Focke-Achgelis Fa 330
|FA 330 Bachstelze|
|An FA 330 on display at the National Museum of the United States Air Force in Dayton, Ohio|
The Focke-Achgelis FA 330 Bachstelze (English: Wagtail) was a type of rotary-wing kite, known as a gyroglider or rotor kite. They were towed behind German U-boats during World War II to allow a lookout to see farther.
Because of their low profile in the water, submarines could not see more than a few miles over the ocean. To solve this, the German admiralty considered a number of different options, including a folding seaplane (Arado Ar 231). In the end, they chose the FA 330, a simple, single-seater, autogyro kite with a three-bladed rotor.
The FA 330 could be deployed to the deck of the submarine by two people and was tethered to the U-boat by a 150 m (500 ft) cable. The airflow on the rotors as the boat motored along on the surface would spin them up. The kite would then be deployed behind the U-boat with its observer-pilot aboard, raising him approximately 120 meters above the surface and allowing him to see much farther — about 25 nautical miles (46 km), compared to the 5 nautical miles (9 km) visible from the conning tower of the U-boat. If the U-boat captain were forced to abandon it on the surface, the tether would be released and the FA 330 descend slowly to the water.
When not in use, the FA 330 was stowed in two watertight compartments aft of the conning tower. Recovering, dismantling, and stowing the FA 330 took approximately 20 minutes and was a difficult operation.
As Allied air cover in other theatres of the war was considered too much of a threat, only U-boats operating in the far southern parts of the Atlantic and the Indian Ocean used the FA 330. Despite its advantages, the use of the FA 330 only resulted in a single sinking when U-177 used one to spot, intercept and sink the Greek steamer Efthalia Mari on 6 August 1943. 
The Allies came into possession of an FA 330 in May 1944 when they captured the submarine U-852 intact. After the war, the British government did successful experiments towing FA 330s behind ships and jeeps, but the development of the helicopter quickly occupied the attention of the military.
U-boats that deployed FA 330 kites included at least U-177, U-181, and U-852.
Legacy and influence
In February 2013, Aviation Week and Space Technology reported that L-3 Communications was testing its Valkyrie, an unpowered, tethered autogyro that weighs 210 lb and is intended to serve as a cheap alternative to a shipborne helicopter. Valkyrie is designed to hover as high as 5,000 feet but is envisioned to operate typically at 500-1,000 feet, offering a 28-39 mile field of view. L-3 states that naval vessels can easily be retrofitted with this system.
Several FA 330s are on public display including:
- National Museum of the United States Air Force, United States
- RAF Museum Cosford, England
- Imperial War Museum Duxford, England
- Deutsches Technikmuseum, Germany
- RAF Millom Museum, England
- Steven F. Udvar-Hazy Center, United States
- Le musée de l'Air et de l'Espace, Paris, France
Data from 
- Crew: 1
- Length: 4.42 m (14 ft 6 in)
- Empty weight: 68 kg (150 lb)
- Main rotor diameter: 7.32 m (24 ft 0 in)
- Main rotor area: 42 m2 (450 sq ft) 3-bladed rotor
- Maximum speed: 40 km/h (25 mph; 22 kn) on tow
- Minimum control speed: 27 km/h (17 mph; 15 kn) on tow
- Hafner Rotabuggy
- Kite mooring
- Kite types
- Man-lifting kite
- Kite applications
- Rotary-wing hang glider
- "Efthalia Mari (Steam merchant) - Ships hit by U-boats - uboat.net". uboat.net. Retrieved 26 August 2011.
- Focke-Achgelis Fa 330A-1 "Bachstelze" — Smithsonian Institution National Air and Space Museum article at the Internet Archive. Retrieved 3 May 2012.
- Osborne, Tony, The autogyro returns, Aviation Week and space Technology, February 25, 2013, p.26
- Green, William (2010). Aircraft of the Third Reich. Vol.1 (1st ed.). London: Aerospace Publishing Limited. p. 338. ISBN 978 1 900732 06 2.
|Wikimedia Commons has media related to Focke-Achgelis Fa 330.|
- The FA 330 at NASM
- The Bachstelze
- "German Submarine-Borne Observation Rotor-Kite", Allied Intelligence Report