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The Development of Neural Network Based System Identification ...

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2.2 HELICOPTER DYNAMICS MODELLING AND SYSTEM IDENTIFICATION 23<br />

Body Reference Frame<br />

East<br />

North<br />

Inertial Frame<br />

Down<br />

Figure 2.4<br />

<strong>The</strong> representation <strong>of</strong> state and input variables.<br />

Kendoul [2012] has suggested that in order to obtain more accurate helicopter<br />

dynamics model, the basic rigid body model needs to be extended with helicopter’s<br />

rotor dynamics and detailed aerodynamic model using theories from simple momentum<br />

theory or blade element theory.<br />

Detailed formulation <strong>of</strong> large scaled helicopter’s<br />

non-linear dynamics model can be found in Prouty [1986], Padfield [2007], Bramwell<br />

et al. [2001], Johnson [1980]. For a smaller scale helicopter, other dynamics from the<br />

actuator and stabiliser bar also need to be included in the rigid body model to increase<br />

the model fidelity [Mettler, 2003]. <strong>The</strong> dynamics model presented above depends on<br />

many parameters which need to be carefully identified through direct measurement<br />

<strong>of</strong> geometrical or structural data. For aerodynamic parameters estimation, elaborate<br />

experiment needs to be performed using wind tunnel facilities. It requires a considerable<br />

amount <strong>of</strong> theoretical knowledge and experiences about rotorcraft flight and potentially<br />

would not produce highly accurate results unless performed with extreme care. In<br />

some cases, the agreement between the predicted and measured dynamic behaviours<br />

is unsatisfactory because <strong>of</strong> the accumulated uncertainty and modelling simplification<br />

[Mettler, 2003, Kendoul, 2012].

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