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.
