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Junkers Ju 52: Europe's ubiquitous transport.

Most American aviation experts would name the Douglas DC-3 as the aircraft that had the greatest impact on expanding commercial aviation before World War II. But from European flying enthusiasts, the response might well be the Junkers Ju 52.

The three-engine Ju 52, which made its maiden flight in May 1932, predated the Douglas DC-3 by about three years. It was the world's first mass-produced airliner, and thousands were built. Ju 52s carried passengers and cargo in Europe, as well as Africa, Asia, and South America. The aircraft saw service in several conflicts of the pre-World War II period, including the Spanish Civil War.

During World War II, the Ju 52, which was called the "Tante Ju" or Auntie Ju by the troops, saw duty with the German military as a transport and a bomber. Even after Germany's defeat, Ju 52s flew for several decades all over the world. Production also continued in France, Spain, and England immediately after the war.

Hugo Junkers, the German aviation pioneer who founded Junkers Flugzeug und Motorenwerke AG in Dessau, Germany, was an enthusiastic advocate of all-metal aircraft in the days of wood and fabric flying machines. In the early days of aviation, most airplane designers were using struts, wires, and bracing for supporting wings. Junkers, however, realized that appendages like struts, braces, and even the fuselage contributed to an aircraft's parasitic drag. He favored a cantilevered wing based on a bridge-truss, and he obtained a patent for this design. An all-metal version of this wing was incorporated into the experimental Junkers J1 "Blechesel," or tin donkey. The plane made its maiden flight in December 1915, demonstrating very stable performance. A series of successful all-metal monoplane civilian transports followed, leading up to the Ju 52.

Airline Connection

The story of the Ju 52 is intertwined with the tale of Germany's national airline. In 1926, Junkers' Luftverkehr division and Deutsche Aero Lloyd merged to form Deutsche Luft Hansa AG (after World War II, the airline adopted the spelling "Lufthansa"). Initially, Luft Hansa was a freight transporter using aircraft like the Junkers W 33, Messerschmitt M 20, and Fokker-Grulich flying on scheduled cargo routes between Berlin, London, and Paris. When Luft Hansa wanted to expand into the domestic and international passenger business, it needed an efficient and reliable airliner. In those early days of passenger service, three-engine aircraft were the obvious answer to safety concerns since the failure of a single engine would not dangerously cripple a plane with multiple power plants.

The task of designing a new transport for Luft Hansa was assigned to Junkers. Two of the key factors that made the Ju 52 a commercial success were that it was designed for the highest payload-per-plane-per-year loads and for minimal maintenance. The former requirement opposed the usual trend of building aircraft with ever-increasing payload-to-takeoff ratios and placed the emphasis on operational reliability. Designing with an emphasis on minimum maintenance resulted in manual systems for just about every function. There were no hydraulic lines that could leak, break, clog, or catch fire in a crash. Control surfaces were activated by push rods, and, in the case of the tail surfaces, control cables. Brakes were operated by compressed air stored in accumulators that could be pressurized by an oxygen or nitrogen bottle on the ground or by ram air while in flight. The result was an extremely rugged and simple aircraft.

The center section was an integral part of the aircraft, forming the lower surface of the fuselage. The wings had eight tubular duraluminum main spars, which were arranged in pairs vertically and braced with short struts that added even more strength to the wings. At the wing roots were extremely strong transverse braces. The plane's aluminum skin carried both flight and structural loads.

While performance depended on the engines and propellers installed on a particular model, as well as on whether the aircraft was fitted with wheels, floats, or skis, the top speed was no more than 150 mph and the cruising speed was just over 100 mph. With a nominal fuel load of about 630 gallons, the Ju 52 had a range of some 750 miles with a takeoff weight of 23,000 pounds. For cargo service, it could be ordered with a large loading hatch in the top and a folding cargo-stowing platform on the side of the fuselage.

The Ju 52 was an exceptionally good short-takeoff-and-landing aircraft, facilitating operation from the many grass airstrips of the day that were not adequate for large transport aircraft. Takeoff speed was a mere 75 mph from runways as short as 1300 feet. Ju 52s could land at speeds as low as 50 to 60 mph and on landing strips as short as 1150 feet. (Note that this is airspeed, not groundspeed; with a 20-mph head-wind, a Ju 52 would be landing at a mere 30 to 40 mph with respect to the ground.)

The plane's exceptionally high lift and controllability at low speeds was the result of its 96-foot wingspan and the "Junkers auxiliary wing," or double wing, which was the forerunner of the modern landing flap. This auxiliary wing ran the whole length of the trailing edge of the wing and each side was divided roughly at its midpoint. Normally, the outboard section performed aileron functions while the inboard portion remained fixed. During landing, the inboard portion was lowered to 40 degrees and the outboard portion was lowered to 15 degrees. This altered the airflow over the wing, greatly increasing low-speed lift and control. The double wing also significantly increased the Ju 52's rate of climb and lowered its stalling speed.

Power Plants

The Ju 52s were powered by a wide variety of engines through their 15 years of production. The first aircraft used Pratt & Whitney Hornet engines, which were rated at 525 to 600 horsepower and were manufactured in the United States or built under license by Bayern Motoren Werke (BMW) in Germany. A large number of the later aircraft used various versions of the nine-cylinder BMW 132 engine that was based on the Pratt & Whitney Hornet but greatly modified through the years by BMW to produce power ratings ranging from 680 to 830 horsepower. Numerous other engines were installed, including the American Pratt & Whitney Wasp, British Bristol Pegasus, and Italian Piaggio Stella. A few Ju 52s were even fitted with the German Jumo diesel aircraft power plant.

Initially, the Ju 52's wing engines were mounted with their centerlines canted outward six degrees to insure adequate airflow to the tail control surfaces. Later, many Ju 52s were modified so the engines pointed directly forward in an attempt to improve the engine's mileage per gallon of fuel and to increase the life of constant-speed propellers.

Each Ju 52 contained many customized features. There were different propellers and cowls, as well as different cargo hatch and passenger seating configurations; a choice of wheels, floats, or skis; individualized instruments and navigation equipment; and a choice of tail skids or tail wheels.

The cabin was sound-protected against the noise of the three air-cooled engines, but it was still loud inside--indeed, so loud that pilots often wore ear muffs. With valves rather than push buttons for many controls, the Ju 52's flight deck looked something like the control room of a steam power plant or steamship rather than an airplane cockpit.

Performance News

By 1932, Ju 52s were making the news. In a contest to determine the best-performing airliner in the world, a Ju 52 christened the Oswald Boelcke won the Circuit of the Alps race, completing the Zurich-GenevaMilan-Zurich route over the Alps in a record time of 3 hours, 43 minutes, and 29 seconds. The Oswald Boelcke made the news in another more dubious way when it collided head-on with a small Udet Flamingo biplane. While suffering heavy damage, the Ju 52 was able to make an emergency landing without injury to the six people aboard. The Flamingo and its two occupants were not so fortunate.

By 1933, the first dozen Ju 52s were in scheduled service with Luft Hansa. Eventually, Luft Hansa had over 80 Ju 52 airliners in its fleet and they carried more than 75 percent of its airline traffic in Europe. Before World War II, the Ju 52/3m was the most widely used civil airliner in European service. For example, it was operated by Syndicato Condor Ltda. in South America and by Eurasia Aviation Corp. in China. It could carry 15 to 17 passengers two abreast with everyone having a window seat and insulated a bit from the roar of the three engines.

Lufthansa used the Ju 52 to chart air routes over the Pamir mountains to China transversing mountain passes at altitudes as high as 17,700 feet. Ju 52s equipped with 660-horsepower BMW 132A engines had a service ceiling of just over 19,000 feet. Ultimately, the aircraft would fly in some 50 different countries.

Rugged Travels

While designed as a civil airliner, the ruggedness of the Ju 52 was soon recognized as an asset by military leaders around the world. The first Ju 52s to see combat were four early models that were shipped to Bolivia for commercial airline service. These aircraft became involved in the Gran Chaco War, a bloody border dispute waged between Bolivia and Paraguay from 1932 through 1935. The Ju 52s were used for everything from transporting men and supplies to evacuating the wounded. They operated from the most primitive runways in the steaming jungle or on the side of mountains.

The exploits of the Ju 52s did not go unnoticed by Nazi Germany's Luftwaffe. Indeed, the Luftwaffe's first Ju 52s, which were delivered in 1934-35, were the Ju 52/3mg3e bombers powered by 600-horsepower BMW 132A engines. This "Behelfsbomber," or auxiliary bomber configuration, could carry approximately 3000 pounds of bombs and had machine guns mounted in a dorsal gunner's station and a ventral "dustbin." Because of the spacing of the spars in the wing that formed the bottom of the fuselage, conventional bomb bays were not feasible and the bombs had to be loaded vertically. Franco's fascist forces also used some 450 Ju 52s--about 50 percent of all the Ju 52s that had been produced to that time--in the Spanish Civil War between 1936 and 1939 either as transports or bombers.

Heavy Losses

By the close of the 1930s, the Ju 52's role as a bomber was surpassed by more specialized aircraft. Its most important contribution to the war effort became as a transport carrying troops and supplies. Well over 90 percent of the Luftwaffe's transports were Tante Jus with an estimate of more than 3500 in use. They flew 95 percent of the Luftwaffe's air transport missions. The transports were designed for 18 troops, though often many more were carried. As an air ambulance, the Ju 52 had room for 12 stretchers.

One interesting military version was the Ju 52/3mg6ms, which was fitted with a degaussing ring and used to detonate mines from the air.

Even though the Ju 52s were rugged aircraft, they suffered very high losses throughout the war. Many of these losses can be attributed to the lack of air cover during some operation. These lumbering aircraft were no match for allied fighters and antiaircraft fire. The fact that the Ju 52s did not have self-sealing fuel tanks did not help matters. Weather also took its toll, especially on the eastern front in Russia. One of the few inherent faults of the Ju 52 was its susceptibility to icing, a problem not corrected until the Ju 52/3mg5e model.

Almost 600 Ju 52s were used when Germany invaded Norway in 1940, and almost as many helped during the invasion of France and the Low Countries. Almost a quarter were lost in both of these campaigns. In North Africa, over 400 Luftwaffe transports were shot down in less than one month alone. But this was nowhere near the disaster that occurred on the Russian front. Some estimates say that more than 800 of the thousand or so Ju 52s used to resupply the German troops' attempt to take Stalingrad were lost, not so much as a result of fighting, but due to the extreme cold, horrible field conditions, and general chaos of the crumbling German war machine.

Unknown Numbers

The total number of Ju 52s produced is not known. Most experts estimate that 4845 were made, but the actual number may well be greater. Total tallies are incomplete because of wartime secrecy, lost records, and production that was spread over several nations, often using slave labor.

Outside of Germany, an estimated 2186 Ju 52/3ms were produced in occupied France at the former Amoit plant in Cherbourg. Ju 52s were also assembled by Pestlorinc Industries in Budapest, Hungary. Even with the end of the war, production continued in France by Ateliers Aeronautiques Colombes with some 400 more produced through 1947. By then, it was designated the AAC.1 Toucan," though even after 15 years of production, the design had hardly changed. Many of the AAC.1s saw military service with the French Air Force in the Indochina War in 1949.

Some 170 more of the planes were produced by Construcciones Aeronauticas S.A. in Spain as the 352-L. Short Brothers in England built 10 Ju 52/3ms for British European Airways using war booty parts. After the war, several hundred were used by many foreign airlines until more-modern aircraft became available. Ju 52s were still being used to carry passengers and cargo into the late 1970s. A few airplanes have even been restored and are flying today.
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Title Annotation:airplanes
Author:Siuru, Bill
Publication:Mechanical Engineering-CIME
Date:Feb 1, 1991
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