Flying machines are awesome, even when shrunk down to the RC level. One video, however, not only shows some beautiful light-painting with an RC helicopter, but actually teaches you something about the physics of helicopter flight.
This video comes from Smarter Every Day, a YouTube channel dedicated making you, of course, a little smarter each day. In this video Destin, who runs the project, shows us his RC helicopter being flown at night.
First, we see it in the video mode, which is already quite pretty, then we see some long-exposure still photos. If you look closely, you’ll see the arc of the rotor blades get bigger as it moves across the photo.
The explanation is simple. There’s a difference between the advancing rotor blades and the retreating rotor blade, which the designers take into account. This also means that helicopters can only go so far before entering into a “retreating blade stall.” A stall like this is self-correcting, fortunately. (A stall on a fixed-wing aircraft, where it doesn’t get enough airflow over its wings, is dangerous and pilots are trained how to avoid and recover from them.)