Anton Flettner Kolibri
Anton Flettner was a German aeronautical
scientist who experimented with helicopters in the 1930s. He built his
first helicopter in 1930—a complicated and odd-looking craft, and realized
it was not a practical helicopter design. It was destroyed during a
tethered flight in 1933, and Flettner turned his attention to autogyros.
He built a craft called the Fl 184, which had full cyclic control that
allowed the pilot to tilt the rotor by moving the control stick in the
direction that he wanted to fly.
Flettner's initial Fl 184 design was
successful, so the inventor added power to the main rotor. He also
developed a collective pitch control, which allowed the pilot to increase
the pitch of all of the lifting blades simultaneously. Flettner also
removed the autogyro's main propeller and replaced it with two smaller
propellers on outriggers located on the side.
In 1937, while the Focke-Achgelis Fa 61
was making its impressive test flights, Flettner began developing the Fl
265. This was a small helicopter, compared to its only contemporary, the
Focke-Achgelis Fa 223. The Fl 265, which was called a synchropter because
of its rotor configuration, had two counter-rotating rotors set close
together and splayed outwards. The rotors intermeshed like the blades of
an eggbeater. Flettner received a small production contract from the
German Navy in 1938, and the aircraft made its first flight in May 1939.
The aircraft proved impressively controllable in flight and was a major
improvement over the Focke-Achgelis designs.
In 1940, Flettner debuted an improved
version designated the Fl 282 Kolibri (hummingbird). The Kolibri
could fly at almost 90 miles per hour (145 kilometres per hour), could
reach 13,000 feet (3,962 meters), and could carry an 800-pound
(383-kilogram) load. The fuselage was approximately 21.5 feet (6.5 meters)
long, and the craft was 7.2 feet (2.1 meters) high. The rotor diameter was
approximately 39.2 feet (12 meters) and had the same synchropter
configuration as the earlier Fl 265.
282 Kolibri was the first to use two closely intermeshing rotors.
Designed by Anton Flettner in 1939, it was put into quantity production by
Germany during World War II.
It was powered with a 138-hp engine and had good performance and flying
A Siemens-Halske Sh14A engine providing
150 to 160 horsepower (112 to 119 kilowatts) powered the Kolibri Fl
282. The radial engine was mounted in the centre fuselage, with a small
propeller to draw in cooling air. A transmission was mounted on the engine
crankcase front. It ran a driveshaft connected to an upper gearbox that
split the power into two opposite rotating drive-shafts that turned the
Flettner designed his craft to carry two
people, a pilot and an observer. The pilot sat in front of the rotors in
an open cockpit affording good visibility. The observer sat in a single
compartment behind the rotors, facing the rear. The observer could spot
submarines at sea or troop movements on the battlefield. The Kolibri
was one of the first helicopters designed with a clear military mission.
The German Navy (Kriegsmarine)
was impressed with the Kolibri and wanted to evaluate its use for
submarine spotting. However, critics argued that fighter planes would
easily attack the slow-flying craft. In 1941, the Navy conducted an
evaluation using two fighter planes to stage a mock attack on a Fl 265.
The fighters could not hold the agile craft in their gun-sights.
Flettner also demonstrated that the
little craft could land on a ship, even in heavy seas. Naval leaders were
impressed and, in 1940, ordered several dozen of the craft with the clear
intention of mass-producing them. Allied bombing ended production efforts,
but 24 of the aircraft still entered service, with a number of them being
used for escort service, flying off the gun turrets of ships to spot
submarines, and performing re-supply missions even in poor weather
conditions. The German Army also evaluated this type of aircraft.
The Fl 282 served in the Baltic, North
Aegean, and Mediterranean Seas. Only three of the craft survived the war;
the Germans destroyed the rest to prevent them from falling into Allied
hands. Two of the survivors went to the United States and Britain, the
third to the Soviet Union.
The Fl 282 was designed so the rotor
blades and landing gear could be removed and the helicopter stored in a
compact area such as the pressure tank of a U-boat. There is no evidence
that it was ever used this way. It was intended to search for submarines,
and in the fairly clear waters of the Mediterranean, a pilot could see a
submerged submarine as deep as 130 feet (40 meters). He could match the
speed and course of the submarine and radio the position to the convoy.
The pilot could also mark the sub's position with a smoke bomb. But the
helicopter was too small to carry weapons, although some tests were
conducted with small anti-submarine bombs. There is no good information on
the helicopter's actual use during the war.
The Kolibri's intermeshing rotors
represented the fourth approach to solving the control and torque
problems, after Bréguet's stacked coaxial counter-rotating blades, Focke's
widely spaced counter-rotating blades, and Sikorsky's tail rotor. The
Kaman Huskie, which saw U.S. Air Force, Navy, and Marine service during
the 1950s and 1960s, and the Kaman K-Max single-seat aerial crane used
this design in the 1990s. The design has not proven to be long lasting or
popular. The biggest problems with this design are that the helicopters
are slow compared to other types and the rotors endanger people on the
The Fl 282 is most notable for
pioneering the Naval use of helicopters, particularly for hunting
submarines. However, it would be many years before a helicopter was
produced that routinely succeeded in this mission.