Bücker Bü 131 Jungmann Bü 131B

In 1936 production switched from the Bü 131A to the Bü 131B, which replaced the Hirth HM 60R with the 105 hp HM 504A-2. According to the Air Britain Digest, the new engine added some eight miles per hour to the maximum speed and greatly improved the climb: 1,000 metres were reached in 5.2 minutes against seven for the A. The Jane's Fighting Aircraft of World War II entry gives the B a length of 6.62 m, a wingspan of 7.4 m, 380 kg empty and 670 kg gross weight, a maximum speed of 183 km/h, a range of 650 km and a service ceiling of 4,300 m; the Bücker-Museum at Rangsdorf quotes 390 kg empty and a 3,000 m ceiling, and the Spanish Wikipedia 4,500 m.

Shortly after its appearance the Bü 131B was selected as the Luftwaffe's primary basic trainer. During the Second World War it served with nearly all of the German primary flying schools and also with the night harassment units Nachtschlachtgruppen 2, 11 and 12, until the Bü 181 Bestmann monoplane gradually supplanted it in the latter half of the conflict. It was also the version that won over export customers: Switzerland evaluated the B and adopted it for its Air Force and Aero Club, the Japanese Navy evaluated one in 1938 before ordering 20 and buying the licence, and the Kingdom of Yugoslavia, the leading pre-war customer, is thought to have received as many as 400 Jungmann. Bulgaria (15) and Romania (around 40) were other buyers.

The B is the starting point of nearly the whole family: the Swiss Dorniers, the Czechoslovak Tatra, the Japanese Kokusai and Kyūshū and the Spanish CASA 1.131 all derive from it, and the Aero factory in Prague itself built it during the occupation under the original designation. In 1938 the D version, with minor improvements, took over on the German line.