Navegando por Autor "Ferreira, Luiz Otávio Furtado"

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    Experimental investigations of stability and aerodynamic interference effects of an x-tail conventional airship
    (2020-06-09) Ferreira, Luiz Otávio Furtado
    Supporting the rising LTA industry, this works focus on investigating the general aerodynamics of a conventional X-tail airship, identifying the most relevant aerodynamic interference effects, besides developing a new method for initial tail design with simple but objective parameters (Tail Volume Coefficient – TVC). A 1:116 scale wind tunnel model of ADB-3-30 airship, under development at Airship do Brasil, was used. Firstly, through a similitude analysis, model and tunnel parameters were adjusted so the aerodynamics could be considered valid for full scale. The test campaigns were divided in two phases; Phase I comprised the steady investigations, obtaining standard aerodynamic polars and trimming curves, besides visualizing and explaining interference effects. During Phase II, oscillation damping tests were conducted in order to evaluate the proposed TVC, assessing the damping of yawing oscillations for different tail arrangements. The flow is strongly three-dimensional, with main interference effects of hull on tail, dominated by longitudinal eddy structures. The behavior at small and large incidences is very different regarding interferences, compromising the X-tail efficiency. The oscillation tests demonstrated a preferential sequence for tail arrangement efficiency, where X-tail figures at the last place; ADB-3-30 was found static and dynamically unstable. Unfortunately, no simple direct law, like TVC, which measures with confidence the degree of stability, was found. Nevertheless, a lower threshold law was determined for directional stability (TVCY-ARb). As a whole, despite all the complexity involved on testing airship models in wind tunnels (geometric scale, flow similitude, manufacturing, positioning, etc.), the objectives were fulfilled, enriching the study field with new aerodynamic and stability information, also showing that properly predicting airship stability is no simple task. The results are useful for academy and industry, and may help detailing and support further researches by presenting new information on a specific configuration.