Bücker Bü 131 Jungmann Bü 131B

In 1936 Jungmann production moved from the A series to the Bü 131B. According to the May-June 1983 issue of the Air Britain Digest, the change followed the Luftwaffe's selection of the Jungmann as its primary trainer: the 105 hp (78 kW) Hirth HM 504A-2 became standard for the B series, replacing the 80 hp Hirth HM 60R that powered the D-3150 prototype and the A series. The airframe was essentially unchanged: a single-bay biplane with two open cockpits in tandem, fabric-covered wooden wings with ailerons on all four planes, dihedral and eleven degrees of sweepback, interchangeable upper and lower wings to ease repairs, and a fabric-covered steel-tube fuselage with light alloy panels around the engine and cockpits.

The new engine added some eight miles per hour (about 13 km/h) to the maximum speed and, above all, improved the climb: the Air Britain Digest gives the B 5.2 minutes to reach 1,000 m against 7 minutes for the A, while the Bücker-Museum at Rangsdorf gives 6.3 minutes for the B. The published figures differ between sources. The Jane's Fighting Aircraft of World War II entry, quoted by the English Wikipedia, gives a length of 6.62 m, a wingspan of 7.4 m, a height of 2.25 m, a wing area of 13.5 m², 380 kg empty, 670 kg gross weight, a maximum speed of 183 km/h, a range of 650 km and a ceiling of 4,300 m. The Rangsdorf museum credits the B with a 100 PS HM 504 A, 390 kg empty, a 290 kg payload, 680 kg take-off weight, a cruising speed of 170 km/h and a 3,000 m ceiling; Jean-Denis Lepage's book, as cited by historyofwar.org, agrees on about 390 kg empty, 680 kg loaded, 183 km/h at sea level, 171 km/h cruising, a ceiling of about 3,000 m and a range of 650 km. The Spanish Wikipedia gives a 4,500 m ceiling.

No production figure exists for the B series on its own. The German Wikipedia records that 223 Jungmann with the HM 60 (A series) and 1,356 with the HM 504, a figure that groups the B and D series together, were delivered against Reich Air Ministry (RLM) orders, 1,579 in all; of these, 200 came from Aero, 15 from a manufacturer abbreviated Sta and the rest from Bücker. The Air Britain Digest instead speaks of 300 Jungmann built at the Aero factory in Prague. The English Wikipedia specifies that in occupied Czechoslovakia the aircraft was mass-produced by Aero under the original Bü 131B designation, and skytamer.com adds that most wartime production for the Luftwaffe came from there; after the war these aircraft kept flying with their Hirth engines. According to the German Wikipedia, from 1938 the D version, with the same HM 504 A-2 and a larger tailwheel, replaced the B on the German line; historyofwar.org, by contrast, treats the B as the last production version and notes that only some sources mention the D.

In service the Bü 131B was the Luftwaffe's primary trainer and passed through virtually all of its primary flying schools during the Second World War. It also flew with night harassment units such as Nachtschlachtgruppen 2, 11 and 12: according to historyofwar.org, late in the war a number of Jungmann were allocated to such units on the Eastern Front, modified to carry 1 kg and 2 kg bombs, and used to keep up a constant stream of minor attacks on the Soviet front lines. Its replacement was the Bü 181 Bestmann monoplane, which used the same 105 hp Hirth HM 504 'as used in the Bü 131B' and, ordered into production in 1940, supplanted the biplanes on the Rangsdorf line within a year; the same engine had powered the Bü 134 touring prototype (D-EOPA) in 1936.

The B was also the version that foreign customers evaluated. Switzerland tested it and decided to buy it for its Air Force and Aero Club, with a manufacturing licence granted to Dornier-Werke at Altenrhein, which has its own page. The Japanese Navy evaluated a single Bü 131B in 1938, ordered 20 the following year and secured the manufacturing rights that led to the K9W1. According to historyofwar.org, the Tatra works obtained a licence to build the Bü 131B as the T-131. Spain received more than a hundred German-built Jungmann from February 1937 before building it under licence as the CASA 1.131, but the sources do not break those deliveries down by version.