Anton Flettner was a German aeronautical scientist who ...



He taught physics and math to high school students, and in 1905 took a job at the Zeppelin company.

During World War I, Flettner developed a device that allowed airplane pilots to raise or lower a plane's nose for better control. It evolved into a mechanism called the "trim tab" which is still used on all airplanes. Flettner also made several improvements to military tanks, and he apparently designed a guided torpedo which was never built.

In the 1920s, Flettner's interest in aerodynamics led him to build one of history's strangest boats: a schooner with two tall rotating cylinders that looked like smokestacks, but were actually sails. (This is such an intriguing story that we promise to write more about it in a future tech history message.)

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, Flettner began developing the Fl 265. This was a small helicopter It 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).

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 gunsights.

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 resupply 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 ground.

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 succeed

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In 1940, Hitler 's Kriegsmarine (German Navy) made a request for a naval helicopter for operate from its units. Derivative from the Flettner FL 265, the FL 282 deliveries begun in 1942 and the next year, 20 prototypes were in service.

The model demonstrate to be very effective so plans for 1000 units where approved but being a Navy aircraft had little claim on production facilities and they were finally aborted due allied bombs to the BMW and Flettner factories.

32 preproduction aircraft were delivered, and three were taken home as war booty by Russia and the United States.

After 1945, Flettner moved to America and started a new Flettner Aircraft Corporation. Now working for the U.S. military, he built helicopters with improved efficiency and control, including some models big enough to carry troops.

The Flettner Fl 282 Kolibri is a single-seat open cockpit intermeshing-rotor helicopter, or synchropter, produced by Anton Flettner of Germany.

The Kolibri ("hummingbird") was one of the first helicopters to be used in warfare. During World War II, Nazi Germany tested the craft in the Mediterranean theatre. Plans to build thousands of Kolibris were abandoned after the Flettner factories were bombed by the Allies. Only three of these helicopters survived the war; the rest were destroyed to prevent capture. [1]

Mr. Flettner was president of the Flettner Aircraft Corporation , a research and development corcern.

he came to USA soon after World War II as a consultant to the office of Naval Research (US Navy Department).

He was actively engaged in carrying out US government research projects for the Army, Air Force and Navy until a few months ago.

Mr. Flettner was born in Germany and attended the Fulda State Teachers College in Germany. When he was teaching mathematics and physics in a high school in Frankfurt, he began to develop ideas leading to his work for Germany in World War I.

During the war he developed what was perhaps his best known invention. It is called Flettner 's control. The control was fashioned to lift or lower a plane's nose. It is considered the model for trim tabs used on almost all planes to aid in control movement or to help ashieve hands-off balance. After the control 's development for aircraft it was adapted to ship rudders.

In the war, Mr. Flettner also invented tanks improvements for Germany.

After the war, he was named managing director of the Institute for Aero and Hydro Dynamics, Amsterdam, The Netherlands. He held that post until 1931.

In the Nineteen-twentys, he developed his Wind Ship or Rotor Ship in which propulsion was achieved by pressures and vacuums created by winds channeled around two rotating towers. The ship received a nosy welcome in USA in 1926 and was praised by Dr. Albert Einstein as having great practical importance, but it was not commercial success.

From 1926 to 1945, Mr. Flettner was president of the Anton Flettner Aircraft Corporation in Berlin. It built helicopters used by Hitler 's forces in World War II. The helicopters had two rotors whose blades intermeshed like egg beaters. This development was widely used by manufacturers in USA.

After the war, Mr Flettner approached US Army with a new helicopter idea. Helicopters need no airfields and are theoretically ideal for short-haul transport of troops, but a big trouble with them has been that the life of the central nerve, the gear box for the rotor, is not nearly so long as military leaders would like. Rotor gears require major overhauls every few hundred flying hours.

In 1954, Mr. Flettner thought that he had the answer. He decided that if the gear life was the main problem, the rotor gears should be used less. He designed a helicopter with a forty troops capacity in which two conventional propellers would assume the burden of forward flight, with the intermeshing overhead rotors , drawing 20 per cent or less of the engine power and simply providing lift. The result, he said, would be gear life 10 times what it is when the rotor does the whole job. The Army financed the design with the idea that it might eventually invest in production

Mr Flettner was an honorary member of the American Helicopter Society and of the Convertible Aircraft Pioneers

The pioneer work of Anton Flettner is often overshadowed by the more publicised activities of his contemporaries Focke and Sikorsky; yet Flettner's first fully practical helicopter, the Fl 265, was far superior to the Fw 61 and made a successful free flight several months before the VS-300 began tethered flights. Flettner's first rotorcraft, flown in 1932, had a 2-blade rotor 29.87m in diameter, with a 30hp Anzani engine mounted part of the way along each blade driving a propeller - a form of propulsion similar to that used by the Italian Vittorio Isacco on his so-called 'helicogyros' developed in the U.S.S.R. in the 1930s. The Flettner machine made a successful tethered take-off, but later overturned during a gale and was written off. His next significant design was the Fl 184 single-seat autogyro; powered by a 150hp Sh.14 radial engine, it flew in 1935 and was due to be evaluated by the German Navy when it, too, was unfortunately destroyed. The next design was the Fl 185, whose prototype (D-EFLT) flew in 1936 and had a 3-blade main rotor. The centrally-mounted Sh.14A engine drove, in addition to the rotor, two small anti-torque propellers on outriggers each side of the cabin and a large cooling fan in the nose.

By this time, however, Flettner had developed the idea of counter-rotating, intermeshing twin rotors. Many of his advisers thought that the airflow disturbed by the intermeshing blades would make this system less efficient than one using a single rotor; but Flettner believed that any problems thus encountered would be more than offset by the reduced drag resulting from having no external rotor-carrying structure. He proved his point by installing such a system in the Fl 265, whose prototype (D-EFLV) flew in May 1939. At this time encouragement for the development of small helicopters came mostly from the German Navy, on whose behalf six Fl 265's had been ordered in 1938 with a view to developing a machine suitable for shipboard reconnaissance and anti-submarine patrol. Service trials of the Fl 265 were more than satisfactory, and plans were made for series production; but by this time work was well advanced on a later model, the Fl 282, which could carry a men and was more versatile. The RLM therefore agreed to wait for the Fl 282, to hasten whose development it ordered thirty prototypes and fifteen pre-production aircraft in spring 1940. Maiden flight was made in 1941. The first three prototypes were completed as single-seaters and had fully enclosed cabins made up of a series of optically flat Plexiglas panels, faired-in rotor pylons and well-contoured fuselages. The Fl 282V3 was fitted with endplate auxiliary fins and a long underfin beneath the rear fuselage. Later machines had more utilitarian bodies and some had semi-enclosed cockpits; others, like the example illustrated, had a completely open pilot's seat.

Like the Fl 265, the Fl 282 underwent exhaustive service trials, and several were used operationally from 1942. Usually they flew from platforms above the gun turrets of convoy escort vessels in the Baltic, Aegean and Mediterranean, often in extreme weather conditions, and revealed control and performance qualities well above expectations. By VE-day, only three of the twenty-four prototypes completed by Flettner at Johannisthal still survived, the others having been destroyed to prevent capture. Two of these, the V15 and V23, were taken to the United States, and the other to the Soviet Union. The RLM had placed an order in 1944 for one thousand Fl 282's from BMW, but Allied bombing attacks prevented production from being started.

At least two other Flettner helicopters were under development when the war ended. These were the Fl 285, another fleet spotter with an Argus As.10C engine, capable of making a 2-hour flight and carrying two small bombs; and the Fl 339, a large transport helicopter project powered by a BMW 132A engine.

An even more significant effort then under way in France was the Breguet Gyroplane, a coaxial helicopter with counterrotating rotors. Returning to his lifelong fascination with helicopters, an older Louis Breguet oversaw but did not participate directly in the construction and testing of this compact single-seater. The Gyroplane was badly damaged in a ground accident at the end of 1933. Rebuilt with extensive modifications and tested conservatively on the ground, it resumed flight tests in June 1935. Breguet then audaciously committed it to maneuvering, speed, altitude, and endurance requirements far in excess of anything so far accomplished by a helicopter. The Breguet Gyroplane flew at 120km/h, climbed to an altitude of 158m, and remained in the air for more than one hour during tests that concluded late in 1936. Arguably the world's first successful helicopter, this historic machine was badly damaged in June 1939 during autorotation tests. It was subsequently destroyed by Allied bombing of historic Villacoublay Airfield in 1943.

J.P.Spencer "Whirlybirds: A History of the U.S. Helicopter Pioneers", 1998

* * *

After the destruction of the Breguet-Richet No.2bis helicopter in 1909, Louis Breguet suspended his experiments into the problems connected with rotary-winged flight in order to concentrate on the development of fixed-wing aircraft. However, towards the end of the 1920s he returned to the study of helicopters and in 1929-30 took out patents for systems for stabilising aircraft of this type while in flight. In 1931 he formed the Syndicat d'Etudes du Gyroplane, with Rene Dorand (who had joined the Breguet company in 1924) as technical director, and began the design and construction of an experimental machine known as the Gyroplane Laboratoire. Intended originally to be powered by a 240hp Breguet-Bugatti engine, it consisted basically of a steel-tube open framework supporting the engine, fuel tank, flight controls and pilot, with rear booms carrying the plywood-covered tail surfaces. An unusually wide track main undercarriage was mounted on outriggers from the central framework, with a small tailwheel and a nosewheel to prevent the machine tipping forward on landing. The transmission from the big radial engine drove a pair of co-axial, counter-rotating, 2-blade metal rotors whose blades had an aerofoil section and an unusually large diameter. One rotor shaft turned inside the other, each rotor thus cancelling out the torque created by the other. Novel features for the time were the use of a cyclic pitch control for lateral and longitudinal movement, and collective pitch for movement in the vertical plane.

The achievements of the Breguet-Dorand aeroplane, eclipsed by the more widely publicised efforts of its near contemporary, the Focke-Achgelis Fw 61, have been accorded less prominence than they deserve. The later Fw 61 was demonstrably the superior machine of the two, but the advance in helicopter technology brought by the French design is most apparent when compared with the best that had gone before it. It is believed that the Breguet-Dorand aircraft was completed by November 1933: it was then little more than three years since the small Italian d'Ascanio machine had set up FAI distance, height and endurance records of 1.078km, 18m, and 8 min. 45.2 sec. respectively. Within a year and a half of its first flight on 26 June 1935 the Breguet-Dorand machine, piloted by Maurice Claisse, had eclipsed these with the following performances:

14 December 1935, distance in a closed circuit of 500m;

26 September 1936, height of 158m;

24 November 1936, endurance of 1 hr. 2 min. 5 sec; distance in a closed circuit of 44km; and speed over a straight course of 44.692km/h.

Apart from advancing helicopter performance in these spheres, the Breguet-Dorand also, after a little early evidence of instability, exhibited good characteristics of controllability, and in 1937 (after a similar achievement by the Fw 61 in Germany) it made its first 'engine off' landing using autorotation. It is not certain whether the Bugatti engine was ever installed; the aircraft did most or all of its flying with the more powerful Hispano engine. It continued to carry out useful experimental work up to the outbreak of World War 2, but was destroyed in 1943 during an Allied air attack on the airfield at Villa-coublay where it was housed.

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