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The flight trajectory of a coaxial rotorcraft during a flight test campaign with dynamic maneuvers has been reconstructed utilizing a Rauch-Tung-Striebel-smoothing and Estimation-Before-Modeling approach. The latter also provides ...
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The flight trajectory of a coaxial rotorcraft during a flight test campaign with dynamic maneuvers has been reconstructed utilizing a Rauch-Tung-Striebel-smoothing and Estimation-Before-Modeling approach. The latter also provides time histories for the external forces and moments as well as their time derivatives, which are valuable additional information for flight dynamics analysis, control design, and system identification. Besides the conventional sensors, the rotorcraft was also instrumented with angular accelerometers. The benefits of such sensors on the reconstructed aircraft states, and the external forces and moments are discussed. Sensor errors and model parameters are identified as a byproduct of the flight path reconstruction. A section of the reconstructed trajectory and the estimated sensor model parameters are provided as the basis for the validation and discussion of the applied methods. Furthermore, the paper summarizes the important implementation aspects and practical lessons learned, unique to rotorcraft flight path reconstruction.
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A flight test campaign is being prepared for system identification on a general aviation aircraft. The goal is to analyze the effectivity and efficiency of different maneuvers, injected in a closed-loop environment with different ...
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A flight test campaign is being prepared for system identification on a general aviation aircraft. The goal is to analyze the effectivity and efficiency of different maneuvers, injected in a closed-loop environment with different controller settings. In a first step, the information content of the planned flight test campaign is evaluated, for the open-loop injection of the system identification maneuvers. Furthermore, the effects of the activation of the feedback controller with different gains during the maneuvers is studied. Preliminary flight tests have been performed on a small drone to validate the simulation based analysis.
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Sufficient excitation is the basis for precise and reliable parameter estimates. Outside of test flights, sufficient excitation often cannot be guaranteed resulting in errors and drift of the estimates. In this study, we present f...
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Sufficient excitation is the basis for precise and reliable parameter estimates. Outside of test flights, sufficient excitation often cannot be guaranteed resulting in errors and drift of the estimates. In this study, we present four approaches for monitoring excitation in online parameter estimation, suitable for use with recursive least squares, sequential least squares, extended Kalman filtering, and output-error methods. The excitation monitoring approaches are based on detecting collinearity in the regressor matrix and sensitivity matrices as well as monitoring the magnitude of the sensitivities. We integrated the monitoring into the joint extended Kalman filter and the sequential least squares in frequency-domain. By this, we mitigate drift and noise in the estimates while maintaining the tracking capabilities for changing parameters. We compared these approaches and demonstrated their effectiveness in simulation of longitudinal aircraft dynamics and based on quadcopter flight test data.
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In this paper, two candidate models describing the inflow of a coaxial rotor system are defined, implemented, and analyzed. As a benchmark, a finite state nonlinear dynamic inflow model is implemented based on potential flow theor...
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In this paper, two candidate models describing the inflow of a coaxial rotor system are defined, implemented, and analyzed. As a benchmark, a finite state nonlinear dynamic inflow model is implemented based on potential flow theory. The extension of this approach to a coaxial rotor system is achieved by the superposition of both rotors' pressure potentials. Furthermore, a simpler static simulation model is developed and extended to a coaxial rotor configuration using geometric considerations. The nonlinear inflow models are both integrated into a rotor simulation model, which is part of a full flight envelope helicopter simulation model implemented at the Institute of Flight System Dynamics of the Technical University of Munich. The influence of the inflow dynamic on the overall rotor response as well as the differences between the two implemented approaches are investigated. The models have been evaluated for the coaxial helicopter CoAX 600, developed by edm aerotec GmbH.
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In this paper, time domain approaches will be applied to estimate the unknown parameters in a physics-based helicopter model. A nonlinear model structure is developed using the blade element momentum theory. We apply the Output Er...
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In this paper, time domain approaches will be applied to estimate the unknown parameters in a physics-based helicopter model. A nonlinear model structure is developed using the blade element momentum theory. We apply the Output Error Method implementation of the Maximum Likelihood estimation theory to estimate the unknown parameters in the model. This nonlinear model is linearized at hover for linear model analysis. The helicopter under investigation in this study is an unmanned helicopter with intermeshing rotors (synchropter). The test data was generated via automatic maneuver injection. We demonstrate that the proposed method provides promising system identification results by combining a physics-based model and parameter estimation based on flight test data.
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摘要 :
In this paper, time domain approaches will be applied to estimate the unknown parameters in a physics-based helicopter model. A nonlinear model structure is developed using the blade element momentum theory. We apply the Output Er...
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In this paper, time domain approaches will be applied to estimate the unknown parameters in a physics-based helicopter model. A nonlinear model structure is developed using the blade element momentum theory. We apply the Output Error Method implementation of the Maximum Likelihood estimation theory to estimate the unknown parameters in the model. This nonlinear model is linearized at hover for linear model analysis. The helicopter under investigation in this study is an unmanned helicopter with intermeshing rotors (synchropter). The test data was generated via automatic maneuver injection. We demonstrate that the proposed method provides promising system identification results by combining a physics-based model and parameter estimation based on flight test data.
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For the development of an unmanned version of an existing helicopter with a maximum takeoff weight of 600 kg and coaxial rotors, a manned flight test campaign is conducted in order to identify the flight physics characteristics of...
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For the development of an unmanned version of an existing helicopter with a maximum takeoff weight of 600 kg and coaxial rotors, a manned flight test campaign is conducted in order to identify the flight physics characteristics of the basis helicopter. Furthermore, the intention of the campaign is to test the future avionics and flight control system which is serving as a measurement system in this campaign. This ensures to incorporate all inherent effects of the avionics system, including sensor dynamics and latencies, for the development of the flight controller of the future unmanned system. Additionally, the flight test campaign is used as a proof of functionality of the avionics system together with the data links under a real physical environment. This paper gives insights into the planning and considerations that went into the flight test campaign. As the identification of the model is performed in the time domain, the focus is set on square wave maneuvers. To identify a set of trim states for the dynamic maneuvers, a simulation study is conducted. At the identified maneuver points, the eigenfrequencies of a linearized flight physics model are calculated to identify the maneuver lengths for the excitation of an appropriate frequency spectrum at the specific flight attitude. To apply maneuvers with the exact length, a way to guide the pilot through the correct maneuver injection via audio input has been developed. This proved to have a significant effect on the maneuver accuracy. Furthermore, a pilot training campaign in a simulator prior to the flight test is carried out and the maneuvers flown by the pilot are analyzed. Finally, the conduction of the flight tests is described and the flown maneuvers and results are evaluated regarding the maneuver quality and the observability of the helicopter dynamics.
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The performance of control algorithms for eVTOL, like incremental nonlinear dynamic inversion (INDI), relies on precise models of the system. Instead of using pre-identified models, we aim to identify the model online. In this pap...
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The performance of control algorithms for eVTOL, like incremental nonlinear dynamic inversion (INDI), relies on precise models of the system. Instead of using pre-identified models, we aim to identify the model online. In this paper we compare sequential least squares in frequency-domain to extended Kalman filtering for identification of the B-matrix, used in INDI. We demonstrated the online identification of the B-matrix in mini-quadcopter flight tests. Both methods can identify constant and time-varying parameters, but only with sufficient excitation. Otherwise, the parameters cannot be estimated precisely and drift away. In this study, we lay the basis for integrating online parameter estimation into INDI.
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Designing the experiments is one of the most important aspects of any system identification and parameter estimation project. The importance of experiment design is even more pronounced in flight vehicle system identification, as ...
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Designing the experiments is one of the most important aspects of any system identification and parameter estimation project. The importance of experiment design is even more pronounced in flight vehicle system identification, as performing the experiments, i.e. flight tests is costly. In this work, we present a novel approach for designing optimal inputs for parameter estimation in frequency domain using the direct method for optimal control. We investigate the developed method by means of the optimal control theory and provide numerical results. The approach presented here allows for maximizing the information content in the acquired data during the experiment for a specific frequency band.
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In this paper, the Blade Element Momentum Theory (BEMT) hast been applied to setup a nonlinear model structure for a coaxial helicopter with a maximum take-off weight (MTOW) of 600kg. The model includes unknown aerodynamic paramet...
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In this paper, the Blade Element Momentum Theory (BEMT) hast been applied to setup a nonlinear model structure for a coaxial helicopter with a maximum take-off weight (MTOW) of 600kg. The model includes unknown aerodynamic parameters, which are estimated using flight test data. An extensive flight test campaign, with a fully instrumented CoAx 600 helicopter has been carried out to generate the required flight test data for parameter estimation. In this study, we use the maneuvers performed in the vicinity of the hover flight condition for system identification. The nonlinear model can be trimmed and linearized for the analysis of the system dynamics and control design. This has been done for one trim point in the study and the corresponding pole plan has been provided.
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