1,720,970 research outputs found
Multi-step strategy for rotorcraft model identification from flight data
No full textThe availability of suitable methods for system identification from flight data of rotorcraft models is a key factor to enhance the competitiveness of the rotorcraft industry in the development process of new vehicles. Indeed, reliable simulation models provided by the identification techniques can be used for the design and validation of the vehicle flight control system. It allows minimizing the number of in flight experimental tests and consequently reducing costs and risks related to flight testing. Identification methodologies generally fall into two categories: frequency-domain and time-domain. Each approach has inherent strengths and weaknesses. Much of the published works on rotorcraft identification deals primarily with frequency-domain methods, which work well at mid and high frequencies associated with the dynamics of the vehicle control inputs and the aero-elastic behaviour of the blades. On the other hand, time-domain methods, which are well assessed for the identification of fixed wing aircraft, provide accurate models at the low frequency scale that is related to the vehicle flight mechanics. In this paper a hybrid time-frequency identification approach is described. The identification process was carried out in the framework of a multi-step strategy and a specific methodology was selected to comply with each step objective. The hybrid time-frequency approach allowed exploiting the advantage of both time and frequency methods, maximizing the information content extracted from the flight data and obtaining an identified model applicable in the whole frequency range of interest. Furthermore the multi-step strategy decomposed the complex starting problem in simplified sub-problems, which are easier to be solved. The proposed methodology was applied to simulated data of the UH60 Black Hawk, generated using the FLIGHTLAB multi-body simulation environment. Preliminary results showed the effectiveness of the proposed identification strategy in terms of convergence and capability of extracting from flight data relevant information on the vehicle dynamic behaviour. Future works will be focused on the refinement of the structure of the rotorcraft model used for identification purpose and on the application of the proposed methodology to set of data gathered during actual rotorcraft flight tests
Hybrid Approach for Rotorcraft Identification from Flight Data
No full textThe availability of suitable methods for rotorcraft model identification from flight data is a key factor to enhance the competitiveness of the rotorcraft industry in the development process of new vehicles. Indeed, reliable simulation models provided by the identification techniques can be used for the design and validation of the vehicle flight control system. It allows minimizing the number of in flight experimental tests and consequently reducing costs and risks related to flight testing. In this paper the complex problem of rotorcraft model identification is decomposed in simpler sub-problems and solved by means of multi-step hybrid time-frequency approach. The hybrid time-frequency approach allows exploiting the advantage of both time and frequency domains methods, maximizing the information content extracted from the flight data and obtaining an identified model applicable in the whole frequency range of interest. The proposed methodology was applied to simulated data of the UH60 Black Hawk generated using the FLIGHTLAB simulation environment both in hover and forward flight conditions. Preliminary results show the effectiveness of the proposed identification strategy in terms of convergence and capability of extracting from flight data relevant information on the vehicle dynamic behavior
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Design of a STOL Ultralight aircraft in composite material
No full textThe class of ULM (Ultra Light Machines) and light aircraft in general has attracted growing interest through Europe in recent years. Only in Italy, in the last 5-6 years, at least 10 companies have started production of ULM aircraft. There is a very active market for this class, used to promote flight at all levels and for sports aircraft. The maximum flight speed for ULM aircraft has been increased in recent years through the use of more powerful engines (100 hp instead of 64 or 80) and better aerodynamics. It is not surprising that a maximum level speed of about 280 km/h has been reached. Since the weight constraints are very strict (maximum take-off weight must be 450 kg), it is important to investigate different solutions to improve structural design, safety, flight qualities, aeroelastic behaviour and systems reliability, without raising costs. Following the experience acquired in our department in designing light and ultra light aircraft, the design of a new composite ULM is being carried out at DPA. The paper deals with the design of a STOL (Short Take-Off and Landing) ultra light aircraft, starting from a market survey, the conceptual design loop and the preliminary choice of dimensions, and leading to the detailed design of efficient high-lift systems and a low-drag fuselage shape. Technological challenges regarding the design of low-cost systems for flap/slat retraction and a simple wing folding system are highlighted
Low Cost Air Data Computer for UAV in-flight Experimentation
No full textThe Italian Aerospace Research Centre (CIRA) is carrying out a national research project, named TECVOL, which aims at developing relevant technologies for fully autonomous flight of fixed unmanned aerial vehicles, from take-off to landing, including mid-air flight and collision avoidance functionalities. Such technologies are tested in flight by means of an experimental set-up constituted by a flying platform, named FLARE (Flying Laboratory for Aerospace Researches), and a Ground Control Station (GCS). The flying platform is an experimental ultra light aircraft with designed empty weight of 281 Kg, max take-off weight of 450 Kg, max speed s/l about 218 km/h, cruising speed about 190 km/h, wing area of 13.2 m2, wing span of 9.6 m and maximum engine power of 100 hp. The FLARE vehicle is also equipped with an avionic system able to put in operation the algorithms developed in the TECVOL project, whereas the ground control station is dedicated, and thus suitably equipped, to supervision and on-line setting of the in-flight experiments. All the critical components of the equipment are Commercial-Off-The-Shelf (COTS) elements.
This paper presents the design, development, integration and flight testing of a low cost air data computer (ADC), developed in the framework of TECVOL project. The main aim of this ADC is to provide accurate and reliable data to the Flight Control System (FCS) during the critical flight phases of take-off and landing. The requirements of the ADC are firstly discussed, because they drove the on board sensors selection. These requirements concern mainly the system size and weight and its performances (in terms of data accuracy, output rate and latency) which are essentially determined by the performances required to the flight control system. The choice to realize a custom air data computer is motivated by the absence of any commercial off the shelf ADC able to fit system requirements, because commercial ADCs are generally designed to provide cockpit information and not to be enslaved to a FCS.
The software/hardware architecture of the ADC and its integration on board the flying platform are then described. The algorithms developed to compute air data (i.e., altitudes, true air speed, indicated air speed and Mach number) and to perform model based self-diagnostic of the ADC are also presented.
This paper also describes the testing process, which includes both laboratory and in-flight tests. Laboratory tests have been carried out using an Air Data Test Set in order to check, before flight, the algorithms and the performances of the sensor setup. Flight tests have been performed for in-flight calibration of the air data computer.
In order to demonstrate the effectiveness of the proposed system, in the paper it will be also presented the performances of the proposed ADC during an UAV autonomous mission
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
LIGHT AIRCRAFT FLIGHT TESTS: PERFORMANCES, STABILITY AND FLYING QUALITIES MEASUREMENT
No full textThe present paper deals with flight test activities performed on light aircraft at University of Naples, Dipartimento di Progettazione Aeronautica (DPA) by the ADAG (Aircraft Design and Aeroflightdynamics Group) research group. Flight tests performed on a Brasilian light aircraft called Curumin and on G97 Spotter ultralight aircraft (ULM) will be presented. An accurate and complete flight test equipment and instrumentation has been designed and assembled by the research group. A complete set of sensors and instruments (pressure transducers, inertial platform, GPS, pitot probe used for angle of attack and sideslip measurement etc.) has been integrated and used to measure flight data and an accurate A/D converter and a flight data logger system has been set up for flight data acquisition. The complete on-board system is light and compact since it is also used for model aircraft (RPV or UAV) flight tests. The flight data are stored on board and sent to the ground where a ground control station is used for real-time monitoring. The ground station allows real-time ground visualization of all flight data parameters and aircraft position and attitude. In the paper all the advantages (i.e. fast evaluation of dynamic stability characteristics of the aircraft) in using a telemetry system for flight test activities will be highlighted. The complete instrumentation constitutes a valid tool for light aircraft flight tests and is also extensively used at our University for teaching purposes. The paper presents some flight test procedures and results concerning light aircraft aerodynamics and performances estimation. The paper will also present our current methodology based on Maximum Likelihood Method (MLM) for aerodynamic and dynamic parameter estimation. This allows the build-up of the complete aircraft aerodynamic data-base to be used for flight simulation. For the prediction of performances and dynamic behaviour of the airplane in flight, specific and detailed maneuvers have been designed and executed in order to excite dynamics modes. Comparison between simulated and measured maneuvers will be performed. Examples of linear and non-linear flight parameters estimation such as longitudinal non-linear aerodynamics from stall maneuver will be presented
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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