Eigenstructure Assignment Techniques Applied to Helicopter Flight Control Law Design

Hughes, Gail (1994) Eigenstructure Assignment Techniques Applied to Helicopter Flight Control Law Design. PhD thesis, University of Glasgow.

Abstract

This thesis is concerned with the application of eigenstructure assignment methods to helicopter flight control law design. Helicopters are inherently multivariable dynamic systems and, in some cases, can be unstable. Pilot workload is increased by the effects of the cross-coupled helicopter dynamics. As well as providing stability and reducing pilot workload the controller has to produce satisfactory handling qualities and ride quality over a range of flight conditions. Eigenstructure assignment methods are reviewed and previous results from the use of these methods are discussed. The need to adopt a modified approach is established by considering the complex nature of the helicopter control problem in that the controller should decouple the helicopter's dynamics, track pilot inputs and meet helicopter handling requirements. A multivariable control law design method which cancels zeros and zero directions and also creates a decoupled tracking system is presented. The effect of output selection on system zero positions is tabulated Control law design is performed on an 8th order linear model of the helicopter's rigid body dynamics. An inner/outer loop structure is adopted. The inner loop contains a scheduled controller which provides stability and a decoupled response across a range of flight conditions while the outer loop involves a proportional plus integral controller to augment performance. The resulting controlled system meets helicopter handling qualities requirements. Actuator and rotor dynamics that were not included at the design stage are added to the model to test for robustness. The controller is then tested on helicopter models for flight conditions other than that at which the design was produced and it is shown to be robust to the changes. The linear helicopter model is then replaced by a non-linear representation. It is shown that the controller continues to give good performance with the non-linear model. The non-linear controlled system is then tested for disturbance rejection by adding turbulence to the simulation. The ability of the system to filter out sensor noise is also investigated. The results show that the controller maintains stable behaviour across the range of flight conditions for which the inner loop controller was scheduled, responses which are decoupled are achieved and handling quality requirements are met.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Adviser: David J Smith-Murray
• Keywords: Electrical engineering, Mechanical engineering, Aerospace engineering
• Date of Award: 1994
• Depositing User: Enlighten Team
• Unique ID: glathesis:1994-75285
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 19 Nov 2019 21:20
• Last Modified: 19 Nov 2019 21:20
• URI: https://theses.gla.ac.uk/id/eprint/75285