There were many pre-airplane aircraft.[1] Many people built gliders, and some of them worked. There were attempts at powered flight using steam engines (too heavy), clockwork (not enough energy storage), and rubber bands (well, why not, it works at toy size).
The real insight of the Wright Brothers was to focus on stability and control. Lilienthal got this - he flew about 2,000 glider flights, before dying in a crash before he got to power. Langley (NASA Langley is named after him) was trying for inherently stable aircraft rather than controllable ones. That's quite possible, but add too much stability and you can't maneuver much.
Somebody was going to succeed at this by the early 1900s.
The real insight of the Wright Brothers was to focus on stability and control. Lilienthal got this - he flew about 2,000 glider flights, before dying in a crash before he got to power. Langley (NASA Langley is named after him) was trying for inherently stable aircraft rather than controllable ones. That's quite possible, but add too much stability and you can't maneuver much.
Somebody was going to succeed at this by the early 1900s.
[1] https://en.wikipedia.org/wiki/Early_flying_machines