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Maurice J.-B.,University of Stuttgart | Maurice J.-B.,Institute of Flight Mechanics and Flight Control | Farolfi R.,University of Stuttgart | Saupe F.,University of Stuttgart | And 5 more authors.
Journal of Guidance, Control, and Dynamics | Year: 2012

Robust stability of a helicopter hingeless rotor model used for air resonance alleviation is investigated in this paper. This aeroelastic phenomenon can be described naturally considering the rotor as a whole through a time-periodic change of coordinates called multiblade coordinates transformation. To assess robust stability of the resulting continuous linear time-periodic system, this paper defines a set of uncertainties specific to the helicopter rotor problem. The uncertain system is written in the form of a linear fractional representation and transformed using a frequency-lifting technique. This leads to a time-invariant representation of the uncertain system, the so-called harmonic transfer function. The extension of the standard μ-analysis to such lifted systems is proposed in the paper. Compared with a similar approach from literature based on an elementary example, the technique requires a moderate increase of the number of inputs and outputs, thus reducing the numerical effort involved in the computation of the μ-bounds. The methodology, applied to the uncertain closed-loop helicopter rotor, shows robust stability for the defined set of uncertainty. The results are compared to an analysis performed on the base of a linear time-invariant system to quantify how strongly robust stability bounds are underestimated when the periodicity is not accounted for. Copyright © 2012 by the American Institute of Aeronautics and Astronautics, Inc.

Zurn M.,Queensland University of Technology | Morton K.,Queensland University of Technology | Heckmann A.,University of Stuttgart | McFadyen A.,Queensland University of Technology | And 2 more authors.
IEEE Aerospace Conference Proceedings | Year: 2016

There is an increased interest in the use of Unmanned Aerial Vehicles for load transportation from environmental remote sensing to construction and parcel delivery. One of the main challenges is accurate control of the load position and trajectory. This paper presents an assessment of real flight trials for the control of an autonomous multi-rotor with a suspended slung load using only visual feedback to determine the load position. This method uses an onboard camera to take advantage of a common visual marker detection algorithm to robustly detect the load location. The load position is calculated using an onboard processor, and transmitted over a wireless network to a ground station integrating MATLAB/SIMULINK and Robotic Operating System (ROS) and a Model Predictive Controller (MPC) to control both the load and the UAV. To evaluate the system performance, the position of the load determined by the visual detection system in real flight is compared with data received by a motion tracking system. The multi-rotor position tracking performance is also analyzed by conducting flight trials using perfect load position data and data obtained only from the visual system. Results show very accurate estimation of the load position (∼5% Offset) using only the visual system and demonstrate that the need for an external motion tracking system is not needed for this task. © 2016 IEEE.

Gros M.,Institute of Flight Mechanics and Flight Control | Schottl A.,MBDA Systems | Fichter W.,Institute of Flight Mechanics and Flight Control
AIAA Guidance, Navigation, and Control (GNC) Conference | Year: 2013

This paper treats with a local-planning algorithm that is suited for real-time re-planning in unknown urban environments on small UAVs with limited computational power. The Finite Receding-Horizon Incremental-Sampling Tree (RHIST) incrementally builds a tree of cubic Beziér-spline paths within a sphere in the vicinity of the plant. To facilitate a distance optimized traverse of complex environments, the tree connection strategy employs samples on the sphere that are connected in an optimal fashion with respect to the current plant state. This enables the planner to achieve locally optimal paths as opposed to the nonoptimal nearest neighbor strategy of the well-known RRT-algorithm. Robustness against unknown but bounded position disturbances is achieved by enclosing spline paths with Oriented Bounding Boxes (OBBs), whose magnitude is dependent on the current position deviation of the plant. As a substitute of an underlying mass-point model, flight path constraints are accounted for on the spline. An approximation of the load factor serves as flight envelope protection through the consideration of the path-following controller structure even for off-path cases. Simulation results and Hardware-in-the-Loop (HiL) testbed results demonstrate the performance in urban environments and the real-time capability of the RHIST algorithm.

Boubakir A.,Jijel University | Souanef T.,Institute of Flight Mechanics and Flight Control | Labiod S.,Jijel University | Plestan F.,École Centrale Nantes | Boudjema F.,Polytechnic School of Algiers
Proceedings of the Institution of Mechanical Engineers. Part I: Journal of Systems and Control Engineering | Year: 2016

This paper proposes an L1 fuzzy adaptive controller for a class of uncertain continuous-time single-input single-output nonaffine nonlinear systems. The structure of this controller is derived based on L1 adaptive control design methodology and integrates a fuzzy system. The latter is used to approximate as best as possible a function of an unknown ideal implicit controller, which provides good results and improves the performance significantly. The L1 fuzzy adaptive controller consists of a predictor, a control law and its adaptive laws. The major advantage of the proposed control scheme is its ability to guarantee uniformly bounded transient and tracking performance for the controlled system. These performance bounds can be rendered arbitrarily small by the systematic choice of design parameters. The effectiveness and feasibility of the proposed L1 fuzzy adaptive controller are examined experimentally in the position control of a pneumatic actuator system. © Institution of Mechanical Engineers 2016.

Graf F.,Institute of Flight Mechanics and Flight Control | Ott T.,Institute of Flight Mechanics and Flight Control | Lejault J.P.,European Space Agency | Fichter W.,Institute of Flight Mechanics and Flight Control
IFAC Proceedings Volumes (IFAC-PapersOnline) | Year: 2013

Future satellite missions have high precision pointing performance requirements. This leads to the necessity of optimizing attitude estimators not only with respect to absolute, but also with respect to window- and stability-time errors. These errors are especially important for achieving unprecedented image quality. The standard attitude estimator is designed to be optimal with respect to its absolute knowledge error. In practice, such an estimator design is either assumed to be almost optimal for window- and stability-time errors or a cumbersome simulation-based optimization is conducted to achieve optimality in this respect. The first assumption is not sufficient for high precision pointing missions and simulation-based design is computationally expensive. In this article frequency-domain metrics are used to develop a continuous-time design approach for a fixed gain attitude estimator that is optimized with respect to window- or stability-time errors. Colored noise is explicitly taken into account in the optimization because its spectrum strongly affects the solution. However, that might lead to instability of the estimator. This issue is addressed and a solution is provided that guarantees stability with the burden of marginal performance losses only. The approach is applied to design a two-state attitude estimator and its results are verified in frequency-domain computations and time-domain simulations for the future ESA mission, Meteosat Third Generation. In this case, the computational time for optimizing the window-time error has been reduced from hours to a few seconds. The fast and high precision estimator design for window- and stability-time errors thus supports time-efficient design trade-offs. © IFAC.

Grzymisch J.,University of Stuttgart | Grzymisch J.,Institute of Flight Mechanics and Flight Control | Fichter W.,University of Stuttgart | Fichter W.,Institute of Flight Mechanics and Flight Control
Journal of Guidance, Control, and Dynamics | Year: 2014

A study was conducted to present an alternative analytic expression for an optimal observability objective that could be used to maximize observability for any given initial trajectory. The proposed objective function was more versatile due to its simple form and could easily be included within a higher-level trajectory optimization scheme. This simple form also helped in the understanding of the conditions that maximize observability, further broadening this understanding. An analytical solution for optimal observability maneuvers was developed using the proposed observability objective. These closed-form solutions are developed in a generic manner, applicable to any maneuver type and any a priori unknown trajectory. It was also show how the proposed framework could be easily modified to provide closed-form solutions for a variety of different constraints on the maneuvers and on the trajectory.

King F.A.,University of Stuttgart | King F.A.,Institute of Flight Mechanics and Flight Control | Maurice J.-B.,University of Stuttgart | Maurice J.-B.,Institute of Flight Mechanics and Flight Control | And 4 more authors.
Journal of Guidance, Control, and Dynamics | Year: 2014

This paper presentsanew active in-flight rotorblade tracking control system for helicopters equipped with trailingedge flap actuators on the rotor blades. The objective of the in-flight rotorblade tracking controller is to minimize vibrations in the helicopter cabin and vibratory loads at the rotor hub induced by static blade dissimilarities. The control design is based on a steady-state transfer matrix from flap inputs to vibration outputs, which is first identified experimentally and then symmetrized. For this design model, an analytically derived Moore-Penrose pseudoinverse, which playsakey role in overcoming restrictions of existing approaches, such as the dependency onfull-rank transfer matrices, is used. The system is verified through flight tests carried out with a full-scale experimental helicopter. The results demonstrate that the presented in-flight tracking system effectively minimizes the tracking error induced vibrations. Copyright © 2013 by University of Stuttgart, iFR.

Joos A.,University of Stuttgart | Joos A.,Institute of Flight Mechanics and Flight Control | Fichter W.,University of Stuttgart | Fichter W.,Institute of Flight Mechanics and Flight Control
AIAA Guidance, Navigation, and Control Conference | Year: 2010

This paper addresses the automatic tracking of a straight trajectory with an airship under the influence of wind and with low cruise velocity requirements. In this case any direct wind measurements are not available. The proposed new method is based on aligning the airship such that the body-fixed aerodynamic sideforce is minimized and thus, direct wind measurements can be avoided. The alignment can be realized through a new airship actuation with two lateral actuators that are used to create a yawing moment by powering them antithetically. At the low airspeeds considered here active yawing is not possible with aerodynamic control surfaces. However, using the aerodynamic sideforce as a control variable introduces a nonlinearity in the control loop. The closed loop stability is analyzed and the performance of this approach is demonstrated with a PC/104 flight control computer in real-time simulations under different conditions. A sophisticated nonlinear 6-degree of freedom airship model with this new actuation approach is used as the demonstrator. Copyright © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

Liu G.,Northwestern Polytechnical University | Guo C.,Northwestern Polytechnical University | Zheng P.,Institute of Flight Mechanics and Flight Control | Ren A.,Northwestern Polytechnical University
2010 9th International Symposium on Antennas Propagation and EM Theory, ISAPE 2010 | Year: 2010

A CPW-fed compact printed monopole antenna is proposed for portable UWB devices. The semi-ellipse and rectangle structure are combined as the radiator to expand the bandwidths of antenna to 2.3∼20.1 GHz (VSWR<2), except for the two sub-bands of 3.1∼4.4 GHz for WiMAX (3.3∼3.7 GHz), the C-band satellite communication systems (3.7∼4.2 GHz), and 5.1∼5.9 GHz for WLAN. These notched sub-bands are obtained by etching two C-shaped (circular arc) slots on the radiating patch. The measured results are in good agreement with the simulated ones. ©2010 IEEE.

Sachs G.,Institute of Flight Mechanics and Flight Control | Moelyadi M.A.,Bandung Institute of Technology
Journal of Bionic Engineering | Year: 2010

Using a sophisticated aerodynamic method, the effects of extremely large dihedral on the aerodynamic characteristics of birds are determined. With this method, it is possible to generate solutions for the addressed aerodynamic problem, which shows a high complexity due to interference effects caused by dihedral and pronounced 3-dimensional flow properties as well as due to complex wing geometries. From the obtained results it follows that extremely large dihedral has substantial effects on the aerodynamic force characteristics. There are significant changes in the lift, the drag and the side force, thus affecting the flight performance. Furthermore, the obtained results show that the aerodynamic rolling and yawing moment characteristics are influenced by extremely large dihedral to a high degree. This is a significant outcome for lateral-directional stability because the aerodynamic rolling and yawing moment characteristics have a determinative influence here. © 2010 Jilin University.

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