Higher Harmonic Control and Flight Control System Interaction

Title: Model for Application to Higher Harmonic Control and Flight Control System Interaction

This dissertation addresses a system, generally known as “Higher Harmonic Control” (HHC) because it consists of superimposing high frequency rotor inputs to the conventional low frequency ones used to control and maneuver the helicopter….


1 Introduction
1.1 Motivation
1.2 Literature review
1.2.1 Higher harmonic control technology
1.2.2 Linear models
1.3 Objectives of study
1.4 Principal contributions
1.5 Organization of the dissertation
2 Mathematical Model
2.1 History of helicopter simulation model
2.2 Helicopter model
2.3 HHC implementation
2.4 Solution methods: trim
2.4.1 Algebraic trim
2.4.2 Periodic trim
2.5 Solution methods: linearization of the equation of motion
2.6 Solution methods: time integration
2.7 Vibration calculation
2.7.1 Hub loads calculation
2.7.2 Cockpit vibration calculation with the rigid fuselage
2.7.3 Cockpit vibration calculation with the flexible fuselage
2.8 Optimization formulation
3 Active Rotor Control System for Vibration Suppression
3.1 Harmonic analyzer
3.1.1 Analog bandpass filter method
3.1.2 Fourier analyzer method
3.1.3 Effect of windowing
3.1.4 Equivalent lowpass filter
3.2 Higher harmonic control algorithm
3.2.1 T-matrix method
3.2.2 T-matrix validation
3.3 Discrete HHC update
4 Extraction of the Constant-Coefficient Linearized Model
4.1 Extraction of a linearized model without higher harmonics
4.2 Extraction of a linearized model with higher harmonics
4.2.1 Definitions
4.2.2 Extraction of the control matrix B
4.2.3 Extraction of the state matrix A
4.2.4 Extraction of the feedforward matrix D
v4.2.5 Extraction of the output matrix C
4.3 Application to simple rotor equations
4.3.1 Prescribed solution form
4.3.2 Perturbation of the equations of motion
4.3.3 Extract four/rev harmonic components
4.3.4 …
5 HHC and AFCS Interaction Study
5.1 Effect of a fixed HHC input on rigid body dynamics
5.1.1 Open-loop frequency response validation
5.1.2 Effect of an optimum three/rev input on rigid body dynamics
5.2 Interaction of HHC and AFCS
5.2.1 Broken control loop response validation
5.2.2 ……
6 Summary and Conclusions

Author: Cheng, Rendy Po-Ren

Source: University of Maryland

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