The UK Civil Aviation Authority (CAA) has published initial findings from a study about the effects on eVTOL aircraft operations of downwash, which is the column of downward-accelerated air generated by rotors or other propulsors. The agency noted that it intends for its CAP2576 report to prompt discussions with aircraft manufacturers and operators and that the study does not necessarily constitute the basis for any future legislation.
The CAA said the report seeks to extend knowledge of downwash beyond that derived from long-standing helicopter operations. It acknowledged that the new work is based on a limited number of “dynamic cases and vehicle orientations” and said that initial conclusions highlight the need for a more focused analysis of downwash issues. The report, published earlier this month, was produced jointly with Richard Brown, a consultant engineer with Sophrodyne Aerospace.
According to the CAA, its main conclusions based on computational techniques are limited in several ways, such as the treatment of viscosity, the use of supposedly "perfect" digital ground surfaces, and the lack of wind data. On this basis, it called for real-world verification and validation testing.
The agency is inviting eVTOL aircraft manufacturers and operators, as well as other regulators, to join it in further studies. These, it said, should also consider outwash of air from propulsors that could have safety impacts on ground operations personnel and passengers.