Junkers Aircraft and Engines 1913-1945

A.Kay - Junkers Aircraft and Engines 1913-1945 /Putnam/

Junkers J1

  The experimental J1 was the world’s first airworthy all-metal aircraft. Nicknamed ‘Blechesel’ (Tin Donkey), it was designed by Dipl.- Ing. Otto Reuter and Dr-Ing. Otto Mader in collaboration with Hugo Junkers. Earlier experiments with a French Voisin biplane had given Dr-Ing. Reiszner some initial experience, and this was increased by the construction of a canard aircraft which had its rear-mounted wings constructed from corrugated sheet iron and was based on Junkers’ early experiments. The corrugations gave the thin metal rigidity. The aircraft first flew (not altogether successfully) on 23 May 1912 and crashed in 1913.
  The construction of the J1 was extraordinarily complex for the time, and many were baffled as to why one would want to attempt to build and fly an apparently heavy iron aeroplane - and at great expense into the bargain. However, the metal used was sheet iron of only 0.1-0.2mm thick, normally used for magnetic purposes. The wing was built up of short, hollow aerofoil sections about 420mm (10.7in) wide, and each section was welded together to give a complete unit. Far from ideal, this method of construction was, however, governed by the sheet material available from Junkers’ heating and other products. Inside each section were iron ribs which gave bracing and shape to the covering, and to these was welded, with great difficulty, the thin iron covering. This covering was corrugated to give the necessary rigidity, and on top of that was welded a smooth iron skin. The assembly of the complete wing was carried out on a jig of wooden formers to ensure true alignment. Large, unbalanced ailerons were provided, and these had horns for the control cables.
  The fuselage was made by wrapping thin corrugated sheet around wooden formers and welding it, a further smooth skin being welded on top. Multiple bracing tubes connected each wing to the fuselage at three points. A tailplane of metal construction carried an unbalanced elevator, and a balanced rudder, without a fixed fin, was used. There was a fixed, braced undercarriage and a tailskid. To power the J1, a Mercedes D.II water-cooled, six-cylinder engine of 120hp was fitted. Static tests were carried out by loading test wings with sandbags to prove their soundness and strength, while bags were also hung on wooden levers attached to the wings to test the latter’s torsional strength.
  Construction of the J1 began in early September 1915 and was virtually complete by the end of November. Soon, on 12 December 1915, the J1 made its maiden flight, taking off from Doeberitz with Lt. Friedrich von Mallinkrodt (on secondment from Idflieg) at the controls. Although it was not equipped as a fighter, the aircraft was compared with fighters and demonstrated superior level speed though an inferior climb rate and turning ability owing to the extra weight conferred by the type of construction. Therefore, development pointed in the direction of reducing weight to enhance performance. One troublesome feature of the J1 was the anchoring of the wings to the fuselage, which had to occur at the pilot’s position. Despite much attention being lavished on the problem, this produced a structural weakness, which became apparent when, during a landing in January 1916, a wing cracked.
  Nevertheless, the J1 had proved that an all-metal aircraft could fly - and fly well. It was taken into the air by many excellent aviators, including Anthony Fokker, who found that its speed exceeded by 20kph (12mph) that of the fastest aircraft at that time. However, its rate of climb of about 45m/min (150ft/min) was poor, mainly because of the weight of the iron wings, caused not just by the metal itself but also by the need to make the covering strong enough to withstand the stresses imposed. The remarkable achievement of the J1 was all the more so for being carried out from start to first flight in only four months.
  After the First World War, the repaired Junkers J1 monoplane was exhibited at the Junkers Lehrschau (Junkers Educational Exhibit), Dessau, and later transferred to the Deutsches Museum in Munich where it was destroyed during the Second World War during an air raid.

Data: Span 12.95m (42ft 5in); length 8.62m (28ft 3 1/2in); height 3.5m (11ft 6in); wing area 24m2 (258 sq ft); loaded weight 1,010kg (2,227lb); max. speed 170kph (106mph); climb rate 45 m/min (150ft/min).
The world's first airworthy all-metal aircraft, the Junkers J1 "Blechesel' (Tin Donkey), seen here running up its 120hp Mercedes D II engine.
Junkers J2

  Since the experimental J1 monoplane had shown itself to be faster than any German fighter and could probably survive more battle damage than the usual wood and fabric aircraft, further development was warranted. The most important modifications were to redesign the way the wings were attached to the fuselage and to pare down the weight of the airframe. By moving the wings forward of the pilot’s cockpit, it was possible to build the wing centre section as an integral part of the fuselage structure with four threads on each side to which the outer wing panels could be attached. This was achieved by means of threaded collars reminiscent of pipe connections. The tube ends of these connections had male and female conical ends to ensure a strong, aligned fit. It is not difficult to see that this idea was inspired by the pipework used in Junkers’ heaters and other equipment.
  The J2 was even more streamlined than the J1, had the engine totally enclosed and was skinned with thin, sheet iron without external bracing. The undercarriage struts were streamlined, with a small inter-wheel plane surface, and there was an engine radiator beneath the cockpit. The control surfaces were similar to those of the J1, and there was a roll bar to protect the pilot in the event of the aircraft overturning on the ground. The Mercedes D II 120hp engine was used again, driving a two-bladed airscrew, and one LMG 08/15 machine gun was to be fitted.
  Seven or eight examples of the J2 fighter were ordered by the Inspektion der Fliegertruppen (Idflieg). The first (E 250/16) made its maiden flight on 11 July 1916 from Doeberitz (there being no airfield at Dessau at that time) with Lt Mallinkrodt as the pilot. This was the prototype of the first all-metal fighter, but flight tests indicated that desirable modifications should be made to subsequent machines. These included a considerable increase in power to 160hp, which was achieved by using the Mercedes D III engine, an increase of 0.7m (2ft 3in) in wing span, a reduction of wing area by 84cm2 (13 sq in), ailerons of longer span and shorter chord, a slight increase of the fuselage length and a revision of the forward fuselage contours. The next five aircraft (E 251/16 to E 255/16) were thus modified, and there was possibly a sixth machine also. From the third machine onwards, a revised rudder with a semi-circular forward edge giving some aerodynamic balance was fitted.
  So modified, the J2s showed good handling characteristics and a speed about 15kph (9mph) higher than that of the best contemporary fighters. However, the climb rate was not adequate for combat, again owing to the weight, and the pilot’s all-round vision was not good. Moreover, the required endurance of five hours and the agility needed could not be given. Because of these shortcomings in an otherwise excellent design - and one which presaged things to come - no further orders were received. Matters were not improved when the second prototype (E 251/16) crashed following a low-level stall on 23 September 1916, killing the pilot Max Schade.

Data (definitive aircraft): Span 11.75m (38ft 6 1/2in); length 7.45m (24ft 5 1/2in); height 3.13m (10ft 3in); wing area 24.64m2 (265 sq ft); empty weight 1,020kg (2,249lb); loaded weight 1,165kg (2,569lb); max. speed 185kph (115mph); time to 3,000m (9,840ft) 21min; range 240km (149 miles).

Junkers J3

  The main lesson learned from work on the J2 was that weight needed to be reduced in order to achieve good climb and turning performances. Therefore, during 1916, Junkers turned its attention to the use of Duralumin lightweight alloy instead of iron, and work began on the J3. The design of the J3, which was to appear in the form of both a single-seat fighter and a two-seat observation aircraft, was undertaken by Mader, Reuter and Brandenburg, while engineer Steudel was in charge of the development of new production technologies for Duralumin. The aircraft had a welded, tubular structure with a light Duralumin covering which, for the wings at least, was corrugated to give lightness with rigidity. Once again the outer wing panels were attached by threaded collars (but with ball-and-socket joints) to a short centre section built integrally with the fuselage structure. Absence of interest from Idflieg led to this aircraft construction being closed down before completion because of a lack of funds, and the airframe was put on display at the Junkers Lehrschau until the end of the Second World War.

Data (J3 fighter): Span 11.45m (37ft 6 3/4in); length 6.65m (21ft 9 3/4in); wing area 21.0m2 (226 sq ft); empty weight 570kg (1,257lb); loaded weight 770kg (1,698lb); max. speed 180kph (112mph); range 170km (105 miles).
The first all-metal fighter, the Junkers J2, was developed from the J1 and was powered by a 160hp Mercedes D III engine. Shown in this two picture is the J2 registered E 252/16.
Junkers J2.
J2s in production in Junkers’ factory in 1916.
Built of Duralumin tubing and covering, the J3 fighter was never actually completed. It is seen here displayed at the Junkers Lehrschau in 1916.
Junkers J5

  This was a study for a single-seat, low-wing monoplane fighter which was not built. An attempt was made to streamline the large airscrew spinner with the engine cowling, but satisfactory cooling arrangements could not be devised.
  Various other studies were made under the J5 designation, although exact information is unavailable. Examples are the J5 I and J5 II, which each had the engine moved to the rear of the fuselage. Both Mercedes D IIIa and Siemens Sh2 engines were considered for J5 designs.

Data (J 5 I): Span 11.8m (38ft 8 1/2in); length 8.0m (26ft 3in); wing area 20.0m2 (215 sq ft); empty weight 465kg (1,025lb); loaded weight 660kg (1,455lb).

Junkers J6

  With the J6 parasol (high-wing) fighter, a new design was begun that, aerodynamically at least, was unrelated to earlier Junkers’ work but reflected the popularity of parasol fighters (such as those from Fokker) with fighter pilots. It resulted in a short, stubby fighter with a Siemens ShIII 158hp radial engine and an underfuselage fuel tank. Construction of the J6 was begun in the summer of 1918 but stopped when half completed at the war’s end in November.

Data: Span 8.0m (26ft 3in); length 5.6m (18ft 4 1/2in); wing area 12.0m2 (129 sq ft); empty weight 420kg (926lb); loaded weight 615kg (1,356lb); max. speed 190kph (118mph); range 270km (168 miles).
Junkers J4 (J.I)

  The Flugzeugmeisterei, although impressed by the revolutionary metal construction of Junkers’ aircraft, did not see them as fighters but rather as ground-attack aircraft having the most useful ability to withstand small-arms fire. Junkers were therefore asked to develop an armoured ground-attack biplane, and this was designated J4 by the company and JI by the military (thus forever causing confusion with the original Junkers J1). The design and development of the J4 was the responsibility of Reuter, Steudel, Brandenburg and also Professor Dr G. Madelung, who was later (1934) to work out designs of flying bombs and aircraft to utilise Paul Schmidt’s pulsejets.
  The J4 was a two-seat sesquiplane (a biplane with the bottom wings of shorter span than the top wings), its bottom wing attached to the base of the fuselage and the top wing supported on struts at the centre section only. Based on work on the J3, a tubular structure was used with corrugated Duralumin covering for the wings and tail surfaces, although early models had fabric-covered elevators. Ailerons were fitted to the top wings only; once the aircraft was in production, these ailerons were lengthened to project beyond the wing tips and the wing span was increased. The engine and the crew of two were enclosed in an armoured chrome-nickel steel tunnel to protect them from ground fire, and the rest of the fuselage was covered in smooth Duralumin sheet (although there was fabric covering on the rear section on early models).
  Power was supplied by a 200hp Benz Bz IV six-cylinder in-line engine, and the armament consisted of two fixed, forward-firing 7.92mm LMG 08/15 machine guns plus one 7.92mm Parabellum machine gun on a trainable mounting for the rear-cockpit observer. Later a Mercedes D IVa engine of 256hp was tried, but this was not fitted in production aircraft.
  Three prototypes were built at Dessau, and the first (c/n 425/17) made its maiden flight on 28 January 1917. By August that year, following many delays and setbacks suffered on the production line, the first batch of fifty J4s (c/ns 100/17 to 149/17) had begun entering service at the Front. They proved to be successful and popular with their crews owing to their survivability, one machine sustaining more than 400 small-arms hits without failing. By the end of the First World War in November 1918, another 177 aircraft had been delivered for service, giving a total production by the war’s end of 227.

Data: Span 16.0m (52ft 6in); length 9.1m (29ft 10 1/4in); height 3.4m (11ft 1 3/4in); wing area 49.4m2 (533 sq ft); empty weight 1,766kg (3,892lb); loaded weight 2,176kg (4,798lb); max. speed 155kph (96mph); endurance 2hr.
The Junkers J4 ground-attack aircraft was also known as the JI by the military. It was highly successful in the First World War and not easily brought down by small-arms fire. This example was registered J 138/17.
Nosed over upon landing, this Junkers J4 shows to advantage the armoured steel protecting the engine and fuselage underside.
Junkers J8 and J10 (CL and CL1)

  The J8 (official designation CL) was an all-metal, corrugated Duralumin-skinned, two-seat close-support aircraft. Similar to the J7, it featured a longer fuselage to allow for the observer’s cockpit and it also had a greater wingspan. Ailerons which extended beyond the wing tips were used, and a Mercedes D IIIa 160hp, six-cylinder, upright, in-line, water-cooled engine was fitted.
  An Idflieg contract for three aircraft was received on 26 December 1916, although the first prototype was not completed until 4 December 1917 on account of the priority accorded to production of the J4 (JI) at Junkers-Fokker. The maiden flight of the prototype was made on 10 December 1917 with Schmidt as pilot, and by May 1918 all three prototypes were undergoing tests. The J8 was demonstrated in a contest in February 1918 and this resulted in an Idflieg contract to build a modified version, the J10 (official designation CL1).
  The J10 was distinguishable from the J8 in having ailerons flush with the wing tips and by being armed with two fixed, forward-firing machine guns and, for the rear observer, one trainable machine gun. Power was increased by using a Mercedes D IIIa 180hp engine. The aircraft was first flown on 4 May 1918 but only six were delivered before the war ended, although another twenty were ordered by Idflieg in October 1918.
  Altogether, some 44 J 10s were built, most of them after the First World War. Some were used by Geschwader Sachsenberg in postwar fighting against the Bolshevik forces in the Baltic while others were demilitarised and put to civilian use, the observer’s seat being filled by a passenger.

Data: Span 12.2m (40ft); length 7.9m (25ft 11in); height 3.1m (10ft 2in); wing area 27.0m2 (291 sq ft); empty weight 735kg (1,621lb); loaded weight 1,155kg (2,547lb); max. speed 190kph (118mph): cruising speed 155kph (96mph); time to 1,000m (3,280ft) 3.9min; endurance 2hr.
A Junkers J8 (CL) close-support aircraft with balanced ailerons. This photograph is dated 2 January 1918. (Cross & Cockade)
The Junkers J10 (CL1) was a modified version of the J8 close-support aircraft. It was armed with machine guns and had ailerons flush with the wing tips. This one is c/n 1802/18.
This picture, dated 24 March 1919, shows a 'civilianised' version of the J10 with a covering for the rear (passenger) seat.
Junkers J7

  Another short, stubby little fighter, the J7 was an experimental private venture by Junkers and was the world’s first all-Duralumin, low-wing monoplane. Corrugated sheet skinning was used overall, on top of a Duralumin tube structure. The designers were Reuter and Mader.
  Originally, rotating wing tips were used for roll control, but these were later replaced with conventional, unbalanced ailerons. The tailplane had a balanced elevator and there was a vertical fin pivoting about its centre to act as the rudder. A very strong, braced undercarriage and tailskid were provided, and power was supplied by a Mercedes D IIIa 120hp engine. Curiously, the radiator for this water-cooled engine was originally mounted atop the engine cowling, but it was later moved to a more aerodynamically acceptable position in front of the cowling.
  The first flight of the J7 took place on 17 September 1917, Arved von Schmidt being the pilot. In February 1918, the last year of the war, an official contest was held at Adlershof to select a new biplane fighter but the J7 was not allowed to compete since it was a monoplane. However, officialdom relented when it was found that the J7 was the fastest fighter. An initial order was mooted, but by then the sole prototype had been overtaken by the development of the J9. Three further prototypes were cancelled when only partially built.

Data: Span 9.2m (30ft 2 1/4in); length 6.7m (22ft); height 2.6m (8ft 6 1/4in); wing area 11.7m2 (126 sq ft); empty weight 656kg (1,446lb); loaded weight 835kg (1,841lb); max. speed 240kph (149mph); time to 5,000m (16,400ft) 23.7 min; ceiling 6,000m (19,680ft)

Junkers J9 (DI)

  An improved version of the J7, the J9 fighter could be readily distinguished by the longer undercarriage legs. The all-corrugated skinning and a Mercedes D III 160hp engine were again used, and the armament comprised two fixed 7.9mm LMG 08/15 machine guns. The J9 first flew in April 1918, and some 27 were delivered by Junkers and 20 by Junkers-Fokker. The prototype did not fare well in a fighter contest held in May/June at Adlershof, and it was thought the aircraft would be better suited to the specialised role of balloon attack. More aircraft were built for service use and experimental purposes. One source states that the type is not known to have been in action before the end of the First World War, but another states that about 40 were in service; the latter seems more likely.
  Alongside the J10, some J9s were used after the war by Geschwader Sachsenburg in Finland, Estonia and Lithuania against Bolshevik forces. Of the experimental versions, one was flown with a 185hp BMW IIIa engine and another with a 185hp Benz Bz IIIb. Some J9s were fitted with Duralumin floats - the first Junkers aircraft to have these - and the type did well in the Tyrrhenic Cup Competition at Naples in 1922.

Data: Span 9.0m (29ft 6 1/4in); length 7.25m (23ft 9 1/2in); height 2.6m (8ft 6 1/4in); wing area 14.8m2 (159 sq ft); empty weight 654kg (1,442lb); loaded weight 834kg (1,839lb); max. speed 225kph (140mph); time to 5,000m (16,400ft) 24min; endurance 1.5hr.
The Junkers J7 was the world's first all-Duralumin fighter. Dated 13 September 1917, this photograph shows the sole prototype with rotating wing tips for roll control.
By 12 October 1917 the J7 fighter had been fitted with conventional, unbalanced ailerons.
The J9 of 1918, with its corrugated skin, did not fare well in a fighter contest but was nevertheless put into production.
The Junkers D.I was the world's first production all-metal fighter and was just entering service at the end of the war. A very fast airplane for its time with maximum speed of 240 km/h (148 mph), its low-wing monoplane configuration foretold the future. Power was a 180 hp BMW .IIIa engine.
The J9 appears to have entered front-line service with the Jastas before World War I ended.
The Junkers J9 (DI) fighter, showing the nine ball joint sockets for wing attachment at each side, later to become the standard Junkers method of attachment.
Junkers J11 (CLS1)

  The J11 was a floatplane version of the J10 for use as a two-seat, maritime patrol aircraft for the German Navy. It began with the modification of two J10s (c/ns 7501 and 7503) of corrugated Duralumin construction. Their rear fuselages were altered, their wing area was increased, a triangular tailfin was added and rudimentary, braced floats were fitted. The J11 was armed with a machine gun on either side of the cockpit and was powered by a Benz Bz IIIa 180hp engine. Only three were built, the first (7501/18) making its initial flight on 23 October 1918 piloted by Navy pilot Richard Thiedemann. The war’s end brought about a closure to the programme.

Data: Span 12.75m (41ft 10in); length 8.8m (28ft 10 1/2in); wing area 26.6m2 (286 sq ft); empty weight 915kg (2,018lb); loaded weight 1,420kg (3,131lb); max. speed 180kph (112mph); range 500km (310 miles).
The Junkers J11 (CLS-1) floatplane version of the J10 for maritime patrol. This is c/n 7501/18.
Junkers J12

  The last design tackled by Junkers before the end of the First World War was the J12 passenger aircraft, reflecting Professor Junkers’ great interest in civil rather than military aircraft. Originally it was hoped to capitalise on the J10 design as a passenger transport, and one example was modified with a hood over the rear passenger seat. March 1919 saw this machine in service with Junkers Luftverkehr, though merely as an interim measure.
  Therefore, using the J10 as a basis, Reuter set about designing a four-seat airliner in December 1919. This corrugated Duralumin monoplane was designated J12. The main modification from the J10 was the redesign of the fuselage to give a totally enclosed cabin for the three passengers. However, this cabin was subsequently deemed insufficiently spacious, and so the J12 project was abandoned in favour of the later famous F13.

Data: Span 12.2m (40ft 2]4in); length 8.25m (27ft Ohm); wing area 25.0m2 (269 sq ft); max. speed 170kph (105mph).
After the First World War

  Even before Armistice Day signalled the end of the First World War on 11 November 1918, Hugo Junkers was looking forward to the development of transport aircraft and the worldwide development of airlines. It can be said that he was the father of Germany’s air transport system which, alongside others, spread over much of the world and created other airlines.
  The J12 passenger aircraft was in development before the end of the First World War but was terminated soon afterwards when work began on the J13, later to become the F13. From the viewpoint of today, this aircraft with its crew of two and room for four passengers seems too small to be a commercial success, but this proved to be far from the case. Despite the fact that the aircraft was far in advance of its contemporaries, initial sales of the F13 were poor owing to Allied restrictions and the surfeit of military aircraft following the war. In fact it was not until 1919 that the first orders, for six, arrived from the United States; these, however, were confiscated by the Inter-Allied Aeronautical Commission for Control since it was considered that the F13 could be used for military purposes. (Much later, the Luftwaffe did use F13s for transport duties.) The Commission reversed its decision in February 1920 and then active promotion of the F13 began. A primary means of this promotion was the establishment by Junkers, in 1921, of its own airline - the Junkers-Luftverkehr, which later merged with Deutscher Aero Lloyd to form Deutsche Luft Hansa on 6 January 1926. A training school for pilots was also established and many schemes were begun to help companies all round the world establish fledgling airlines and air transport services. F13s appeared with wheels, floats and skis according to the dictates of operational conditions.

Junkers J13 (F13)

  When the design of the J13 was begun in 1919 it was to become not only the world’s first all-metal airliner but also the forerunner of all commercial transport aircraft. Despite the enforced destruction of more than 15,000 military aircraft and 27,000 engines, the postwar market had plenty of surplus aeroplanes which could be bought cheaply, and Junkers realised that something special was required for commercial success. Fortunately, by now the company had considerable experience in light metal working and many patents to draw upon, and these were to give the edge over the many wooden aircraft then extant.
  It now fell to Dipl.-Ing. Otto Reuter to design the J13, and he produced a single-engined, low-wing, cabin monoplane of quite small dimensions since it was necessary to work within the onerous restrictions diligently forced upon Germany by the victorious Allies. For civilian aircraft, these restrictions included a maximum speed of 170kph (105mph), a ceiling of 4,000m (13,120ft), a payload of 600kg (1,323lb) and a range of 300km (186 miles). It was not until 21 May 1926 that these restrictions were lifted by the Paris Air Agreement, but that was after the J13 had been produced. Considering the restrictions, it was remarkable that a useful and very successful aircraft was produced.
  The J13, commercially designated F13, had a cantilever, tapered, thick-section wing and tailplane with unbalanced ailerons, rudder and elevator and also a triangular fin. There were no landing flaps, but airfields were large grass affairs in those days and contemporary landing speeds were not high (about 110kph or 68mph). The construction of the aircraft was entirely of Duralumin, and it was designed to be dismantled into sections for ease of shipment, Junkers having the export market very much in mind.
  The strongest part of the aircraft was the centre section, comprising the wing centre section, engine mountings, cockpit, passenger cabin and the undercarriage struts. Each wing was attached to the centre section by means of nine threaded collars, the tube ends of which had ball-and-socket joints to assure alignment. Attachment was performed quickly and easily with the use of ‘C’ spanners, the access slots then being covered with metal strips. The wing structure consisted of tubular spars with tetrahedral bracing of Z-section struts, and the whole aircraft was covered with corrugated Duralumin sheet. All four main undercarriage legs had rubber shock absorbers, and the wheels could readily be exchanged for floats or skis. Combination wheel and skis were also possible. To prevent the aircraft from turning over, the undercarriage would collapse in the event of a hard crash-landing. Another safety innovation, aside from the strong crew and passenger section, was the fitting of seat belts in later aircraft. Triangular fuel tanks, to fit inside the internal bracing and holding a total of 338 litres (74 gallons), were installed in the wing centre section, and various engines could be fitted. These included the 160hp Mercedes D IIIa, the 180hp Mercedes D IIIav, the 185hp BMW IIIa, the 200hp Junkers L2 (Junkers first series-production engine) and the 230hp Armstrong Siddeley Puma, each driving a two-bladed, wooden airscrew.
  The two crew members were originally provided with only one set of controls (dual controls were fitted later) and few instruments, but a curious feature of their cabin was the absence of any glazing in the two windows, there being instead an airflow deflector in front of each opening. Problems of vision due to icing and fogging were thereby avoided, although one would have thought that Junkers’ experience in manufacturing heating equipment could have suggested something better. A radio service for air transport was not available until after 1920, when the first radio station was set up by the Marconi company at Croydon near London, while from 1922, again in Britain, the first radio beacons and DF loop aerials appeared. The four passengers were completely enclosed in more comfort in the cabin and their windows were glazed. Originally, there was no passage between the passengers’ cabin and the pilots’ cockpit and the two were partitioned by a bulkhead, but some later F13s had an access door here.
  By the summer of 1919 the prototype of the F13 was ready, its first flight being made on 25 June with Junkers’ company pilot, Emil Monz, at the controls. This prototype (c/n 533) was named Annelise after Hugo Junkers’ daughter. This flight was a success, and during subsequent testing an unofficial altitude record was made with the aircraft when on 13 September 1919 it reached 6,750m (22,145ft) with eight people on board in 86min (reduced figures: 6,290m or 20,635ft in 81.6min). The flight details were recorded on a Flugzeugmeisterei barometer but could not be officially recognised since, at that time, Germany was denied membership of the FAI. The engine was a BMW IIIa of 185hp and, probably, the increased-span wings used on production aircraft were fitted. This record demonstration flight did much to publicise the F13. However, during a flight from Berlin to Moscow, a forced landing was made at Kovno (now Kaunas) in Lithuania and Annelise was impounded by the authorities. It was returned to Germany later and given the registration D-41.
  The second F13, named Herta (c/n 531), was first flown on 18 July 1919 and given the registration D-183 (later changed to D-1 and renamed Nachtigall, Annelise and Herta at different times in DLH service). The first order for an F13 came from outside Germany. An American businessman John Larsen took delivery of it (c/n 536) in February 1920 and it was planned to sell the type as the JL6 in the USA. However, in November 1920 the Inter-Allied Control Commission thwarted these plans by impounding eleven crated JL6s (c/n 574-584) which were awaiting shipment from Hamburg to the USA. Later it was decided that the F13 was non-military and the restrictions were lifted, the aircraft then being taken back to Dessau and subsequently sold to other customers. (In due time, of course, the Luftwaffe did find some use for the F13.) The Junkers-Larsen Corporation was founded in the United States in May 1920, and up until 1921 it had taken delivery of 28 F13s (JL6s) from Germany. To advise on the assembly of the aircraft and also to train pilots, the Junkers company pilot Emil Monz went to Roosevelt Airport, Mineola, New York, where this work was carried out. Most JL6s were taken on by the US Air Mail Service but some also went to Canadian oil companies (for example, Imperial Oil G-CADP). Other customers included the US Navy (3), US Army Air Service (2), Mercury Airlines (1), Detroit-Chicago Airline (1) and TNCA of Mexico (2).
  Larsen worked hard to promote the JL6 by demonstration and record flights. A new endurance record was set on 28 September 1921 by Eddie Stinson and Lloyd Bertaud. They took off from Mineola and stayed aloft for some 26hr 5min 32sec and travelled 4,270km (2,652 miles) in that time.
  Some 26 JL6s were sold by Larsen, mostly in 1920, before his business collapsed and ideas of mass producing the aircraft in the United States were abandoned. This unfortunate end came about after a series of crashes involving the JL6 - all in 1920/21 and all five aircraft affected being in use with the US Air Mail Service. In all cases fire occurred, and it seems that this was caused by a modification by Larsen in which a fixed fuel pipe was replaced with a flexible one. A corrective modification was carried out, but the damage to potential sales was done. Larsen’s final attempt to recover sales was with a JL6 modified into a military ground-attack aircraft known as the JL12. It was re-engined with the Liberty L12 V-12, of which there was an enormous war surplus in the USA. The JL12 was fitted with the amazing number of twelve machine guns but the potential customer, the US Army, showed no interest in the project.
  The initial idea behind the Junkers-Larsen co-operation was to instigate manufacture of the F13 in the USA, but when this venture failed Junkers tried to interest the Wright Aeronautical Corporation in production of the F13. However, negotiations came to nothing, apparently because Wright did not find the designs of Junkers to their liking. Other attempts to market the F13 in the USA bore little fruit.
  During late 1920 and early 1921 the Allied Commission confiscated a further twenty completed F13s which went towards war reparation payments. Six of these aircraft went to England (c/n 594-599), two to Belgium (600 and 601), seven to France (603-609) and five to Italy (620-624).
  The sales to the USA had helped to keep the Junkers F13 alive but then, in order to bring in orders which were no longer to be obtained from abroad, Junkers had to seek them from inside Germany, the Allied restrictions having been eased by 1922. Already companies such as Fokker and Dornier were selling their aircraft to the first airline, Deutsche Luftreederei (DLR). Amongst these competitors the Fokker F.II single-engined, high-wing monoplane was especially successful for KLM of Holland. Another airline, Lloyd Ostflug GmbH, was established by the ex-German Navy fighter squadron officer Gothard Sachsenburg and Hugo Junkers on 7 November 1920 and, naturally, this airline was to operate F13s. However, other shareholders in this venture were the aircraft manufacturer Albatross-Flugzeugwerke GmbH and the shipping company Norddeutscher Lloyd. Air mail and passenger services were actually begun with some ex-military aircraft, but Lloyd Ostflug was dissolved on 31 May 1922. August 1922 saw the first passenger aircraft cross the Alps, this being achieved by the F13 D-191 Marahu (c/n 613), which was later re-registered M-AAAJ in Spanish service.
  Working with Junkers, Sachsenburg then set about founding new local airlines all over Germany and Europe. Many were formed, usually by the local authority finding a suitable airfield, with support from local businesses and Junkers supplying the new airlines with his F13s. Not until 13 August 1924 was Junkers’ own airline - the Junkers Luftverkehrs AG - formed, but by then the company controlled a wide network of businesses ranging from Scandinavia and the Baltic States to Hungary and Switzerland. This control was exercised by the Junkers division known as Europa Union.
  Also used by the proliferating airlines in Europe during the 1920s and 1930s were Fokker monoplane aircraft, but these, in contrast to Junkers’ designs, were of high-wing design. They used fuselages and tails with welded tubular steel construction covered with fabric, while the wings were of wooden construction with smooth, 3-ply wooden skinning. The only advantage over Junkers’ aircraft was that they produced less drag than Junkers’ corrugated surfaces. For the purpose of comparison with the Junkers F13, the first Fokker airliner, the F.II of 1920, also used the 185hp BMW engine and could carry four passengers, though it was also subject to the Allies’ restrictions.
  The first F13 deliveries in Germany were to Danziger Luftpost (c/n 533) and Lloyd Ostflug GmbH (c/n 534, D-219 Kasnar). Altogether, some 94 F13s were delivered to German fledgeling airlines, many later being transferred to Luft Hansa and, finally, the Luftwaffe.
  The F13 was operated in the following countries:
Afghanistan 2
Argentina 3
Australia 1
Austria 7
Belgium 3
Bolivia 8
Bulgaria 1
Chile 1
China 4
Colombia 17
Czechoslovakia 2
Finland 7
France 7
Germany 94
Great Britain 6
Hungary 6
Italy 12
Japan 8
Persia 6
Poland 16
Portugal 1
Romania 1
Russia 49
Spain 3
Sweden 5
Switzerland 5
Turkey 4
USA 26
Yemen 1
Others 5
Total: 314

  In addition to its airline and air freight duties, the F13 was also marketed for private use by businessmen, industrialists and the rich as ‘the Junkers Limousine equipped with the famous 6-cylinder Junkers L5 aero engine’. Much was made of the reliability and economy of this engine: after all, it had world endurance records to its credit and had powered the Bremen on the first east-west crossing of the Atlantic (see below). A typical advertisement in England gave two examples of travelling from London to a meeting in Belfast as follows: ‘'Usually. A night journey by rail and steamer, 13 hours; remain at destination all day, when 2 hours might perhaps have sufficed; then another night journey of 13 hours home again. Total time 36 hours. By private aeroplane: Breakfast at home as usual; fly there in 3 hours; lunch and meeting; fly back home in time for dinner. Total time 8 hours." This was a very enticing time-saver, much like the attraction that Concorde held in recent times, but of course it came at a price.
  In Germany, similar advertisements regaled the businessman and the well-heeled with examples of flying from Berlin to London (6 1/2 hours), Oslo (5 1/2 hours), Riga (6 hours), Warsaw (3 1/2 hours), Vienna (3 1/2 hours), Garmisch (4 hours) and so on. The aircraft was marketed as the F13 Privat-Reiseflugzeug and the passenger cabins were very well appointed, particularly if they were fitted out for only two people when
the forward seats were removed and replaced with a table.
  In order to promote the F13, Junkers demonstrated the aircraft all over the world. Various noteworthy flights were also undertaken. These included the participation of F13 D-260 Eisvogel (c/n 650) in the Junkers Polar Expedition from Spitzbergen in 1923 with Germany’s first Arctic pilot Arthur Neumann. In 1925, two F13s, R-RDAP Pravda and R-RDAO, performed the long flight from Moscow to Peking. Another long flight, not so successful, was attempted with the F13 Erlenzeisig (later Freundschaft, c/n 2042) in September 1931, but this was let down by the early type of floats when the aircraft capsized off the coast of India. In 1931 also, an F13ke, Gastrikland (c/n 2069), was used for an expedition to Greenland.

Production in Moscow

  The effect of the Allied restrictions and the impounding at Hamburg of finished F13s bound for the United States was to galvanise Junkers’ search for production centres outside of Germany. Negotiations led to the establishment of an aircraft and engine factory in an old-established factory at Fili in the western suburbs of Moscow, an agreement between the Soviet government and Junkers being signed on 6 February 1922. This arrangement had the blessing of, and some subsidies from, the German government and suited the Soviets very well since it brought with it knowledge of, and training in, the new all-metal-aircraft technology.
  The basis for the new Fili facility, known as Zavod Junkers, was an old factory, but by early 1923 machine tools began arriving from Germany and aircraft and engine production got under way. German engineers taught the Soviets the methods used to produce Junkers all-metal aircraft, beginning with the Ju 20 for the Soviet Air Force. Within a year the plant had about 1,000 workers. The production plan was for a modest 300 aircraft and 450 engines a year, although the repair of conventional wood and fabric aircraft for the Soviet forces in support of their war with Poland was also undertaken. F13s built at Fili were designated Ju 13 or, if for military use, PS-2.
  Besides this manufacturing facility, Junkers were allowed to inaugurate airline transport services inside Russia. These air services were known as Junkers Luftverkehr Russland, or Dobrolet, and up to 49 Ju 13s (F13s) were employed by them.

Military F13s

  The main use of the F13 was, of course, for the transport of personnel and materiel. The only armed F13s known (apart from Larsen’s experimental JL12 version) were two aircraft (c/n 675 and 676), each with a machine-gun position on top of the fuselage, used by the Persian Air Force in 1924. Apart from those later taken over by the Luftwaffe from commercial airlines, one aircraft was used militarily by, for example, the Chilean Army in 1924 (c/n 709), one (but possibly three) by the Afghan Air Force in 1926 (including c/n 666) and one by the Kuomintang Air Force (China) in 1926 (c/n 677). One aircraft (c/n 2005) was taken over by the South African Air Force in 1940, and F13s were also used for coastguard duties by the Finns. During 1925, Junkers set up facilities in Sweden (Limhamn) and Turkey (Kaissarie and Eskischehir) to produce other Junkers aircraft as military machines (see below).

Further F13 Development

  The first major modification to the F13 was an increase in wing span from 14.8m (48ft 6 1/2in) to 17.75m (58ft 3in) in 1920, this version being designated F13a. Further but minor modifications produced the subtypes F13b, c, and d. The year 1923 saw the first use of a Junkers engine in the F13, the F13ba, ca and da types being fitted with the 260hp L2 and the F13be, ce and de types using the 305hp L5. These Junkers engines were considerably more powerful than the previously used BMW and Mercedes powerplants, and the L2-powered F13s could, therefore, lift a greater payload, though at the expense of a higher fuel consumption and a shorter range. Alternatively, the L5-powered F13s had a greater empty weight and were superior to the Mercedes- and BMW-powered versions only in terms of speed.
  By 1925 more powerful BMW engines had become available: the 315hp BMW IV was fitted to the F13bi, ci, di and fi and the 355hp BMW Va to the F13bo, co, do and fo. Other sub-types of the aircraft were the F13fa (Junkers L2 engine), F13fy (Armstrong Siddeley 225hp Puma) and F13fy (Gnome-Rhone 450hp Jupiter). However, by 1926, the Junkers L5 had become the engine most frequently installed in the F13. In order to maintain range with these larger, thirstier engines, it was possible to fit a large, cylindrical auxiliary fuel tank in place of the two forward passenger seats.
  The F13f series had modifications to the wings, tail surfaces and the undercarriage. The fuselage of the W33 (see below) was married to the 17.75m wing to produce the F13g, while a version for the United States had slightly more wing sweep and wing area and was designated F13h. Comfort for the crew was finally improved, in 1930, by enclosing the cockpit in the version designated F13k; this type also featured a toilet and an improved wing with more area. Various engines were employed for the k versions, the most powerful and fastest F13 being the F13kay with a 560hp Armstrong Siddeley Jaguar Major engine and a Heine two-bladed airscrew.
  Special versions of the F13 included a variant of the F13ge equipped as an ambulance for use from land, water or snow and powered by the Junkers 305hp L5 engine. The ambulance cabin had a length of 2.29m (7ft 6in), a height of 1.6m (5ft 3in) and a width of 1.3m (4ft 3in). For the injured there were slings and brackets to facilitate the carriage of two stretchers, and for less seriously incapacitated patients there were two armchairs. An attendant could be accommodated with the pilot. To load the stretchers, a large hatch with a flap was provided. The cabin had washable walls to maximise hygiene and there was a communicating door to the cockpit. The F13 ambulance aircraft was supplied to the Italian Flying Corps, the Spanish Red Cross, the Japanese Flying Corps and the Swedish Red Cross.
  In 1925 Junkers began F13 trials in crop-spraying, a later example of such a machine being named Schnee Ente (c/n 777). Quite a lot of development work was needed to produce such aircraft, and it was necessary to build them so that they could be hosed down inside and out after a spraying sortie.

Durability of the F13

  At the time of the F13 and later, the useful life of a Junkers all-metal aircraft was, for the purposes of its depreciation allowance, taken to be 3,000 hours. However, in about five years of service with Polish Airlines, for example, F13s had each achieved at least 2,250 hours by 1926. The F13 was employed without ill effects everywhere from Siberia to the tropics - as often as not without hangarage.
  Proof of the ruggedness and durability of Junkers all-metal construction over wood construction is given by the history of F13a D-343 Scheiervogel (c/n 715), which was initially delivered to Junkers Luftverkehr and then, on 1 June 1924, to A. B. Aerotransport of Sweden as S-AAAC (later SE-AAC). It was used to fly passengers on the Stockholm-Helsinki route and then, in 1928, for night mail operations on the Stockholm-Malmo-Amsterdam-London route. It had a fuselage letterbox and mail sorter plus the pilot. Finally withdrawn from service in 1935, this F13 was presented to the Tekniska Museet (Technical Museum) in Stockholm. Apart from a period of storage during the Second World War, the aircraft stood outside in all weathers for over 30 years. Finally, in 1971, SE-AAC was restored for exhibition inside the museum.
  A total of 322 F13s were produced, mainly between 1923 and 1925, and most went into service in Germany and Russia. By 1932 production had ceased after some 60 or more variants had been manufactured. This proliferation was the result largely of the great many permutations of airframe and engine. Simplified designations were often used in marketing, such as F13L, S or W to denote a landing gear with wheels, skis or floats.
  The following data are for land versions of the F13: data for ski-equipped versions were about the same, but floats reduced the performance on account of the extra drag (for example, range was reduced by about 38%).

  Data (F13 with 158hp Mercedes): Span 14.8m (48ft 6 3/4in); length 9.6m (31ft 6in); wing area 34.5m2 (371 sq ft); empty weight 950kg (2,095lb); loaded weight 1,640kg (3,616lb); speed 170kph (106mph); range 1,400km (870 miles).
  Data (F13a with 158hp Mercedes): Span 17.75m (58ft 3in); length 9.6m (31ft 6in); wing area 43.0m2 (463 sq ft); empty weight 1,160kg (2,558lb); loaded weight 1,815kg (4,002lb); speed 170kph (106mph); range 1,200km (745 miles).
  Data (F13fc with 305hp Junkers L5): Span 17.75m (58ft 3in); length 9.6m (31ft 6in); wing area 43.0m2 (463 sq ft); empty weight 1,350kg (2,977lb); loaded weight 2,300kg (5,072lb); speed 195kph (121mph); range 930km (578 miles).
  Data (F13kae with 475hp Jupiter IV): Span 17.75m (58ft 3in); length 10.5m (34ft 5 1/2in); wing area 45.0m2 (484 sq ft); empty weight 1,425kg (3,142lb); loaded weight 2,700kg (5,954lb); speed 210kph (130mph); range 525km (326 miles).
  Data (F13kao with 425hp Jaguar): Span 17.75m (58ft 3in); length 10.5m (34ft 5 1/2in); wing area 45.0m2 (484 sq ft); empty weight 1,430kg (3,153lb); loaded weight 2,700kg (5,954lb); max. speed 203kph (126mph); service ceiling 4,200m (13,780ft); theoretical ceiling 5,000m (16,400ft); time to 2,000m (6,560ft) 13.5min; range 575km (357 miles).
  Data (F13kay with 560hp Jaguar Major): Span 17.75m (58ft 3in); length 10.5m (34ft 5 1/2in); wing area 45.0 m2 (484 sq ft); empty weight 1,505kg (3,319lb); loaded weight 3,000kg (6,615lb); max. speed 230kph (143mph); service ceiling 5,200m (17,060ft); time to 2,000m (6,560ft) 10min; range 520km (323 miles).
This view of the second F13a, registered D-1 (c/n 531) in Luft Hansa service, shows to good effect the relatively high aspect ratio of the wing. (Via Martyn Chorlton)
‘Swinging the prop' to start D-203 Bussard (c/n 581). This aircraft was actually a JL6 intended for export to the United States hut was confiscated in Hamburg harbour, along with others, by the Allied Commissioners. From July 1921 it went into service with various German airlines as an F13b.
A nicely turned-out F13bi, D 433 Baumlaufer (c/n 743), with ground crew standing by. Previously, in 1925, this aircraft mas used by Sachsische L.V.A.G.
Passengers are welcomed aboard an F13, D-582 of Luft Hansa, about 1926. A Luftboy assists al the wing.
The Junkers F13 was the workhorse of the Luft Hansa airline fleet between 1926 and 1934. The heated cabin provided four passenger seals equipped with safety belts. This example is an F13bi, D-556 Praeriehuhn (c/n 768), which first flew in December 1925.
Passengers and sightseers are transported by horse-drawn trams to the field where an F13, D-ONIL, is preparing for take-off In those days (the late 1930s) a full airport facility in smaller towns was neither economic nor necessary.
The British-registered F13fe G-EBZV (c/n 2027) started life in Italy as I-ABAA Brandente in 1929. It finished up in Sweden as SE-AFW.
The ruggedness of the all-metal F13 is demonstrated here by this Russian machine on skis. RR-DAA Mossowjet (c/n 649), al Turuchansk in the Siberian cold without a hangar. This aircraft was used for spraying during 1923.
A labour-saving, efficient system of refuelling was evident at some of the smaller airfields using fuel drums on rails. The board shows that this F13 is due to fly from Mannheim to Karlsruhe al 1500. In the background is a Fokker F.III. (Deutsche Lufthansa)
A line-up of F13as of Lloyd Ostflug (nearest) and Danziger Luftpost (second and third) airmail services of the early 1920s. From the front, the aircraft are Dz 152 Kasuar (c/n 543), Dz 34 Annelise (c/n 532) and Dz 31 Geier (c/n 537). The ‘Dz’ was the ‘Danzig Freestates' registration, a ruse to prevent confiscation by the Allied Commission.
Beginning in the winter of 1922, this F13, D-217 Flamingo (c/n 633), was used for a marketing tour of South America. It is seen here at Rio de Janeiro.
This F13S, D-207 Falke (c/n 592), began its commercial life with Bodensee L. V. Truckenbrodt in the summer of 1923. It crashed a year later.
This F13, A-32 Pacifico, belonged Io SCADTA and is seen here in Colombia in about 1928. Later registered C-32, it crashed in 1934.
A 1922 production line for the Junkers F13, the world's first all-metal airliner, at Dessau. (Deutsche Lufthansa)
An F13 fuselage is taken outside the factory for the fitting of the wings, tail unit and engine. There were nine threaded collars to attach each wing to the fuselage, using a ‘C' spanner.
The F13 derived much of its strength and safety from the manner in which the wing centre section, engine mountings, cockpit and passenger cabin were built as an integral structure before being covered in corrugated Duralumin.
The cockpit of the F13 airliner. Dual controls were fitted to later models. Note the extremely sparse instruments, navigation being by 'Mark One Eyeball’ in the early 1920s.
Considerable comfort was offered to the four passengers in an F13 with these leather-upholstered seats and a heated cabin. The seatbelts were an innovative safety feature.
Further proof of the F13’s ruggedness, and the security of the passenger/pilot section, is shown in this aircraft, which crash-landed in woodland. It is S-ATAA Pfau (c/n 689) of the Swedish airline A. B. Aerotransport, circa 1923.
J13 F13