Bigourdan - Helicopter Flying Machines, British Patent 14926 of 1911
A British patent specification of 1912 covering Edouard Jean Bigourdan's helicopter flying machine, filed in London in 1911 for examiners and engineers. The single sheet holds pen-and-ink figures on aged paper: a circular plan of a rotor with radial blades and arrows for direction, sectional elevations of the hub and shaft, thin edge profiles, letter keys, and inked file numbers and office stamps.
