1,720,972 research outputs found
Performance Analysis of a Lightweight Helicopter Featuring a Two-Bladed Gimballed Rotor
No full textThis paper deals with the investigation of performance and sta- bility characteristics of a two-seater, two-bladed, lightweight he- licopter developed in the framework of VLR certification spec- ifications. The main rotor features a gimballed hub with elas- tomeric bearings equipped with a Bell-Hiller to improve stabil- ity, while the fixed pitch, rpm controlled, five-bladed tail rotor is a fenestron design.
The main technical drivers of the novel design are to reduce the high level of 2/rev vibrations occurring in teetering rotors, to retain adequate control power in low–g maneuvering and to improve handling qualities using the stabilizing bar to increase roll and pitch damping. A specific aspect of the gimballed rotor is the presence of a sustained wobbling motion of the hub, even in steady–state conditions.
A nonlinear model of the vehicle is derived that includes, among other aspects, a detailed model of main rotor, nonlin- ear, quasi–static blade aerodynamics, inflow dynamics, a simple fuselage aerodynamic model and a tail rotor model derived from experimental wind–tunnel tests.
Periodic trim conditions are evaluated using a shooting method in order to assess the impact of rotor wobbling mo- tion on helicopter steady–states. Results on performance and controllability are presented and discussed. Finally, the stability characteristics of the vehicle are assessed in order to gain some preliminary insight on the handling qualities of the helicopter
Dynamic Behaviour and Response of a Two–Bladed Gimballed Rotor
No full textThis paper aims to analyze the characteristics of a novel, two-bladed gimbaled rotor featuring a homokinetic joint between driving shaft and rotor yoke and a fly-bar with paddles. The design and testing of this novel rotor configuration is part of the development program of a lightweight helicopter in the VLR rotorcraft certification framework. The rotor is designed with the main objective of solving some of the negative issues that affect the use of teetering rotors on light helicopters, such as strong 2/rev oscillatory loads, poor response at low g's and a pronounced sensitivity to gusts and/or large pilot inputs. A simple dynamic model is developed to allow for the interpretation of periodic motions of the system and to determine the effects of design parameters on the rotor response by means of numerical simulation and a stability analysis, a study carried out to fully assess the possible advantages of the gimbaled configuration with respect to a more traditional teetering rotor. © 2010 Association Aeronautique et Astronautique de France. All rights reserved
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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