Junkers G 24

Original line drawings

The increased German air traffic in the 1920s led to a requirement for a larger passenger transport aircraft. The G 24 was an enlarged development of the F 13. It was originally designed by Ernst Zindel as a single-engine aircraft. Under the restrictions imposed on aircraft in Germany by the Treaty of Versailles, only low powered engines were allowed. So the Junkers company designed their large G24 airliner to be single-engined, but built it as a tri-motor. With three low powered engines the G24 could fly, but was not a viable airliner. The plan was to sell the tri-motors to airlines outside of Germany, who would then install a single, high-powered engine (e.g. 450 hp Napier Lion) on the nose, and simply remove the wing center-section plugs that carried the other two engines. However the Military Inter-Allied Commission of Control declared the G24 design to be a military type aircraft, and outlawed it.

Junkers G.23 (CH-133) operated by Ad Astra Aero

Junkers then resubmitted what was essentially the same design, but under a new designation: Junkers G23. The Allied Commission ultimately allowed Junkers to build the G23, even in the single engined version, because it was clearly an airline type. The plane was always marketed under the G24 designation. (This paragraph based on 'Wagner' pages 230–234[1])

Junkers continued to build the G24/G23 as a tri-motor, because the ruse to circumvent the Allied restrictions also had the benefit that the plane could fly, and even climb, with one engine out. In 1925 most airliners were single-engined, since one big engine will usually be more efficient than several small ones. Twin-engine types could not maintain altitude with an engine out, unless they were so overpowered that the airlines could not afford to operate them (similarly to how twinjets were impractical on long-range routes before 1980s, and how trijets were used instead). A tri-motor did not have to be so grossly overpowered, to be able to fly with one engine out.

The G 23 cockpit

On May 1, 1926 newly formed German airline Deutsche Luft Hansa started flying passengers on the route Berlin – Königsberg at night using G24 aircraft ('Wagner' page 232[1] 'Seifert' page 376[2]). This was the first time any airline, anywhere in the world, flew passengers at night. Previously airlines had flown only mail and freight after dark. If an engine failed, the pilot bailed out by parachute, since a forced landing in the dark is too dangerous. The Junkers G24 could carry passengers, since there would not be any forced landings. The G24s of Luft Hansa also had blind flying instruments and radio navigation (with the radio operator sitting in the passenger cabin, as there was no room in the open two seat cockpit[3]).

The aircraft was manufactured in three main batches, with different engine alternatives. Between 1925 and 1929, at least 72 aircraft were manufactured, 26 of which went to Luft Hansa. The G 24 managed to set a number of aviation records involving pay loads. Fritz Horn flew 2,020 km (1,256 mi) with a payload of 1,000 kg (2,200 lb) on 14 h 23 min, having an average speed of 140 km/h (90 mph), setting a new world record.

On 24 July 1926, two G 24s became famous after having flown the 20,000 km (12,400 mi) route between Berlin and Peking in just 10 stops. This flight ended on 8 September. It was initially meant that they would fly all the way to Shanghai, but they were prevented by military conflicts. On 26 September 1926, the two aircraft landed again in Berlin. Later during the year, a trans-Euro-Asiatic line was created.

Luft Hansa, which operated the largest G 24 fleet in the world, decided to modify their G 24s to a single engine standard. The first modifications were done in March 1928. The wing was shortened and the center engine was replaced with a BMW VIU engine. Junkers called this aircraft F 24ko. A total of 11 G 24s were modified to F 24 standard between 1928 and 1930. By July 1933, most of these BMW-equipped F 24s were again modified with the new Jumo 4 and designated as F 24kay. Most of these F 24s remained in service at the beginning of World War II in 1939. Most of them were used by Luft Hansa as freighter aircraft.

The Soviet-German aircraft cooperation in the 1920s led to a Soviet request for a new bomber aircraft. Junkers then designed the Junkers Ju 25 as a twin-engine bomber. But the development of this aircraft was too expensive for Junkers, especially since there were some difficulties with his Russian partners. Junkers then advised his lead designers – Ernst Zindel and Hermann Pohlmann – to design a military derivate of the G 24. By November 1924, the new aircraft was ready, and given the designation G3S1 24 and it was a direct modification of the G 24ba. The aircraft was said to be an air ambulance. Junkers followed up this design with several reconnaissance designs e.g. the G1Sa 24 which was a modified G 24 with only a single engine. The next design, the G2sB 24 was also a bomber, directly derived from the G 24he. This aircraft had a new center wing section and a new nose section, to allow an open shooting area to the forward areas. Junkers decided to produce this design as the general military version of the G 24 and gave it the designation K 30 in 1926.

In 1926, the Finnish airline Aero O/Y acquired a Junkers G 24, which went into service on the Stockholm route. The aircraft was equipped with floats, but not skis, and so could be used in summer only. It remained in service until 1935.

A Swedish G 24 also participated in the rescue of the unfortunate Italian Umberto Nobile expedition to the North pole. This was the first time an aircraft had flown over the Arctic Sea without stops.

Military versions

Junkers R 42 photo from L'Aéronautique October,1926

Junkers offered the K 30 design to the Soviet forces, which ordered a total of 23 K 30s in 1925 and 1926. A production line for the military version K 30 was set up at A.B. Flygindustri at Limhamn in Sweden as the German aviation industry was prevented from building military aircraft in 1926. The parts for the K 30 aircraft were built at Dessau and then shipped to Limhamn, where A.B. Flygindustri built the K 30 under the designation R 42. Some of the R 42s were equipped with machine gun positions and bomb mountings. But several of the R 42s were also shipped without military equipment to Russia. These were later fitted with military equipment at Junkers' factory in Fili, Moscow. The R 42/K 30 was designated JuG-1 in the Soviet Union. They received five 7.62 mm (.30 in) machine guns and could carry a bomb load of 500 kg (1,100 lb). This version was used to rescue the expedition of downed balloonist General Umberto Nobile in 1928.

Six more R 42s were delivered to Chile during 1926 plus three K 30s to Spain and two K 30s to Yugoslavia until 1931. The Spanish and Yugoslavian aircraft were produced at Dessau. The K 30 was equipped with either wheels, skis or floats. With the successful conversion of the G 24 into the single-engine aircraft F 24, Junkers was also thinking about a single-engine K 30 in 1931. Like the F 24, this K30do was to be equipped with the Jumo 4 engine and was similar to the initial G1Sa 24. However, no single-engine K 30s were built.

• On 6 November 1929, a Deutsche Luft Hansa Junkers G 24bi Oberschlesien (registration D-903) crashed after striking trees on a hill in Marden Park, Surrey, England, while attempting to return to Croydon Airport, London, in thick fog after taking off from Croydon for a flight to Amsterdam in the Netherlands. All four crew members and three of the four passengers died.[4][5]
• On 7 February 1930, Chilean Air Force Junkers R-42 J6 ditched off Punta Arenas due to engine failure, killing three of six on board.[6]
• On 7 November 1930, a Syndicato Condor Junkers G 24 (P-BAHA, named Potyguar) sank off Iguape, São Paulo, killing one of eight on board.[7]
• On 31 August 1932, an AB Aerotransport Junkers G 24 (SE-AAE, named Svealand) crashed at Tubbingen, Netherlands while the crew was attempting a forced landing after the number three engine failed, killing both pilots.[8]
• On 1 October 1938, a Syndicato Condor G.24ce (PP-CAB, Ypiranga) made an emergency landing at the port of Coruripe, with no fatalities. The aircraft was later scrapped.[9]
• On 24 August 1939, a Deutsche Luft Hansa Junkers F.24 (D-ULIS, named Düsseldorf) force-landed at Glindow, Germany following an engine fire, killing both pilots. The aircraft was manufactured in 1925 as a three-engined G 24 and was converted to an F 24kay in December 1931 as a test bed for the Junkers Jumo 4 engine. In 1936 the aircraft was re-engined with a Daimler-Benz DB 600 V12 for test flights, and a DB 601 V12 in 1938 for 200 hours of test flying, and it was during one of these test flights that the engine caught fire, leading to the crash.[10]

Data from:Hugo Junkers Pionier der Luftfahrt – Seine Flugzeuge,[1] Junkers Aircraft & Engines 1913–1945[11]

G 24 Prototype

Powered by one 130 kW (180 hp) BMW IIIa and two 75 kW (100 hp) Mercedes D.I engines in 1924.

G 24

Improved version with one 145 kW (195 hp) Junkers L2 (195 hp) and two 120 kW (160 hp) Mercedes D.IIIa engines in 1925

G 24a

Powered by three 145 kW (195 hp) Junkers L2 engines, attachment on wings, smaller engine cowlings, sometimes also a 230 kW (310 hp) Junkers L5 as a central engine. Two aircraft destined for Italy were fitted with 221 kW (296 hp) Isotta Fraschini central engines.

G 24ba

with three Junkers L2, strengthened attachments and engine mountings

G 24b1a

seaplane version of the G 24ba for Aero O/Y[12]

G 24bi

with one Junkers L5 center engine and two L2 engines

G 24ce

with three Junkers L5, enlarged wing attachment since 1926

G 24e

with three Junkers L5

G 24de

strengthened attachments, smaller engine cowlings

G 24fe

enlarged center wing attachments

G 24ge

further enlarged wing attachments

G 24g1e

seaplane version of G 24ge, used for torpedo experiments

G 24gu

one 317 kW (425 hp) Junkers L5G central engine and two Junkers L5

G 24gn

230 kW (310 hp) Junkers L5 center engine with 310 kW (420 hp), one built

G 24he

with modified wing, separate undercarriage, aerodynamic cockpit, 14 passengers

G 24h1e

seaplane version of G 24he

G 24hu

with three BMW Va engines, one built

G 24li

modified G 24a/b with Junkers L5 center engine

G 24mai

Two modified G 24e aircraft with a 190 kW (250 hp) Isotta Fraschini Asso 200 centre engine for Italy

G 24nao

with three Rhone Jupiter engines, prototype for the K30

G 24L

with three 317 kW (425 hp) Junkers L5G engines

F 24kae

was a single test bench for DB 600/DB 601 engines.

F 24kai

a single test bench for the Jumo 211 engine

F 24kau

with BMW VIau

F 24kay

Junkers F 24kay photo from L'Aérophile December,1929

Test bench for Jumo 4 in October 1933 (c/n 839), plus surviving Deutsche Luft Hansa F 24ko aircraft re-engined with Jumo 4 engines.

F 24ko

with a single BMW VIU engine

G3 S1 24

a projected ambulance aircraft from 1924, three Junkers L2 engines

G1 Sa 24

a projected reconnaissance aircraft from 1924, single-engine

G2 Sb 24

a projected bomber aircraft with several three-engine approaches

K 30

military G 24 version of 1926

K 30b

a fictitious Russian designation for the land version of the K 30 (not the official Junkers designation)

K 30c

a fictitious Russian designation for the seaplane version of K 30 (not the official Junkers designation)

K 30do

single-engine version of the K 30 of 1931, with a Jumo 4;not built

W 41

test bench for Fo 4 diesel engine in August 1928 (c/n 843)

TB-2

Soviet military designation for the K 30 (not the official Junkers designation)

YuG-1

designation for Fili military conversions of the K 30/R 42

 Afghanistan

• Afghan Air Force

 Austria

• Ölag[13]

 Brazil

• Syndicato Condor[13]

 Chile

• Chilean Air Force[13]

 Finland

Aero O/Y[13]

 Germany

• Deutsche Luft Hansa[14]
• Luftwaffe
• Condor Syndikat

 Greece

• SCHA[13]
• Hellenic Air Force[13]

 Italy

• Ala Littoria[13]
• Regia Aeronautica[13]
• Transadriatica[14]

 Poland

• Aerolot operated one Junkers G 23W floatplane in 1925, but returned it to the producer later the same year

 Spain

• Unión Aérea Española[13]
• CLASSA[13]
• LAPE[13]
• Spanish Republican Air Force

 Sweden

• AB Aerotransport[15][13]

  Switzerland

• Ad Astra Aero[15]
• Swissair

 Turkey

 Soviet Union

• Aeroflot[13]
• Soviet Air Force[13]

 Yugoslavia

• Yugoslav Royal Air Force

Data from Junkers Aircraft & Engines 1913–1945[11] Wagner pp. 239–242[1]

General characteristics

• Crew: 2
• Capacity: 14 passengers
• Length: 15.8 m (51 ft 10 in)
• Wingspan: 29.37 m (96 ft 4 in)
• Height: 5.80 m (19 ft 0 in)
• Wing area: 99 m² (1,070 sq ft)
• Empty weight: 4,330 kg (9,546 lb)
• Gross weight: 7,200 kg (15,873 lb)
• Powerplant: 3 × Junkers L5 6-cyl. in-line water-cooled piston engine, 230 kW (310 hp) each

Performance

• Maximum speed: 210 km/h (130 mph, 110 kn)
• Cruise speed: 170 km/h (110 mph, 92 kn)
• Range: 660 km (410 mi, 360 nmi)
• Service ceiling: 4,000 m (13,000 ft) with maximum payload
• Rate of climb: 2.47 m/s (486 ft/min)
• Time to altitude: 2,000 m (6,600 ft) in 13.5 minutes

Related development

• Junkers G 31
• Junkers Ju 52

• Stroud, John (August 1984). "Wings of Peace: No. 11: Junkers G 23 and 24". Aeroplane Monthly. Vol. 12, no. 8. pp. 436–441. ISSN 0143-7240.