Quadcopter or Quadrotor: More formally called the quad-rotor helicopter, this kind of machine is best known in the form of those little camera-toting drones. Full-size quadcopters with human pilots on board can trace their roots back to around 1907. Regular single rotor helicopters have two basic problems: they want to spin around, and they want to tip over when they go forwards. The first comes from torque, and can be corrected with a tail rotor. The second comes from the advancing blade producing more lift than the retreating blade, and fancy moving parts offset this by varying the angle of the blade as it swings. Both problems go away if you use four rotors and rotate two of them in the opposite direction. I’d call it an elegant solution, but the machines usually look pretty ungainly. The Achilles’ heel of this design is the need to keep all four rotors precisely powered; a loss of lift in one corner would be disastrous.
Tech Level: Once again, the need for lightweight engines puts us at twentieth-century levels. Dieselpunk it is, with one magnificent exception: the Atlas Human-Powered Helicopter that took the AHS Sikorsky Prize was a quadcopter. It had four featherweight rotors the size of glider wings that turned very slowly. My favourite factoid about it? After the incredibly athletic pilot secured the prize with a flight of just over one minute, even his nerdiest teammates were able to get it airborne for a few seconds each.
Appeared In: Drawing a blank here. I thought I might find a quadcopter in my anime collection, because some of those artists like crazy aircraft as much as I do, but no such luck.
For Your Plot: One of those pizza-sized drones equipped with a tiny seat would be the perfect vehicle for Stuart Little. As for human-sized quadrotors, the machine has essentially the same strengths and weaknesses as a normal helicopter, so apart from a geek-chic vibe, I don’t know what it brings to your story.