Kurt Waldemar Tank was born on February 24, 1898, and died on June 5, 1983. He was a German aircraft engineer and test pilot who worked at Focke-Wulf from 1931 to 1945. During this time, he was in charge of the design department and created several important aircraft used by the Luftwaffe during World War II. These included the Fw 190 fighter aircraft, the Ta 152 fighter-interceptor, and the Fw 200 Condor airliner. After the war, Tank worked for 20 years designing planes in other countries, first in Argentina and then in India. In the late 1960s, he returned to West Germany and worked as a consultant for Messerschmitt-Bölkow-Blohm (MBB).
Early life
Tank was born on February 24, 1898, in Bromberg-Schwedenhöhe, which is now known as Bydgoszcz and the Szwederowo district, located in present-day Poland. He grew up near the Netze River in the former Province of Posen. His grandfather served as a cavalry sergeant in the Uhlans, and his father, Willi Tank, was a grenadier sergeant in the 3rd Division. After leaving the military, his father worked as a technician in Nakel at a power plant on the Netze River.
Education
When World War I began in 1914, Tank wished to join the Imperial German Army's Fliegertruppe air force. However, his father insisted that Tank follow the family tradition and join the cavalry regiment he had served in. Tank ended the war as a lieutenant and company commander, having been wounded in battle several times and receiving many awards and honors. He earned the Iron Cross 1st and 2nd Class of 1914, the Ehrenkreuz Schwarzburg-Sondershausen, and the Ehrenkreuz für Frontkämpfer.
During the war, Tank spent four years reading an unnamed physics book. He was interested in hydrodynamics, the study of how liquids move. Tank wanted to use the knowledge he gained to become a pilot. He applied many times to transfer to the Fliegertruppe, but his senior officers wanted to keep him in the army because he was a strong soldier. After the war, Tank studied at and graduated from the Technische Hochschule Berlin (now the Technische Universität Berlin) in 1923. He studied electro-technology, but his hobby of gliding led him to focus on aviation. Tank also worked on building sailplanes with Akaflieg Berlin and helped start the Akaflieg (aviation) club at his university with seven other students. These eight students formed the club to support aviation development at their university despite the restrictions from the Treaty of Versailles. The club was supported by army officer Adolf Baeumker and their professor, August von Parseval.
The other seven students who started the club were Hermann Winter, Werner Henninger, Pauleduard Punk, Seppl Kutin, Viktor Gohlke, Edmund Pfister, and Georg Gillert. The eight students built a workshop in the university's loft, where they constructed two gliders and learned aeronautics from professors Emil Everling and Hans Reissner. Tank built a monoplane with a large wingspan and strut bracing. Winter built 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 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 crashed near Gersfeld due to a downdraft. The group moved the plane to Gotha, where Gothaer Waggonfabrik sent it to Berlin for repairs. Meanwhile, Tank built a shoulder-wing plane with a large wingspan, which the group entered in the 1923 Rhön Competition. This plane was the Akaflieg Berlin B2 Teufelchen ("Little Devil").
However, the group could not build both the B2 and B1 planes in their small university workshop. The students also could not build the planes themselves, as it would affect their studies. Therefore, Tank and Gillert visited the Albatros Flugzeugwerke factory in Johannisthal, a Berlin suburb. There, they met Robert Thelen, an aviation world record holder and company director. Thelen refused to build a sailplane for free, especially because it used wing warping wingtips instead of ailerons. Tank and Gillert then went to Luft-Fahrzeug-Gesellschaft in Stralsund, who agreed to build the B2 Teufelchen. By building the B2, Tank passed his preliminary exams, and his academic work was praised by professors Parseval and Wilhelm Hoff. At the Rhön Competition in August 1923, Tank had to land the B2 on rough terrain during practice. The B2 was damaged, and the group had spent all their money by then. Later, the group repaired the B2 and flew it in Rositten. Tank then trained and earned a flying license at Staaken, flying the DFS Kranich with Rudolf Rienau as his instructor.
Early career
In 1924, Tank met Professor M. Weber at a train station in Potsdam. Weber told Tank about job openings at Rohrbach Metallflugzeug, a company working on aircraft design. Weber had been asked to recommend engineers who had recently graduated. Tank accepted the offer quickly because he had experience in flying and aircraft design. At Rohrbach, Tank was given the task of creating a design bureau for the company. His first work involved testing the Ro III, a flying boat powered by two Rolls-Royce Eagle IX engines. During these tests, the front hull of the Ro III experienced heavy stress when landing on rough water. The stiffeners on the bulkhead plates often cracked after these landings. Tank suggested adding a cushioned keel to reduce the stress on the hull. To test this idea, Rohrbach allowed Tank to tow models of the Ro III with different keel designs on water.
These tests were first conducted at the Preußische Versuchsanstalt für Wasser-, Erd- und Schiffbau in Berlin. Later, larger models were tested at the Hamburgische Schiffbau-Versuchsanstalt in Hamburg. Tank towed many different designs over thousands of kilometers. The tests confirmed his ideas, and Rohrbach used them in their production models. The new designs spread the force of landing over longer areas, reducing pressure on the hull without affecting takeoff performance. These changes were applied to the Rohrbach Ro V Rocco, Rohrbach Romar, Rohrbach Ro XI Rostra, and both versions of the Rohrbach Ro VII Robbe. After further testing, Tank introduced an improved design with a modified tail and wings. Older models used rectangular wings with a constant width, while newer models used tapered wings that were lighter. The tapered wings had a higher taper at the same thickness. These changes improved flight control and made the planes more maneuverable.
In 1925, the Turkish Air Force ordered two prototypes of the Rohrbach Ro IX Rofix as fighter aircraft. Tank designed these planes with a full metal structure, a significant dihedral angle, and two cables to support the wings. This design was similar to the later Rohrbach Ro VIII Roland. Tank said the design allowed pilots to see clearly in all directions. Testing showed that the dihedral angle improved visibility but made the plane unstable, causing it to enter Dutch rolls during yaw and roll movements. The plane also had difficulty with spins.
The second Ro IX prototype crashed in January 1927 with pilot Werner Landmann. As a result, the dihedral angle was removed. Ernst Udet later flew the plane and gave it a positive review on July 1, 1927. Udet suggested improvements, such as better aileron control, improved stability, and better handling during slips. After these changes were made, the Ro IX was tested and approved by the German Aerospace Center. On July 15, 1927, pilot Paul Bäumer crashed in the Ro IX. Tank said Bäumer had not realized that large planes can only perform spin maneuvers at low engine power. Tank represented Rohrbach during an investigation into the crash. Fighter pilot Friedrich Mallinckrodt questioned why a monoplane was used instead of a biplane, as many World War I pilots believed monoplanes were unsafe. Tank reminded them that the Fokker D.VI, a monoplane, had been successfully used during the war, and the issue was resolved.
The Rohrbach Ro VII Robbe I was likely designed by Tank. It was the first flying boat to use a pusher configuration, which ensured enough airflow to reduce drag from the engines. This design also protected the propellers from sea spray. Tank tested the plane’s dimensions to see if the propeller arc would be affected by airflow from 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 involved in the experiments. When the propeller blades entered the boundary layer, a loud sound was heard, which Prandtl identified as an A note. Tank also used a system developed by Professor Albert Betz to measure drag. He compared two of his designs and found the first had 30% more drag. He improved his design, resulting in lighter wings and a tailplane positioned 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 record attempts. Aviation experts warned that the high taper could cause one wing to stall, as Landmann noted. Tank said the tapered wings gave pilots more control because they created less drag than rectangular wings. Landmann, who was initially hesitant, later found the Robbe II to be very maneuverable. Ernst Udet wanted to attempt a trans-Atlantic flight and chose the Robbe II as his plane. Tank told Udet the aircraft had a high landing speed. Udet performed the takeoff and flight correctly but slowed down during landing. The plane stalled at about 50 feet (15 meters) and dropped into the water. It appeared to sink but resurfaced with little damage. The plane stayed straight as it descended.
Three weeks later, Udet and Tank attempted a record flight. Tank ensured Udet had a fast takeoff and ascent. The flight was expected to last ten hours and cover 2,000 kilometers (1,200 miles). They followed a triangular route three times from Copenhagen to the Swedish coast, with officials from the Fédération Aéronautique Internationale observing. They flew well until a sharp sound occurred, the engines buzzed, and the plane began shaking. Tank and Udet regained control but lost altitude and crashed into the water. Both propellers had blown off, and the engines shut down. The plane landed safely and did not sink. A small fire started because the fuel tanks were hit by pieces of the propellers. The idea of a trans-Atlantic flight was abandoned.
Tank’s most successful design was the Ro VIII Roland, a fast passenger airliner with three engines built for Lufthansa. Tank said the semi-cantilever shoulder-wing design allowed passengers to see the ground clearly. He also said the engines were placed below the wings to maintain airflow over the upper control surfaces. While building the plane, Lufthansa asked Tank and Adolf Rohrbach to reduce the wing loading from 80 kg/sqm to less than 60 kg/sqm, or they would cancel the order. One solution was to lengthen the wingspan, but this would be very expensive.
At Focke-Wulf
Tank moved to the firm Albatros Flugzeugwerke, where he worked as a test pilot. The Albatros company went bankrupt in 1929 and in 1931, because of government pressure, was combined with Focke-Wulf. In November 1931, Tank joined Focke-Wulf in Bremen as the head of design and flight testing. Tank initially focused on test flying aircraft, mostly those brought over from Albatros. He worked on adding his special features to these aircraft. The first aircraft he test flew were the Albatros Al 101 and the Albatros L102. Tank almost died when the L102 he was flying crashed after he dove at 4,000 feet (1,200 m). He managed to get out of the plane before it exploded and did not sustain any significant injuries. Tank also found ways to improve the Focke-Wulf Fw 43 Falke, but he could not use his ideas because only a few models of the plane were built.
Tank then test flew the Focke-Wulf Fw 47 Höhengeier, developed by Henrich Focke. Focke believed the aircraft could not perform spinning maneuvers because of its unique wing shape. Tank widened the tail and used the rudder to show the aircraft could be spun. Tank then started work on the design of the Focke-Wulf Fw 44 Stieglitz, a biplane trainer. While flying the aircraft at Bremen, Tank found it would shake uncontrollably. The two separate elevators were the problem, so they were combined into one unit. After the Fw 44 was moved to production in 1934, Tank worked on test piloting the Albatros L103. During this period, Tank also began building a team that could make complex aircraft like airliners because the new German government did not restrict aviation. Tank convinced Focke-Wulf director Werner Naumann to fund these new projects. Tank brought over Hans Schuberth, Andreas Faehlmann, and other engineers to Focke-Wulf. New groups and teams were formed to build these aircraft, with Tank managing and advising them.
In 1934, Tank's Focke-Wulf Fw 56 Stösser advanced trainer began production. In 1935, Ernst Udet used the Stösser to demonstrate the usefulness of dive bombing to German officials. A total of 900 to 1,000 Stössers were built, but none are still around today. Tank then wanted to build a full-metal aircraft so he could modernize the company's production processes and help employees learn new skills. Three models of the Focke-Wulf Fw 57, a heavy strike aircraft, were built as a result. However, production models of the Fw 57 were not built because the RLM (Nazi Aviation Ministry) decided to use light strike aircraft instead. In 1934, Tank also designed the Focke-Wulf Fw 159, a single-seater chase fighter according to the RLM's requirements. Tank modeled the Fw 159 after the Polish PZL P.24, considered the best fighter during the early 1930s. However, it was not