Novel Unmanned Aircraft System Propeller Design—Part 1: Using an Unloaded Tip to Reduce Power Requirements and Lower Generated Sound Levels for Propellers Designed for Minimum Induced Drag

Abstract

Today, over 500 eVTOL vehicles are being developed for everything from Urban Air Mobility to package delivery. In addition, unmanned aircraft systems (UASs) are used in a variety of applications to include intelligence, surveillance, and reconnaissance (ISR) as well as resupply for the military. Most of these vehicles utilize electric propulsion systems with propellers. Efficient propellers with reduced noise generation are necessary for these vehicles to coexist in urban environments or be used for ISR missions. Traditional propeller design uses blade element momentum theory (BEMT) to minimize induced losses. The current investigation describes a novel propeller design approach that minimizes induced drag by reducing the thrust loading near tip. This reduces the tip vortex strength lowering the sound pressure level (SPL) and power required. A parametric study of 18 propellers examined performance using traditional BEMT design near the hub and progressing to zero thrust loading at the tip. A microphone on a traverse mounted behind the propeller was used to measure the peak SPL and its location in a wind tunnel. The best performing unloaded tip propeller showed 5.2% reduction in power required and 12 dB SPL reduction compared to a commercial propeller at the same test conditions.