Flight Path Reconstruction Research Articles

Insectivorous bats alter their flight and feeding behaviour at ground‐mounted solar farms

Abstract Efforts to mitigate the climate crisis result in a green‐green dilemma: the development of renewable energy technology is required worldwide to reduce greenhouse gas emissions but can have negative impacts on biodiversity. Impacts are being documented for wind farms, but effects of solar farms (photovoltaic power stations) on habitat use of vertebrates remain extremely poorly known. Using insectivorous bats as a biological model for high trophic levels, we tested whether the presence of ground‐mounted solar farms affected flight and feeding behaviour. We assessed behaviour using three‐dimensional flight path reconstruction systems from echolocation calls, via standardised paired sampling of 16 control and 16 solar farm (treatment) sites. We quantified bat flight and feeding behaviour as flight speed, sinuosity of flight trajectories, and the probability of emission of feeding buzzes (acoustic signatures of prey capture attempts), and demonstrated that feeding was characterised by slow, sinuous flight with feeding buzzes. We recorded 15,273 three‐dimensional bat positions, resulting in 1317 flight trajectories. We found strong behavioural responses to ground‐mounted solar farms in two of three bat guilds and five of seven taxa. Specifically, bats shifted their flight towards faster (+10 to +44%) and straighter trajectories (+33%) with lower probability of prey capture attempts (−18 to −39%) at solar farms. Since these changes in flight features are explicit indicators of a decrease in bat feeding behaviour, the implementation of ground‐mounted solar farms is likely to result in reduced feeding habitat quality for bats. Synthesis and applications: The negative effects of solar farms on bat flight and feeding behaviour should be considered when solar energy projects are planned. Research is needed to understand the mechanisms underlying the effects; for example, shading underneath solar panels may reduce plant biomass and therefore insect prey availability. Until exact mechanisms are identified, efforts should be made, first to avoid building solar farms on sites with great feeding potential for bats, and second to offset residual effects by improving the surrounding land and/or solar farms to provide better foraging opportunities. In this way, populations of bats can be supported alongside the generation of renewable energy.

Advancements in the Theory and Practice of Flight Vehicle System Identification

System identification methods have played an essential role in the research and industry projects at the Institute of Flight System Dynamics of the Technical University of Munich. Besides the application of the established system identification approaches to multiple aircraft, novel methods have been developed at the institute to deal with the challenges associated with fixed- and rotary-wing aircraft system identification in the time and frequency domains. This paper provides an overview of these new developments, as well as practical application examples from the past and ongoing projects at the institute. After a brief introduction to the work at the institute, the paper describes the new advancements in the fields of time domain system identification and optimal input design by introducing optimal control methods. It continues with an alternative problem formulation for applying frequency domain system identification and parameter estimation methods to a novel flight control design and tuning approach. Additional topics from the past and ongoing research at the institute such as novel methods and practical findings in rotorcraft system identification and flight path reconstruction for different applications will be discussed and referenced.

Retrospective and Recent Examples of Aircraft and Rotorcraft System Identification at DLR

Aircraft system identification has a five-decades-long tradition at German Aerospace Center (DLR). Over the last two decades, the research covered various topics related to system identification of fixed- and rotary-wing aircraft, nonconventional applications and atmospheric effects, the development of new flight-test procedures for system identification purposes, and specific aircraft model enhancements and corresponding parameter estimation. Comprehensive tools were developed that support this research and can be applied to a variety of different problems and types of vehicles. The paper starts with a short description of the different system identification methods used at DLR and the corresponding tools. The discussion of flight-test procedures and maneuver design as well as sensor fusion and flight-path reconstruction provides information on how to optimize the flight tests for system identification and to arrive at a consistent flight-test database. The examples for fixed-wing aircraft provide information on identification including abnormal conditions such as icing and interaction with atmospheric disturbances as well as modeling of structural mechanics and loads. The identification of high-order rotorcraft models that account for rotor and engine dynamics and even structural modes is discussed, and the identification of rotor mast moments as well as the identification of non-physics-based models and their integration into physics-based models are also covered. A final section shows that system identification can also be used to derive models for gyroplanes and parachutes as well as to derive control equivalent turbulence input models and to estimate complex wind field geometries. Thus, a broad overview of possible applications of system identification is given.

Recent Applications of System Identification Techniques at IPEV

This paper presents an overview of the system identification techniques developed and applied at the Flight Test and Research Institute during the last decade. System identification techniques have been used extensively to obtain aerodynamic models for a flight-test simulator, which was developed in house and specifically tailored for flight-test instruction and preparation for actual test flights. The methods applied were mostly the output error for data compatibility check and equation error in the time domain for model structure selection and parameter estimation. The most relevant applications are summarized in this paper, including identification of a high angle of attack model with compressibility effects for a jet trainer; estimation of drag polars at high subsonic regime for a jet fighter; identification of aerodynamic model in real-time for a propeller-driven fighter; application of flight-path reconstruction techniques to spin tests, in order to correct errors in the air data sensors; and identification of power effects on the longitudinal stability of a propeller-driven trainer. The examples show that system identification has become crucial to 1) obtain accurate aerodynamic models for training in the flight-test simulator and 2) develop more efficient flight-test techniques.

Drone GPS data analysis for flight path reconstruction: A study on DJI, Parrot & Yuneec make drones

In past few years, the technological growth in field of drones has not only offered multiple opportunities, but has also thrown numerous threats and challenges. Drone is a potential weapon in itself and can be used to carry out a targeted attack, carry out reconnaissance, smuggling of arms/drugs, etc. Due to cheap and easy availability of commercial drones in the market, the security threat posed by the drones has increased manifold. Additionally, the possibility of customization and option of assembling a drone by an individual makes it an even bigger threat. Unfortunately it is difficult to completely restrict/stop use of such aerial platforms by malicious actors. Therefore there is a need to develop techniques and procedures in the field of drone forensics to be able to extract and accurately analyse the positioning data, provide valuable tactical information about flight take-off location, flight path taken and reconstruct the flight operation, if required. The study in this paper aims at extracting and analysing GPS data from three different drone models belonging to three different families, followed by representing the positioning data as flight path. This paper also introduces a newly developed utility tool named “FlyLog Converter Tool” which processes and converts the.txt/.json flight log of Parrot make drones into easily understandable.csv format.

Identification of kite aerodynamic characteristics using the estimation before modeling technique

AbstractThe aerodynamic characteristics of a leading edge inflatable (LEI) kite and a rigid‐framed delta (RFD) kite were investigated. Flight data were recorded by using an experimental setup that includes an inertial measurement unit, a GPS, a magnetometer, and a multi‐hole Pitot tube onboard the kites, load cells at every tether, and a wind station that measures the velocity and heading angle of the wind. These data were used to feed a flight path reconstruction algorithm that estimated the full state vector of the kite. Since the latter includes the aerodynamic force and moment about the center of mass of the kite, quantitative information about the aerodynamic characteristics of the kites was obtained. Due to limitation of the experimental setup, the LEI kite flew most of the time in post‐stall conditions, which resulted in a poor maneuverability and data acquisition. This assumption was corroborated by a particular maneuver where the lift coefficient decreased from 1 to 0.4, while its angle of attack increased from 35° to 50°. On the contrary, abundant flight data were obtained for the RFD kite during more than 10 figure‐eight maneuvers. Although the angle of attack was high, between 20° and 40°, the kite did not reach its maximum lift coefficient. High tether tensions and a good maneuverability were achieved. Statistical analysis of the behavior of the lift, drag, and pitch moment coefficients as a function of the angle of attack and the sideslip angle allowed to identify some basic aerodynamic parameters of the kite.

Flight dynamics modeling of a flexible wing unmanned aerial vehicle

This paper shows the results of traditional aerodynamic analysis and the flexible flight dynamics modeling including the effects of structural motion for a flexible wing unmanned aerial vehicle. The influence of some design parameters such as wing flexibility, horizontal/vertical tail aerodynamics is investigated for aeroelasticity and flight dynamics of flexible aircraft. The research platform is an Unmanned Aerial Vehicle (UAV), made of composite material. Its wing span is 4 m and reaches a high aspect ratio, whose value is 18.9. For a traditional analysis, the Vortex Lattice Method (VLM) was used to obtain conventional aerodynamic and control derivatives. The flexible flight dynamics model is based on the work of Waszack and Schmidt. In this approach, it is used the mean-axes reference system and it is assumed that structural deformations is small and described by a set of eigenmodes. The dynamics model incorporates the first normal modes obtained by Ground Vibration Test (GVT) campaigns. A focus of the paper lies on providing a useful model for dynamics system identification and in-flight aeroelastic testing. A developed platform for in-flight system identification and the acquisition system is described. A flight path reconstruction process from a flight test campaign results is shown.

Wind Profile Estimation during Flight Path Reconstruction

Accuracy of flow angles measurements becomes crucial as the aircraft approaches higher angle of attack. Flight path reconstruction (FPR) is an excellent tool for air data calibration. An important element of air data calibration is the estimation of wind velocities. The objective of this paper is to evaluate different approaches of wind estimation within the framework of FPR. Flight test data of a high performance aircraft is subjected to FPR and the estimated wind velocities and flow angle trajectories are presented and discussed to demonstrate the impact of wind estimation on aircraft flow angles. Results clearly show that accuracy of reconstructed flow angles improves when time varying wind models are used. The proposed analytical wind model is found to be as effective as augmented parameters in Extended Kalman filter and computationally less intensive.

Inflight Aerodynamic Parameter Estimation for Fixed Wing Unmanned Aerial Vehicle

This paper presents the frame work for aerodynamic parameter estimation for small fixed wing unmanned aerial vehicle (UAV). The recent development in autopilot hardware for small UAV enables the in-flight data collection of flight characteristics. A methodology is outlined to collect, process and arrive at a conclusion from the in-flight data using commercial flight controller of under 2kg (micro) fixed wing aircraft, ‘VAF01’ for which a Fault Detection and Identification (FDI) system is under development. As a part of the FDI, the linear longitudinal (3 DOF) aerodynamic model is developed and in-flight experimental data is used to estimate the longitudinal aerodynamic parameters. The Flight Path Reconstruction is completed with the acquired parameters from in-flight experiments and results are discussed for further utilization of them.

Bat overpasses as an alternative solution to restore habitat connectivity in the context of road requalification

Roads have a multitude of negative effects on wildlife, including their prominent role in habitat fragmentation. Habitat fragmentation particularly affects bats during their nightly movements between roosts and foraging areas. Bat overpasses are among the proposed improvements intended to reduce the fragmentation impact of roads, but they have rarely been tested. In this study, we performed a Before-After Control-Impact analysis (BACI) to assess the efficiency of one bat overpass on the number of bat crossings, by using an acoustic flight path reconstruction (AFPR) approach. We obtained 888 bat crossings of five taxa. Our results showed that the number of bat crossings increased significantly after the installation of the bat overpass. Finally, we demonstrated that an overpass correctly placed with respect to a narrow commuting route (a twenty-meter-wide hedgerow) could efficiently restore bat habitat connectivity.

Web data for computing real-world noise from civil aviation

A large amount of data on civil air traffic is now available on the web, thanks to the recent development of flight tracker websites. This paper presents a novel methodology to exploit these data for computing real-world noise around airports. The proposed approach consists of data collection and pre-processing, flight path reconstruction, aircraft noise computation using a best-practice model (ECAC Doc.29), and rendering of ground track and noise contour maps in airport areas. Applications are shown for nine European airports, where the daily air traffic reconstructed from 10,752 collected flights compares well with official records from EUROCONTROL. Among these airports, London Heathrow, Amsterdam Schiphol and Vienna-Schwechat have been considered for the validation of the present methodology, and a good agreement is found between predicted ground noise levels and available historical data, with the largest deviations being detected in the portions of the airport areas most affected by departure events. The present work constitutes the first step to harnessing the potential of web data in aviation, unlocking unprecedented possibilities for assessing the environmental impact of civil aviation and providing policy-makers with a powerful tool for developing guidelines and regulations aimed at mitigating the detrimental effects of air traffic in densely inhabited regions.

Limitations of Flight Path Reconstruction techniques

The Flight Path Reconstruction (FPR) techniques are performed to verify the data compatibility check and post-flight. This is often achieved by calibrating the onboard sensors such as inertial and airdata sensors. In this paper, the limitations of FPR techniques in terms of Maximum Likelihood Estimation (MLE) and Extended Kalman Filter (EKF) and Unscented Kalman Filter (UKF) have been reported. To demonstrate the FPR and sensor calibration, kinematic trajectory simulations with wind box type maneuvers have been performed. It is also shown as how a kinematic simulation is valid for the studies carried out in this work.

Bat overpasses: An insufficient solution to restore habitat connectivity across roads

Abstract Roads have many negative effects on wildlife, including their role in habitat fragmentation. Habitat fragmentation affects bats during their daily movements between roosts and foraging areas. As bats are protected in Europe, developers must implement specific mitigation measures that are hierarchically structured to achieve a null net impact. However, very few specific mitigation measures have been undertaken specifically for bats. Bat overpasses (e.g. gantries) are among proposed improvements intended to reduce the impact of roads, but they have rarely been tested. The effectiveness of overpasses in facilitating safe road crossing of bats is critical for justifying the implementation of this mitigation measure. We therefore assessed whether bat overpasses are effectively used by bats. We studied three bat overpasses with different designs in France. We developed an innovative method to characterize bat crossings using acoustic flight path reconstruction (AFPR). We used six pairs of stereo acoustic recorders in different habitat types that were located on both sides of the road, and operated simultaneously throughout the night. Recording data contained 57,941 bat passes and 284 bat crossings from six species of bats at the three study sites. Our results suggest that crossings are more numerous if an overpass is located where bat commuting routes have been identified by environmental impact assessment. However, we found that the proportion of bat crossings along the commuting route was the same with or without an overpass; thus highlighting that bat overpasses do not fully restore habitat connectivity. Synthesis and applications. Our study demonstrates that acoustic flight path reconstruction (AFPR) is a useful approach to obtain information on bat flight behaviour. We also emphasize the importance of field testing the effectiveness of mitigation measures, such as those intended to offset the impact of roads on biodiversity, and highlight that such measures should not be implemented based on their theoretical effectiveness alone.

Flight-Path Reconstruction and Flight Test of Four-Line Power Kites

A flight-path reconstruction algorithm for tethered aircraft, which is based on an extended Kalman filter, is presented. The algorithm is fed by the measurements of a set of onboard and ground-based instruments and provides the optimal estimation of the system state-space trajectory, which includes typical aircraft variables such as position and velocity, as well as an estimation of the aerodynamic force and torque. Therefore, it can be applied to closed-loop control in airborne wind energy systems and it is a first step toward aerodynamic parameter identification of tethered aircraft using flight-test data. The performance of the algorithm is investigated by feeding it with real flight data obtained from a low-cost and highly portable experimental setup with a four-line kite. Several flight tests, which include pullup and lateral-directional steering maneuvers with two kites of different areas, are conducted. The coherence of the estimations provided by the filter, such as the kite state-space trajectory and aerodynamic forces and torques, is analyzed. For some standard variables, such as kite Euler angles and position, the results are also compared with a second independent onboard estimator.

Terrestrial and Marine Foraging Strategies of an Opportunistic Seabird Species Breeding in the Wadden Sea.

Lesser black-backed gulls Larus fuscus are considered to be mainly pelagic. We assessed the importance of different landscape elements (open sea, tidal flats and inland) by comparing marine and terrestrial foraging behaviours in lesser black-backed gulls breeding along the coast of the southern North Sea. We attached GPS data loggers to eight incubating birds and collected information on diet and habitat use. The loggers recorded data for 10–19 days to allow flight-path reconstruction. Lesser black-backed gulls foraged in both offshore and inland areas, but rarely on tidal flats. Targets and directions were similar among all eight individuals. Foraging trips (n = 108) lasted 0.5–26.4 h (mean 8.7 h), and ranges varied from 3.0–79.9 km (mean 30.9 km). The total distance travelled per foraging trip ranged from 7.5–333.6 km (mean 97.9 km). Trips out to sea were significantly more variable in all parameters than inland trips. Presence in inland areas was closely associated with daylight, whereas trips to sea occurred at day and night, but mostly at night. The most common items in pellets were grass (48%), insects (38%), fish (28%), litter (26%) and earthworms (20%). There was a significant relationship between the carbon and nitrogen isotope signals in blood and the proportional time each individual spent foraging at sea/land. On land, gulls preferentially foraged on bare ground, with significantly higher use of potato fields and significantly less use of grassland. The flight patterns of lesser black-backed gulls at sea overlapped with fishing-vessel distribution, including small beam trawlers fishing for shrimps in coastal waters close to the colony and large beam-trawlers fishing for flatfish at greater distances. Our data show that individuals made intensive use of the anthropogenic landscape and seascape, indicating that lesser black-backed gulls are not a predominantly marine species during the incubation period.

Longitudinal parameter estimation from real flight data of unmanned cropped delta flat plate configuration

Purpose – The purpose of this paper is to describe the longitudinal aerodynamic characterization of an unmanned cropped delta configuration from real flight data. In order to perform this task an unmanned configuration with cropped delta planform and rectangular cross-section has been designed, fabricated, instrumented and flight tested at flight laboratory in Indian Institute of Technology Kanpur (IITK), India. Design/methodology/approach – As a part of flight test program a real flight database, through various maneuvers, have been generated for the designed unmanned configuration. A dedicated flight data acquisition system, capable of onboard logging and telemetry to ground station, has been used to record the flight data during these flight test experiments. In order to identify the systematic errors in the measurements, the generated flight data has been processed through data compatibility check. Findings – It is observed from the flight path reconstruction that the obtained biases are negligible and the scale factors are almost close to unity. The linear aerodynamic model along with maximum likelihood and least-square methods have been used to perform the parameter estimation from the obtained compatible flight data. The lower values of Cramer-Rao bounds obtained for various parameters has shown significant confidence in the estimated parameters using maximum likelihood method. In order to validate the aerodynamic model used and to increase the confidence in the estimated parameters a proof-of-match exercise has been carried out. Originality/value – The entire work presented is original and all the experiments have been carried out in Flight laboratory of IITK.

Sensor fusion and flight path reconstruction of the ACT/FHS rotorcraft

DLR’s active control technology/flying helicopter simulator (ACT/FHS) research rotorcraft supports research in a variety of fields. This paper presents the flight path reconstruction (FPR) of the ACT/FHS for post-flight data processing and its online sensor fusion during flight. Both are fundamental for system identification and flight control research. First, the ACT/FHS rotorcraft, its system architecture and the used sensor instrumentation are described. Then, the implemented unscented and extended Kalman filters are briefly explained and the applied kinematic and measurement models of the FPR are introduced. The wind estimation performance of the FPR is evaluated using simulation and flight test data accordingly. Subsequently, the online sensor fusion is motivated and its behaviour following a simulated differential GPS failure is analysed and explained.

Trawling bats exploit an echo-acoustic ground effect

A water surface acts not only as an optic mirror but also as an acoustic mirror. Echolocation calls emitted by bats at low heights above water are reflected away from the bat, and hence the background clutter is reduced. Moreover, targets on the surface create an enhanced echo. Here, we formally quantified the effect of the surface and target height on both target detection and -discrimination in a combined laboratory and field approach with Myotis daubentonii. In a two-alternative, forced-choice paradigm, the bats had to detect a mealworm and discriminate it from an inedible dummy (20 mm PVC disc). Psychophysical performance was measured as a function of height above either smooth surfaces (water or PVC) or above a clutter surface (artificial grass). At low heights above the clutter surface (10, 20, or 35 cm), the bats' detection performance was worse than above a smooth surface. At a height of 50 cm, the surface structure had no influence on target detection. Above the clutter surface, also target discrimination was significantly impaired with decreasing target height. A detailed analysis of the bats' echolocation calls during target approach shows that above the clutter surface, the bats produce calls with significantly higher peak frequency. Flight-path reconstruction revealed that the bats attacked an target from below over water but from above over a clutter surface. These results are consistent with the hypothesis that trawling bats exploit an echo-acoustic ground effect, in terms of a spatio-temporal integration of direct reflections with indirect reflections from the water surface, to optimize prey detection and -discrimination not only for prey on the water but also for some range above.

Multi sensor data fusion based approach for the calibration of airdata systems

AbstractAccurate and reliable airdata systems are critical for aircraft flight control system. In this paper, both extended Kalman filter (EKF) and unscented Kalman filter (UKF) based various multi sensor data fusion methods are applied to dynamic manoeuvres with rapid variations in the aircraft motion to calibrate the angle-of-attack (AOA) and angle-of-sideslip (AOSS) and are compared. The main goal of the investigations reported is to obtain online accurate flow angles from the measured vane deflection and differential pressures from probes sensitive to flow angles even in the adverse effect of wind or turbulence. The proposed algorithms are applied to both simulated as well as flight test data. Investigations are initially made using simulated flight data that include external winds and turbulence effects. When performance of the sensor fusion methods based on both EKF and UKF are compared, UKF is found to be better. The same procedures are then applied to flight test data of a high performance fighter aircraft. The results are verified with results obtained using proven an offline method, namely, output error method (OEM) for flight-path reconstruction (FPR) using ESTIMA software package. The consistently good results obtained using sensor data fusion approaches proposed in this paper establish that these approaches are of great value for online implementations.

Flight path reconstruction – A comparison of nonlinear Kalman filter and smoother algorithms

This paper is concerned with the choice of a state-estimation algorithm to perform the flight path reconstruction (FPR) procedure. Both simulated data and experimental data collected from a sailplane aircraft are used to illustrate the methods investigated. In both cases the unscented Kalman filter (UKF) is employed to determine the biases associated to each accelerometer and gyro in the inertial measurement unit (IMU), together with high sampling-rate trajectory reconstruction from low frequency sampled GPS data. A comparison between UKF and the well-known extended Kalman filter (EKF) shows that the former outperforms the latter in the presence of high noise level and large initialization error, sensitivity to the tuning of covariance matrices, and joint estimation of IMU bias terms. Furthermore, substantial accuracy improvement due to the adoption of the unscented Kalman smoother (UKS) for high sampling-rate FPR is quantified, whereas the same cannot be claimed on the use of an iterated filtering approach.