Focke-Achgelis Fa 330 A-1 Bachstelze (Water Wagtail)
Henrich Focke startled the aviation world when he flew his Focke-Wulf Fw 61 helicopter in 1937. It quickly shattered all records for helicopter speed, altitude, distance, and endurance. Thanks to Focke and fellow helicopter pioneer, Anton Flettner, Germany entered World War II as the leader in rotorcraft technology. By 1942, the German Navy was already testing Flettner's twin-rotor helicopter, the Fl 282. Navy leaders hoped to use this aircraft to hunt for enemy submarines and protect convoys. The tests convinced them to continue to develop rotary-winged aircraft for shipboard use.
During World War 2, German naval strategy and Britain's survival hinged on the success or failure of the U-boat service to interdict the flow of material from the United States. However, the U-boats depended primarily on visual acquisition of their targets. They rode low in the water and a lookout could not see vessels more than 8 km (5 miles) away, even when surfaced. Small, submarine-launched aircraft offered a novel solution in regions free of enemy patrol aircraft.
Beginning in World War I, several nations experimented with submarine-based observation aircraft with mediocre results and interest waned after the Armistice. The start of World War II renewed interest in Germany and Japan in developing this technology. The German Navy looked first at the Arado Ar 231 but this collapsible seaplane proved a failure. It handled poorly on the water and took too long to assemble and disassemble. As the sub's crew put the airplane together on the open deck, the submarine was extremely vulnerable. As a result, the German Navy quickly terminated the Ar 231 program.
By the spring of 1942, the Battle of the Atlantic was beginning to turn against Germany. The U. S. Navy was deploying increasing numbers of anti-submarine assets to protect the eastern seaboard, once a fertile hunting ground for prowling U-boats. The submarine commanders moved their patrols far out to sea to avoid Allied air cover and roaming destroyers. High sea states in these open waters restricted visibility to several kilometers or less, and U-boat commanders were hard-pressed to acquire targets. The expanse of the open ocean also worsened the target detection problem. Near the coast, Allied ships traveled in relatively narrow areas. A U-boat could wait, just beneath the waves in daylight or float on the surface at night, and expect with some certainty that a target would steam within detection range. Away from the coast, U-boats had to patrol much larger areas and this reduced the chances of detecting Allied ships. German sonar and radar technology lagged behind Allied developments and also made detection of the U-boats easier.
The navy asked Focke-Achgelis GmbH to build a rotorkite that a U-boat could tow aloft to search for targets. The aircraft had to fly high enough to substantially boost the scouting range, yet remain small, easy to store, and mechanically simple to maintain and operate. Focke-Achgelis proposed a clever design best characterized by simplicity. The Fa 330 was simple to fabricate, easy to assemble on deck for flight, and weighed so little that two men could comfortably hoist the entire machine. The Fa 330 needed no engine because the submarine towed the gyro kite through the air. Like a gyro plane, the rotorkite flew by autorotation, meaning that the movement of relative wind through the rotors caused them to turn with sufficient speed to generate lift.
The airframe consisted of two 6.35 cm (2.5 in) diameter steel tubes joined to form an inverted 'T.' One tube served as the fuselage of the aircraft, which mounted the pilot's seat and rear control surfaces. The other tube served as the rotor mast. A control stick hung from the blade hub atop the mast. The pilot moved the stick for direct (no intervening control linkage) pitch and roll control, and he used foot pedals to move the large rudder and control yaw. The horizontal stabilizer had no moving control surfaces. Weight was saved on the rotor hub by using steel cables to support the blades against blade droop when the aircraft was not flying. The cables also limited the blades' range of movement when during flight. Instrumentation consisted of an altimeter, airspeed indicator, and tachometer. Its landing gear consisted of two small skids.
The three-bladed rotor turned freely but was limited to 250 rpm. This limit was reached if the aircraft attained a never-exceed speed of 80 kph (50 mph). Normal flight rpm was about 205 at a standard towing airspeed of 40 km/h (25 mph). A minimum speed of 27 kph (17 mph) was required to maintain autorotation. Blade pitch could only be set before flight by turning adjustment screws. The blades used flapping and dragging hinges equipped with variable dampers. The rotor blades consisted of a 3.2 m (10 ft 4 in) steel spar that supported plywood ribs. The blades were 0.3 m (12 in) wide and skinned with fabric-covered plywood. The blade airfoil was almost symmetrical. The blades were precisely balanced during the manufacturing process, which eliminated the need for difficult and time-consuming manual balancing at sea.
The Fa-330 was stowed in two tubes of approximately 3.75 meters (12 ft 4in) length built vertically into the U-boat's conning tower. One tube contained the blades and tail and the other contained the fuselage. Four crewmen could assemble the entire structure in three minutes in calm conditions. Rotation of the blades in preparation for flight could be done by hand, but if a course pitch (which provided the best operating performance) was preset on the rotor blades this became extremely difficult. In that case, a rope wrapped around drum on the rotor hub was used to get the rotor turning. The Fa 330 took off from a small platform attached to the aft railing of the U-boat's conning tower. A towline extended from an electric winch to a quick release coupling on the Fa 330. Since the primary duty of the Fa 330 was to spot suitable targets, communication with the towing vessel was essential. The pilot used an interphone system that consisted of a telephone cable, which paralleled the towline. Upon landing a rotor brake was provided to quickly stop the rotor spinning. Disassembly time was not much greater than that required for assembly. If the U-boat came under attack and had to make a crash dive the pilot could pull a quick release lever above the seat, and the towline would separate from the aircraft in addition to releasing the rotor hub from the mast. As the rotors departed they pulled a line out, which deployed a parachute. Once the parachute opened, the pilot released his seat buckle, which allowed the remainder of the aircraft structure to fall away. Additionally, the towline quick release coupling could be manually operated without engaging the rotor release.
By early August 1942, Focke-Achgelis had completed the first prototype Fa 330 and had begun operational testing aboard U 523 in the Baltic Sea with positive results, though it clearly demonstrated that the Type VIIC U-boats were to slow to tow the aircraft successfully. A wind tunnel at Chalais-Meudon, France served as a simulator to train several crewmembers from each vessel that carried a Fa 330. Since very few of the prospective pilots had previous flight experience, and would have little opportunity to practice while on patrol, it was essential that the aircraft be easy to fly. The Fa 330 was stable enough that the pilot could release the stick for seconds at a time without a loss of control.
At the time the Fa 330 received clearance for deployment at the beginning of 1943, only the Type IX U-boat, with its surface speed of 18 knots, had sufficient speed to ensure the Fa 330 remained airborne in low wind conditions. The Fa 330 used a steel tow cable 300 meters (984 ft) in length, which allowed it to ascend to a maximum altitude of 220 meters (722 ft) when flying at the top speed of 80 km/h (50 mph). At that altitude, spotting distance was 53 kilometers (33 miles) in clear conditions. Like a kite, the maximum altitude attainable was dependent on airspeed. If the airspeed dropped to 50 km/h (31 mph), then the maximum altitude became 200 meters (656 ft) with a possible spotting distance of 50 kilometers (31 miles). If the speed dropped to the minimum safe towing speed of 35 km/h (22 mph) then the maximum altitude was only 100 meters (328 ft), with a possible spotting distance of 35 kilometers (22 miles).
Unfortunately, the Fa 330 possessed a large radar signature and because most of the Atlantic convoys employed numerous escort vessels for anti-submarine duty by the time the Fa 330 entered service, it was impractical to deploy the rotorkite in that ocean. However, in the Indian Ocean, merchantmen still plied the seas without benefit of the convoy system and the Fa 330 could serve the U-boat service to some effect. The U-boat service began committing its longest-range vessels - the Type IX D2, known as the Monsoon boats, to operate with the Fa 330 in the Indian Ocean, frequently operating out of bases borrowed from the Japanese. The first operational deployment of the type occurred in April 1943 aboard U 177, which managed to sink one vessel on August 5 with the aid of the Fa 330.
Operational details of the Fa 330's combat service are almost nonexistent after the U 177 deployment. This is undoubtedly because of the extremely high loss rate among U-boats, which has meant that very few ships' logs have survived. There were several concerns that prevented wider employment of the Fa 330. A U-boat commander was faced with a choice between risking his entire vessel and crew to recover the pilot, or to crash dive the submarine and leave the unfortunate individual to suffer an almost certain death, in the event that the submarine had been spotted, in addition to the fact that it gave away the U-boats primary advantage - stealth. It appears that some U-boat commanders who were not enamored with the Fa 330 took the opportunity to trade them to the Japanese in exchange for floatplanes to patrol around U-boat bases in Java and Malaya. The Japanese Navy enjoyed more success with submarine launched aircraft. They had several classes of large submarines that could carry, launch and recover seaplanes capable of carrying reasonable weapon loads and which would not give away the submarine's position.
Although Focke-Achgelis was responsible for the development of the Fa 330, Weser-Flugzeugbau in Hoyenkamp actually produced the aircraft with approximately 200 Fa 330s produced alongside Focke-Achgelis's most significant product - the Fa 223 helicopter, which was the largest rotary wing aircraft of the war. The only notable variation that occurred during Fa 330 production was increase in the span of the rotor blades to 3.79 meters (12 ft 5 in). Later production Fa 330s also had mountings for small wheels to be added to the skids to aid in moving the aircraft on the ground. A version of the Fa 330 was under consideration for surface vessels, which was actually a true helicopter that used a 200 lb, 60 horsepower engine, however this design did not progress much beyond the drawing board.
The Fa 330 was viewed with a great deal of interest by the Allies following its discovery on U-852 after it ran aground off the Somali coast during an air attack on May 3, 1944. The performance of the Fa 330 was not as interesting to Allied Intelligence as was the simplicity, ease of production, and speed with which it could be assembled. It was apparent that such a design allowed a significant increase in visual range at sea for very little effort.
After the war, the United States and Britain conducted extensive tests on the Fa 330 to evaluate this type of aircraft for observation purposes. Captured Fa 330s towed behind boats and even jeeps provided positive results, but the introduction of the helicopter into naval operations rendered such concepts obsolete. A number of these easily stored aircraft appeared on the collector's market, even occasionally showing up in Army-Navy surplus stores and a number survive in museums around the world.
The National Air and Space Museum fully restored its Fa 330 in 1975. It bears the captured aircraft registration number of T2-4618, but it appears likely that the museum's aircraft is actually T2-4616, which was in a display example of captured German technology at Freeman Field in 1946. The Army Air Force then loaned it to Eastern Rotor Craft of Pennsylvania in 1947 for an evaluation after which it into storage for the National Air Museum. T2-4618 conducted a number of flight tests at Wright Field in 1946, during which it was equipped with a wheeled landing gear and towed by a truck. However the relatively large landing gear upset the center-of-gravity and made the aircraft difficult to takeoff and land. After four successful flights the aircraft rolled on landing and sustained some damage. The aircraft was repaired and sent to MacDill Air Force Base for further testing in 1948. There it was towed behind a boat, minus the wheeled undercarriage, for consideration as an aid for U.S. Air Force small rescue boats in spotting downed airmen in the water. Unfortunately in August 1948 the towline broke and the aircraft sank in Tampa Bay, but pilot Capt. Raymond A. Popson managed to escape. The aircraft mysteriously disappeared from where it sank and rumors state that it may have turned up in an army surplus store over twenty years later.
The Fa 330 undoubtedly achieved its designed objectives, however by the time the aircraft entered service the tide had irreversibly turn against the U-boat service. If this simplest of aircraft had been available at the beginning of the war, then merchant shipping might have suffered significantly higher losses. The fact that this design was not used more extensively is more an acknowledgement of allied air and naval supremacy over the sea-lanes than any failure of the equipment to live up to its expectations.
Rotor Diameter: 8.53 m (28 ft)
Length: 4.47 m (14 ft 8 in)
Height: 1.67 m (5 ft 6 in)
Weight: Empty, 75 kg (165 lb) [not including 10 kg (22 lb) parachute]
Gross, 175 kg (386 lb)
Serial Number: T2-4616
