This study examined the effectiveness of helicopter patrols in reducing violent crime rates in three Swedish cities: Malmö, Lund, and Helsingborg. Utilizing Swedish official crime records from 2016 to 2019 and helicopter data from an intervention conducted between August 9th and October 9th, 2019, the study employed quantitative methods, including multiple linear regressions and two-way fixed effects models, to analyse the impact of helicopter presence and dosage on various types of violent crimes. Findings indicated that neither helicopter presence nor dosage demonstrated a significant effect on violent crime variables across the three cities. Moreover, when included as control variables in the fixed effects models, Malmöfestivalen and weather variables did not alter the relationship between the helicopter intervention and any of the violent crime variables. The study concludes that helicopter patrols lack a deterrent effect on violent crimes, suggesting the need for reallocating resources to more effective policing strategies. Suggestions for future research include exploring other crime types, conducting cost-benefit analyses, and investigating the long-term implications of helicopter patrols.

This thesis studies the counterpiracy in the Gulf of Aden. Pirates has made the international community deploy military forces to police the Gulf of Aden. However most of the systems usedare not designed for counterpiracy. Many are remnants from the cold war. Also downsizing of military forces in the West has resulted in the need to prioritize resources. The purpose of this thesis is to analyze five systems fighting pirates in the Gulf of Aden using Andersson et al. (2015)´s theory of military utility. The five systems are: light utility helicopter, medium utility helicopter, reconnaissance aircraft, combat boat and drone on tasks of detect, disrupt and deter. With the analysis the thesis discuss how the Swedish Armed Forces can use available recourses more efficiently as possible to aid in producing a greater operative effect on the national and international arena. The conclusions show that all systems have the potential to contribute to counterpiracy. Reconnaissance aircraft and drones are suitable to detect pirates. Light utility helicopters are able to detect and disrupt and partially deter. The combat boats are suitable to disrupt and deter. The medium utility helicopters are suitable for all three tasks. The thesis concludes with discussing the importance of the subsystems carried and its effects on a system´s military utility. / Den här rapporten undersöker piratbekämpningen i Adenviken. Piraterna har gjort att världssamfundet skickat militära styrkor för att patrullera Adenviken. De flesta system som används för piratbekämpningen är däremot inte designade för det ändamålet. Många är kvarlevor från det kalla kriget. Samtidigt som en minskning av de militära styrkorna har lett till behovet att bättre prioritera tillgängliga resurser. Syftet med den här rapporten är att analysera fem system som bekämpar pirater i Adenviken genom att använda Andersson et al. (2015)´s teori om militär nytta. De fem systemen är: Lätt helikopter, medeltung helikopter, spaningsflygplan, stridsbåt och drönare. Uppgifterna de ställs mot är: att upptäcka, avbryta samt avskräcka. För att med den analysen diskutera hur Försvarsmakten kan använda tillgängliga resurser effektivare och skapa operativ effekt, nationellt såväl som internationellt. Slutsatserna visar att alla system har potential att bidra till piratbekämpningen. Spaningsflygplan och drönare är lämpliga för att upptäcka pirater. Lätt helikopter är lämplig för att upptäcka och avbryta samt delvis avskräcka. Stridsbåten är lämplig för att avbryta och avskräcka. Medeltung helikopter är lämplig för alla tre uppgifter. Rapporten har diskuterat den betydelse som subsystemen har för systemens militära nytta.

L’une des principales sources d’inconfort dans un hélicoptère sont les vibrations transmises par le rotor à la structure de l’appareil. En vol d’avancement, des efforts aérodynamiques cycliques sont subis par l’ensemble des pales en tête rotor et génèrent de très fortes vibrations basse fréquence (aux alentours des 17Hz) transmises aux passagers via la boîte de transmission principale puis le fuselage lui-même. Afin de garantir le confort des membres d’équipage et des passagers, de nombreux systèmes antivibratoires ont été conçus. Ces systèmes sont généralement passifs car la majorité de l’énergie vibratoire transmise à la structure se situe à une fréquence unique ωc correspondant à bΩ avec b le nombre de pales et Ω la fréquence de rotation du rotor. Cependant, les appareils modernes évoluent et le régime rotor jusqu’alors fixe durant toutes les phases de vol varie à présent pour des préoccupations de performances et de consommation (variation de l’ordre de +/-10% autour de bΩ). Cette nouvelle contrainte dans la conception des hélicoptères rend pertinente la technologie des systèmes antivibratoires actifs, pouvant s’adapter à la sollicitation en termes d’amplitude et fréquence. Lors de ces travaux de thèse, la suspension passive SARIB de Airbus Helicopters basée sur le principe du DAVI (Dynamic Antiresonant Vibration Isolator) est modifiée afin d’être rendue active par ajout d’une partie actuation/commande. La théorie des lois et algorithmes de contrôle utilisés dans ces travaux, est présentée en détail afin de poser solidement les bases du contrôle actif du prototype de suspension conceptualisé ici à savoir le contrôle FXLMS (adaptatif) et le contrôle optimal LQG. Afin de simuler le fonctionnement du système, un modèle tridimensionnel de la suspension active est construit, couplé à la structure souple de l’hélicoptère (NH90). Sur ce modèle sont alors appliquées les différentes lois de commande introduites auparavant et leurs performances comparées dans différents cas de chargement en tête rotor et surtout pour différentes fréquences de sollicitation. De même, pour chaque algorithme, différentes localisations des capteurs d’erreur sont étudiées afin de converger vers une configuration optimale. Les simulations démontrent que l’algorithme FXLMS feedforward est très bien adapté au contrôle des perturbations harmoniques et permet de réduire très significativement le niveau vibratoire du plancher cabine, sans réinjection parasite dans le reste de la structure. Une comparaison de l’efficacité du SARIB actif avec les systèmes d’absorbeurs en cabine est ensuite effectuée pour démontrer la pertinence d’utiliser le principe du DAVI comme base d’un système actif. Les travaux de cette thèse traitent également des essais réalisés en laboratoire sur le prototype échelle 1 de la suspension SARIB active avec contrôle FXLMS. / One of the main causes of discomfort in helicopters are the vibrations transmitted from the rotor to the structure. In forward flight, the blades are submitted to cyclic aerodynamic loads which generate low frequency (around 17Hz) but high energy mechanical vibrations. These vibrations are transmitted from the rotor to the main gearbox, then to the structure and finally to the crew and passengers. In order to maintain acceptable comfort for crew members and passengers, a lot of antivibration devices have been developed since the last 30 years. These systems are generally passive because most of the mechanical energy transmitted to the structure is at only one frequency ωc which is equal to the product bΩ with b the number of blades and Ω the rotor rotational speed. However, modern helicopters evolve and the rotor rpm, which has always been considered as fixed during flight is now a function of time, depending on the flight phases in order to increase performances and reduce energy consumption (variation bandwidth of Ω +/- 10%). This new constraint on the design of helicopters makes the active antivibration technology completely relevant with its capacity to adapt in terms of amplitude and frequency to the perturbation. During this thesis, the passive suspension called SARIB from Airbus Helicopters, based on the DAVI principle (Dynamic Antiresonant Vibration Isolator) is modified in order to implement active components and command (actuation). The theory of the control algorithms used in this thesis is presented in detail in order to define the theoretical tools of the active DAVI control which are : FXLMS control (adaptive control) and LQG (optimal control). To simulate the complete system, a 3D multibody model of the active suspension has been set up, coupled to a the flexible structure of a NH90 (Airbus Helicopters). On this model are applied the different control algorithms presented before and their performances are compared for different loads with variable frequency on the rotor hub. In the same way, different locations for the error sensors in the structure are studied to find the optimal control configuration. The simulations show that the FXLMS algorithm is well suited for the control of harmonic perturbations and reduce significantly the dynamic acceleration level on the cabin floor, without parasite reinjection on other parts of the structure. A comparison of the active SARIB with classical cabin vibration absorbers is also made in terms of efficiency in order to show the advantages of using the DAVI system as a base for an active antivibration device. Finally, this thesis also presents the experiments realized in the dynamics laboratory of Airbus Helicopters on a 1:1 scale prototype of the active SARIB suspension with FXLMS control. The results demonstrate the efficiency of the active suspension architecture and control algorithms.

The present work focuses on the two areas of investigation: system identification of helicopter and design of controller for the helicopter. Helicopter system identification, the first subject of investigation in this thesis, can be described as the extraction of system characteristics/dynamics from measured flight test data. Wind tunnel experimental data suffers from scale effects and model deficiencies. The increasing need for accurate models for the design of high bandwidth control system for helicopters has initiated a renewed interest in and a more active use of system identification. Besides, system identification is likely to become mandatory in the future for model validation of ground based helicopter simulators. Such simulators require accurate models in order to be accepted by pilots and regulatory authorities like Federal Aviation Regulation for realistic complementary helicopter mission training. Two approaches are widely used for system identification, namely, black box and gray box approach. In the black-box approach, the relationship between input-output data is approximated using nonparametric methods such as neural networks and in such a case, internal details of the system and model structure may not be known. In the gray box approach, parameters are estimated after defining the model structure. In this thesis, both black box and gray box approaches are investigated. In the black box approach, in this thesis, a comparative study and analysis of different Recurrent Neural Networks(RNN) for the identification of helicopter dynamics using flight data is investigated. Three different RNN architectures namely, Nonlinear Auto Regressive eXogenous input(NARX) model, neural network with internal memory known as Memory Neuron Networks(MNN)and Recurrent MultiLayer perceptron (RMLP) networks are used to identify dynamics of the helicopter at various flight conditions. Based on the results, the practical utility, advantages and limitations of the three models are critically appraised and it is found that the NARX model is most suitable for the identification of helicopter dynamics. In the gray box approach, helicopter model parameters are estimated after defining the model structure. The identification process becomes more difficult as the number of degrees-of-freedom and model parameters increase. To avoid the drawbacks of conventional methods, neural network based techniques, called the delta method is investigated in this thesis. This method does not require initial estimates of the parameters and the parameters can be directly extracted from the flight data. The Radial Basis Function Network(RBFN)is used for the purpose of estimation of parameters. It is shown that RBFN is able to satisfactorily estimate stability and control derivatives using the delta method. The second area of investigation addressed in this thesis is the control of helicopter in flight. Helicopter requires use of a control system to achieve satisfactory flight. Designing a classical controller involves developing a nonlinear model of the helicopter and extracting linearized state space matrices from the nonlinear model at various flight conditions. After examining the stability characteristics of the helicopter, the desired response is obtained using a feedback control system. The scheduling of controller gains over the entire envelope is used to obtain the desired response. In the present work, a helicopter having a soft inplane four bladed hingeless main rotor and a four-bladed tail rotor with conventional mechanical controls is considered. For this helicopter, a mathematical model and also a model based on neural network (using flight data) has been developed. As a precursor, a feed back controller, the Stability Augmentation System(SAS), is designed using linear quadratic regulator control with full state feedback and LQR with out put feedback approaches. SAS is designed to meet the handling qualities specification known as Aeronautical Design Standard ADS-33E-PRF. The control gains have been tuned with respect to forward speed and gain scheduling has been arrived at. The SAS in the longitudinal axis meets the requirement of the Level1 handling quality specifications in hover and low speed as well as for forward speed flight conditions. The SAS in the lateral axis meets the requirement of the Level2 handling quality specifications in both hover and low speed as well as for forward speed flight conditions. Such conventional design of control has served useful purposes, however, it requires considerable flight testing which is time consuming, to demonstrate and tune these control law gains. In modern helicopters, the stringent requirements and non-linear maneuvers make the controller design further complicated. Hence, new design tools have to be explored to control such helicopters. Among the many approaches in adaptive control, neural networks present a potential alternative for modeling and control of nonlinear dynamical systems due to their approximating capabilities and inherent adaptive features. Furthermore, from a practical perspective, the massive parallelism and fast adaptability of neural network implementations provide more incentive for further investigation in problems involving dynamical systems with unknown non-linearity. Therefore, adaptive control approach based on neural networks is proposed in this thesis. A neural network based Feedback Error Neural adaptive Controller(FENC) is designed for a helicopter. The proposed controller scheme is based on feedback error learning strategy in which the outer loop neural controller enhances the inner loop conventional controller by compensating for unknown non-linearity and parameter un-certainties. Nonlinear Auto Regressive eXogenous input(NARX)neural network architecture is used to approximate the control law and the controller network parameters are adapted using updated rules Lyapunov synthesis. An offline (finite time interval)and on-line adaptation strategy is used to approximate system uncertainties. The results are validated using simulation studies on helicopter undergoing an agile maneuver. The study shows that the neuro-controller meets the requirements of ADS-33 handling quality specifications. Even though the tracking error is less in FENC scheme, the control effort required to follow the command is very high. To overcome these problems, a Direct Adaptive Neural Control(DANC)scheme to track the rate command signal is presented. The neural controller is designed to track rate command signal generated using the reference model. For the simulation study, a linearized helicopter model at different straight and level flight conditions is considered. A neural network with a linear filter architecture trained using back propagation through time is used to approximate the control law. The controller network parameters are adapted using updated rules Lyapunov synthesis. The off-line trained (for finite time interval)network provides the necessary stability and tracking performance. The on-line learning is used to adapt the network under varying flight conditions. The on-line learning ability is demonstrated through parameter uncertainties. The performance of the proposed direct adaptive neural controller is compared with feedback error learning neural controller. The performance of the controller has been validated at various flight conditions. The theoretical results are validated using simulation studies based on a nonlinear six degree-of-freedom helicopter undergoing an agile maneuver. Realistic gust and sensor noise are added to the system to study the disturbance rejection properties of the neural controllers. To investigate the on-line learning ability of the proposed neural controller, different fault scenarios representing large model error and control surface loss are considered. The performances of the proposed DANC scheme is compared with the FENC scheme. The study shows that the neuro-controller meets the requirements of ADS-33 handling quality specifications.

Thesis's Topic: The Activity Analysis of the Czech Police Aviation Department 2008-2010. Aim of the thesis: Analysis of the operation of the Czech Police Aviation Department. Method: Research of available sources, data collection and the cooperation with the dispatching of the Czech Police Aviation Department. Results: All here listed statistics data is bases on intervention documentation of the Czech Police Aviation Department. Therefore the presented results for the Czech Republic. Keywords: Czech Police Aviation Department, helicopter, Integrated Emergency Services, activities.

The purpose of the study was to examine how Sweden’s two biggest tabloids, Aftonbladet and Expressen, frame spectacular crime and specifically how they covered the Helicopter robbery that occurred in 2009. We identified three main participants in the story, the police, the culprits and the victims. We examined how much and what kind of space the identified participants were given and how the two newspapers constructed the participants in a dramaturgic sense.   Using a quantitative content analysis method we found that the time period included 433 articles in both newspapers. From the original articles, we picked and examined 19 articles with a qualitative content analysis method and also used framing theory in order to be able to examine how the participants were portrayed in Aftonbladet and Expressen.   The culprits were given far most space in both Aftonbladet and Expressen. The study show that the police was given second most space and that the victims were hardly ever written about at all, in contrast to recent studies showing that victims of crime often are depicted as the main character in articles regarding crime. The results also show that the story as a whole carried a lot of resemblance to the classic Hollywood movie plot. The police were portrayed as incompetent, creating a conflict within the justice system community. The culprits were portrayed as the protagonist of the story with highly competent features, whilst the victims were portrayed as scared and helpless.

This dissertation investigates the application of Genetic Algorithms (GA) and Simulated Annealing (SA) based search techniques to the problem of deriving an auto-pilot that can emulate a human operator or other controller flying a Small unmanned Helicopter (SH). A Helicopter is a type of Vertical Take Off and Landing Vehicle (VTOL). The maneuvers are none aggressive, mild maneuvers, that include u-turns, ascending spirals and other none extreme flight paths. The pilot of the helicopter is a Fuzzy logic Controller (FC) pilot; it is assumed that the pilot executes the maneuvers with skill and precision. The FC pilot is given set- points (points in space) that represent a path/flight maneuver and is expected to follow them as closely as possible. Input/Output data is then collected from the FC pilot executing maneuvers in real time. The collected data include control signals from the FC pilot to the SH and the resulting output signals from the SH that include time, x, y, z coordinates and yaw (the angle of the SH relative to the x, y axis). The Genetic Algorithm/Simulated Annealing based search algorithm attempts to generate a set of mathematical formulas that best map the collected data. The search algorithm presented in this dissertation was implemented in Java and has a JSP (Java Server Pages) graphical user interface. The results obtained show that the search technique developed; termed Genetic Algorithm / Simulated Annealing controller or (GA/SA) controller allows for the derivation of accurate SH control equations. The results include performance quantification of the algorithm in the derivation phase and the testing phase. Graphs are included; they demonstrate the accuracy and path data of the GA/SA controller as compared to the FC pilot and other controllers. The final results showing the formulas found are also included. A technique was also developed during this dissertation to encode the genetic strings that represent the candidate formulas during the search. This technique allowed the combination of strings to yield new formulas that are valid. The results can be used by other investigators to expand the complexity of the formulas generated during the search. The technique has advantages such as the ability to operate in open-loop conditions and is able to fly the SH without the need for set-point data and without the need for GPS or some other location determination technology. The technique may be used as a backup controller that can take over control of a helicopter in case the main controller is unable to function due to a GPS malfunction or another situation where accurate positioning data cannot be obtained.

<p>The market for unmanned aerial vehicles (UAVs) is growing rapidly. In order to meet the demand for marine applications CybAero AB has recently started a project named Mobile Automatic Launch and Landing Station (MALLS). MALLS enables the uav to land on moving targets such as ships. This thesis studies a system that estimates the pose of a helicopter in order to land on a moving target.</p><p>The main focus has been on developing a pose estimation system using computer vision. Two different methods for estimating the pose have been studied, one using homography and one using an Extended Kalman Filter (ekf). Both methods have been tested on real flight data from a camera mounted on a RC-helicopter. The accuracy of the pose estimation system has been verified with data from a test with the camera mounted on an industrial robot. The test results show that the ekf-based system is less sensitive to noise than the homography-based system. The ekf-based system however requires initial values which the homography-based system does not. The accuracy of both systems is found to be good enough for the purpose.</p><p>A novel control system with control rules for performing an autonomous landing on a moving target has been developed. The control system has not been tested during flight.</p> / <p>Marknaden for obemannade autonoma luftburna farkoster (UAV:er) växer snabbt. För att möta behovet av marina tillämpningar har CybAero AB nyligen startat ett projekt som kallas Mobil Automatisk Start- och Landningsstation (MALLS). Syftet med malls är att möjliggöra autonom start och landning på objekt i rörelse, som till exempel ett fartyg. I det här examensarbetet studeras ett system för att bestämma position och attityd för en helikopter relativt en helikopterplatta, för att möjliggöra landning på ett ojekt i rörelse.</p><p>Fokus har främst legat på att utveckla ett positionerings- och attitydbestämningssystem. Ett datorseende positionerings- och attitydbestämningssystem har utvecklats. Två olika metoder har undersökts, ett system som bygger på homografi och ett annat som bygger på Extended Kalman Filter (EKF). Båda metoderna har testats med verklig data från en kamera monterad på en RC helikopter. Noggrannheten i positionsbestämmelsen har undersökts med hjälp av data från en industrirobot. Testresultaten visar att det EKF-baserade systemet är mindre bruskänsligt än det homografibaserade systemet. En nackdel med det ekf-baserade systemet är däremot att det kräver initialvillkor vilket det homografibaserade systemet inte gör. Noggrannheten på båda systemen finner vi tillfredsställande för syftet.</p><p>Ett enkelt styrsystem med styrlagar för att genomföra landningar på ett rörligtobjekt har utvecklats. Styrsystemet har dock inte testats under verklig flygning.</p>

<p>A control system for autonomous landing of an unmanned aerial vehicle (UAV)with high precision has been developed. The UAV is a medium sized model he-licopter. Measurements from a GPS, a camera and a compass are fused with anextended Kalman filter for state estimation of the helicopter. Four PID-controllers,one for each control signal of the helicopter, are used for the helicopter control.During the final test flights fifteen landings were performed with an average land-ing accuracy of 35 cm.    A bias in the GPS measurements makes it impossible to land the helicopter withhigh precision using only the GPS. Therefore, a vision system using a camera anda pattern provided landing platform has been developed. The vision system givesaccurate measurement of the 6-DOF pose of the helicopter relative the platform.These measurements are used to guide the helicopter to the landing target. Inorder to use the vision system in real time, fast image processing algorithms havebeen developed. The vision system can easily match up the with the camera framerate of 30 Hz.</p> / <p>Ett kontrolsystem för att autonomt landa en modellhelikopter har utvecklats.Mätdata från en GPS, en kamera samt en kompass fusioneras med ett Extend-ed Kalman Filter för tillståndsestimering av helikoptern. Fyra PID-regulatorer,en för varje kontrolsignal på helikoptern, har används för regleringen. Under densista provflygningen gjordes tre landingar av vilken den minst lyckade slutade35 cm från målet.    På grund av en drift i GPS-mätningarna är det omöjligt att landa helikopternmed hög precision med bara en GPS. Därför har ett bildbehandlingssystem som an-vänder en kamera samt ett mönster på platformen utvecklats. Bidbehandlingssys-temet mäter positionen och orienteringen av helikoptern relativt platformen. Dessamätningar används kompensera för GPS-mätningarnas drift. Snabba bildbehan-dlingsalgoritmer har utvecklats för att kunna använda bildbehandlingssystemet irealtid. Systemet är mycket snabbare än 30 bilder per sekund vilket är kameranshastighet.</p>

Helicopters in forward flight experience complex aerodynamic phenomena to various degrees. In low speed level flight, the vortex wake remains close to the rotor disk and interacts with the rotor blades to give rise to blade vortex interaction phenomena. In high speed flight, compressibility effects dominate leading to the formation of shocks. If the required thrust is high, the combination of high collective pitch and cyclic pitch variations give rise to three-dimensional dynamic stall phenomena. Maneuvers further exacerbate the unsteady airloads and affect rotor and hub design. The strength and durability of the rotor blades and hub components is dependent on accurate estimates of peak-to-peak structural loads. Accurate knowledge of control loads is important for sizing the expensive swash-plate components and assuring long fatigue life. Over the last two decades, computational tools have been developed for modeling rotorcraft aeromechanics. In spite of this progress, loads prediction in unsteady maneuvers which is critical for peak design loads continues to be a challenging task. The primary goal of this research effort is to investigate important physical phenomena that cause severe loads on the rotor in steady flight and in extreme maneuvers. The present work utilizes a hybrid Navier-Stokes/free-wake CFD methodology coupled to a finite element based multi-body dynamics analysis to systematically study steady level and maneuvering flight conditions. Computational results are presented for the UH-60A rotor for a parametric sweep of speed and thrust conditions and correlated with test data at the NFAC Wind Tunnel. Good agreement with test data has been achieved using the current methodology for trim settings and integrated hub loads, torque, and power. Two severe diving turn maneuvers for the UH-60A recorded in the NASA/Army Airloads Flight Tests Database have also been investigated. These maneuvers are characterized by high load factors and high speed flight. The helicopter experiences significant vibration during these maneuvers. Mean and peak-to-peak structural loads and extensive stall phenomena including an advancing side stall phenomena have been captured by the present analyses.