With the development of unmanned aircraft systems (UASs), interest in the design of propellers is growing. UASs are being used in the military for a variety of applications to include intelligence, surveillance, and reconnaissance (ISR) as well as resupply. Larger scale Urban Air Mobility (UAM) and eVTOL (electric vertical take-off and landing) vehicles are also receiving attention. Many of these systems use electric motors with a fixed pitch propeller. More efficient, quiet propellers are needed if these systems are to operate near populated areas. Selection of an appropriate airfoil is critical to satisfy these requirements.
This study proposes seven guidelines to evaluate airfoils: 1) sufficient thickness, 2) high lift coefficient, 3) high maximum lift to drag ratio, 4) broad peak at the maximum lift-to-drag ratio, 5) linear lift curve slope over propeller’s airfoil operating angle-of-attack (AOA) range, 6) low drag over the operating AOA range, and 7) selecting the appropriate Reynolds number for airfoil design aerodynamic data.
The Clark Y, GM15, GOE 225, GOE 358 and S1223 airfoils were analyzed using the selection guidelines. Propellers were designed for each airfoil using Blade Element Momentum Theory and tested in a low-speed wind tunnel. The aerodynamic performance of each propeller is reported as well as the noise generated in the near field. The GM15 required the lowest mechanical power to meet the on-design conditions of T = 2.5 lbf at a freestream velocity of 44 ft/s. This propeller also had the lowest measured peak Sound Pressure Level. While no airfoil satisfies all the selection guidelines perfectly, having an awareness of these guidelines will help with the selection of a suitable propeller airfoil for the mission and design point.