The US Federal Aviation Administration (FAA) measured air flows created by the propellers of aircraft weighing up to 3 tons. This category includes promising electric aircraft with vertical takeoff and landing. The names of the models tested were not disclosed, but test results showed that they are just as dangerous to people on the ground as helicopters. This discovery will require a review of the security requirements for vertiports and air taxi sites.
Image Source: US Air Force
One reason for the limited use of helicopters as air taxis in cities is the strong air flow generated by their blades. Helicopter operation is permitted only in specially equipped and fenced areas to eliminate the risk to bystanders. Flying cars and air taxis, on the contrary, are positioned as means of individual air transport, implying the ability to take off and land on unprepared sites. However, FAA research has shown that electric aircraft create significantly more powerful and dangerous air flows during takeoff and landing than previously thought.
When a helicopter takes off, its blades create a combined downward and sideward flow of air, referred to as DWOW (DownWash and OutWash). We know that this current can knock over an adult or throw heavy objects off the site. Therefore, there are strict requirements for the equipment of helipads and rules for their operation.
The FAA measured the DWOW flows generated by the three electric aircraft using standard procedures and sensors. It turned out that the force of the flows from the propellers of these devices, regardless of the diameter of the blades and their number, reaches 12 points on the Beaufort scale. This is equivalent to hurricane-force winds of about 160 km/h, which is comparable to the air currents generated by helicopters. For humans, wind speeds of 55.5 km/h are considered dangerous, that is, three times less.
It is obvious that vertiports and the operation of flying machines will require the development of a new set of norms and rules governing the safety of their use. Abandoning flying taxis is not being considered, but their operation in arbitrary locations will become impossible.