Flettner Rotors - Why Intermeshing Rotor Systems Actually Have Their Purpose - YouTube
Flettner Fl 282 - Wikipedia
Amazon.com: Flettner Fl 282 Kolibri German Military Helicopter Air Force helicopter twin rotor reconnaissance Border Kunder - Coffee Cup Mug : Home & Kitchen
Video: Die Umwandlung einer Sikorsky CH-53 in einen Flettner-Hubschrauber - ROTOR Magazin
Ship Flettner rotor - Norsepower Oy Ltd.
Basic Helicopter Aerodynamics: An Account of First Principles in the Fluid Mechanics and Flight Dynamics of the Single Rotor Helicopter (AIAA Education Series): Seddon, J., Newman, Simon: 9781563475108: Amazon.com: Books
Sikorsky tests radical dual rotor helicopter that can reach 276 mph | Daily Mail Online