The Focke-Achgelis Fa 330 Backstelze (Water Wagtail) was the most numerous and simplest of Focke's rotor craft and was a simple unpowered gyro kite designed to increase the viewing distance from a U-boat.
One of the problems faced by the U-boats throughout the war was that the viewing range from the bridge of a surfaced U-boat was only 5 miles. In the vastness of the ocean this made it easy to miss ships or even large convoys, and as Allied anti-submarine weapons became more dangerous the Germans were forced to operate further into the Atlantic, where targets were further apart.
In 1942 Focke-Achgelis were asked to design a gyro kite that could be used by the U-boats to improve their view. The aircraft would need to be small enough to fit through a U-boat hatch when dismantled, and simple enough only to take a few minutes to assemble.
The Focke-Achgelis Fa 330 was certainly simple. It was built around two steel tubes. The horizontal tube linked all of the main components, and had a small conventional tail at the rear, the pilot's seat and controls at the front and was attacked to the vertical tube in the middle. The vertical tube rose up to an unpowered, freely rotating, three-blade rotor with a diameter of 24ft. Early tests in the wind tunnel at Chalais-Meudon uncovered a series of problems wit the rotor, but these were fixed by adding thin bracing wires (between the blades and to a tripod above the rotor hub).
In normal use there were also a pair of landing skids near the front so that the aircraft could land back on the U-boat. There was also an emergency landing system - if the U-boat was attacked or needed to dive for any other reason the pilot could eject the rotor. As it went the rotor would pull out a parachute which was mounted behind the vertical tube. The pilot then undid his safety belt, allowing the horizontal part of the aircraft to fall away. He would then parachute back to the submarine. In normal use the aircraft would be winched back onto the sub, dismantled and stowed.
In operation the aircraft would be assembled on deck. The U-boat would then get up to speed, producing some airflow over its deck. The rotor would be manually brought up to speed, and the aircraft would then take to the air. The pilot could tilt the rotor head to move horizontals, or use his rudder to turn. The Fa 330 was connected to its U-boat by a 492ft long cable, and could operate at up to 394ft. From that altitude the pilot could see up to 25 miles, and could communicate with the submarine via a telephone.
The Fa 330 was built by the Weser Flugzeugbau near Bremen, a factory that also worked on the Fw 190 and the Fa 223. Sources differ greatly on the number of Fa 330s that were completed, with estimates ranging from a low of 112 to a high of 300.
The service record of the Fa 330 is also somewhat unclear. They may have entered service in the Atlantic in mid-1942. They weren't popular with the U-boat crews. The U-boat's best chance of surviving an attack, especially an unexpected air attack, was to dive as quickly as possible. If an Fa 330 was in the air the U-boat commander had two choices - either wait for the pilot to be recovered or dive quickly and hope to rescue him later - neither of these were good options.
The Fa 330 could only be used by the ocean-going Type IX U-boat, with a surface speed of 18kts and the Type IX-D/2 supply boat, with a speed of 19.2kt. Slower boats didn't produce enough air flow to keep the aircraft in the skies.
In less dangerous waters, such as the Indian Ocean, the Fa 330 was a little more useful. It was certainly used by U-861 during a patrol east of Madagascar. However even here its use was limited, and at least one U-boat commanders was able to acquire a Japanese floatplane that could operate from the U-boat and potentially escape from an Allied attack under its own power. Focke-Achgelis did put forward a design for the Fa 336, a powered version of the Fa 330, but this wasn't built.
The Fa 330 survives in larger quantities that any other type of German rotary winged aircraft, partly because more were produced and partly because they were so simple to maintain (and perhaps because of their lack of operational use!).
Rotor Span: 24ft
Length: 14ft 6in
Height: 5ft 5in
Empty weight: 70kg
Loaded weight: 170kg
Max speed: n/a
Climb Rate: n/a