Helicogyre Invention Lecture, Royal Aeronautical Society - 1929

Pre-print of a lecture before the Royal Aeronautical Society announcing the invention of a helicopter-like aircraft.  Brochure announces the lecture to be delivered March 18, 1929.  28pp, wrps, stapled, 2-hole punched, 6.75x8.75", illus with drawings and photos.  Good; one horz fold, staple light rust.  Interesting design with internal combustion motors and small props at the main rotor blade tips.