Murat Bronz

Towards a Long Endurance MAV

A conceptual design and performance analysis method (Long Endurance Conceptual Design Program) for long-endurance mini-micro UAVs is presented. Recent long endurance oriented results and achievements are looked through for possible usage for mini-micro scale. A real mission is also explained, whose objective is to accomplish a 200 km straight line flight autonomously with the smallest electric platform possible. Design phases of the platform by using the presented method, flight tests and comparison of the results are included. On the following section a design study for long-endurance MAVs using a hybrid energy system combining solar energy and Lithium batteries and the effect of size and cruise speed are investigated. We demonstrate that under a certain size, the use of solar energy becomes not useful at all. We conclude with the study of a candidate design for EMAV09 Endurance Mission in the light of the rules and scoring of the mission.

Guidance algorithm for smooth trajectory tracking of a fixed wing UAV flying in wind flows

This paper presents an algorithm for solving the problem of tracking smooth curves by a fixed wing unmanned aerial vehicle travelling with a constant airspeed and under a constant wind disturbance. The algorithm is based on the idea of following a guiding vector field which is constructed from the implicit function that describes the desired (possibly time-varying) trajectory. The output of the algorithm can be directly expressed in terms of the bank angle of the UAV in order to achieve coordinated turns. Furthermore, the algorithm can be tuned offline such that physical constraints of the UAV, e.g. the maximum bank angle, will not be violated in a neighborhood of the desired trajectory. We provide the corresponding theoretical convergence analysis and performance results from actual flights.

Flexible open architecture for UASs integration into the airspace: Paparazzi autopilot system

Air safety authorities are forced to develop regulations for UAS due to incidents disturbing public safety and demands from UAS operators. Despite numerous studies from the FAA and EASA, none of them decided on a regulation for UASs. The reliability of the flight is considered to be one of the main obstacles for UAVs integration. This is not an easy topic considering the unknowns of the systems, environment and possible failures. We believe the flexibility required for such solutions calls for open architectures. More specifically, this paper shows how the use of the Paparazzi open source auto-pilot system can ease the integration of low altitude UAS. To ensure safety, this integration needs to be achieved through airspace management and UAS reliability. Preliminary airspace designs, e.g. Amazons, identify different zones depending on the UAS capabilities, population density and altitude. Plus, national rules evolution push to cope with a variety of requirements. Open source and modular architectures are key to adapt to these requirements. From a UTM point of view, Paparazzi provide features to ease congestion management, such as dynamic geofencing, trajectory communication and collision avoidance. Concerning reliability, current regulations focus on flight constraints but might be expected to involve regulations on software and hardware components as well. In such case, the increased cost will be inevitable for the demands of certification. In the Paparazzi software case, parts of the code have been formally proved and stable versions have thousands of flight hours. Such heritage might ease the certification process for smaller companies. On top of its flexibility and reliability, Paparazzi offers a unique set of features, as an open source software, to achieve safe integration of low altitude UAS in the G airspace. To conclude this work, desirable new features and future work are discussed.

Design of A High-Performance Tailless MAV Through Planform Optimization

The paper presents the development of a high-performance tailless micro air vehicle. Design is optimized via a conceptual design optimizer according to the requirements of an atmospheric-research flight mission. Main focus is on the elevator control surface configuration that generates a lifting force which is placed in front of the center of gravity without requiring a high aspect ratio thanks to the particular wing planform shape. As a result, the longitudinal maneuvers are performed more efficiently such as, pitch-up maneuver requires a positive flap deflection which is also beneficial for the local airfoil’s maximum lift coefficient. This distinguishing feature of the design allows to design the wing surface more efficiently for maximum range and endurance performance speeds without too much compromising from the take-off and landing performance. Additionally, the angle of attack envelope of the aircraft is significantly reduced with the use of positive local camber change that was necessary for the selected mission requirements. Flight tests of the two prototypes and a final version is presented including the comparison between the expected theoretical results and the real-flight results. The resultant FENIX UAV enlarges the flight envelope of a compact tailless vehicle with hand-launch, low-speed flight, and more than 90minutes of endurance capabilities.

Adaptive sampling of cumulus clouds with UAVs

This paper presents an approach to guide a fleet of Unmanned Aerial Vehicles (UAVs) to actively gather data in low-altitude cumulus clouds with the aim of mapping atmospheric variables. Building on-line maps based on very sparse local measurements is the first challenge to overcome, for which an approach based on Gaussian Processes is proposed. A particular attention is given to the on-line hyperparameters optimization, since atmospheric phenomena are strongly dynamical processes. The obtained local map is then exploited by a trajectory planner based on a stochastic optimization algorithm. The goal is to generate feasible trajectories which exploit air flows to perform energy-efficient flights, while maximizing the information collected along the mission. The system is then tested in simulations carried out using realistic models of cumulus clouds and of the UAVs flight dynamics. Results on mapping achieved by multiple UAVs and an extensive analysis on the evolution of Gaussian processes hyperparameters is proposed.

Aerodynamic Characterization of an Off-the-Shelf Aircraft via Flight Test and Numerical Simulation

Characterization of an off-the-shelf small tailless aircraft with a wing span of 1:3m is presented. Mentioned aircraft is being used in several scientific measurement projects by authors, whereas the ight performance and quality such as endurance, and stability plays an important role on the measurement quality. Hence the main objective is to use the extracted and fine tuned aerodynamic and ight performance characteristics of the aircraft for a better flight control and mission planning during simulations and real flights. Aerodynamic characteristics are obtained through flight tests, numerical analyses, and some isolated ground experiments for the propulsion system. The comparison of different measurement and estimation techniques are discussed.

Preliminary Design Estimation of the V/STOL Airplane Performance

A preliminary study on estimating aerodynamic forces of a Vertical/Short Takeoff and Landing (V/STOL) mini Unmanned Air Vehicle (UAV) configuration with Distributed Electric Propulsion (DEP) system is presented. The main objective is to offer the next generation fixed wing mini UAV aircraft configuration with high-speed cruise flight and vertical take-off capabilities. The proposed concept uses four electric motors and propellers combination located on the leading edge of the wing. The described method uses semi-empirical formulations in order to estimate the forces and moments generated by the wing immersed in its distributed propeller slipstreams. Actuator disk theory is used for the propeller slipstream, where the thrust is assumed to be known for the calculations. Upwash of the fuselage and each propeller slipstream are taken into account for the wing and propeller inflow angle calculations. The resulting method, which is written as a program, serves as a conceptual design program for this type of configuration. Additionally, the program will be used for generating data for flight dynamics simulations. A candidate design is also presented, which is being manufactured for the on-going developments and tests.

Bioinspired wind field estimation—part 1: Angle of attack measurements through surface pressure distribution

One of the major challenges of Mini-Unmanned Aerial Vehicle flight is the 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 aircraft has been used with totally four span-wise locations for local angle of attack estimation. In-flight angle of attack estimation from differential pressure measurements on the wing has been compared with magnetic sensor with wind vane. The results have shown that pressure ports give more reliable estimation of angle of attack when compared to values given by wind vane attached to a specially designed air-boom. Difference in local angle of attack at four span-wise locations has confirmed spatial variation of turbulence in low altitude flight. Moreover, theoretical law of energy dissipation for wind components described by Kaimal spectrum has shown acceptable match with estimated ones.

Fault detection & diagnosis for small UAVs via machine learning

The new era of small UAVs necessitates intelligent approaches towards the issue of fault diagnosis to ensure a safe flight. A recent attempt to accommodate quite a number of UAVs in the airspace requires to assure a safety level. The hardware limitations for these small vehicles point the utilization of analytical redundancy rather than the usual practice of hardware redundancy in the conventional flights. In the course of this study, fault detection and diagnosis for aircraft is reviewed. An approach of implementing machine learning practices to diagnose faults on a small fixed-wing is selected. The selection criteria behind is that, data-driven fault diagnosis enables avoiding the burden of accurate modeling needed in model-based fault diagnosis. In this study, first, a model of an aircraft is simulated. This model is not used for the design of Fault Detection and Diagnosis (FDD) algorithms, but instead utilized to generate data and test the designed algorithms. The measurements are simulated using the statistics of the hardware in the house. Simulated data is opted instead of flight data to isolate the probable effects of the controller on the diagnosis, which will complicate this preliminary study on FDD for drones. A supervised classification method, SVM (Support Vector Machines) is used to classify the faulty and nominal flight conditions. The features selected are the gyro and accelerometer measurements. The fault considered is loss of effectiveness in the control surfaces of the drone. Principle component analysis is used to investigate the data by reducing the feature space dimension. The training is held offline due to the need of labeled data. The results show that for simulated measurements, SVM gives very accurate results on the classification of loss of effectiveness fault on the control surfaces.

In-Flight Thrust Measurement using On-Board Force Sensor

Preliminary results of an in-flight thrust measurement method are presented in order to determine the drag force. Flight experiments are conducted by an off-the-shelf aircraft which has been equipped with an autopilot system and additional sensors measuring the electric motor rotation speed, battery voltage, drawn current, and direct thrust of the motor. Several level cruise flights have been performed in order to measure the thrust, thus the drag force generated by the aircraft. The propulsion system used on the aircraft is first characterized in the wind-tunnel. The direct thrust measurement system which is on-board the aircraft presents a lot of noise coming from vibrations, characteristics of the sensor itself, and also the fuselage wake and propeller interaction. Hence a better estimation of the in-flight thrust and the resultant drag is obtained by sensor fusion of Gaussian signals.