFC architecture are discussedin order to introduce further applications in real flight experiments. Flight tests clarifyand validate the proposed control methodology in a practical context, thus solving the principalissue of HMAVs; that is, the formulation of accurate HMAV dynamic equations to designcontrol laws. In addition, from simple mathematical algorithms, MFC is easily implemented ona microprocessor without the need for high computational costs, such as time processing andmemory resources. The results obtained provide a straightforward way in which to validatethe methodological principles presented in this thesis, to certify the designed MFC parametersand to establish a conclusion regarding MFC advantages and disadvantages in theoretical andpractical contexts related to aerospace systems., Les micro drones à capacités de vol de transition, ou simplement HMAVs (de l’anglais Hybrid MicroAir Vehicles), regroupent les principales caractéristiques aérodynamiques des configurationsà voilure fixe, en termes d’endurance, avec les capacités de décollage et d’atterrissage verticaldes voilures tournantes afin d’effectuer cinq phases de vol au cours de ses missions, telles quele décollage vertical, le vol de transition, le vol en croisière, le vol stationnaire et l’atterrissagevertical. Cette nouvelle classe de micro drones a un domaine de vol plus large que les microdrones conventionnels, ce qui implique de nouveaux défis pour les automaticiens et les concepteursaérodynamiques. L’un des principaux défis des HMAVs est la variation rapide des forces etdes moments aérodynamiques pendant la phase de vol de transition, qui est difficile à modéliseret à contrôle avec précision. Dans cette thèse, nous nous concentrons sur le développement delois de pilotage pour une classe spécifique des HMAVs, à savoir les tail-sitters.Afin de stabiliser la dynamique des tail-sitters et de surmonter leur problème de modélisation,nous proposons une architecture de contrôle de vol qui estime en temps réel leurs dynamiquesgrâce à un contrôleur à rétroaction intelligent. Le contrôleur de vol proposé est conçu pourstabiliser l’attitude du tail-sitter ainsi que sa vitesse, et sa position pendant toutes ses phasesde vol. En utilisant des algorithmes de la commande sans modèle, l’architecture de contrôle devol proposée contourne le besoin d’un modèle dynamique précis dont l’obtention est coûteuseet longue. Une série complète de simulations de vol couvrant l’ensemble du domaine de vol destail-sitters est présentée et, pour chaque phase de vol, son analyse respective.Avant d’introduire des expériences de vol réel, nous évaluons les performances et les limites del’architecture de commande sans modèle en simulation. Les essais en vol permettent de clarifier etde valider notre méthodologie de contrôle dans un contexte pratique, résolvant ainsi le principalproblème des tail-sitters, à savoir la formulation d’équations dynamiques précises pour concevoirles lois de commande. En outre, à partir d’algorithmes mathématiques simples, la commandesans modèle est facilement implémentée sur microprocesseurs sans nécessiter de coûts de calculélevés, tels que la fréquence de traitement et les ressources de mémoire. Les résultats obtenusfournissent un moyen simple de valider les principes méthodologiques présentés dans cette thèse,de certifier les paramètres obtenus lors de la conception de la commande sans modèle et d’établirune conclusion concernant ses avantages et ses inconvénients dans des contextes théoriques etpratiques liés aux systèmes aérospatiaux.