Analyses of Aircraft Responses

to Atmospheric Turbulence

By Willem van Staveren

December 2003

Delft University Press

ISBN: 90-407-2453-9

502 pages, Illustrated, 6 ½" x 9 ½"

$125.00 Paper Original

This is a Ph.D. dissertation. The response of aircraft to stochastic atmospheric turbulence plays an important role in, for example, aircraft design (load calculations) and flight simulation (handling qualities research and pilot training). In order to simulate these aircraft responses, an accurate mathematical model is required. Two classical models will be discussed in this thesis that is the Delft University of Technology (DUT) model and the Four Point Aircraft (FPA) model. Although they are well established, their fidelity remains obscure. The cause lies in one of the requirements for system identification; it has always been necessary to relate inputs to outputs to determine, or identify, system dynamic characteristics. From experiments, using both the measured input and the measured output, a mathematical model of any system can be obtained.

When considering an input-output system such as an aircraft subjected to stochastic atmospheric turbulence, a major problem emerges. During flight tests, no practical difficulty arises measuring the aircraft-system's outputs, such as the angle-of-attack, the pitch-angle, the roll-angle, etc. However, a huge problem arises when the input to the aircraft-system is considered; this input is stochastic atmospheric turbulence in this thesis. Currently, it still remains extremely difficult to identify the entire flowfield around an aircraft's geometry subjected to a turbulent field of flow; an infinite amount of sensors would be required to identify the atmospheric turbulence velocity component's distribution (the input) over it. As a consequence, it is difficult, if not impossible, to identify atmospheric turbulence models from flight tests.

Contents include: Atmospheric Turbulence Modeling: The atmospheric turbulence model; Linearized Potential Flow Theory: Steady linearized potential flow simulations, Unsteady linearized potential flow simulations; A Linearized Potential Flow Application: Aircraft motion perturbations and the atmospheric turbulence inputs, The aircraft grid and steady aerodynamic results, PCA-model symmetrical aerodynamic frequency-response functions, PCA-model asymmetrical aerodynamic frequency-response functions; The Mathematical Aircraft Models: Time-domain LPF solutions for 2D atmospheric gust fields, The parametric computational aerodynamics model, The Delft University of Technology model, The four point aircraft model; Comparison of Gust Response Calculations: Comparison of results and discussion; Conclusions and Recommendations.

Aerospace Engineering; Aviation

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