Flettner Fl 265 Experimental Helicopter
The German Kriegsmarine was interested in this Anton Flettner design concept for use in spotting enemy warships.
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The Flettner Fl 265 served as an experimental helicopter system for the German Kriegsmarine during World War 2. In many ways, the Germans were on the cutting edge along several military fronts of the time and helicopters proved no exception. While only a few Fl 265 examples were ultimately constructed, the type served well in laying down the foundation for the much improved upcoming Flettner Fl 282 helicopter. Both designs were the brainchild of Anton Flettner, a German aviation engineer and inventor with military experience dating back to the First World War. During the Second World War, Flettner headed up the Anton Flettner, Flugzeugbau GmbH bureau centralizing on the development and construction of rotary wing aircraft.
Flettner flew his first rotary wing-based aircraft in 1932 and continued to evolve his ideas through his burgeoning firm. His first helicopter design was a monster 2-bladed machine powered by a 30 horsepower Anzani engine driving a 100-foot diameter rotor - this aircraft was accordingly dubbed "Gigant". First flight was achieved with a successful take-off, although she was still tethered to the ground for safety's sake, but was soon lost when a gust of wind took her back down to earth. By 1935, Flettner had revealed his Fl 184 autogyro powered by a 150 horsepower Sh 14 radial piston engine. The German Navy, by this time, had already developed an interest in Flettner's devices and had asked for an evaluation of the Fl 184. Unfortunately for all involved, the Fl 184 was lost to an accident before the showcasing could ensue. The interesting Fl 185 followed next and first flew in 1936 with three rotors - the main rotor located centrally above the cockpit compartment and the smaller additional pair outboard on strut fixtures. From there, Flettner moved on to the idea of counter-rotating intermeshing rotor systems in the Fl 265.
The German Navy spearheaded the development of the Fl 265 and ordered six such examples in 1938. They saw the possible battlefield value inherent in a hovering system such as the one Flettner had devised with the idea being that the Kriegsmarine could field these small, one-man systems aboard their surface ships or even with specially-modified U-boats to achieve the all-important "eye-in-the-sky", first sighting of the enemy at sea. She could be effectively used against warships and submarines in turn. First flight of the Fl 265 was achieved in May of 1939.
Further evaluation of the Fl 265 ensued and proved promising enough to the point that the Kriegsmarine began entertaining the idea of producing the Flettner system. However, Flettner's firm had already been hard at work in developing an improved version - the Fl 282 - a twin-seat creation with improved features and mission variety. As such, the RLM postponed contracting the production of the Fl 265 and decided to wait for the improved Fl 282 to come online. To speed the project along, funding and manpower was deviated to the Fl 282 program - effectively ending the short legacy of the Fl 265, only six whole examples being built by the end of her run.
Externally, the Fl 265 made use of what could be characterized as an aircraft fuselage, complete with an open-front radial piston engine placement. The cockpit was fitted amidships and housed under the rotor mast area, sporting framed windowed sides and a front windscreen. The fuselage tapered off into a shortened empennage featuring a single well-rounded, large-area vertical tail fin and smaller low-mounted tailplanes to each rear fuselage side. The undercarriage was made up of two main single wheeled landing gear legs and a diminutive tail wheel at the rear. The main legs were held away from the fuselage by a complicated series of interconnected struts. Each two-blade rotor was fitted to an identifiable raised structure atop the cockpit roof, operating in unison in what was termed as "intermeshing". This concept proved a pioneering attempt in the realm of the "synchrocopter" - the use of two individual rotors rotating in opposite directions to achieve lift. This also served well in cancelling out torque, the natural pull that was generated by an engine with an externally-mounted rotating blade. Helicopters making use of counter-rotating blades therefore do not make use of a tail rotor as a tail rotor functions to counter the effects of torque caused from a single main rotor. A modern example of this is the Kamov Ka-50 "Black Shark" attack helicopter which stacks its main rotors one atop the other and does not use a tail rotor as a result.
The Fl 265 was powered by a single Bramo Sh 14A 7-cylinder radial piston engine delivering some 160 horsepower, allowing for speeds of up to 99 miles per hour. The aircraft maintained an empty weight of 1,764lbs with a gross weight of up to 2,205lbs. Each rotor measured in at roughly 40 feet, 4 inches in diameter.
Further development and production of the Fl 265 was given up in favor of the more promising Flettner Fl 282.