Junkers J 1
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|Junkers J 1|
|The Junkers J.1 Blechesel, the world's first practical all-metal aircraft|
|Manufacturer||Junkers & Co|
|First flight||18 January 1916|
The Junkers J 1, nicknamed the Blechesel ("Tin Donkey" or "Sheet Metal Donkey"), was the world's first practical all-metal aircraft. Built early in World War I, when aircraft designers relied largely on fabric-covered wooden structures, braced with struts and exposed rigging lines, the Junkers J 1 was a revolutionary development in aircraft design, being built and flown only 12 years after the Wright Brothers had first flown the "Flyer I" biplane in December 1903. Herr Junkers' experimental all-metal aircraft never received an official "A" nor an "E-series" monoplane designation from IdFlieg and the then-designated Fliegertruppe, probably because it was primarily intended as a practical demonstration of Junkers' metal-based structural ideas, and was officially only known by its Junkers factory model number of J 1. It should not be confused with the later, armoured all-metal Junkers J 4 sesquiplane, accepted by the later Luftstreitkräfte as the Junkers J.I (using a Roman numeral).
Design and development
Hugo Junkers, who had already established his engineering credentials by the invention of a type of calorimeter and in the construction of internal combustion engines, first became interested in aviation in 1907 when a colleague named Hans Reissner, a professor at the Technische Hochschule in Aachen, approached him for assistance in aircraft construction. Five years later Reissner, with Junkers' help, began construction of his all-metal canard design, which he named the Ente ("Duck"). Junkers' firm built the flying surfaces , and radiator of Reissner's design. The problems encountered in constructing the Ente got Junkers' mind working on the problems of airframe design, and solving the problem of eliminating the then-prevalent exterior bracing from airframes. He patented the concept of the flying wing aircraft in Germany in 1910. When World War I broke out his mind turned to military matters.
After the the outbreak of World War I Hugo Junkers and his company's research institute, or Forschungsanstalt, began the engineering work to realize Junkers' idea of creating aircraft designs that dispensed with drag-producing exterior bracing. His work on Reissner's Ente design had convinced him of the necessity to use metal as the main structural material, but since the apparently ideal metal alloy for aircraft construction, duralumin, had only been invented some six years earlier in Germany, and was initially prone to flaking and other undesirable characteristics when worked in sheet metal form, Junkers first all-metal aircraft designs had to use sheets of heavier electrical steel, similar to the types of ferrous sheet metals used in laminated-core AC electrical transformers.
In July 1915 the Junkers firm got its first aircraft construction contract No. 96/7.17 A7/L from the German government, to produce a two-seat all-metal aircraft with a 130 km/h (81 mph) top speed, a wing loading of 50 kg/m² (10.2 lb/ft²) and using a 75 kW (100 hp) engine. Junkers engineers Otto Mader, head of Junkers' Forschungsanstalt, and Hans Steudel, director of Junkers' structural materials and testing department, started the work on the design of what would become the Junkers J 1 in September of that year, and by November 1915 the completed J 1 was ready for initial flight testing.
Pioneering design features
When the Junkers J 1 was first rolled out for government examination by the Kaiser's military aviation experts in November 1915, they were looking at what was the pioneering example of future aviation design — a sleek, well-thought-out low drag design that had completely eliminated the need for major exterior bracing struts, except on the empennage, for support of the horizontal stabilizer (which had a variable incidence feature built into it) and tailskid structures, and only two crossed bracing cables along the front vertical plane of the main landing gear struts, exposed outside the structure.
The fuselage used welded strip-steel angle stock and I-beam sections along with some steel tubing to form its main internal structure, with 42 cm (17 in) wide sheet steel panels wrapped around the fuselage to form its covering. The innovative cantilever structure for the wings allowed their exterior surfaces to be strikingly smooth, being likewise covered in chordwise sheet steel panels. The wing root had a depth of about 75% of the height of the fuselage at the root's thickest point, and the wing had at least three airfoil changes, along with tapering of the leading and trailing edge angles between the wing's root and the wingtip. These changes in wing section would become a Junkers design hallmark on the later 1918 Junkers D.I single seat all metal fighter design, which was covered with corrugated duralumin. The J 1 also relied on steel panels with "spanwise" corrugations, running from root to tip as a structural element, hidden under the smooth outer metal covering, to increase the wing's strength. This particular design element of the J 1 was used on later all-metal aircraft, such as the wings of the American Boeing B-17 Flying Fortress heavy bomber design of 1935.
The 90 kW (120 hp) Mercedes D.II six-cylinder liquid-cooled inline engine selected for the design had a simple, clamshell-like horizontally split cowling enclosing the engine's crankcase and lower cylinder block, and an advanced engine radiator layout, placing the radiator in a ventral position under the forward fuselage, with the front of the radiator housing's opening just behind the front gear strut's attachment points to the fuselage, and with the radiator's housing having a width equal to that of the fuselage above it.
Like the Fokker Eindecker, the single vertical tail surface was of an "all-flying" design (with no fixed fin) and the entire tail surface structure and covering also consisted of formed and sheet steel, much like the wings, however the angle of incidenceof the stabilizer could be adjusted on the ground.
Before the Junkers J 1 could fly for the first time, IdFlieg, the Inspektorat der Fliegertruppen, the aviation administration arm of the German army, required that static load tests be done on the J 1, with the usual static loading trials carried out on the J 1's structure with sand bags, loading and strength tests, as well as a test of the static thrust that would be obtained with the chosen engine and propeller combination. The static tests were completed on 3 December 1915, preceding the engine thrust tests. The Junkers factory did not yet have its own test field in Dessau, so the completed J 1 was taken to the Fliegerersatzabteilung 1 (FEA 1) airfield in Döberitz just west of Berlin for its flight testing program.
On 12 December, Leutnant Theodor Mallinckrodt of FEA 1 was assigned to taxi and briefly "hop" the J 1, which he managed to do successfully up to almost a 3 m (10 ft) altitude, but a gust of wind caught the starboard wing during the "hop" as the J 1 descended, with the port wingtip scraping the ground and the J 1's left side of the fuselage was bent inwards towards the rear of the wing mount. Repairs were made through the holiday period at the end of 1915, and more static load tests were carried out to check on the integrity of the repairs.
The second attempt at flight for the J 1 was carried out at Döberitz by Gefreiter (Private) Paul Arnold of the FEA 1 unit, on 18 January 1916. During this flight the J 1 reached an altitude of only 80 m (260 ft), following a 200 m (660 ft) takeoff run, and the variable incidence stabilizer had been incorrectly set, in the mistaken belief that the J 1 was tail-heavy. Later that day, after the stabilizer's incidence adjustment was corrected to give level flight trim, Leutnant Mallinckrodt made another attempt, this time reaching 900 m (2,950 ft), with a shorter takeoff run than before. The in-flight handling of the J 1 was acceptable, and it was stable in flight.
On the following day, 19 January, Mallinckrodt once again took the J 1 up for its only known "high performance" flight test, which consisted of a 7 km (4 mi) course, at varying altitudes from 200–300 m (650–985 ft), and managed to get the J 1 up to a top speed of 170 km/h (106 mph). The J 1 was compared to the popular Rumpler C.I two-seat armed observation biplane, which was some 30 km/h (19 mph) slower in its top speed, even though the Rumpler biplane had the more powerful Mercedes D.III engine, but due to the lighter weight of the Rumpler's wood-and-fabric structure it had a much better climb rate than the J 1 with its experimental steel structure.
By the end of January 1916, Junkers had been given a contract to further develop his all-metal concept, and the later Junkers J 2 single seat fighter, which would never see front line service, was the follow-on to the J 1.
The Junkers J 1 was probably not flown again after January 1916. However, it survived World War I, and was placed on display in a Berlin aviation museum. Sadly, it met its end during one of the earliest Royal Air Force bombing raids on Berlin during World War II.
Rumours have existed that a scale display model of the J 1, made of metal, had been built by the Junkers factory workers during the years following its initial flights, and exhibited at the Franklin Institute in Philadelphia, Pennsylvania after the close of World War I, but no information exists on the eventual fate of this model.
Data from 
- Crew: 1
- Length: 8.64 m (28 ft 4 in)
- Wingspan: 12.92 m (42 ft 5 in)
- Height: 2.49 m (8 ft 2 in)
- Wing area: 24.34 m2 (262.0 sq ft)
- Empty weight: 920 kg (2,028 lb)
- Gross weight: 1,080 kg (2,381 lb)
- Powerplant: 1 × Mercedes D.II 6-cyl. water-cooled in-line piston engine, 90 kW (120 hp)
- Maximum speed: 170 km/h (106 mph; 92 kn)
- Turner, P. St.J. and H. Nowarra. Junkers: An Aircraft Album. New York: Arco Publishing Inc, 1971. ISBN 0-668-02506-9.
- Grosz, Peter and Gerard Terry. "The Way to the World's First All-Metal Fighter", AirEnthusiast Twenty-Five, 1984, Pilot Press, pp. 60–63. ISSN 0143-5450.
- Wagner, Ray and Heinz Nowarra. German Combat Planes: A Comprehensive Survey and History of the Development of German Military Aircraft from 1914 to 1945. New York: Doubleday, 1971.
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