Browsing by Author "Siikonen, Timo, Prof., Aalto University, Department of Applied Mechanics, Finland"

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    Studies on Unmanned Atmospheric Flight
    (Aalto University, 2016) Sailaranta, Timo; Konetekniikan laitos; Department of Mechanical Engineering; Insinööritieteiden korkeakoulu; School of Engineering; Siikonen, Timo, Prof., Aalto University, Department of Applied Mechanics, Finland
    The thesis deals with topics emerging in the field of aerial flight of unmanned vehicles. In this framework, aerodynamics, flight mechanics, flight control and the guidance of unmanned vehicles are discussed. In addition, some issues related to vehicle design and flight optimization are considered. An underlying principle of the thesis has been to increase general knowledge concerning the flight of unmanned airborne vehicles. The work was carried out in order to benefit the industry. It is also hoped that the wide perspective of the thesis will support education on the university level. In the scope of pure aerodynamics, the thesis proposes a modification to the well-known Newtonian Flow theory. The Newtonian theory does not take into account information propagation to upstream and is applicable only for very high speed flows. The modification implicitly incorporates shock-wave effects addressing the information limited to travel upstream. This novel approach extends the method to cover also low and moderate supersonic speeds. The method was developed mainly for optimization purposes and the simple law form makes it easy to use in this context. The work portion concerning unguided vehicle flight mechanics is also linked to the real world through the pursuit to develop, in co-operation with industry, a "safe" bullet. In this part, high angle-of-attack aerodynamic interactions and the flight mechanics of a fast spinning bullet are studied in order to understand the phenomena of the fall of an upwards fired bullet. The ultimate goal is to ensure, under strongly unstable flight, retarding the impact velocity of a falling bullet beyond lethal. The vehicle instability mechanism is caused by an aerodynamic interaction called the Magnus effect.  The third issue of the thesis is flight control and particularly a smart-structure based passive means to stabilize the flight of an unguided vehicle and minimize disturbance effects on the flight. Linear and non-linear theory studies are utilized and a concept of properly delayed turning fins is proposed. The fourth topic covers unmanned vehicle guidance.The transposed Hamiltonian reveals linearized system sensitivities and provides a powerful tool for any system analysis over the typical time-domain considerations. The approach is not as widely used as it should be, which is probably due to the quite obscure way of presenting the theory in textbooks under the title of "adjoint".  Finally, the thesis considers the effects of atmospheric turbulence on the momentary orientation of an airborne vehicle. The turbulence influences the radar cross section (RCS) of a vehicle and furthermore recognition of the target.