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Aerodynamic design and testing of a ram air turbine for small fixed-wing uavs

Abstract:

Ram Air Turbines (RAT) have been widely studied as auxiliary power units for civil aircraft. However, their use at low Reynolds and low Mach numbers, at which small Unmanned Aerial Vehicles (UAVs) usually operate, have not been deeply examined. The versatility of airframe configurations and electrical propulsion systems of UAVs present potential synergies that can be exploited by the implementation of RATs as a secondary power source for increasing the energy supply on emergency situations. The present work aims to design a RAT for small fixed-wing UAV, which is expected to power the telemetry system in such events. For this purpose, both parametric and quasi two-dimensional approaches are utilized in the design process of the RAT. Then, CFD simulation is performed to corroborate the parametric results. Finally, a wind tunnel testing is carried out to validate the models pbkp_redictions. From the aforesaid assessment techniques, the turbine power coefficient obtained in the wind tunnel testing is used as main reference to measure the feasibility of implementing the RAT technology as a secondary power source. Hence, this parameter was used within an in-house parametric script to evaluate the aircraft performance and the viability of its implementation. From the experimental results, it is observed that the designed RAT provides approximately 5 [w], which can be potentially used to power the telemetry system. Nevertheless, this latter analysis comes from the adaptation of brushless motors as generators, which induces high losses and detriment of the power generated. From the performance analysis, it is noticed that neglecting the additional drag caused by the RAT implementation, the UAV weight increases by 3.5%, which slightly reduces endurance at lower cruise speeds, whilst at higher speeds the RAT power generation overcomes the weight-increment performance-deficit, providing an improvement in endurance.