Flettner Fl 282

The Flettner Fl 282 Kolibri ("Hummingbird") is a single-seat intermeshing rotor helicopter, or synchropter, produced by Anton Flettner of Germany.
According to Yves Le Bec, the Flettner Fl 282 was the world's first series production helicopter.

The Fl 282 Kolibri was an improved version of the Flettner Fl 265 announced in July 1940, which pioneered the same intermeshing rotor configuration that the Kolibri used. It had a 7.7 litre displacement, seven-cylinder Siemens-Halske Sh 14 radial engine of 150-160 hp mounted in the center of the fuselage, with a transmission mounted on the front of the engine from which a drive shaft ran to an upper gearbox, which then split the power to a pair of opposite-rotation drive shafts to turn the rotors.

The Sh 14 engine was a tried-and-true design that only required servicing every 400 hours, as opposed to the nearly 27 litre displacement, nine-cylinder BMW/Bramo Fafnir 750 hp radial engine powering the larger Focke Achgelis Fa 223 helicopter, whose outdated design required maintenance every 25 hours. The Fl 282's fuselage was constructed from steel tube covered with doped fabric, and it was fitted with a fixed undercarriage.

The German Navy was impressed with the Kolibri and wanted to evaluate it for submarine spotting duties, ordering an initial 15 examples, to be followed by 30 production models. Flight testing of the first two prototypes was carried out through 1941, including repeated takeoffs and landings from a pad mounted on the German cruiser Köln.

The first two "A" series prototypes had enclosed cockpits; all subsequent examples had open cockpits and were designated "B" series.

In case of an engine failure, the switch from helicopter to autorotation was automatic.

Three-bladed rotors were installed on a test bed and found smoother than the vibrating 2-blade rotor, but the concept was not pursued further. The hover efficiency ("Figure of Merit") was 0.72 whereas for modern helicopters it is around 60%.

After the war, Anton Flettner emigrated to the United States[6] and became the chief designer for Kaman Aircraft, creating the Kaman HH-43 Huskie. Intermeshing rotors have become noted with Kaman helicopters, which continues this concept with the Kaman K-MAX.

Model of the 282
Intended roles of Fl 282 included ferrying items between ships and reconnaissance. However, as the war progressed, the Luftwaffe began considering converting the Fl 282 for battlefield use. 

Until this time the craft had been flown by a single pilot, but by then a position for an observer was added at the very rear of the craft, resulting in the B-2 version. Later the B-2 proved a useful artillery spotting aircraft and an observation unit was established in 1945 comprising three Fl 282 and three Fa 223 helicopters.

Good handling in bad weather led the German Air Ministry to issue a contract in 1944 to BMW to produce 1,000 units. However, the company's Munich plant was destroyed by Allied bombing raids after producing just 24 machines.

Towards the end of World War II most of the surviving Fl 282s were stationed at Rangsdorf, in their role as artillery spotters, but gradually fell victim to Soviet fighters and anti-aircraft fire.

Variants
Fl 282 V1/7
Prototypes.
Fl 282A-1
Single-seat naval reconnaissance type, for operation from cruisers and other warships. Tested in the Baltic, Mediterranean and Aegean Seas.
Fl 282A-2
Single-seat reconnaissance type for submarines equipped with special deck hangar, project only.
Fl 282B-1/B-2
Two-seat land reconnaissance-liaison helicopter
Operatos
Luftwaffe
Survivors
A single Fl 282 was captured at Rangsdorf by Soviet forces
Two, which had been assigned to Transportstaffel 40 (TS/40) — the Luftwaffe's only operational helicopter squadron — at Mühldorf, Bavaria, were captured by U.S. forces.

Fl 282 V-10 28368 Midland Air Museum, Coventry, England. Partial aircraft, frame with rotor head & wheels.

Fl 282 V-23 was at one time to be found at the National Museum of the United States Air Force, Dayton, Ohio.
Specifications (Fl 282 V21)

General characteristics
Crew: 1
Length: 6.56 m 
Height: 2.2 m 
Empty weight: 760 kg 
Max takeoff weight: 1,000 kg 
Powerplant: 1 × Bramo Sh.14A 7-cyl. a-c radial piston engine, 119 kW (160 hp)
Main rotor diameter: 2× 11.96 m 
Main rotor area: 224.69 m2 
Maximum speed: 150 km/h  at sea level
Range: 170 km 
Service ceiling: 3,300 m 
Hover ceiling: 300 m 
Rate of climb: 1.52 m/s 
Rotor loading: 8.84 kg/m2