2,224 research outputs found
Analysis of medium-speed runway exit manoeuvres
No full textRecent studies suggest that fuel savings can be realised if more efficient surface movements can be achieved through means other than the engines of an aircraft, or by optimising the scheduling of aircraft on the ground. All aspects of ground manoeuvring therefore need to be studied to understand the impact of such changes. This paper presents an analysis method for medium-speed manoeuvres, and, more specifically, runway exit manoeuvres. Kinematic equations that were derived for towing analysis form the basis of the runway exit study, from which empirical formulas are derived for steering angle and clearance predictions. The results of the empirical method compare very well with kinematic studies, as well as detailed dynamic model simulations, as is demonstrated with the test case example of an A380 model. The empirical formulas can be used to great effect during the early design phases of an aircraft programme for the prediction of steering angles and clearance distances, when very little data is available. The greatest advantage of the proposed method is that any aircraft configuration or runway exit can be analysed
Design of a gain scheduled flight control system using bifurcation analysis
No full textA method for identifying regions of instability in closed-loop systems has been developed for flight dynamics applications. This forms a novel approach in which a surface of equilibria is generated in the region of interest as the influence of the control system is increased. In this way, the creation and destruction of equilibria in the controlled system can be easily found and visualized. This systematic approach allows the stability of the closed- loop system to be directly related to that of the open loop. Results are given for a highly nonlinear aircraft model and demonstrate the power of a combined analytical and graphical approach to control system synthesis
Operational Parameter Study of Aircraft Dynamics on the Ground
No full textThe dynamics of passenger aircraft on the ground are influenced by the nonlinear characteristics of several components, including geometric nonlinearities, the aerody- namics and interactions at the tyre-ground interface. We present a fully parametrised mathematical model of a typical passenger aircraft that includes all relevant nonlinear effects. The full equations of motion are derived from first principles in terms of forces and moments acting on a rigid airframe, and they include implementations of the local models of individual components. The overall model has been developed from and validated against an existing industry-tested SimMechanics model. The key advantage of the mathematical model is that it allows for comprehensive studies of solutions and their stability with methods from dynamical systems theory, in particular, the powerful tool of numerical continuation. As a concrete example, we present a bifurcation study of how fixed-radius turning solutions depend on the aircraft’s steering angle and centre of gravity position. These results are represented in a compact form as surfaces of solutions, on which we identify regions of stable turning and regions of laterally unstable solutions. The boundaries between these regions are computed directly and they allow us to determine ranges of parameter values for safe operation. The robustness of these results under the variation of additional parameters, specifically, the engine thrust and aircraft mass, are investigated. Qualitative changes in the structure of the solutions are identified and explained in detail. Overall our results give a complete description of the possible turning dynamics of the aircraft in dependence on four parameters of operational relevance
Bifurcation analysis of nose landing gear shimmy with lateral and longitudinal bending
No full textWe develop and study a model of an aircraft nose landing gear with torsional, lateral and longitudinal degrees of freedom. The corresponding three modes are coupled in a nonlinear fashion via the geometry of the landing gear in the presence of a nonzero rake angle, as well as via the nonlinear tyre forces. Their interplay may lead to different types of shimmy oscillations as a function of the forward velocity and the vertical force on the landing gear. Methods from nonlinear dynamics, especially numerical continuation of equilibria and periodic solutions, are used to asses how the three modes contribute to different types of shimmy dynamics. We conclude that the longitudinal mode does not actively participate in the nose landing gear dynamics over the entire range of forward velocity and vertical force
Geometric nonlinearities of aircraft systems
No full textNonlinearities due to geometric effects, in particular, via angular variables that are not small, are important for aircraft operation. Geometric nonlinearities have a strong effect on the dynamics of the aircraft system under consideration, and they are especially pronounced in aircraft ground operations. As a concrete example we consider here the effect of a non-zero rake angle on the dynamics of a nose landing gear. More specifically, we use tools from bifurcation theory to investigate the stability of the straight-rolling motion during a take-off run
Application of bifurcation methods for the prediction of low-speed aircraft ground performance
No full textThe design of aircraft for ground manoeuvres is an essential part in satisfying the demanding requirements of the aircraft operators. Extensive analysis is done to ensure that a new civil aircraft type will adhere to these requirements, where the nonlinear nature of the problem generally adds to the complexity of such calculations. Small perturbations in velocity, steering angle or brake application may lead to significant differences in the final turn-widths that can be achieved. Here, the U-turn manoeuvre is analysed in detail, with a comparison between the two ways in which this manoeuvre is conducted. A comparison is also made between existing turn-width prediction methods that consist mainly of geometric methods and simulations, and a proposed new method that uses dynamical systems theory. Some assumptions are made with regards to the transient behaviour, where it is shown that these assumptions are conservative when an upper bound is chosen for the transient distance. Furthermore, we demonstrate that the results from the dynamical systems analysis are sufficiently close to the results from simulations to be used as a valuable design tool. Overall, dynamical systems methods provide an order of magnitude increase in analysis speed and capability for the prediction of turn-widths on the ground, compared to simulations
Non-alloy Mg anode for Ni-MH batteries: Multiple approaches towards a stable cycling performance
No full textMg attracts much research interest as anode material for Ni-MH batteries thanks to its lightweight, cost-effectiveness and high theoretical capacity (2200 mA h g−1). However, its practical application is tremendously challenged by the poor hydrogen sorption kinetics, passivation from aggressive aqueous electrolytes, and insulating nature of MgH2. Mg-based alloys exhibit enhanced hydrogen sorption kinetics and electrical conductivity, but significant amount of costly transition metal elements are required. In this work, we have, for the first time, utilized non-alloyed but catalyzed Mg as anode for Ni-MH batteries. 5 mol.% TiF3 was added to nanosized Mg for accelerating the hydrogen sorption kinetics. Several strategies for preventing the problematic passivation of Mg have been studied, including protective encapsulation of the electrode and utilizing room-temperature/high-temperature ionic liquids and an alkaline polymer membrane as working electrolyte. Promising electrochemical performance has been achieved in this Mg–TiF3 composite anode based Ni-MH batteries with room for further improvements.</p
A bifurcation study to guide the design of a landing gear with a combined uplock/downlock mechanism
No full textThis paper discusses the insights that a bifurcation analysis can provide when designing mechanisms. A model, in the form of a set of coupled steady-state equations, can be derived to describe the mechanism. Solutions to this model can be traced through the mechanism's state versus parameter space via numerical continuation, under the simultaneous variation of one or more parameters. With this approach, crucial features in the response surface, such as bifurcation points, can be identified. By numerically continuing these points in the appropriate parameter space, the resulting bifurcation diagram can be used to guide parameter selection and optimization. In this paper, we demonstrate the potential of this technique by considering an aircraft nose landing gear, with a novel locking strategy that uses a combined uplock/downlock mechanism. The landing gear is locked when in the retracted or deployed states. Transitions between these locked states and the unlocked state (where the landing gear is a mechanism) are shown to depend upon the positions of two fold point bifurcations. By performing a two-parameter continuation, the critical points are traced to identify operational boundaries. Following the variation of the fold points through parameter space, a minimum spring stiffness is identified that enables the landing gear to be locked in the retracted state. The bifurcation analysis also shows that the unlocking of a retracted landing gear should use an unlock force measure, rather than a position indicator, to de-couple the effects of the retraction and locking actuators. Overall, the study demonstrates that bifurcation analysis can enhance the understanding of the influence of design choices over a wide operating range where nonlinearity is significant
Assessing risk of self-harm in acute paediatric settings: A multicentre exploratory evaluation of the CYP-MH SAPhE instrument
No full textOBJECTIVE: To psychometrically assess the Children and Young People-Mental Health Self-harm Assessment in Paediatric healthcare Environments (CYP-MH SAPhE) instrument for the identification of immediate risk of self-harm in CYP, aged 10-19 years, in acute paediatric wards or emergency departments., DESIGN: The CYP-MH SAPhE Instrument was developed through a robust scoping review and Delphi consensus with 30 clinicians/topic experts. To evaluate the psychometric properties, a multicentre exploratory study was conducted., SETTING: Three acute hospitals in the UK., PARTICIPANTS: 163 CYP presenting at acute hospital settings with primary mental health (cases) or physical health (non-cases) conditions., PRIMARY AND SECONDARY OUTCOME MEASURES: Psychometric properties of the CYP-MH SAPhE instrument were evaluated through Principle Axis Factoring (PAF) with Oblimin (Kaiser normalisation) alongside measures of internal consistency (Cronbach's alpha), convergent, discriminant and face validity., RESULTS: PAF of the dichotomous items (n=9) loaded onto three factors (1) behaviours and intentions; (2) suicidality and (3) self-harm. Factors 1 (Cronbach's alpha=0.960) and 3 (Cronbach's alpha=1) had high internal consistency. There was: good level of agreement between raters (kappa=0.65); a moderately positive correlation between the CYP-MH SAPhE instrument and the Columbia-Suicide Severity Rating Scale; and discrimination between cases and non-cases across the three factors (factor 1: m=88 vs 70; factor 2: m=102 vs 70; factor 3: m=104 vs 68). Assessment of face validity resulted in six items being removed, culminating in an eight question, rapid assessment instrument., CONCLUSIONS: The results support the CYP-MH SAPhE Tool as a potentially reliable and valid instrument to identify immediate risk of self-harm in CYP presenting to acute paediatric healthcare environments, which is a burgeoning and significant global health issue. Copyright © Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.https://dx.doi.org/10.1136/bmjopen-2020-04376
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