Focke-Wulf Fw 61/Focke-Achgelis Fa 61
One
of the world’s first practical, controllable helicopters
First
fight: June 25, 1936
After in-depth investigations of the theory of the helicopter and licensed production of Cierva Autogiros, Prof. Henrich Focke began construction of his first helicopter – initially designated the Focke-Wulf Fw 61, but changed to the Focke-Achgelis Fa 61 when Focke started a new company – in Germany in 1934. The aircraft, which made its first flights in June 1936, was a groundbreaking development and outperformed the world records of all helicopters that existing to date.
On each side of a Fw-44 Stieglitz biplane fuselage, an outrigger carried the three-bladed counter-rotating rotors with 4 m (13.1 ft) radius. The reasons for this arrangement were: the rotors and their slipstreams were free of disturbances, and the avoidance of oscillation excitements of one rotor from the other. The final decision was made due to the perspective of static and dynamic stability about the longitudinal axis even in the hovering case.
A 7-cylinder radial engine Siemens SH 14A, providing 150 hp (111 kW) served as motor and was cooled by an airscrew. The rotor blades had a trapezoidal shape with the largest chord at about 1/3 of the radius. They were made of solid wood glued in several layers and twisted. The rudder of the vertical tail was also taken from the Fw-44 and coupled to the rotor control, while the horizontal stabilizer had no rudder and was attached as one piece element for trimming above the fin.
- with a gross weight of 950 kg (2095 lb), a height of 2439 m (8002 ft) was achieved
- climb velocity at sea level was 3.6 m/s (11.8 ft/s)
- horizontal velocity with fairing of the outriggers was 147 km/h (79.4 kt)
- the distance flown in straight line was 230 km (124 nm)
- the autorotative landing speed was 55 km/h (30 kt)
(Text by Berend van der Wall)
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