328 research outputs found
Capturing nonlinear time-dependent aircraft dynamics using a wind tunnel manoeuvre rig
No full textThis paper considers a novel multi-degree-of-freedom dynamic manoeuvre rig,with the aim of assessing its potential for capturing aircraft model nonlinear time dependent dynamics in the wind tunnel. The dynamic manoeuvre rig capabilities are demonstrated via a series of experiments involving a model aircraft in a closed section low-speed wind tunnel. A series of open loop experiments show that the aircraft model exhibits nonlinear time dependent dynamics. This nonlinear behaviour manifests itself as limit cycle oscillations that increase in complexity with the number of degrees-of-freedom in which the aircraft is allowed to move. Two real-time closed loop control experiments further illustrate the manoeuvre rig potential: first, using a pitch motion configuration, an experiment is conducted to investigate the limit cycle behaviour in more detail, allowing the stability properties of the pitch oscillations to be assessed; secondly, using a 5-DOF motion configuration, the test motion envelope is extended by using a compensating feedback control law to track the aircraft’s roll motion. Together, these experiments demonstrate the manoeuvre rig potential to reveal aircraft nonlinear and unsteady phenomena.<br/
Wind tunnel manoeuvre rig:a multi-DOF test platform for model aircraft
No full textThis paper presents recent progress in the development of a novel multi-degree-of-freedom dynamic manoeuvre rig aimed at investigation of aircraft model nonlinear and time dependent aerodynamics in the wind tunnel. The purpose and characteristics of the rig are first described, along with a description of the data acquisition, processing and presentation system. The dynamic manoeuvre rig capabilities are demonstrated via a series of experiments involving a wind tunnel model aircraft in a closed section low-speed wind tunnel. First, an experiment illustrating low-speed wind tunnel aerodynamic model identification is presented. Then, examples of experiments involving real-time control of the rig/aircraft model are shown; these are evaluated in terms of testing productivity with a focus on the development and design of aircraft control laws
Real-Time Hybrid Testing of Strut-Braced Wing Under Aerodynamic Loading Using an Electrodynamic Actuator
No full textDataset for: "Real-Time Hybrid Testing of Strut-Braced Wing Under Aerodynamic Loading Using an Electrodynamic Actuator". Authors: V. Ruffini, C. Szczyglowski, D.A.W. Barton, M. Lowenberg, S.A. Neild Journal: Experimental Techniques
Experimental Investigation of Aerodynamic Hysteresis Using a Five-Degree-of-Freedom Wind-Tunnel Maneuver Rig
No full textThe high incidence aerodynamics of a lightweight jet trainer aircraft model has been investigated using a novel five degree-of-freedom (DoF) dynamic manoeuvre rig, recently updated with improved actuation and data acquisition systems, in the 7' x 5' closed-section low-speed wind tunnel at the University of Bristol. The major focus was to identify the nonlinear and unsteady aerodynamic characteristics specific to the stall region and which affect free-to-move aircraft model behaviour. First, the unstable equilibrium states in the limit cycle regions were stabilized, and so observed, over a wide range of angles of attack using a simple elevator feedback control law based on pitch angle and pitch-rate sensor measurements.Tests with two degrees-of-freedom, namely the aircraft model and rig arm pitch angles, revealed the existence of static hysteresis in the normal force acting on the aircraft model in the stall region. Unlocking the aircraft model in roll and yaw accompanied by feedback stabilization of the lateral-directional modes of motion demonstrated onset of asymmetric aerodynamic rolling and yawing moments in this four degree-of-freedom configuration. This observation implicitly indicates a link between the static hysteresis in the normal aerodynamic force with an onset of aerodynamic asymmetry. The experimental results show the efficiency of the updated multi-degree-of-freedom actively controlled manoeuvre rig in providing insight into complicated aerodynamic effects within the stall region
Evaluation of Aircraft Model Upset Behaviour Using Wind Tunnel Manoeuvre Rig
No full textThis paper discusses the development of a novel multi-degree-of-freedom dynamic manoeuvre rig aimed at investigation of aircraft upset/LOC-related behaviour in the wind tunnel. The motivation behind the development and characteristics of the rig are first described, along with example behaviour of an aircraft model exhibiting nonlinear time-dependent aerodynamics in an open-jet low-speed wind tunnel. Test objectives for assessment of upset onset scenarios – both for parameter estimation purposes and to ‘physically simulate’ the behaviour – are then described, as is the design of the upgraded instrumentation system to facilitate experimental investigation. Finally, examples of relevant behaviour involving real-time control of the rig to explore nonlinear conditions leading to upset are presented; these are evaluated in terms of prospects for such testing in aircraft development and analysis projects.</p
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
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
Influence of Variable Side-Stay Geometry on the Shimmy Dynamics of an Aircraft Dual-Wheel Main Landing Gear
No full textCommercial aircraft are designed to fly but also need to operate safely and efficiently as vehicles on the ground. During taxiing, take-off, and landing the landing gear must operate reliably over a wide range of forward velocities and vertical loads. Specifically, it must maintain straight rolling under a wide variety of operating conditions. It is well known, however, that under certain conditions the wheels of the landing gear may display unwanted oscillations, referred to as shimmy oscillations, during ground maneuvers. Such oscillations are highly unwanted from a safety and a ride-comfort perspective. In this paper we conduct a study into the occurrence of shimmy oscillations in a main landing gear (MLG) of a typical midsize passenger aircraft. Such a gear is characterized by a main strut attached to the wing spar with a side-stay that connects the main strut to an attachment point closer to the fuselage center line. Nonlinear equations of motion are developed for the specific case of a two-wheeled MLG configuration and allow for large angle deflections within the geometrical framework of the system. The dynamics of the MLG are expressed in terms of three degrees of freedom: torsional motion, in-plane motion, and out-of-plane motion (with respect to the side-stay plane). These are modeled by oscillators that are coupled directly through the geometric configuration of the system as well as through the tire/ground interface, which is modeled here by the von Schlippe stretched string approximation of the tire dynamics. The mathematical model is fully parameterized and parameters are chosen to represent a generic (rather than a specific) landing gear. In particular, the positions of the attachment points are fully parameterized so that any orientation of the side-stay plane can be considered. The occurrence of shimmy oscillations is studied by means of a two-parameter bifurcation analysis of the system in terms of the forward velocity of the aircraft and the vertical force acting on the gear. The effect of a changing side-stay plane orientation angle on the bifurcation diagram is investigated. We present a consistent picture that captures the transition of the two-parameter bifurcation diagram as a function of this angle, with a considerable complexity of regions of different types of shimmy oscillations for intermediate and realistic side-stay plane orientations. In particular, we find a region of tristability in which stable torsional, in-plane, and out-of-plane shimmy oscillations coexist
Bifurcation Analysis of a Coupled Nose Landing Gear-Fuselage System
No full textUnder certain conditions during takeoff and landing, pilots may sometimes experience vibrations in the cockpit. Because the cockpit is located right above the nose landing gear, which is known to potentially be prone to self-excited vibrations at certain velocities, an explanation for those vibrations might be oscillations of the landing gear feeding into the fuselage. However, the fuselage dynamics itself may also influence the dynamics of the landing gear, meaning that the coupling must be considered as bidirectional. A mathematical model is developed to study a coupled nose-landing-gear–fuselage system, which allows to assess the overall influence of the coupling on the system dynamics. Bifurcation analysis reveals that this interaction may be significant in both directions and that the system behavior depends strongly on the modal characteristics of the fuselage
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