Glider: an unpowered airplane, sometimes called a sailplane. Otto Lilienthal was gliding down slopes in wood and cloth contraptions long before the Wright Brothers built the Flyer. Later gliders were good enough to gain altitude in even mild updrafts, and long-distance flights became possible, if challenging. A surprising development was the discovery that towing a glider behind a powered plane is remarkably efficient, and gliders full of troopers were towed across the channel and released to glide into France during WWII.
Tech Level: Pre-industrial. Suitable for everything from Clockpunk to Post-Apocalyptic.
Appeared In: My debut SF novel, Avians, is all about gliders and the girls that fly them, but it won’t be out until 2017. So how about Hal Clement’s Cycle of Fire? Aliens with gliders, and an imperative need for aviation.
For Your Plot: Your time-traveller can hook up with Leonardo and help him work the kinks out. No gasoline in your dystopia? Gliders are the way to go. Perils abound, many of them conveniently non-fatal.
Ground-Effect Vehicle: an aircraft designed for flight very close to the surface. (You’ll want to make that a relatively level surface, such as water or prairie.) Any airplane with wings experiences ground-effect when it flies lower than its own wingspan; efficiency increases as a bubble of air builds up between the wing and the ground. Tales abound of crippled WWII bombers limping home by skimming the waves. The Russians set out to deliberately exploit this quirk during the Cold War. They designed some planes with wings that were optimized for cupping air beneath the aircraft, and flying so low they were literally below the radar. Today, there are sport-craft versions like the Skimmer.
Tech Level: Usually Dieselpunk, because engines. However, the efficiency of ground-effect makes Steampunk a distinct possibility.
Appeared In: No clue. Maybe you can be the first.
For Your Plot: Bonus points if you tow your GEV behind a steamboat, like tubing, but in the air. Cut loose to skim over the waves and flip the bird at our alien jellyfish overlords.