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Estudo experimental de um sistema de propulsão coaxial de UAVs
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Neste trabalho analisou-se experimentalmente o desempenho de dois tipos diferentes de hélices usadas em UAVs (Unmanned Aerial Vehicles) e o impacto no desempenho propulsivo das hélices quando colocadas no interior de uma conduta de entrada suave (tipo bellmouth) com 17,1” de diâmetro, utilizando um banco de ensaios desenvolvido no âmbito do projeto ILAN-VR. Foram realizados ensaios com hélices de 16’’ e 17’’ em configurações simples e coaxiais, em que se avaliou o impulso, potência elétrica, rotação e eficiência propulsiva. Comparando os resultados obtidos com e sem conduta verificou-se que esta só tem vantagens para velocidades de rotação elevadas e quando a distância entre a parede da conduta e a ponta das hélices é reduzida. Com a hélice de 17’’ em configuração simples, beneficiando da reduzida folga entre a ponta e a parede da conduta, registou-se um aumento da força de impulso de 18% para a velocidade máxima testada. Com a hélice de 17” em baixas velocidades de rotação e para as
hélices de 16’’ o uso da tubeira não melhora o impulso, apenas melhora ligeiramente a eficiência propulsiva. No estudo experimental realizado com as hélices coaxiais procurou-se identificar a relação ótima de velocidades de rotação entre a primeira e a segunda hélice. Os ensaios revelaram que o conjunto das duas hélices opera com maior eficiência quando a segunda hélice possui velocidade de rotação inferior à primeira em cerca de 20%. Esta conclusão deverá ser utilizada para controlo diferenciado da velocidade de rotação das hélices, dado que o aumento da eficiência propulsiva permitirá aumentar a autonomia de voo dos UAVs. Este estudo permitiu aprofundar o conhecimento do comportamento de hélices em ambiente confinado e validar metodologias experimentais, recomendando-se como trabalho futuro a melhoria da geometria da entrada da conduta, usando outros perfis alares, a redução da folga entre a ponta da hélice e a parede com aumento da rigidez da conduta de modo a evitar o contacto com as hélices.
This work experimentally analyzed the performance of two different types of propellers used in UAVs (Unmanned Aerial Vehicles) and the impact on propulsive performance when operating inside a smooth-inlet duct (bellmouth type) with a 17.1’’ diameter, using a test bench developed within the ILAN-VR project. Tests were carried out with 16’’ and 17’’ propellers in single and coaxial configurations, evaluating thrust, electrical power, rotational speed and propulsive efficiency. Comparing the results obtained with and without the duct showed that performance gains only occur at high rotational speeds and when the distance between the duct wall and the blade tip is small. With the 17’’ propeller in single configuration, benefiting from the reduced tip clearance, a thrust increase of 18% was recorded at the maximum tested speed. At low rotational speeds, and for the 16’’ propellers, the duct did not improve thrust, providing only a slight increase in propulsive efficiency. In the coaxial study, the objective was to identify the optimal rotational speed ratio between the upper and lower propellers. The tests revealed that the system operates more efficiently when the lower propeller rotates approximately 20% slower than the upper one. This finding should support differentiated rotor-speed control, as improved propulsive efficiency can extend UAV flight endurance. This study enhanced the understanding of propeller behavior in confined environments and validated experimental methodologies, recommending as future work the optimization of the duct inlet geometry using alternative airfoil profiles, reduction of tip clearance, and increased duct stiffness to prevent blade contact.
This work experimentally analyzed the performance of two different types of propellers used in UAVs (Unmanned Aerial Vehicles) and the impact on propulsive performance when operating inside a smooth-inlet duct (bellmouth type) with a 17.1’’ diameter, using a test bench developed within the ILAN-VR project. Tests were carried out with 16’’ and 17’’ propellers in single and coaxial configurations, evaluating thrust, electrical power, rotational speed and propulsive efficiency. Comparing the results obtained with and without the duct showed that performance gains only occur at high rotational speeds and when the distance between the duct wall and the blade tip is small. With the 17’’ propeller in single configuration, benefiting from the reduced tip clearance, a thrust increase of 18% was recorded at the maximum tested speed. At low rotational speeds, and for the 16’’ propellers, the duct did not improve thrust, providing only a slight increase in propulsive efficiency. In the coaxial study, the objective was to identify the optimal rotational speed ratio between the upper and lower propellers. The tests revealed that the system operates more efficiently when the lower propeller rotates approximately 20% slower than the upper one. This finding should support differentiated rotor-speed control, as improved propulsive efficiency can extend UAV flight endurance. This study enhanced the understanding of propeller behavior in confined environments and validated experimental methodologies, recommending as future work the optimization of the duct inlet geometry using alternative airfoil profiles, reduction of tip clearance, and increased duct stiffness to prevent blade contact.
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Palavras-chave
Hélices Coaxial Conduta Impulso Eficiência Ensaios experimentais Drones Propeller Duct Thrust Efficiency Experimental tests