FE - DCA | Dissertações de Mestrado e Teses de Doutoramento
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- Trajectory and aerodynamic analyses of air launched fire-extinguishing projectilesPublication . Rocha, Hugo Filipe Leça Pereira da; Gamboa, Pedro VieiraWildfires are a devastating source of human and environmental loss, and the available means to combat them in their early stages can be improved. With the aid of Unmanned Aerial Systems and FEB (Fire-extinguishing balls), wildfires’ early stages might be suppressed while keeping human lives safe and firefighters risk-free. Considering the use of a fixed wing Unmanned Aircraft Vehicle to launch the fire-extinguishing projectile, launching the FEB as it is, without any modification, does not seem to be the best available option, with problems ranging from difficulty in predicting its trajectory to the possible bad impact performance, with the possibility of the FEB rolling away from the target as it lands. Therefore, three other configurations for the projectile with FEB as its basis were studied, all of them utilizing fins for the means of stability. These configurations differed in terms of tail design attached to the FEB: one is a tube, the other a tangential cone, and the other a symmetrical NACA airfoil revolved around its axis. Their aerodynamic static coefficients were obtained through CFD (computational fluid dynamics), while the dynamic ones were obtained through analytical expressions. Using an implemented 6-DOF (degrees of freedom) model, 17 trajectories were studied for each of these configurations. Other analyses were carried out, as the consideration of the influence of wind turbulence, consideration of a fourth configuration with double the area of the fins, and asserting the importance of the consideration of the dynamic coefficients while testing different values for some of these coefficients. Regarding the FEB-projectile configurations, CFD results suggest that the tube configuration has a transient behavior in the tested speeds, and that the tangential cone is a very suitable way of streamlining the FEB in these range of speeds, with no considerable difference to the NACA tail configuration. Trajectory results highlight the importance of considering the mean wind speed and direction, the importance of obtaining an appropriate estimate of the wind turbulence, and the importance of the dynamic coefficients for the full aerodynamic characterization of the projectile, concretely for its stability and attitude results. Ultimately, between the tested configurations, the best candidate is the cone tail configuration, for its simplicity in construction and performance in the trajectories.