Analysing dynamic deep stall recovery using a nonlinear frequency approach

Nonlinear Dynamics - Based on bifurcation theory, nonlinear frequency response analysis is a recent development in the field of flight dynamics studies. Here, we consider how this method can be...     

Real-Time Hybrid Testing of Strut-Braced Wing Under Aerodynamic Loading Using an Electrodynamic Actuator

Experimental Techniques - Real-Time Hybrid Simulation (RTHS) is an experimental framework that allows the testing of components or substructures under realistic, dynamic boundary conditions, by...     

Interaction of torsion and lateral bending in aircraft nose landing gear shimmy

In this paper we consider the onset of shimmy oscillations of an aircraft nose landing gear. To this end we develop and study a mathematical model with torsional and lateral bending modes that are coupled through a wheel-mounted elastic tyre. The geometric effects of a positive rake angle are fully incorporated into the resulting five-dimensional ordinary differential equation model. A bifurcation analysis in terms of the forward velocity and the vertical force on the gear reveals routes to different types of shimmy oscillations. In particular, we find regions of stable torsional and stable lateral shimmy oscillations, as well as transient quasiperiodic shimmy where both modes are excited.     

Numerical continuation analysis of a three-dimensional aircraft main landing gear mechanism

Nonlinear Dynamics - A method of investigating quasi-static landing gear mechanisms is presented and applied to a three-dimensional aircraft main landing gear mechanism model. The model has 19...     

Two-state dynamic gain scheduling control applied to an F16 aircraft model

The feasibility and benefits of applying a novel multi-variable dynamic gain scheduling (DGS) approach to a complex ‘industry-scale’ aircraft model are investigated; the latter model being a non-linear representation of the intrinsically unstable F16 aircraft incorporating detailed aerodynamic data. DGS is a novel control approach, which involves scheduling controller gains with one (or more) of the system states whilst accounting for the ‘hidden coupling terms’ ensuring a near-ideal response. It is effective for non-linear systems exhibiting rapid dynamic changes between operating points. Recently, this approach has been extended to a multi-variable and multi-input context. Hence, unlike previous DGS work on realistic aircraft models, relevant feedback gains are to be scheduled with all (i.e. two) state variables in order to demonstrate the ability of the approach to compensate for non-linearity during rapid manoeuvres and consequently achieving better flying qualities over a range of conditions than standard gain scheduling. Time history simulations are used to draw comparisons with the more traditional ‘static’ gain scheduling and input gain scheduling methods.     

On the effect of model uncertainty on the Hopf bifurcation of aeroelastic systems

Nonlinear Dynamics - Nowadays, humanity is facing one of the most dangerous pandemics known as COVID-19. Due to its high inter-person contagiousness, COVID-19 is rapidly spreading across the world....     

Canard cycles in aircraft ground dynamics

The loss of lateral stability of an aircraft turning on the ground is associated with a rapid transition from small-amplitude oscillations to large-amplitude relaxation oscillations over a very small parameter range. This phenomenon is shown to correspond to a canard explosion, which is known to be an important feature of systems that exhibit a separation of time scales. While the industry-tested model of aircraft ground dynamics that we consider does not feature an explicit splitting of time scales, we show that, locally near the transition from stable turning to laterally unstable behaviour, the forward speed of the aircraft acts as a slow variable. The associated family of canard cycles is identified, and the canard explosion is shown to be directly related to the successive saturation of tyre forces at the two main landing gears. We present a canonical two-dimensional slow–fast vector field model that captures the key features of this type of canard explosion; it differs from the canard explosion in the archetypical Van der Pol system in terms of the shape of the associated critical manifold.     

Multi-parameter bifurcation study of shimmy oscillations in a dual-wheel aircraft nose landing gear

We develop and investigate a mathematical model of an aircraft nose landing gear with a dual-wheel configuration. The main aim here is to study the influence of a dual-wheel configuration on the existence of shimmy oscillations. To this end, we consider a model that describes the torsional and lateral vibrational modes and the non-linear interaction between them via the tyre-ground contact. More specifically, we perform a bifurcation analysis (with the software package auto) of the model in the two-parameter plane of forward velocity of the aircraft and vertical load on the nose landing gear. This two-parameter bifurcation diagram allows one to identify regions of different dynamics, and the question addressed here is how it depends on two key parameters of the dual-wheel configuration. Namely, we consider the influence of, first, the separation distance between the two wheels and, second, of gyroscopic effects arising from the inertia of the wheels. For both cases, we find that with increasing separation distance and wheel inertia, respectively, the lateral mode becomes more stable and the torsional mode becomes less stable. More specifically, we present associated bifurcation scenarios that explain the transitions between qualitatively different two-parameter bifurcation diagrams. Overall, we find that the separation distance and gyroscopic effects due to wheel inertia may have a significant influence on the quantitative and qualitative nature of shimmy oscillations in aircraft nose landing gears. In particular, the torsional and the lateral modes of a dual-wheel nose landing gear may interact in a quite complicated fashion.