Junkers F 13de

Junkers identified F 13 versions with a two-letter code after the type name: the first letter denoted the airframe and the second the engine. Every Junkers L5-engined variant carries -e as its second letter, so the F 13de is the d airframe fitted with an L5. The d airframe comes from the aircraft's early evolution: in 1920 the first major modification of the original F 13 increased the span by 2.90 m, to 17.75 m, producing the F 13a; a series of minor design modifications then became the F 13b, F 13c and F 13d. The Spanish-language Wikipedia adds that the F 13d, like the F 13g and F 13h, received a wide variety of engines, which is why the same airframe appears with several different engine letters.

The F 13de should not be confused with the F 13dle, which Stroud lists among the later L5-powered aircraft together with the F 13fle, ge, he and ke: one extra letter in the code makes it a different variant, and the material consulted does not explain what the "l" adds.

The F 13de did not come from nowhere. According to the Spanish-language Wikipedia, in 1923 the F 13da became the first F 13 series powered by an engine of Junkers' own, the L2, a water-cooled four-stroke inline six and the company's first engine built on a production line, rated at 230/195 hp. Compared with the Mercedes- and BMW-engined F 13s, the da could carry 40 per cent more payload than the former and 25 per cent more than the latter, but its range fell by 250 km.

John Stroud's history, reproduced on flyingmachines.ru, describes the origin of the sub-type precisely: modifications and the installation of L5 engines in F 13ba, F 13ca, F 13da and F 13fa aircraft made them the F 13be, F 13ce, F 13de and F 13fe respectively. In that source, then, the F 13de is a modified and re-engined F 13da rather than a new design; the material does not say whether aircraft were also built from new as "de".

The date differs between sources. The Spanish-language Wikipedia states that the first L5s were installed in the F 13 in 1926 and that the result was the F 13de. Antony Kay's text, also on flyingmachines.ru, places the first use of a Junkers engine in the F 13 in 1923, with the be, ce and de fitted with the 305 hp L5. The English-language Wikipedia article on the engine says in its text that the L5 first ran in 1925, although its infobox gives 1922. Where the sources do agree is that by 1926 the L5 had become the engine most frequently installed in the F 13.

The L5 was an upright, four-stroke, water-cooled inline six, a much enlarged development of the L2 with four times its swept volume: 160 mm bore, 190 mm stroke and 22.92 litres. The English-language Wikipedia credits it with 260 kW (350 hp) for take-off at 1450 rpm and 280 hp in cruise, and with more than 1000 built. The power quoted for the F 13de varies with source and rating: the Spanish-language Wikipedia gives 349/280 hp in its text and 208 kW (283 CV) in its specification, and Kay gives 305 hp.

According to the Spanish-language Wikipedia, the greater empty weight forced the F 13de's payload back down to that of the earlier BMW- and Mercedes-engined versions; speed rose by 10 per cent over them, but range shortened as it already had in the F 13da. Kay sums it up the same way: L5-powered F 13s were heavier empty and were superior to the Mercedes- and BMW-powered versions only in speed. To maintain range with these larger, thirstier engines, a large cylindrical auxiliary fuel tank could be fitted in place of the two forward passenger seats.

The Spanish-language Wikipedia devotes its specification box to the F 13de itself: two crew and four passengers, 725 kg of load, 9.60 m long, 17.75 m span, 4.10 m high and 43 m² of wing area; 1225 kg empty and 2000 kg maximum take-off weight; one L5 driving a two-bladed, fixed-pitch laminated-wood propeller; a never-exceed speed of 170 km/h, 140 km/h cruise, 980 km range and a 4600 m ceiling. The material consulted does not give how many F 13de existed, their serial numbers or their specific operators.