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Thesis

French

ID: <

10670/1.f9ygl7

>

Where these data come from
Lateral stability and control of an aircraft equiped with a small fin by differential use of propulsion systems or by actuators such that butterfly airbrakes. Use of co-design methods

Abstract

The possibility to increase the performance of a transport aircraft through a relaxation of the directional static stability, also called weathercock stability, is studied in this thesis. A change of paradigm brought by the concept of distributed electric propulsion allows the consideration of an active use of differential thrust. This additional means of flight control and the reduction of the vertical tail are the main ideas explored in this work. In a first part, the directional static stability and controllability of an aircraft are evaluated to find the sizing flight conditions for the vertical tail. The contribution here is to take into account the specificities of the unconventional propulsion system. Mathematical tools are developed to trim the aircraft using differential thrust as a mean of directional control and aerodynamic tools are constructed to describe the variable vertical tail size and the aero-propulsive interactions taking place between a propeller and a wing. This analysis isolates a sizing flight condition, particularly the case of engine failure at take-off, for the vertical tail and leads to a significant reduction in surface area. It is also shown that the rudder control surface could be removed and replaced by differential thrust. In a second part, the flight dynamic aspects of an aircraft with a small vertical tail and differential thrust as the only means of directional control are studied. A methodology is proposed to answer the question of how should the vertical tail and propulsion system be designed to satisfy a set of prescribed flight handling qualities ? An automatic control architecture and co-design methodology relying on structured H1 control design and non convex optimisation tools are utilized and developed to manage the trade off between vertical tail size and engine bandwidth. This framework is used in the flight conditions defined in the first part and notably in presence of engine failures. In a last part, a means of experimental research is developed to contribute to an effort to produce experimental data on distributed electric propulsion. This flight demonstrator is specifically oriented toward the study of the lateral flight mechanics of an aircraft having a large portion of the wing embedded in the propeller slipstream. It was possible to identify the aerodynamic derivatives and their dependence on the thrust from the flight data to illustrate the particularity of flight dynamics with distributed propulsion and blown wing.

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