The US Federal Aviation Administration (FAA) has published a new research paper “Electric Vertical Takeoff and Landing (eVTOL) Downwash and Outwash Surveys”
“As part of the Federal Aviation Administration’s (FAA) effort to establish vertiport design guidance for facilities intended to accept powered lift and special class rotorcraft, it is of growing importance to determine the risk factors related to vertical takeoff and landing (VTOL) operations and how to mitigate them,” says the FAA. “The airflow generated from the aircraft’s rotors/propellers during takeoff and landing, known as downwash and outwash (DWOW), can pose significant risks to people and property in the vicinity of aircraft operations. Downwash is the vertical, downward flow of air produced by rotors/propellers while outwash is the lateral, radial, outward airflow that occurs as the downwash contacts the landing surface. The negative impacts of DWOW may be exacerbated at vertiport locations in urban areas where high-volume, high-tempo operations are proposed because of the dense populations and higher throughput in those areas. However, current research on the effects and mitigation of DWOW is limited. This report describes the collection and analysis of VTOL DWOW data and the need to mitigate associated risks.
“The most reliable way to obtain eVTOL DWOW data is from full-scale aircraft surveys. This research measured the DWOW of three prototype eVTOL aircraft for their maximum velocity at various locations on a vertiport. A ground-level array and a vertical array of ultrasonic three-dimensional anemometers were used for collecting the DWOW wind velocities. The DWOW surveys were performed at various times and locations and conducted under daylight visual meteorological conditions. DWOW wind data were collected at each anemometer location on the ground or vertical sensor array. The aircraft pilots performed several preset maneuvers within the bounds of their respective aircraft flight envelopes. Analysis of the results included maximum instantaneous velocities, moving means and moving standard deviations based on a 3-second time frame, and a 3-second moving 95th percentile. The survey measurements for the three prototype eVTOL aircraft included in the research were compared to viscous vortex particle method modeling and simulation where possible.”
According to the report’s executive summary:
“The maximum velocities measured during the surveys taken varied from survey to survey and from aircraft to aircraft. The highest instantaneous maximum measured was almost 100 mph at 41 ft from the TLOF (touch down and lift off) center. The highest moving 3-second 95th percentile was 84 mph at 23 ft from the TLOF center. Speeds of more than 60 mph were measured at 100 ft from the TLOF center. The eVTOL aircraft surveyed produced high-velocity DWOW flow fields that could easily go beyond the safety area of a vertiport. The high-velocity DWOW of eVTOL aircraft should be considered when designing a vertiport because it can create safety risks to people, aircraft, x equipment, and infrastructure, on and off the vertiport. eVTOL OEMs propose high-volume, high-tempo eVTOL operations in urban areas, which have an even greater potential of impacting bystanders with DWOW than traditional helicopters at heliports. In these target areas, the vertiports will likely be surrounded by dense populations in confined spaces and will experience higher throughput. Accordingly, it is recommended to mitigate DWOW by creating a downwash caution area (DCA). The DCA should be operational when and wherever DWOW velocities exceed 34.5 mph.”
For more information
https://www.airporttech.tc.faa.gov/Products/Airport-Pavement-Papers-Publications/Airport-Pavement-Detail/electric-vertical-takeoff-and-landing-evtol-downwash-and-outwash-surveys
(Image: FAA)