1,702 research outputs found
Design and testing methodologies for UAVs under extreme environmental conditions
Get PDFL'abstract è presente nell'allegato / the abstract is in the attachmen
A new facility for UAV testing in climate-controlled environments
No full textEnvironmental conditions have a great influence on aircraft performance. Thrust reduction with altitude and temperature increase is a well known problem in the aviation industry. For commercial multirotor (UAVs) a systematic approach on performance varying environmental conditions is still an open research field. Many of the existing applications designed for UAVs (e.g. precision agriculture, delivery of instruments or medical supplies) have not been fully exploited by the market so far. This is due to the lack of existing knowledge about flight under variable weather conditions. A bias in the existing tests has been the non-reproducibility of the same climatic conditions. In this paper a dedicated test facility for a systematic study on UAV performance in a climate-controlled laboratory is presented: use cases as well as technical challenges related to the particular environment are discussed. Preliminary tests on thrust performance at different temperatures are reported to provide insight and highlight measurement complexities involved in harsh environmental conditions. Ultimately, this work will facilitate the development of UAV design and safety accounting for weather influence to improve flight stability and controllability
A methodology for multirotor aircraft power budget analysis
Get PDFThe primary purpose of this study is to analyse the performance of multirotor unmanned aircraft system platforms for passenger transport and compare them with an ordinary helicopter solution. This study aims to define a standard procedure for power budget analysis of unconventional vehicles recently proposed in the aerospace industry, providing guidelines on rotor sizing in terms of required power and the total number of rotors. The ultimate purpose of the proposed work is to describe a methodology for power estimation with regard to emerging electric vertical takeoff and landing (EVTOL) vehicles.
In the context of urban mobility, short-range passenger transport between critical hubs in cities is taken into account and innovative aircraft and traditional helicopters are compared according to a common mission profile. The power budget equations used in the helicopter literature are revisited to consider different multirotor configurations (up to 20 rotors) and evaluate the feasibility of innovative aerospace vehicle design.
The paper includes insights into the maximum number of rotors that ensure a significative, relative power reduction compared to helicopter platforms (the power-to-cruise over power-to-hover ratio appears to be improved). Based on this preliminary analysis, the results suggest the benefit of reducing the installed rotors to avoid excessive power loss in forward flight.
The proposed study provides guidelines for further design considerations and the future development of EVTOL multirotor aircraft.
This paper fulfils the identified need for a systematic approach on performance analysis for innovative vehicles involved in commercial applications
Numerical modelling of sinusoidal brushless motor for aerospace actuator systems
Get PDFThe interest in electromechanical actuators (EMA) has been growing because of the development of next generation aircraft, based on the More Electric design. Electromechanical actuators have been gaining increased acceptance as they are becoming more and more safety-critical actuation devices: for prognostics and health management purposes of EMA, reliable and representative simulation models are needed in order to identify failures. This paper presents a multi domain model of EMA and it focuses on the numerical modelling of the Permanent Magnet Synchronous Motor (PMSM), also kwon as Sinusoidal Brushless Motor. The choice of the multi domain simulation is necessary to improve the simplifying hypotheses that are typically considered in numerical models and that are mostly used for prognostic analyses of electromechanical actuators
An Experimental Analysis on Propeller Performance in a Climate-controlled Facility
No full textDespite many commercial applications make extensive use of Unmanned Aircraft Systems (UAS), there is still lack of published data about their performance under unconventional weather conditions. In the last years, multirotors and fixed wing vehicles, commonly referred to as drones, have been studied in wind environments so that stability and controllability have been improved. However, other important weather variables have impact on UAS performance and they should be properly investigated for a deeper understanding of such vehicles. The primary objective of our study is the preliminary characterization of a propeller in a climate-controlled chamber. Mechanical and electrical data have been measured while testing the propeller at low pressure and cold temperatures. Test results point out that thrust and electric power are strongly affected by air density. A comparison between the experimental data and the results of the Blade Element Theory is carried out to assess the theory capability to estimate thrust in unconventional environments. The overlap between experimental data and theory computation is appropriate despite geometrical uncertainties and corroborate the need of a reliable aerodynamic database. Propeller performance data under unconventional atmospheres will be leveraged to improve UAS design, propulsion system modelling as well as provide guidelines to certify operations in extreme environments
UAS testing in low pressure and temperature conditions
Get PDFThe increasing demand of UAS has generated interest in the scientific community to understand how the environmental parameters affect performance of these emerging vehicles. A bias in the existing tests has been the nonreproducibility of the same climatic conditions. Therefore, UAS have not been fully exploited by the marker so far. Standard protocols for UAS testing in unconventional weather conditions have not been investigated from both industry and academic research. Temperature and pressure are environmental parameters that affect the aerodynamics of Unmanned Aircraft Systems (UAS). Low Reynolds numbers are common for small scale UAS and have a strongly influence on propeller and vehicle capabilities. In the past years, experimental studies on the effects of low Reynolds numbers have been carried out in wind tunnel facilities in conventional atmospheres (ambient temperature and pressure). Moreover, the complexity of the aerodynamic field results in propeller and full vehicle performance prediction methods with limited accuracy. In this paper an experimental setup inside a climatic and hypobaric laboratory is used to highlight temperature and pressure influence on single propeller and full vehicle performance in static conditions (hover). Test results are discussed and provided to the reader, highlighting the complexities of the measurements when extreme temperature and low pressure are set. The main contribution of this study is a set of experimental data to pave the way for a deep investigation on harsh environmental conditions on UAS propulsion system
Modelling and simulation of a tethered UAS
Get PDFBattery lifetime is one of the most challenging problems for Unmanned Aircraft System (UAS) applications. Multi-rotor platforms usually suffer limited payload capabilities and flight time. To overcome this problem, tethered vehicle solutions have been developed. In this paper, we propose a mathematical model able to describe the dynamic behaviour of a tethered UAS. The approach is based on the Finite Element Method and Lagrange’s Equation of motion. The cable is divided into segments linked to each other by spherical joints. An additional virtual element is used to represent the vehicle dynamics. Compared to other works, a variable cable length is implemented as well as wind effects on overall system are included. Simulation results corroborate that the proposed approach is able to simulate how the cable and UAS work in different operating conditions, such as take-off and hovering in both still air and wind scenario
A Risk-based Path Planning Strategy to Compute Optimum Risk Path for Unmanned Aircraft Systems over Populated Areas
Get PDFThe large diffusion of Unmanned Aircraft Systems (UAS) requires a suitable strategy to design safe flight missions. In this paper, we propose a novel path planning strategy to compute optimum risk path for UAS over populated areas.
The proposed strategy is based on a variant of the RRT* (Rapidly-exploring Random Tree "Star") algorithm, performing a risk assessment during the path planning phase. Like other RRT-based algorithms, the proposed path planning explores the state space by constructing a graph. Each time a new node is added to the graph, the algorithm estimates the risk level involved by the new node, evaluating the flight direction and velocity of the UAS placed in the analyzed node.
The risk level quantifies the risk of flying over a specific location and it is defined using a probabilistic risk assessment approach taking into account the drone parameters and environmental characteristics.
Then, the proposed algorithm computes an asymptotically optimal path by minimizing the overall risk and flight time.
Simulation results in realistic environments corroborate the proposed approach proving how the proposed risk-based path planning is able to compute an effective and safe path in urban areas
Permanent Magnet Synchronous Motor (PMSM) for Aerospace Servomechanisms: Proposal of a Lumped Model for Prognostics
Get PDFPrognostics and health management of electromechanical actuators (EMA) must rely on affordable and representative simulation models to be effective in predicting the evolution of failures, so to identify them before they occur through the assessment of monitored parameters, leading to on-spot maintenance operations. In the last years, electromechanical actuators (EMA) and the related modelling and monitoring issues are subjected to a rising attention because of the design of next generation aircraft, based on the More Electric paradigm. In fact, especially in aeronautical fields (such as primary flight control systems), electromechanical actuators are progressively replacing traditional hydraulic and pneumatic systems because of their effectiveness and performances and, then, they are becoming safety-critical actuation devices: for prognostics and health management purposes of EMA, reliable and representative simulation models are needed in order to identify failures. In view of the above, this work proposes a multi-domain numerical simulation model of EMA, putting special attention on the fidelity of the numerical modelling of the inverter and of the related electromagnetic aspects; in particular, authors' research is focused on the modelling of the Permanent Magnet Synchronous Motor (PMSM), also known as Sinusoidal Brushless Motor. The choice of the multi-domain simulation is essential in order to enhance the behaviors of the said PMSM model and to overcome shortcomings related to the simplifying hypotheses that are typically considered in numerical models, which are commonly used also for prognostic analyses of electromechanical actuators
TUTELA DEL LAVORO E LIBERTA' D'IMPRESA NEI PROCESSI DI ESTERNALIZZAZIONE
No full textL’elaborato analizza le conseguenze lavoristiche della successione fra imprenditori, muovendo da una ricognizione delle varie tipologie di esternalizzazione con le relative esigenze e principali criticità.
L’indagine si concentra in primo luogo sul trasferimento d’azienda, esaminando la normativa e la giurisprudenza europee per passare poi alla disciplina di diritto interno, alle procedure sindacali e a uno specifico focus sul trasferimento delle aziende in crisi.
Successivamente l’autore si sofferma sull’appalto, prendendone in particolare considerazione gli indici di genuinità, i criteri di distinzione dalla somministrazione illecita di manodopera e la tutela delle maestranze in caso di avvicendamento fra imprese.
Da ultimo, la ricerca approfondisce le c.d. “clausole sociali”, sia di prima che di seconda generazione, valutandone la compatibilità con il diritto eurounitario e con la costituzione nonché riflettendo sui possibili rimedi in caso di loro violazione.The author analyzes the labour consequences of the succession between entrepreneurs, starting from a recognition of the various types of outsourcing with the related needs and main critical issues.
The survey focuses primarily on the transfer of businesses, examining European legislation and case-law and then moving on to internal legislation, trade union procedures and a specific focus on the transfer of companies in crisis.
The author then dwells on the contract, taking into account in particular the indications of authenticity, the criteria of distinction from the illicit administration of labour and the protection of workers in the event of turnover between companies.
Finally, the research deepens the "social clauses", both first and second generation, assessing their compatibility with European law and with the constitution and reflecting on possible remedies in case of their violation
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