Experimental and numerical analysis of hovering multicopter performance in low-Reynolds number conditions

Experimental and numerical analysis of multicopter rotor aerodynamics

Despite many research studies focus on strategies to improve autopilot capabilities and bring artificial intelligence onboard Unmanned Aircraft Systems (UAS), there are still few experimental activities related to these vehicle performance under unconventional weather conditions. Air temperature and altitudes directly affect thrust and power coefficients of small scale propeller for UAS applications. Reynolds numbers are usually within the range 10,000 to 100,000 and important aerodynamic effects, such as the laminar separation bubbles, occur with a negative impact on propulsion performance. The development of autonomous UAS platforms to reduce pilot work-load and allow Beyond Visual Line of Sight (BVLOS) operations requires experimental data to validate capabilities of these innovative vehicles. High quality data are needed for a deep understanding of limitations and opportunities of UAS under unconventional flight conditions. The primary objective of this article is to present the characterization of a propeller and a quadrotor capabilities in a pressure-climate-controlled chamber. Mechanical and electrical data are measured with a dedicated test setup over a wide range of temperatures and altitudes. Test results are presented in terms of thrust and power coefficient trends. The experimental data shows low Reynolds numbers are responsible for degraded thrust performance. Moreover, details on brushless motor capabilities are also discussed considering different temperature and pressure conditions. The experimental data collected in the test campaign will be leveraged to improve UAS design, propulsion system modelling as well as to provide guidelines for safe UAS operations in extreme environments.

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Unmanned Aircraft Systems Performance in a Climate-Controlled Laboratory

The increasing demand of UAS has generated interest in the scientific community to understand how the environmental parameters affect performance of these emerging vehicles. A bias in the existing tests has been the non-reproducibility of the same climatic conditions. Therefore, UAS have not been fully exploited by the marker so far. Standard protocols for UAS testing in unconventional weather conditions have not been investigated from both industry and academic research. Temperature and pressure are environmental parameters that affect the aerodynamics of Unmanned Aircraft Systems (UAS). Low Reynolds numbers are common for small scale UAS and have a strongly influence on propeller and vehicle capabilities. In the past years, experimental studies on the effects of low Reynolds numbers have been carried out in wind tunnel facilities in conventional atmospheres (ambient temperature and pressure). Moreover, the complexity of the aerodynamic field results in propeller and full vehicle performance prediction methods with limited accuracy. In this paper an experimental setup inside a climatic and hypobaric laboratory is used to highlight temperature and pressure influence on single propeller and full vehicle performance in static conditions (hover). Test results are discussed and provided to the reader, highlighting the complexities of the measurements when extreme temperature and low pressure are set. The main contribution of this study is a set of experimental data to pave the way for a deep investigation on harsh environmental conditions on UAS propulsion system.

Arrigo Avi

Papers

UAS testing in low pressure and temperature conditions

Unmanned Aircraft Systems Performance in a Climate-Controlled Laboratory