Junkers F 13 F 13de

In 1926 Junkers fitted the F 13 with its new water-cooled inline six, the L5, appreciably more powerful than the L2 it replaced. The result was the F 13de, and from that year the L5 became the type's reference engine: almost every later sub-type carries the letter e as the second character of its designation, because that letter denotes the L5.

Speed rose by roughly ten per cent over the previous versions. Against that, the heavier installation forced payload back down to the level of the Mercedes- and BMW-engined aircraft, and range shortened again, as it had with the L2. The trade was deliberate: on the German routes of the late 1920s, journey time mattered more than endurance.

The Spanish specification describes an aircraft 9.60 m long, spanning 17.75 m and standing 4.10 m high, with 43 m² of wing and a maximum take-off weight of 2000 kg. It cruised at 140 km/h against a never-exceed speed of 170 km/h, ranged 980 km and topped out at 4600 m, carrying two crew, four passengers and 725 kg of load.

The L5 brought the F 13 to commercial maturity just as Deutsche Luft Hansa was consolidating the German fleet. The airline operated around 110 of them and by 1928 was flying them on 43 domestic routes; as late as 1937 its F 13s still covered more than fifty flights a week on four routes, before final withdrawal in 1938.