There is increasing talk about employing passenger-carrying multicopters ("taxi drones") to extend urban mobility into the third dimension. These aircraft will have MTOMs in the range of several hundred kgs.

In case this catches on on a larger scale, airspace use will increase considerably compared to the current occasional helicopter and sight-seeing flight.

For safety reasons, presumably a certain minimum vertical separation will be required due to the downwash from the rotors.

Is there any information available about the current thinking on required minimum vertical separation between manned/passenger-carrying multicopters? Also, will there be any difference for this requirement between hovering and cruise flight modes?


1 Answer 1


The downwash is directly related to total lift; more rotors just means each rotor is producing a smaller fraction of the total, and the end result should be no different for separation purposes than for one or two rotors.

There are a lot of obstacles to mass adoption of personal aircraft, but the exact lift mechanism is arguably the smallest.

  • $\begingroup$ Thanks for the comment. I realise the question was maybe not clear enough, and I agree that the exact number of rotors in not relevant. So, the question was: What is the required minimum vertical separation between two multicopters, especially with regard to the downwash from the rotors. $\endgroup$
    – Monolo
    Commented Dec 2, 2018 at 17:15
  • $\begingroup$ ICAO rules require a minimum of 500ft vertical separation between all civil aircraft; helicopter downwash is irrelevant at that distance. This is more due to altimetry margin of error than aerodynamics. Wake turbulence can be a problem at several times that distance, but it shouldn't be an issue between two aircraft of similar size. $\endgroup$
    – StephenS
    Commented Dec 2, 2018 at 18:04

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