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Closed-Loop Control of Spanwise Lift Distribution for Morphing Wing Applications


M. Quack


The work presented here, is part of the SmartAirfoil Project, a collaborative highly interdisciplinary research project (CHIRP) at ETH Zurich with the goal to enable shape adaptation techniques for aircraft airfoils and to investigate the potential of this technology in combination with wing morphing.

For the formulation of requirements on morphing airfoils, a tailless glider in cross-country flight with a minimal time objective is considered as a showcase mission. This mission is well suited to demonstrate the potential of wing morphing, since such a tailless glider relies on the adaptation of spanwise lift distribution to generate control moments and needs to operate efficiently at a wide range of operating points to achieve good overall performance.

Effective wing morphing requires careful system integration and adequate control strategies. The considered morphing wing concept provides a high number of actuators and a control strategy to make optimal use of this redundancy at a wide range of operating conditions is necessary. A 3.3m-span six-flapped tailless RC model glider with conventional servo-actuators is considered in the first part of this thesis as an approximation to a morphing wing and has been used as a basis for a test-platform. Flight tests demonstrated the feasibility of sensor integration and closed-loop control of the span-wise lift distribution providing stable straight and turning flight at different airspeeds. Stable flight allowed data acquisition over extended flight periods and hence acquired data can be used for averaged performance data as well as for parameter identification.

A parametrical numerical model explaining the effect of changes in spanwise lift distribution on the flight trajectory has been developed. The model is in differential algebraic equation (DAE) formulation and couples an extended lifting line method to the flight dynamic equations. Due to its low complexity and the parametric description, which allows to treat sectional aerodynamic coefficients as uncertain parameters, it is well suited for parameter identification, on-line estimation and model-based control methods.

The second part of this thesis addresses design and control methods, necessary to enable wing morphing based on Macro Fibre Composite (MFC) Piezo actuators. First, a novel multi-disciplinary design optimization methodology is presented, which not only employs a 2D aero-structural simulation method, but is also able to exploit aero-structural coupling, since it concurrently optimizes structural and aerodynamical parameters. The method has been applied to a morphing concept example using dielectric elastomer actuators and provides significantly better results in comparison to the commonly applied sequential optimization approach. Closed-loop control of multiple MFC-Piezo actuators is presented and demonstrated on a morphing wing prototype featuring multiple MFC-Piezo actuators in bi-morph configuration. A simple feedback control law is used in combination with flexural strain gauge sensor signals to overcome the hysteresis and creep behaviour, which is typically found in MFC Piezo-actuators. Robustness of the control method to external disturbance has been experimentally validated in Wind Tunnel tests.

A light-weight, small-size integrated electronic circuit design suitable to drive in- dependently multiple active sections using MFC-Piezos in bi-morph configuration in closed-loop control is presented. In combination with compact off-the-shelf high voltage power supplies, a rise time of less than 200 ms for the trailing edge deflection is expected. Furthermore, the solution is designed to scale up to at least six independent active sections, which will allow to apply the control methods from the six-flapped flying wing platform to a new prototype employing the same number of active sections.

With this, the thesis presents all the building blocks necessary to enable the closed- loop control of span-wise lift distribution on a morphing tailless glider at UAV scale.

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Type of Publication:

(03)Ph.D. Thesis

M. Morari

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% Autogenerated BibTeX entry
@PhDThesis { Xxx:2014:IFA_5085,
    author={M. Quack},
    title={{Closed-Loop Control of Spanwise Lift Distribution for
	  Morphing Wing Applications}},
    school={ETH Zurich},
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