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The solution of the equations of motion of an aircraft fuselage-landing gear configuration during landings is of interest to the designer who must predict the landing loads which an airplane encounters in service. In general such solutions are difficult because of the highly nonlinear characteristics of the oleo-pneumatic shock strut which couples the lower mass of the landing gear to the fuselage. In the past, attempts to obtain solutions by linearization of these shock strut characteristics have resulted in unrealistic predictions of landing gear motions. Therefore, it has been necessary to carry out most of the theoretical analysis associated with landing gears by means of numerical integration procedures. These numerical methods are tedious, and as a result a large portion of design work has been carried out by means of trial and error drop testing of a system of masses representative of an airplane and landing gear. This in turn has proved to be time consuming and expensive. This paper presents a method for obtaining an analytical solution of the equations of motion for a basically nonlinear system which closely resembles an actual airplane and landing gear configuration. The nonlinear system considered has two degrees of freedom and is composed of a large mass representative of the fuselage-wing combination connected by an oleo-pneumatic shock strut to a wheel. The shock strut is assumed to have velocity-squared hydraulic damping and coulomb friction forces on the strut bearings. The nonlinear spring characteristic of the tire is represented by a sectionally linear spring. In the first part of this paper the equations of motion for this nonlinear system are derived making use of a few simplifications which previous papers have shown to be justified. Also, the degree to which these assumptions limit the results is discussed. Next these equations of motion are solved in analytical form by a method which may be called "equivalent non linearisation." It is shown that this solution is exact only for a specific combination of impact parameters, but that for a wide range of parameters the solution describes the motion of the system adequately for design purposes. Finally, a few analytical solutions are compared with solutions obtained by numerical integration methods; and the results are compared with experimental data for a typical impact. / Master of Science

This thesis reports the investigation into the modelling and simulation of an aircraft tyre and wheel assembly in finite element environment. The finite element simulations basing on aircraft tyre test and operational scenarios could predict the loads transferred from tyre and the stresses distributed to the wheel rim. The virtual analysis could assess the safety criteria of different tyre structures, which would lead to the cost and time circle reduction in tyre R&D process. An H41x16.0R20 radial ply aircraft test tyre and its corresponding test wheel, provided by Dunlop Aircraft Tyres Limited, are adopted as the subject of this research. The material properties, especially the rubber and fabric materials, have been investigated. The finite element hyperelastic models have been utilized to represent rubbers and been correlated to experimental data. The 2D and 3D finite element tyre models, along with the finite element wheel models are created in the commercial finite element code, LS-Dyna. The finite element models have been validated with either industrial standardised simulation results or experimental data. Basing on the validated models, simulations that duplicating static test and dynamic operational scenarios have been developed. The researches have provided knowledge in comparing single and double bead tyre designs with respect to wheel loading mechanisms. The computational model also allowed manufacturers to assess the performance and safety criteria of a particular tyre at its design stage. The development of such models would add to the general drive towards the use of more virtual prototypes in an area traditionally reliant on experimental testing.

Kenntnisse über Parametereigenschaften und Charakteristiken von Flugzeugkomponenten sind eine wesentliche Grundlage für Methoden des Flugzeugentwurfs. Daher ist Ziel dieser Arbeit, statistische Merkmale und Kenngrößen einer für den Flugzeugbau und Entwurf relevanten Auswahl an Komponenten zu erschließen. Dabei wurden zunächst superkritische Tragflügelprofile hinsichtlich ihrer geometrischen Eigenschaften (relative Profildicke, Wölbung, Dickenrücklage, Wölbungsrücklage und der sogenannte "Leading Edge Sharpness Parameter") untersucht. Diese Eigenschaften wurden mit der Software XFLR5 aus einer Auswahl an superkritischen Profilgeometrien erhoben und mit grafischen und beschreibenden Statistikmethoden ausgewertet. Die Profile wiesen relative Wölbungen von 0 % bis 3,4 % auf, die Mehrzahl entfiel auf Wölbungen von 1 % bis 2 %. Die Wölbungsrücklagen zeigten die für superkritische Profile typische Lage im hinteren Profilbereich zwischen 70 % und 90 % der Profiltiefe. Die Dickenrücklagen verteilten sich um einen Mittelwert von 37 % der Profiltiefe. Eine Betrachtung von Flugzeugreifendimensionen sollte das Verhältnis von Reifenbreite zum Durchmesser w/d charakterisieren. Es wurde ein annähernd lineares Verhalten festgestellt. Die Werte des Parameters w/d umfassten einen Bereich von 0,3 bis 0,4. Durch Regressionsanalysen konnten auch die Abhängigkeiten des Parameters w/d von nur einer bekannten Reifendimension (Breite oder Durchmesser) aufgezeigt werden. Die im Rahmen dieser Arbeit dargestellten Erkenntnisse können als Grundlage weiterführender Untersuchungen genutzt werden.