Aircraft active inceptor dynamics under vibration loads

  • Edward J H Yap

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Inceptors are the controls that pilots use to orientate and manoeuvre an aircraft. They are inherent Multi-Body Dynamic (MBD) systems and in preliminary design stages, challenges often arise in adequately assessing and predicting their dynamic characteristics. High fidelity models may be unavailable or inefficient in assessing the inceptor’s dynamic characteristics until detailed design stages. However, the inceptor’s resonances may be found to occur at or in the proximity of the target aircraft’s forcing frequencies, which is to be avoided. The prospect of an undefined number of inceptor design iterations to ensure sufficient clearance, highlights the need and desirability of a mathematical inceptor model, and an associated design process, that can be used to provide necessary insights into an inceptor’s dynamic characteristics during preliminary design stages.

This thesis presents a study into the mathematical modelling of a candidate active inceptor to provide early low-cost means of predicting its dynamic characteristics, namely natural frequencies, at preliminary design stages. Focus is placed on frequencies due to the inceptor’s aforementioned adverse vibration issues. The primary modelling approach proposed in this work is the Udwadia-Kalaba (U-K) formulation. It is firstly demonstrated for modelling generic constrained nonlinear multibody systems through a case study of a planar crank slider mechanism. A novel framework is developed showing how a U-K formulated model can be used to shift and thereby tune a modelled system’s dynamic characteristics, namely natural frequencies, to desired levels by recommending adjustments in design parameters. Tuning studies demonstrated this framework on the U-K crank-slider mechanism model; the parameter outputs were validated by a model produced in MATLAB’s MBD toolkit Simscape. The U-K formulation is then extended to model flexible multibody systems using a lumped parameter approach. A flexible planar crank-slider mechanism is modelled and its predicted natural frequencies agreed well with those from a Simscape model.

The candidate inceptor is then introduced and a three-dimensional, configurable and low order U-K candidate inceptor model is presented. It includes the capacity to predict the inceptor’s flexible modes from the planar bending flexibility of the control stick. This model is validated, and its predicted natural frequencies shown to agree strongly with those from a Simscape model. A finite element (FE) inceptor model was provided by BAE Systems, serving as a high fidelity representation of the inceptor from which the low-order U-K model could be compared. The U-K model revealed a satisfactory correlation with the FE model’s predicted modes, verifying the U-K model’s representativeness. A physical candidate inceptor unit was also made available by BAE Systems; experimental vibration surveys validated that the U-K model adequately represented the dynamics of the physical inceptor. Conceptual design studies are then presented, demonstrating how the U-K inceptor model can shift the inceptor’s natural frequencies to desired levels by recommending adjustments in design parameters. The application of the U-K modelling approach to an inceptor, and the demonstration of its ability to contribute to preliminary design studies and provide powerful insights into the inceptor’s dynamics, is to our knowledge, a new contribution to the field.
Date of Award30 May 2023
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorMark H Lowenberg (Supervisor), Djamel Rezgui (Supervisor), Simon A Neild (Supervisor) & Khosru Rahman (Supervisor)

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