UAS testing in low pressure and temperature conditions
01 Sep 2020-pp 1757-1765
TL;DR: In this article, 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).
Abstract: 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.
Citations
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TL;DR: In this paper , experimental data on small-scale multicopter propulsion systems are presented and combined with a Computational Fluid Dynamics (CFD) model to describe the aerodynamics of these vehicles in low Reynolds numbers conditions.
7 citations
02 Aug 2021
5 citations
TL;DR: In this paper, the authors present the characterization of a propeller and a quadrotor capabilities in a pressure-climate-controlled chamber and show that low Reynolds numbers are responsible for degraded thrust performance.
Abstract: 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.
References
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04 Jan 2011
TL;DR: In this article, the propeller speed (RPM) was fixed while changing the wind-tunnel speed to sweep over a range of advance ratios until reaching the windmill state (zero thrust).
Abstract: While much research has been carried out on propellers for full-scale aircraft, not much data exists on propellers applicable to the ever growing number of UAVs. Many of these UAVs use propellers that must operate in the low Reynolds number range of 50,000 to 100,000 based on the propeller chord at the 75% propeller-blade station. Tests were performed at the University of Illinois at Urbana-Champaign (UIUC) to quantify the propeller efficiency at these conditions. In total, 79 propellers were tested and the majority fit in the 9- to 11-in diameter range. During the tests, the propeller speed (RPM) was fixed while changing the wind-tunnel speed to sweep over a range of advance ratios until reaching the windmill state (zero thrust). To examine Reynolds number effects, typically four RPM’s were tested in the range 1,500 to 7,500 RPM depending on the propeller diameter. Propeller efficiencies varied greatly from a peak near 0.65 (for an efficient pr opeller) to near 0.28 (for an exceptionally poor propeller). Thus, these results indicate that proper propeller selection for UAVs can have a dramatic effect on aircraft performance.
302 citations
"UAS testing in low pressure and tem..." refers background in this paper
...Wind tunnel propeller analyses [9] have provided a complete database of performance for propellers installed on small UAS....
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13 Jul 2017
TL;DR: In this paper, a review of unmanned aerial systems technology and their subsystems (frame, propellers, motors and batteries, payloads, and data processing) is presented, related to remote sensing, spraying of liquids, and logistics.
Abstract: The present work is a review of unmanned aerial systems technology and their subsystems (frame, propellers, motors and batteries, payloads, and data processing). Different applications are evaluated, related to remote sensing, spraying of liquids, and logistics. An overview of the regulatory framework is also developed.
126 citations
"UAS testing in low pressure and tem..." refers background in this paper
...A wide range of applications [1] are possible including precision farming, surveillance and monitoring as well as delivery....
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05 Jun 2017
TL;DR: An experimental investigation was performed to study the effects of rotor-to-rotor interactions on the aerodynamic and aeroacoustic performances of small UAVs and it was found that, while the thrust coefficients of rotor were independent of the separation distance, the thrust fluctuations were found to increase dramatically as the separationdistance decreased.
Abstract: In the present study, an experimental investigation was performed to study the effects of rotor-to-rotor interactions on the aerodynamic and aeroacoustic performances of small UAVs. It was found that, while the thrust coefficients of rotor were independent of the separation distance, the thrust fluctuations were found to increase dramatically as the separation distance decreased. An enhancement of ~ 250% was confirmed for the twin-rotor case (i.e., L= 0.05D) in comparison with that of the single rotor case, which is believed to be caused by the complex flow interactions within rotors as revealed by the detailed PIV and Stereoscopic PIV measurements. Reducing the separation distance not only intensified the force fluctuations, but also increased the aeroacoustic noise level of the baseline case. Comparing to the L = 1.0D case, a maximum enhancement of ~3 dB in aeroacoustic noise was recorded for the L = 0.05D case, which is caused by the severely thrust fluctuations and turbulent flow interactions within rotors.
84 citations
"UAS testing in low pressure and tem..." refers background in this paper
...Isolated rotor tests provide insight on propeller low Reynolds aerodynamics; however, full vehicle measurements are important as they account for the interaction between rotor wakes and vehicle airframe as suggested by [10], [11] and [12]....
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07 Jun 2016
TL;DR: In this paper, the influence of pusher or puller configuration of the propeller, number of blades, shape and dimensions of the arm, coaxial and overlapping propellers is presented.
Abstract: Multi-rotor Unmanned Aerial Vehicles make use of multiple propellers, mounted on arms, to produce the required lift. This article investigates the influence on propulsion system efficiency in hover due to the configuration of these propellers. Influence of pusher or puller configuration of the propeller, number of blades, shape and dimensions of the arm, coaxial and overlapping propellers, is presented. A dedicated test bench that allows testing of various experimental setups is designed and built in order to realistically represent multi-rotor arms. Test results show that a two-bladed pusher configuration is most efficient and slenderness of the arm has more influence on efficiency than shape. A coaxial propulsion system approaches the efficiency of a single-prop system at high disk loadings. Finally, interference effects due to overlapping propellers are discussed.
70 citations
TL;DR: In this article, hover acoustic measurements are taken on isolated rotor-airframe configurations representative of small-scale, rotary-wing unmanned aircraft systems (UAS), with a simplified airframe geometry intended to represent a generic multicopter arm.
Abstract: In this study, hover acoustic measurements are taken on isolated rotor-airframe configurations representative of smallscale, rotary-wing unmanned aircraft systems (UAS). Each rotor-airframe configuration consists of two fixed-pitch blades powered by a brushless motor, with a simplified airframe geometry intended to represent a generic multicopter arm. In addition to acoustic measurements, CFD-based aeroacoustic predictions are implemented on a subset of the experimentally tested rotor-airframe configurations in an effort to better understand the noise content of the rotor-airframe systems. Favorable agreements are obtained between acoustic measurements and predictions, based on both time- and frequency-domain post-processing techniques. Results indicate that close proximity of airframe surfaces result in the generation of considerable tonal acoustic content in the form of harmonics of the rotor blade passage frequency (BPF). Analysis of the acoustic prediction data shows that the presence of the airframe surfaces can generate noise levels either comparable to or greater than the rotor blade surfaces under certain rotor tip clearance conditions. Analysis of the on-surface Ffowcs Williams and Hawkings (FW-H) source terms provide insight as to the predicted physical noise-generating mechanisms on the rotor and airframe surfaces.
35 citations