1,720,962 research outputs found
In-flight Loads evaluation by means of Strain measurements: a Numerical case study
No full textThis paper is concerned with one of the steps to be made for recovering of flight loads from strain measurements during flight: the ground calibration aimed at calculating the best Load evaluation matrices for the structural item to be considered.
A methodology based on the Skopinski approach and aimed at selecting the best set and numbers of strain measurements on a two-spar wing has been set up. The work is of a numerical nature. It is intended to be a preliminary step before the real ground calibration to be made before flight.
“Virtual” calibrations by means of extensive finite element calculations have been performed. The choice of the best set of strain sensors measurements and calibration loads has been made according to Skopinski approach.
In particular two calibrations have been performed, the first with simple sets of loads, resulting in unacceptable results in terms of flight loads recovering (high percent errors). The second calibration has been carried out with sets of loads more similar to typical maneuvers or gusts encountered during flight, leading to quite reliable load evaluation matrices resulting in acceptable percent errors coherent with literature
Pre-test Analyses for Flight Flutter Test of an EASA CS-23 Aircraft
No full textSmall aircraft manufacturers are typically constrained by stringent budget requirements. Among all the cost headings the certification process cost is a non-negligible part, especially as regards the tests.
Flight Flutter Test is a crucial means to state flutter clearance. A fundamental issue connected to this test is the choice of good excitation devices or maneuvers in order to excite the flutter mode. Different types of excitation means are available, each one more or less suitable to the aircraft which will be tested. The choice of the best excitation device among the various available solutions basically depends upon the flutter mode frequency to be excited as well as time and budget constraints. If a rational analysis able to predict the reliability of the excitation is available, significant time/cost expenses reduction can be achieved.
In this paper a pre-test analysis aimed at correctly exciting the flutter mode during Flight Flutter test on an EASA CS-23 aircraft is presented. The Aeroelastic Dynamic Response under external forces (State Space representation and modal approach) has been investigated to assess the reliability of two different types of excitation devices: the control surface pulse (with zero additional cost) and the pyrotechnical thruster (bonker).
Actually no pre-Flight Flutter Test rational analyses are strictly required by Airworthiness Requirements, but it would be desirable if such an approach was followed, especially in the viewpoint of a better addressing of the test and of course the cost reduction
Symmetric Quasi Steady Maneuver Load Alleviation – a method to predict the control surface efficiency when used as load alleviator
No full textThe main purpose of the Load Alleviation system on which this paper is focused is a drop in structural wing loads for improved performances, fatigue life, Operative Empty Weight reduction.
The driving idea is to perform the alleviation during a quasi-steady symmetric maneuver by means of a symmetric actuation of dedicated control surfaces. The control effectiveness of the load alleviator is evaluated, in terms of required deflection for a desired bending moment reduction in the wing, but keeping the same maximum vertical load factor attained during the unalleviated maneuver.
When high performance is important, internal structural loads (maneuver loads) reduction becomes significant, if the alleviated maneuver can be performed with the vertical load factor kept unvarying. Consequently evaluations on the load alleviator effectiveness in the early design process are appropriate to find the best set of controls.
The load alleviator deflection time history is evaluated a priori, without feed-back calculations, simply depending upon elevators time history, system characteristics and flight condition.
An application on a business aircraft has been performed (not neglecting structural flexibility) for two kinds of symmetric maneuvers. By adopting the ailerons as load alleviators, the maximum bending reduction at the wing root is about 37 percent, with a maximum aileron deflection less than 12 deg
Load Alleviation on a Joined-Wing Unmanned Aircraft
No full textIn this paper a method of alleviating wing structural load of a flexible aircraft during a symmetric balanced maneuver is presented. An application on the unmanned aircraft in development at the Italian Aerospace Research Center, high altitude performance demonstrator, characterized by a joined-wing configuration, is illustrated. This load alleviation technique enables a desired value of the bending moment on a fixed wing control station to be obtained. The load reduction is achieved by deflecting a suitable set of flight-control surfaces, by always keeping the vertical load factor constant to preserve the maneuvering performance. The main hypotheses are: significant aeroelastic effects, linear behavior of aerodynamics and structure, and unvarying tensor of inertia under structural deflections. High-altitude performance demonstrator is a scaled performance demonstrator of an 80m-wing span high-altitude and long endurance unmanned aircraft in a joined-wing configuration. The advantages in terms of performance, fatigue life extension, and weight reduction can be achieved from the integration of an onboard load alleviation system. The results show that the attainable value of load alleviation in terms of bending moment reduction at the wing root is 37%. Moreover, the test-case analyses show that the maximum value of the alleviation increases with respect to the dynamic pressure although the load distribution varies because of significant aeroelastic effects
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
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
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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