title_body: Why did a quadcopter in vertical descent appear to lose thrust and descend rapidly? Towards the end of a flight with a quadcopter, I started a vertical descent to come in and land. There was no wind on that particular day so I just came straight down.
  
  Shortly after starting to descend, the quadcopter started falling faster. I increased the throttle to compensate, but it only seemed to fall faster.
  
  After a rather unceremonious landing, I checked the quad over and found it still had power enough to take off and hover, so I don't think it outright lost power. It came down level with the motors going.
  
  What would have caused the rapid loss of vertical thrust?
upvoted_answer: It sounds like you've encountered what's called "vortex ring state", when a rotorcraft descends into its own wake -- essentially, a self-created downdraft.
  
  There are two ways to escape from such a situation:
  
  
  Power out of it.  Climbing out of the craft's wake vortex requires about twice as much power as hovering, so while most full-sized helicopters can't do this, most quadcopters and other small-scale craft can.
  Move forwards (or backward, or sideways) out of the craft's wake.  This is the standard procedure for helicopters.
  
  
  You can also avoid it entirely by not descending too fast, or by not descending straight down.