"In Germany, Anton Flettner developed a series of helicopters using counter-rotating intermeshing rotors with the hubs close together and angled slightly outward. In 1942, the two seat Fl 282 Kolibri ("Humming Bird") became the first helicopter anywhere to enter operational military service. It was the most advanced helicopter developed during WWII. The German air force and navy ordered production of 1,000 aircraft, but only about 30 survived Allied bombing long enough to be completed."

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The intermeshing Flettner FL-282 was the world's first production helicopter.

"It was capable of lifting 16 lbs. per horsepower - a figure not attained to this day by any of the modern helicopters." ["this date" - unknown]

Evaluation and Tests of the Flettner-282 German Helicopter ~ by Prewitt Aircraft Company for Headquarters Air Materiel /Command, Wright-Patterson Air Force Base

"two three-blade rotors - was tried out on the test bed. It proved to run extraordinarily smoothly, however this was not a consideration for military use." ~ from The Luftwaffe Profiles Series No.6

Anton Flettner in the USA - from Mr. Glidden Doman:

A gentleman has amassed a considerable amount of information on the Flettner Fl-282. His objective is to build a full-size, operational re-production of this craft.

The German patent for the intermeshing helicopter rotor (synchropter) was granted in 1902.

At the end of World War 2, the only operational FL-282 that remained was sent to the United States where the Prewitt Aircraft Company evaluated it for the USAF intelligence department.

The following is the Prewitt's Report Summary.

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Flight tests were made on the Flettner FL-282 Helicopter to determine the power requirements, control response, couple response between rudder and aileron, static stability, and the difference between a straight and a butterfly stabilizer.

The performance of the helicopter was found to be very high, due to a very low disk loading and to a comparatively high figure of merit.

The controls of the helicopter are relatively sensitive and substantially unaffected by rotor loading. The large size of rudder makes directional response more sensitive with increasing speed. Lateral control is one-half as sensitive as longitudinal control. Rudder control is one-half as sensitive as lateral control.

Fore and aft control and changes In throttle setting do not affect roll or yaw. There is, however, a coupling between fixed-stick rudder control and fixed-rudder stick control.

The lateral static stability is substantially neutral. There is, however, considerable damping to lateral roll, and lateral control presents no special problem. Directional stability Is Influenced by collective blade pitch angles (good at high pitch, poor at low pitch). The helicopter has static longitudinal stability at between 10 and 80 mph. The longitudinal dynamic stability appears to follow the longitudinal static stability.

The tests show that there Is no observable difference between the straight and the butterfly stabilizers In either the control tests or stability tests.

The maintenance on the helicopter during the test period was nil.

The Inertia stick dampers were found to be very effective as was the rotor governor.