Junkers F 13

This page covers the F 13 in its original 1919 configuration: the first aircraft built at Dessau, with a Mercedes D IIIa engine and a smaller wing than the one production machines would carry. The variant list in the English Wikipedia describes it as the first prototype. Later production, the sub-series with other engines and the total number built belong to other variants and to the model, not to this one.

Before the end of the First World War Junkers was already working on a passenger aircraft, the J 12, which was dropped shortly afterwards when work began on the J 13, the internal designation under which the future F 13 was developed. Hugo Junkers asked his chief designer, Otto Reuter, for a passenger aircraft built entirely of metal and meant for civil use only; military considerations played no part. The letter F, for Flugzeug (aircraft), launched a new designation system at the company. The design had to fit within the restrictions the Allies imposed on German civil aviation: a maximum speed of 170 km/h, a ceiling of 4000 m, a payload of 600 kg and a range of 300 km, limits that were not lifted until the Paris Air Agreement of 21 May 1926. Hence its modest size, with room for two crew and four passengers.

The result was a cantilever low-wing monoplane with a thick, tapered wing and tailplane, a triangular fin and no flaps. The whole structure was Duralumin, with tubular spars and corrugated sheet skin, the technique Junkers had used since the J 7 of 1917, and the aircraft could be dismantled into sections for shipping. In the first aircraft the two crew had a single set of controls (dual controls came later) and few instruments; the two windows of their station had no glazing, only an airflow deflector in front of each opening, to avoid icing and fogging. The four passengers sat in an enclosed cabin with glazed windows, at first separated from the cockpit by a bulkhead with no passage.

The first flight took place at Dessau on 25 June 1919, with company pilot Emil Monz at the controls and a water-cooled six-cylinder inline Mercedes D IIIa driving a fixed-pitch two-bladed laminated wooden propeller. Sources disagree on which airframe flew that day. The German Wikipedia credits works number 531, named Herta after Hugo Junkers' eldest daughter, which was registered D-183 on 18 July 1919 and, in the register in force from 22 May 1920, D-1; the name was assigned on 30 July, when Junkers also approved calling the second F 13, still under construction, Anneliese. The flyingmachines.ru account reverses the order: the 25 June prototype would be number 533, Annelise, while 531, Herta, first flew on 18 July with the registration D-183, later D-1; in Deutsche Luft Hansa service that aircraft carried the names Nachtigall, Annelise and Herta at different times.

The power of the Mercedes D IIIa varies by source: 127 kW (170 hp) in the English and Spanish Wikipedias, while flyingmachines.ru lists it at 160 hp and gives data for the F 13 with a 158 hp Mercedes. The wing does not match either: the English Wikipedia gives a span of 14.47 m and an area of 38.9 m²; flyingmachines.ru gives 14.8 m and 34.5 m². The latter account credits this version with a length of 9.6 m, an empty weight of 950 kg, a loaded weight of 1640 kg, 170 km/h and a range of 1400 km. Production aircraft received a wing of greater span and area and the more powerful BMW IIIa.

During testing, on 13 September 1919, Monz took an F 13 to 6750 m with eight people on board in 86 minutes; flyingmachines.ru also records reduced figures of 6290 m in 81.6 minutes. The climb was logged on a Flugzeugmeisterei barograph but could not be officially recognised because Germany was then denied membership of the FAI; the Alte Adler association, by contrast, speaks of six occupants and a recognised record. That aircraft no longer had the original configuration: it carried a 185 hp BMW IIIa and, probably, the enlarged production wing. The flight did much to publicise the F 13.

On a flight from Berlin to Moscow, Annelise had to make a forced landing at Kovno (now Kaunas) in Lithuania and was impounded by the authorities; it later returned to Germany and was registered D-41. A static replica built by Pflumm reproduces the appearance of the first prototype, D1 "Nachtigall": it was displayed until 2013 at the Albatros-Flugmuseum at Stuttgart airport and, after several years of restoration, has been on show at Mönchengladbach airport since September 2019.