Bücker Bü 131 Jungmann Bü 131D

The Bü 131D was the last production version that Bücker Flugzeugbau introduced in Germany for its Jungmann training biplane. The company history published in the May-June 1983 issue of the Air Britain Digest, reproduced in Steve Beaver's archive on Bücker aircraft, calls it “the final German production version”, introduced in 1938 with minor improvements. The German Wikipedia is more specific about the changeover: from 1938 the D replaced the B version, was outwardly distinguished by a larger tailwheel and kept the same engine, the 105 PS (about 77 kW) four-cylinder inverted Hirth HM 504 A-2. It was therefore not a new aircraft but a production refinement of the model that had already made the Jungmann the Luftwaffe's basic trainer.

That low profile explains why the version appears so unevenly in the literature. History of War warns that “some, but not all, sources” mention a slightly improved Bü 131D that might have been introduced in 1938, and none of the sources consulted details those minor improvements beyond the tailwheel, or gives a first flight date or performance figures specific to the D. Its production is not broken out either: the tally of Reich Air Ministry (RLM) orders given in the German Wikipedia groups 1356 aircraft with the HM 504 engine for the B and D series together, against 223 of the A series with the HM 60, for a total of 1579 Bü 131s delivered. Of these, according to the same table, 200 came from Aero in Prague and 15 from a firm identified only as “Sta”; the rest were built by Bücker.

Czech production is the best documented chapter of the D. The Czech Wikipedia relates that, after the German occupation, licence manufacture at Tatra was stopped once the thirty-fifth aircraft was finished, and in the spring of 1939 it moved to the Aero factory, then located in Prague, where Bücker Bü 131D-2s were built for the Luftwaffe. Around 24 Jungmann a month left the line there until September 1940, when, according to the English Wikipedia, the plant switched to the Focke-Wulf Fw 189 Uhu; the latter puts Aero's output at about 300 aircraft, the same number the Air Britain Digest gives for the Prague factory, whereas the RLM table quoted above credits it with 200. Skytamer, for its part, describes that wartime production at Aero as built under the original Bü 131B designation, so the D-2 attribution comes from the Czech and English Wikipedias. After the war the Czech line was reopened on that basis with the Aero C-4 and C-104, variants that have their own histories.

Hungary was the foreign customer most clearly associated with the D. The Air Britain Digest states that it received 151 Bü 131Ds from 1939 onwards, although most Hungarian aircraft were destroyed when the Germans retreated. By salvaging parts and building new wings, the Hungarians rebuilt 42 Jungmann by 1947, but the lack of spares grounded the last one in 1953. The Hungarian figures do not match across sources: the same article counts, in another passage, 119 aircraft ordered by Hungary, and the Hungarian Wikipedia list of aircraft used by the Royal Hungarian Air Force gives about 105 Bü 131s in service between 1936 and 1945, without distinguishing versions.

In Spain the D-2 served as the pattern for the first licence production. The Bücker Prado text held in the same archive stresses that the Spanish Air Force was the only air force to use every active variant of the Bü 131 (the A, the B, the D and finally the CASA 1.131E of the 1950s) and that the latter was designed as an improved version of the Bü 131-D2, of which CASA had previously built 200 under licence. The Fundación Infante de Orleans dates the first flight of the first Spanish-built Bücker to 14 March 1941 and says that, after two hundred had been built with the German engine, deliveries with the Spanish Tigre engine began in 1950; the Air Britain Digest, by contrast, places the appearance of the first CASA 1.131s with the Hirth HM 504 in 1938. The Spanish series has its own page as the CASA 1.131.

The D brought the Jungmann's development in Germany to an end. Although none of the sources consulted gives a production figure or a first flight date exclusive to this version, its footprint is clear: it was the version built in Prague for the Luftwaffe, the one Hungary received and the one that served as the model for CASA's first Bückers.