High noise levels during flight have long been a barrier to the advancement of urban air mobility (UAM) vehicles, or “air taxis.” Thanks to new research being conducted at Embry-Riddle Aeronautical University and backed by a recently awarded $1.4 million NASA grant, however, low-noise multirotor aircraft are becoming a reality — one that could precipitate a boom of autonomous flight options available.

“By some estimates, UAM operations may become a reality in some urban areas by 2024-2025, first piloted then gradually shifting to autonomous operations controlled from the ground,” said Dr. Vladimir Golubev, Embry-Riddle professor of Aerospace Engineering and a principal investigator on the project.

Working in collaboration with Boston University, Virginia Tech, Tuskegee University and Joby Aviation, Golubev’s team will focus specifically on how air taxis can take off and land quietly at vertiports located in dense urban environments where wind gusts tend to be unpredictable. These turbulent flight conditions present unique aerodynamic and aeroacoustic challenges.

“Those need to be controlled through development of accurate response-prediction tools and optimization strategies,” Golubev added.

Over the three-year span of the project, the team will also provide guidance on suitable locations for city-based rooftop vertiports and flight corridors that would minimize noise during takeoff and landings.

“Noise is a critical aspect for public acceptance,” Golubev said of electric-powered UAM vehicles, noting that major strides have already been made to mitigate their sound and pressure levels.

Last year, for example, NASA and Joby Aviation released preliminary findings from a simulation to capture noise profile data from a full-size UAM prototype. A remotely piloted aircraft loaded to near-maximum weight capacity (the equivalent of a pilot plus four passengers) was flown during a two-week test period at Joby’s Electric Flight Base in California. The aircraft registered decibel levels almost 1,000 times (30dB) quieter than that of a typical helicopter.

Embry-Riddle’s research, conducted as part of NASA’s University Leadership Initiative, will address the sustainability of such noise reduction in highly unsteady flow conditions. Work will be led by Golubev, along with co-principal investigators Dr. Tasos Lyrintzis, distinguished professor and chair of the Aerospace Engineering Department, and Dr. Reda Mankbadi, distinguished professor. Four Ph.D. candidates and several undergraduate students will also be involved.

By focusing on the sound levels associated with UAM’s vertical lift capabilities, the team hopes to reduce the environmental impact of these vehicles, helping to ease their entry into new markets.

“Addressing this aerodynamically generated noise is a new technology challenge, and the demand for trained engineers is high,” said Mankbadi. “Because of this market demand, one of our tasks is to involve undergraduate students to train them on the design and development of small multi-rotor vehicles and to prepare them for this emerging market.”

Graduate students will also play a part by focusing on creating computational simulations of noise aerodynamics and controlling multi-rotor vehicles in urban environments.

Additionally, an outreach program will be developed as part of the project to raise awareness and educate the community on how this emerging technology will be incorporated safely into our skies.

“Several students have already been working in this research area to produce preliminary results and pave the way to this award,” Golubev said, citing a handful of students who have planted a flag in this topic as an area of ongoing research.

Work on the project will begin later this year, in September.