Junkers Ju 52
The Junkers Ju 52/3m is a transport aircraft that was designed and manufactured by German aviation company Junkers. First introduced during 1930 as a civilian airliner, it was adapted into a military transport aircraft by Germany's Nazi regime.
Development of the Ju 52 commenced in the late 1920s, headed by German aeronautical engineer Ernst Zindel. The aircraft's design incorporated a corrugated duralumin metal skin as a strengthening measure, which was a material design pioneered by Junkers and used on many of their aircraft, including the popular Junkers F 13 1920s, the record-setting Junkers W 33, and Junkers W34. The corrugation was both a strength and a weakness; it provided increased structural strength but also increased aerodynamic drag. But more importantly it allowed the practical use of aluminum before newer alloys were developed.
The Ju 52's maiden flight was performed on 13 October 1930. It was initially designed with a single-engine version and a trimotor version; the single-engine version was to be the freighter while the trimotor was the passenger airliner. In the long run, the trimotor configuration was produced in far greater numbers. The primary early production model, the Ju 52/3m, was principally operated as a 17-seat airliner or utility transport aircraft by various civil operators during the 1930s. Starting in 1933, the Nazi regime that had taken power in Germany demanded that Junkers produce military versions of the Ju 52. Thousands of Ju 52s were procured as a staple military transport of the Luftwaffe. The Ju 52/3mg7e was the principal production model.
The Ju 52 was in production between 1931 and 1952. In a civilian role, it flew with over 12 airlines, including Swissair and Deutsche Luft Hansa, as both a passenger carrier and a freight hauler. In a military role, large numbers flew with the Luftwaffe, being deployed on virtually all fronts of the Second World War as a troop and cargo transport; it was also briefly used as a medium bomber. Additionally, the type was deployed by other nations' militaries in conflicts such as the Spanish Civil War, the Chaco War, the First Indochina War, and the Portuguese Colonial War. During the postwar era, the Ju 52 had a lengthy service life with numerous military and civilian operators; large numbers were still in use by the 1980s. Even in the 21st century, several aircraft have remained operational, typically used for heritage aviation displays and aerial sightseeing.
Development
Origins
The Ju 52 was designed starting in 1925, in two versions, a single engine version for freight transport and trimotor passenger version for 17, both as civilian versions. Both designs were overseen by the German aeronautical engineer Ernst Zindel, the design team being based at the Junkers works at Dessau. A driving force in the project was the commercial prospects presented by the German airline Deutsche Luft Hansa. Work on turning the design into a prototype started in 1928. The Ju 52 had numerous similarities to several previous Junkers aircraft, such as the previous Junkers W 33, noted for its crossing of the Atlantic in 1928, and the smaller Junkers W 34. Sharing features included the distinctive corrugated duraluminum exterior. According to aviation author J. Richard Smith, the Ju 52 directly drew upon the company's First World War-era Junkers J 1 - the world's first all-metal aeroplane.On 13 October 1930, the first prototype, designated Ju 52ba, performed the type's maiden flight; it was initially powered by a single Junkers-built liquid-cooled V-12 engine, capable of generating up to. During the aircraft's extensive trials, it was reengined with a BMW IV water-cooled inline-6 powerplant. The second prototype, designated Ju 52de, featured an increased wing span and was powered by the BMW IV engine at first; it was soon reengined with the 14-cylinder twin-row air-cooled radial Armstrong Siddeley Leopard and re-designated Ju 52di. Later on, the Ju 52di was again reengined with the Junkers Jumo 204 air-cooled inverted inline-6, after which it was re-designated Ju 52do. The third prototype, designated Ju 52ce, had a strengthened structure, a modified leading edge, and was fitted with both a wheeled and float undercarriages.
During May 1931, one of the prototypes, designated Ju 52cai, was written off after a crash. While these initial aircraft had been powered by a single engine, Junkers decided to develop the Ju 52 into a trimotor configuration. Accordingly, the Ju 52/3m was developed, being powered by an arrangement of three radial engines. According to Smith, the earliest known Ju 52/3m was delivered to Bolivian airline Lloyd Aéreo Boliviano during 1932. During its initial production years, airlines were the type's most common customers. By the mid-1930s, the Ju 52/3mce and Ju 52/3fe, were the two primary production variants, both being powered by the BMW 132 radial engine.
Militarized versions
During 1934, work commenced on a militarised model of the Ju 52/3m, designated Ju 52/3mg3e, on behalf of the then-secret Luftwaffe. This model could function as a medium bomber, being furnished with a pair of machine gun positions, each with single machine guns and operated by a crew of four. Between 1934 and 1935, a total of 450 Ju 52/3mg3e aircraft were delivered to the Luftwaffe.Wartime and postwar
Numerous improved models would be introduced prior to and during the Second World War. The dominant production model was the Ju 52/3mg7e, featuring advances such as an autopilot, enlarged doors to the cabin, and other general enhancements. It was configured as a pure transport aircraft, being capable of carrying up to 18 fully-equipped troops. Defensive armaments comprised a dorsal-mounted 13 mm MG 131 machine gun and a pair of beam 7.9mm MG 15 machine guns. Successive models saw other improvements, such as revised glazing, newer engines, undercarriage strengthening, and increased take-off weight. The final wartime model to be developed, designated Ju 52/3mg14e, featured improved armour protection for the pilot and a bolstered defensive armament.From mid-1943 onwards, the Luftwaffe began to make less use of the Ju 52, interest having waned in the type. German officials were interested in procuring a successor to the type; at one stage, the Reich Air Ministry showed enthusiasm for the Junkers Ju 352, a larger transport aircraft somewhat resembling the Ju 52. Actions were taken to convert Junkers' Ju 52 production lines to instead manufacture Ju 352s; however, the conflict's end in May 1945 led to the effort being abandoned in an unfinished state. As such, German production of the Ju 52 was terminated during 1944; Smith claims that a total of 3,234 aircraft of various models were constructed during the conflict.
In the postwar era, manufacture of the Ju 52 resumed, albeit in foreign countries. It was constructed in France by Avions Amiot as the Amiot AAC.1 Toucan; it was also produced in Spain by Construcciones Aeronáuticas SA as the CASA 352. A handful of captured wartime aircraft were also rebuilt by Short Brothers of Northern Ireland for civilian service.
Design
The Ju 52 had a low cantilever wing, the midsection of which was built into the fuselage, forming its underside. It was formed around four pairs of circular cross-section duralumin spars with a corrugated surface that provided torsional stiffening. A narrow control surface, with its outer section functioning as the aileron, and the inner section functioning as a flap, ran along the whole trailing edge of each wing panel, well separated from it. The inner flap section lowered the stalling speed and the arrangement became known as the Doppelflügel, or "double wing". The outer sections of this operated differentially as ailerons, projecting slightly beyond the wingtips with control horns. The strutted horizontal stabilizer carried horn-balanced elevators which again projected and showed a significant gap between them and the stabilizer, which was adjustable in-flight. All stabilizer surfaces were corrugated.The Ju 52 featured an unusual corrugated duralumin metal skin, which had been pioneered by Junkers during the First World War; the corrugation served to strengthen the whole structure over a smoother approach. The fuselage was of rectangular section with a domed decking, comprising a tubular steel structure that was entirely covered by the corrugated metal skin. A port-side passenger door was placed just aft of the wings; this entrance also acted as a loading hatch for freight, the lower half functioning as a platform to ease cargo movements. The cabin had a dimensional capacity of, and was lined with numerous windows stretching forward to the pilots' cockpit. The main undercarriage was fixed and divided; some aircraft had wheel fairings, others did not. A fixed tailskid, or a later tailwheel, was used. Some aircraft were fitted with floats or skis instead of the main wheels.
In its original configuration, designated the Ju 52/1m, the Ju 52 was a single-engined aircraft, powered by either a BMW IV or Junkers liquid-cooled V-12 engine. However, the single-engined model was deemed to have been underpowered and, after seven prototypes had been completed, all subsequent Ju 52s were built with three radial engines as the Ju 52/3m. Originally powered by three Pratt & Whitney R-1690 Hornet radial engines, later production models mainly received 574 kW BMW 132 engines, a licence-built refinement of the Pratt & Whitney design. Export models were also built with 447 kW Pratt & Whitney R-1340 Wasp and 578 kW Bristol Pegasus VI engines.
The two wing-mounted radial engines of the Ju 52/3m had half-chord cowlings and in planform view appeared to be splayed outwards, being mounted at an almost perpendicular angle to the tapered wing's sweptback leading edge. The three engines had either Townend ring or NACA cowlings to reduce drag from the engine cylinders, although a mixture of the two was most common, with deeper-chord NACA cowlings on the wing engines and a narrow Townend ring on the center engine. Production Ju 52/3m aircraft flown by Deutsche Luft Hansa before the Second World War, as well as Luftwaffe-flown Ju 52s flown during the war, usually used an air-start system to turn over their trio of radial engines, using a common compressed air supply that also operated the main wheels' brakes.
In a military context, the Ju 52 could carry up to 18 fully-equipped soldiers, or 12 stretchers when used as an air ambulance. Transported material was loaded and unloaded through side doors by means of a ramp. Air-dropped supplies were jettisoned through two double chutes; supply containers were dropped by parachute through the bomb-bay doors, and paratroopers jumped through the side doors. Sd.Kfz. 2 Kettenkrafträder and supply canisters for parachute troops were secured under the fuselage at the bomb bay exits and were dropped with four parachutes. A tow coupling was built into the tail-skid for use in towing freight gliders. The Ju 52 could tow up to two DFS 230 gliders.