Narrow Results

The aerodynamic characteristics of a propeller near the rigid ground and static water surface have been investigated numerically and experimentally. The aerodynamic performance of the propeller in various elevations from the ground and the static water surface and tilt angle settings at constant propeller rotational speed have been evaluated. The results indicated that ground and water surface can strongly affect the aerodynamic performance of rotating propellers in close distances up to 1.24 times its diameter. A decrease in the distance between the propeller rotation plane and the surface leads to a remarkable increase of the propeller efficiency up to 15%. Similarly, it has been found that the tilt angle has also noticeable effect on the near-surface aerodynamic characteristics of the propeller. At a tilt angle above 25^∘ almost at any distance from the surface, near-surface effects tend to vanish and propeller thrust reaches its value of free flight condition. Drawing a comparison between near-ground thrust values of the propeller and the thrust values over the surface of water at any predetermined distance from surfaces and tilt angle indicated that the rigid ground has notably higher thrust efficiency than the flexible water surface. At a height of 0.3D (D is propeller diameter) from the ground surface, thrust increased by about 15% while the growth of thrust efficiency near the water surface was about 8%. CFD and Experimental results confirm each other.

This study investigates the possibility analysis of UAV propeller made by commercial 3D printing machine. The primary experimental facility is 3D printer based on Fused Deposition Modeling method (FDM). The main methodology of this work is to construct standard test piece according to ASTM standard and use for standard test. The Polylactic Acid (PLA) and carbon fiber composite material are the main two printing materials in this work. Experimental results reveal that the strength and bending of these two materials are enough to be the propeller of middle size UAV, especially the carbon fiber composite material. This study not only confirms the application possibility of UAV propeller made by 3D printing, but also carries out the real flight test to identify performance enhancement and future application.

This paper investigates the tone noise generation by submarine propellers operating in nonuniform flows. A frequency domain numerical approach is proposed. The flow nonuniformities due to submarine wakes are obtained from Computational Fluid Dynamics method. The results show that the velocity field and its harmonics depend greatly on the hull geometry and its appendages. The prediction of the radiated far-field tone noise due to a seven-bladed, highly-skewed propeller has been performed. A prediction of the acoustic pressure level for various blade skew angles shows that the tone noise reduction amount increases as the inflow velocity increases. The predicted dependence of the radiated noise on the inflow velocity, propeller diameter and blade rotational speed shows that the mean square sound pressure at the first-order blade passing frequency varies as the 3.3 power of the characteristic inflow velocity, the third power of the propeller diameter and with the second power of the blade rotational speed. Effects of blade number on the propeller tone noise directivity are also discussed, which shows that the characteristic coupling order between the main inflow harmonic and the rotating blades is the key to determine the directivity pattern.

Although there exist a number of accurate unmanned aerial vehicle (UAV) thruster models, these models require the precise measurements of several motor and propeller characteristics. This paper presents a simple motor and propeller model that relies solely upon data provided by manufacturers. The model is validated by comparing theoretical motor and propeller behavior to experimental results obtained from thrust tests in a wind tunnel. The objective is to provide an accurate yet simple model to facilitate the selection of appropriate brushless DC motor and propeller combinations for flight applications.

This paper investigates the interference that arises from overlapping Unmanned Aerial Vehicle (UAV) propellers during hovering flight. The tests have been conducted on $28^{\prime \prime }\times 8.4^{\prime \prime }$ ultralight carbon fiber propellers using a bespoke mount and the RCBenchmark Series 1780 dynamometer at various degrees of overlap $(d∕D)$ and vertical separation $(z∕D)$. A great deal of confusion regarding the losses that are associated with mounting propellers in a co-axial configuration is reported in the literature, with a summary of historical tandem helicopters having been conducted. The results highlight a region of beneficial overlap (0–20%), which has the potential to be advantageous to a wide range of UAVs.