Recently, I've seen some instances where pilots have reported that their UAVs have fallen from the sky for no apparent reason. And that got me thinking... I was wondering if some of these instances are really the result of VRS (Vortex Ring State). This is a phenomenon that the more experienced UAV pilot will be familiar with, but I wonder if some of the newer pilots on this forum are aware of it. I'm not going to explain it...I'll leave that to a video from Simon Newton for explanation and how to avoid it. The following video makes heavy reference to quadcopters but the principle is the same for a Hex or any rotor aircraft.