Kurt Waldemar Tank (24 February 1898 – 5 June 1983) was a German aeronautical engineer and test pilot who led the design department at Focke-Wulf from 1931 to 1945. He was responsible for the creation of several important Luftwaffe aircraft of World War II, including the Fw 190 fighter aircraft, the Ta 152 fighter-interceptor and the Fw 200 Condor airliner. After the war, Tank spent two decades designing aircraft abroad, working first in Argentina and then in India, before returning to West Germany in the late 1960s to work as a consultant for Messerschmitt-Bölkow-Blohm (MBB).
Early life Tank was born on 24 February 1898 in Bromberg-Schwedenhöhe, now Bydgoszcz and Szwederowo district respectively, located in present-day Poland. Tank grew up near the Netze River in the now dissolved Province of Posen. His grandfather was a cavalry sergeant in the Uhlans and his father, Willi Tank, was a grenadier sergeant in the 3rd Division. After retiring from military service, his father worked as a technician in Nakel, at a power plant located on the Netze river.
Education When World War I broke out in 1914, Tank wanted to join the Imperial German Armys Fliegertruppe air force. However, his father insisted that Tank instead follow the family tradition and enlist in the cavalry regiment he had served in. Tank ended the war as a lieutenant and a company commander, having been wounded in action multiple times and winning many awards and honors. He had won the Iron Cross 1st and 2nd Class of 1914, the and the Ehrenkreuz für Frontkämpfer.
Tank had spent the four years of the war reading an unnamed physics book. He was very interested in hydrodynamics, the laws which govern theoretical fluid dynamics. Tank wanted to apply the theories he had learned in real life by becoming a pilot. He applied many times for a transfer to the Fliegertruppe, however, unbeknownst to him, his senior officers wanted to retain him in the army because he was a great soldier. After the war, Tank studied at and graduated from the Technische Hochschule Berlin (now the Technische Universität Berlin) in 1923. Tank had studied electro-technology, but his recreational pursuit of gliding made him inclined towards aviation. Tank had also worked on building sailplanes with Akaflieg Berlin, and had started the Akaflieg (aviation) club at his university along with seven other students. These eight students had started the Akaflieg club to protect aviation development at their university from the rigid constraints imposed by the Treaty of Versailles. The Akaflieg club was supported mainly by army officer Adolf Baeumker, and also by their professor August von Parseval.
The other seven students who had established the club were , Werner Henninger, Pauleduard Punk, Seppl Kutin, Viktor Gohlke, Edmund Pfister and Georg Gillert. These eight students had created a workshop at the university's loft, where they started building two gliders while learning aeronautics from professors Emil Everling and Hans Reissner. Tank was building a monoplane which was strut-braced and had a big wingspan. Winter was building a monoplane without a tail, which he named Charlotte after the daughter of professor Parseval. This monoplane was the Akaflieg Berlin B1, which the group used to participate in the 2nd Rhön Competition organized by the Rhön-Rossitten Gesellschaft in 1922. Winter piloted the plane's flying wing model during the competition, but the plane was hit by a downdraft and it crashed near Gersfeld. The group then moved the plane on a wagon to Gotha. There, Gothaer Waggonfabrik had the plane sent to Berlin, where the group repaired it. Meanwhile, Tank had built a shoulder-wing plane with a big wingspan, which the group entered in the 1923 Rhön Competition. This plane was the Akaflieg Berlin B2 Teufelchen.
However, it was not possible to build both the B2 and B1 planes at the group's small workshop in the university's loft. The students also couldn't build it themselves, or their academics would be impacted. Therefore, Tank and Gillert went to the Albatros Flugzeugwerke factory in the Berlin suburb of Johannisthal. There, they met Robert Thelen, then an aviation world record holder who was a director at the company. However, Thelen did not want to build an entire sailplane for free, especially because it used wing warping wingtips in place of ailerons. Tank and Gillert then went to Luft-Fahrzeug-Gesellschaft in Stralsund, who agreed to build the B2 Teufelchen ("Little Devil"). By building the B2, Tank had passed his preliminary exams; his academic output was assessed favorably by professors Parseval and . At the Rhön Competition in August 1923, Tank had to force land the B2 on unfavorable terrain when he was practicing flying. The B2 was wrecked and the group had used up all their money by then. The group was later able to repair the B2 and fly it in Rositten. Tank then trained and qualified for a flying license at Staaken, flying the DFS Kranich with Rudolf Rienau as his trainer.
Early career
Rohrbach Ro III
One of Tank's professors, , had already offered him a job at Siemens. In early 1924 however, he met another professor of his, M. Weber, at a train station in Potsdam. Weber told him about the openings at Rohrbach Metallflugzeug, which was working on aircraft design, a field Weber knew Tank was interested in. Rohrbach had asked Weber to recommend recently graduated engineers to them. Tank took up the offer quickly, as he already had experience in both flying and aircraft design. At Rohrbach, Tank was assigned the task of establishing a design bureau at the company. Tank began his work at Rohrbach by conducting flight tests on the Ro III, a flying boat powered by two Rolls-Royce Eagle IX engines. Tank meanwhile continued his flight training and began training on flying boats. During testing, the Ro III's front hull was found to undergo a lot of strain when landing on choppy waters. The stiffeners on the bulkhead plates would usually crack after these landings. Tank suggested that a cushioned keel would reduce the strain on the front hull and keep it within an endurable range. To test this idea, Rohrbach allowed Tank to tow Ro III models with varying keel types on water.
Such testing was first done at the in Berlin. This testing was later done at in Hamburg with bigger models. Tank towed varying designs for 1000s of kilometres; these tests verified his ideas and Rohrbach incorporated them into their production models. The changed designs had a keel which spread landing impact over longer durations and lengths, lowering landing pressure on the hull without impacting takeoff performance. These changes were implemented on the Rohrbach Ro V Rocco, Rohrbach Romar, Rohrbach Ro XI Rostra and both variants (I and II) of the Rohrbach Ro VII Robbe. After more testing and with observations on the aforementioned planes, Tank introduced an improved design with a modified empennage and wings. The older designs used a constant chord rectangular wing, while the newer designs used a tapered wing which had a significantly lower weight. The new tapered wings had higher taper at an invariant thickness. These modifications enhanced flight handling and also allowed for more maneuverability.
Rohrbach Ro IX Rofix
In 1925, the Turkish Air Force ordered two prototypes of the Rohrbach Ro IX Rofix to function as fighter aircraft. Tank designed these two aircraft as full metal planes with a significant dihedral and two cables which braced the wings. This design was much like the design of the latter Rohrbach Ro VIII Roland. Tank had said the distinct structure of the aircraft was intended to allow the pilot unconstrained visibility in all directions. Testing showed that the significant dihedral angle allowed the pilot great visibility, but made the aircraft unstable and sent it into Dutch rolls on the yaw and roll axes. The aircraft was also found to have difficulties with spins.
The second Ro IX prototype crashed in January 1927 with as its pilot. As a result, the dihedral angle was eliminated. Ernst Udet then flew the plane and issued a positive assessment on 1 July 1927. Udet also noted down a few potential improvements, namely greater aileron control, enhanced lateral stability and better handling during slip maneuvers. After Udet's feedback was implemented, the Ro IX was tested and approved for flying by the German Aerospace Center. On 15 July 1927, pilot Paul Bäumer crashed in the Ro IX; Tank said Bäumer had not considered that such large planes can execute spin maneuvers only at low throttle. Tank represented Rohrbach in an inquiry into the incident. At the inquiry, fighter pilot Friedrich Mallinckrodt questioned why a fighter aircraft was designed as a monoplane and not a biplane. Many other WWI fighter pilots also said a monoplane fighter was very dangerous and not suitable for flight. Tank reminded the fighter pilots they had flown the Fokker D.VIII, a monoplane, with great success during the war; thereafter, the issue of a monoplane fighter was settled.
Rohrbach Ro VII Robbe
The Rohrbach Ro VII Robbe I was most probably developed by Tank. It was the first flying boat to have a pusher configuration, which ensures sufficient airflow is available to neutralize the greater drag caused by the aircraft's engines. The configuration also shielded the propellers from sea spray. Tank began by measuring the plane's dimensions to ascertain whether the propeller arc would be impaired by the boundary layer streaming off of the wing. These tests were done at the Max Planck Institute for Dynamics and Self-Organization in Göttingen. Professors Ludwig Prandtl and Jakob Ackeret were also involved in these experiments. When the propeller blades entered the boundary layer, a loud sound was heard, which Prandtl proved was an A note. Tank also conducted other tests in Göttingen. Professor Albert Betz had created a system to assess the real drag of an aircraft. Tank used this system to compare two of his designs, and found the first one had 30% more drag than the second one. He then improved his design, which resulted in lighter wings, and a higher tailplane which was outside the range of sea spray.
The Rohrbach Ro VII Robbe II, with a sharp taper and an aspect ratio of 8.40, was built for research and setting records. Aviation experts cautioned Rohrbach about the very high taper and said it would stall on one wing, so did Landmann. Tank said the tapered wings provided much more control to the pilots because the incremental drag would be quite lower compared to rectangular wings. Landmann, initially hesitant, later found the Robbe II to be very maneuverable. Udet wanted to attempt a trans-Atlantic flight, he teamed up with Tank and chose the Robbe II as his plane. Udet flew his first practice flight on the same day, after Tank had told Udet the aircraft had a high landing speed. Udet executed both the takeoff and sky flying properly, but he slowed down on his landing approach. The plane stalled at approximately and dropped into the water. It seemed as if the plane had sunk, but then it appeared again on the water with only little damage. The aircraft hadn't tilted towards either wing, it had stayed straight while its altitude dropped.