Abstract
Increased interest in eVTOL (electronic vertical take-off and landing) vehicles is growing. These vehicles will become urban air taxis and delivery vehicles, reducing the time involved for moving people and goods in the cities. There is also growth in the small Unmanned Aircraft System (sUAS). The propulsion system for both vehicles use an electric motor with propellers. These vehicles need propellers which are more efficient and have reduced noise generation if they are to coexist in either an urban environment or be used on ISR missions.
Previous studies show that a propeller designed for minimum induced drag using a 50% “hub” break with a “tip” break of 90% leading to zero tip thrust loading results in a propeller that is both quieter and more aerodynamically efficient. This design incorporates a constant angle of attack (AOA) from the hub to an r/R of 50% where the section propeller thrust loading then dropped to an AOA with zero lift at an r/R of 90%. AOA sensitivity of both the hub and the tip are studied. Using a hub AOA lower than the value for Cl/Cd max can result in an mechanical power reduction of 6.4% compared to a commercial propeller. A slightly less negative tip AOA than zero lift will also lead to the lowest mechanical power required. However, if a lower sound pressure level is desired, then, for the lower hub angles of attack, a tip angle of attack slightly more negative than zero lift should be used, resulting in up to a 7.8% reduction in SPL. As seen in the data, there exists a tradeoff with between lower aerodynamic power and lower SPL using various combinations of hub and tip angles of attack.
