“Propellers are louder over ground.” This study seems to state the obvious, but I am sure I didn’t read the article closely enough to understand what was novel. That said, it also seems to be speaking to its relevance in a near future urban environment with more VTOL air taxis and ubiquitous drones. But I am going to imagine it bears directly on present-day Washington, D.C. which seems to be increasingly (over the past twenty years of living here in three of the four quadrants) plagued by helicopters, seemingly flying lower too. So much so that our non-voting Congresswoman has made repeat protest actions that in yet another way, mark the failure of the Congress to be a steward of the city. (There’s no change that bill will be acted on.)