| Abstract [eng] |
This final degree project presents a preliminary static and dynamic stability analysis of a small fixed-wing unmanned aerial vehicle. The analysed UAV is limited by the main project requirements: maximum take-off mass of 5 kg, maximum wingspan of 2 m and stall velocity of 10 m/s. The aim of the work is to evaluate the influence of centre of gravity position on longitudinal and lateral-directional stability and to define the allowable CG envelope for the benchmark UAV configuration. The research includes a review of mass and balance principles, static stability, dynamic stability modes and numerical tools suitable for light UAV stability analysis. The benchmark aircraft geometry was defined using preliminary aircraft sizing relations and tail volume coefficient methodology. The final configuration includes a rectangular main wing, horizontal tail plane and vertical tail plane. FLOW5 was selected as the main numerical tool for aerodynamic and stability analysis. A component-based mass and balance model was prepared. The initial centre of gravity position was obtained at 25.1% MAC. Based on the pitching moment curve, the neutral point was calculated as 50.8% MAC and the initial static margin was 25.7% MAC. Using the selected static margin range of 20–25% MAC, the allowable CG envelope was defined as 25.8–30.8% MAC. Three CG positions were analysed: 25.8%, 28.3% and 30.8% MAC. The results showed that the benchmark UAV is longitudinally statically stable for all investigated CG positions. Dynamic stability analysis showed that the short-period, phugoid, roll subsidence and Dutch roll modes are dynamically stable. The short-period mode recovered in less than 2 seconds, roll subsidence recovered in less than 0.2 seconds and Dutch roll recovered in less than 3 seconds. The phugoid mode was stable but lightly damped, with recovery time to 10% amplitude between 92 and 165 seconds. A limited high-fidelity CFD validation was also performed in Ansys Fluent for the forward CG position of 25.8% MAC. The CFD results confirmed the same longitudinal static stability trend as FLOW5, since the pitching moment coefficient decreased with increasing lift coefficient. Therefore, the benchmark UAV can be considered longitudinally statically stable within the investigated CG range. |
