Individual Channel Analysis and Design and its Application to Helicopter Flight Control

Dudgeon, Graham John William (1996) Individual Channel Analysis and Design and its Application to Helicopter Flight Control. PhD thesis, University of Glasgow.

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The publication in 1989 of the Aeronautical Design Standard (ADS)-33C (which, in 1994, was upgraded to ADS-33D) has provided a focus for helicopter flight control research, by both industrial and academic engineers. Helicopters are highly coupled, open-loop unstable systems with complex dynamics, mainly due to the main rotor, and as a consequence available mathematical models have a high degree of uncertainty. Because of these reasons, the design of control laws to enable ADS-33 Level 1 Handling Qualities requirements to be met has been thought to preclude the use of classical one-loop-at-a-time control system design techniques (the helicopter will exhibit Level 1 Handling Qualities if minimal pilot compensation is required during a flying task). The need for control laws which are robust to model uncertainty and demonstrate good decoupling has caused recent attention to be focused on so called 'modern' techniques which synthesis controllers by closing all loops simultaneously and can cater, to some degree, for performance and robustness issues. However, it can be argued that much of the physical insight that classical techniques allow is lost when using modern techniques. A recent development in classical control theory known as Individual Channel Analysis and Design (1CAD) is unique in that it explicitly captures multivariable metrics as part of the single-input single-output (SISO) analysis and design process. These multivariable metrics are known as multivariable structure functions (MSFs) and have three important uses. First they provide a robustness diagnostic which indicates when classical SISO gain and phase margins can be reliably interpreted as robustness measures of a multivariable system. Second, they are used to establish sequential (one-loop-at-a-time) design procedures which will guarantee closed-loop stability and third, they indicate attainable performance of the control system. This thesis develops the theory of ICAD to a level where it can effectively and efficiently be applied to the design of helicopter flight control laws and which will cater for meeting the requirements of ADS-33 in the design process. The development includes the extension of ICAD to cater for non-square systems and a technique to express the MSFs in state space form, thus enabling numerically reliable state space algorithms to be used for computation. The development is generic in nature and therefore can be applied to a wide range of control problems. The analysis and design of four different helicopter flight control laws is described in detail. The control laws are of low order and after extensive linear and non-linear simulation are found to satisfy Level 1 requirements over a wide flight envelope. ICAD is found to be a highly effective technique for the analysis and design of helicopter flight control laws which will meet ADS-33 Level 1 requirements.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Jeremy J Gribble
Keywords: Electrical engineering, Aerospace engineering
Date of Award: 1996
Depositing User: Enlighten Team
Unique ID: glathesis:1996-74422
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 27 Sep 2019 18:26
Last Modified: 27 Sep 2019 18:26

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