The Influence of Airfoil Shape, Tip Geometry, Reynolds Number and Chord Length on Small Propeller Performance and Noise

摘要

An extensive experimental investigation to determine the overall efficiency and near field noise signature of propellers utilized by small hand launched UASs has been conducted. This investigation has included wind tunnel performance comparisons of both off-the-shelf and custom designed propellers at realistic thrust and freestream velocities. A propeller design program has been developed that gives a user the ability to quickly design a propeller, predict its performance, and then create a 3D model in SolidWorks for fabrication using an SLA printer. This computer code was used to design propellers for a parametric study of airfoil cross-section, chord length and tip geometry which led to an optimized design configuration that greatly out performs available off-the-shelf propellers. The results of this design approach are high pitch propellers with low aspect ratios. The increased chord lengths create large surface areas that lower the rotational speed required to achieve the desired thrust for a given freestream velocity flight condition. These low aspect ratio propeller designs place emphasis on tip geometry to increase aerodynamic efficiency and reduce noise generating vortex strength. The result is a 5 bladed oval tipped propeller configuration that is 12 dB quieter than the stock commercial propeller and 6% percent more aerodynamically efficient. This represents an elimination of 70% of the baseline propeller near-field noise signature with the potential of increasing the aircraft endurance by 6%.