The Junkers G 24 was a German three-engine, all-metal low-wing monoplane passenger aircraft manufactured by Junkers from 1925. Junkers F 24 was the designation for single-engine versions of the same aircraft.
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 G 24 airliner to be single-engined, but built it as a tri-motor. With three low powered engines the G 24 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 G 24 design to be a military type aircraft, and outlawed it. 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 G 24 designation.[1]
Junkers continued to build the G 24/G 23 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.
On 1 May 1926, the newly formed German airline Deutsche Luft Hansa started flying passengers on the route Berlin – Königsberg at night using its G 24 fleet.[2] [3] 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 was then considered to be too dangerous. The G 24 could carry passengers, since there would not be any forced landings. The G 24s operated by 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.[4]
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.
The Soviet-German aircraft cooperation during the 1920s included a Soviet request for a new bomber aircraft. In response, Junkers prepared the Ju 25 twin-engine bomber. However, the development of this aircraft was deemed to be too expensive by Junkers, especially in light of several difficulties with his Russian partners. Accordingly, Junkers instructed 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; receiving the designation G3S1 24, it was a direct modification of the G 24ba. The aircraft was stated to be an air ambulance. Junkers followed up this design with several reconnaissance designs, such as 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.
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.
The Junkers G 24 was a trimotor all-metal low-wing monoplane passenger aircraft. Its construction maintained the principles of the earlier and successful Junkers F 13 twin-engined airliner, while also building upon them. The trimotor configuration combines the advantageous propeller thrust characteristics of a centrally-positioned engine while the two wing-mounted engines provided an additional margin of safety via redundancy; the reserve energy of these engines exceeded 50 percent. Furthermore, this arrangement kept the structural drag, particularly in light of the streamlined cowlings for the wing-mounted engines that ensured smooth air flow around them, while the positioning of the propellers meant that any pieces thrown off from a broken propeller would not strike any vital part of the aircraft, unlike more commonplace tandem arrangements. The design incorporated measures for maintaining manoeuvrability in the event of a wing-mounted engine stalling.[5]
Both the cantilever wings and fuselage were covered with corrugated sheets of duralumin, a feature that bolstered the material's ability to both absorb and distribute various stresses imposed upon it. The corrugated sheeting worked in conjunction with a series of bulkheads to fully absorb all of the fuselage stresses.[6] The foundation for the aircraft's structure was the central section, which received the principal loads and worked in conjunction with the low-mounted wing which, in the event of a hard landing, provided considerable protection to the cabin and its occupants. The terminal bulkhead of the fuselage was secured to the framework using screw caps.
Sectional construction, a practice adopted from the earlier F 13, was practiced in various areas, including the wing, fuselage, supporting structure of the central engine, and those wing sections that supported the side engines. This construction principle enabled larger numbers of workers to effectively participate in the manufacturing process up to the aircraft's final assembly; it also facilitated ground transportation (sections could be easily loaded upon ordinary trucks) and the substitution of damaged sections. In the event of an engine sustaining damage, it could have been quickly removed and replaced. It was also possible to remove the complete wing section, including the engine and its mounting.[7]
In an airliner configuration, the cabin would be furnished with around 14 leather-covered chairs, each aligned to their own window, while an aisle permitted travellers to move about. A door was present between the cabin and the cockpit; a window was provided that provided passengers with a view of various instruments, including the altimeter and air-speed indicator. Nets were used to stow hand baggage while the majority of luggage was stored in a dedicated room alongside the toilet. The useable volume within the fuselage was relatively high towards the rear, a element that proved to be quite convenient for the travelling public as passengers did not have to remain in allocated positions, unlike many other airliners of the era, as equilibrium was maintained via adjustments made by the pilot to the stabiliser throughout the flight.[8]
The cockpit was provided with extensive instrumentation and dual flight controls, the latter featured permitted a pair of pilots to relieve each other throughout long distance flights. Wheels located between the pilots seats were used to adjust the stabiliser and rudder (the latter was typically used in the event of a wing-mounted engine stall). The rudder was typically controlled using pedals.[9] Typical instruments included a compass, gyroscopic inclinometer, engine rev counter, thermometers (for the radiators), oil pressure indicator, fuel gauges, and longitudinal inclinometer. Other controls included the ignition switches, throttles, fuel cocks and shutter levels for regulating the radiator's temperature.[10]
The undercarriage consisted of steel struts that were faired with sheet duralumin to lessen structural drag.[6] It was attached by a combination of bolts and a set of bayonet fastenings, permitting its rapid removal. It featured a typical Junkers-designed shock absorber arrangement that was both proven and sturdy even in the event of rough landings; these were placed inside sheet duralumin that protected them from both debris and bad weather conditions, an arrangement that also had aerodynamic benefits.[6] The undercarriage was outfitted with sizable disk-wheels and balloon tires that had a breaking strength of 20 metric tons. Akin to many of Junkers airplanes, it was possible to replace the standard undercarriage for land use with either floats or skis in a manner that was both practical and speedy to perform.[7] These floats, which were entirely composed of aluminium, possessed so much displacement that float alone was sufficient to support the weight of the whole aircraft. The internal volume of the floats was divided into numerous water-tight compartments; sizable manholes were present to permit inspection of the interior spaces.[11] While the float struts were attached to removable intermediate wing sections, the standard wheeled undercarriage attached only the fuselage.[12]
The first G 24s were delivered at the start of 1925. By late 1927, the type was reportedly in operation across virtually all of the Central European scheduled air routes then in use.[13]
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 such modifications were performed 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 the Second World War in 1939. Most of them were used by Luft Hansa as freighter aircraft.
During 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.
Data from:Hugo Junkers Pionier der Luftfahrt – Seine Flugzeuge, Junkers Aircraft & Engines 1913–1945[16]