| Junkers J 1 | |
|---|---|
 | |
| The Junkers J.1Blechesel | |
| Role | experimental/Pioneer aircraft Type of aircraft |
| Manufacturer | Junkers & Co |
| First flight | 12 December 1915 |
| Retired | 1916 |
| Status | Retired |
| Primary user | Luftstreitkräfte |
| Produced | 1915 |
| Number built | 1 |
TheJunkers J 1, nicknamed theBlechesel (Tin Donkey or Sheet Metal Donkey), was an experimentalmonoplane aircraft developed byJunkers. It was the first all-metal aircraft in the world. Manufactured early in theFirst World War, an era in which aircraft designers relied largely on fabric-covered wooden structures braced with wires, the J 1 was a revolutionary development in aircraft design, making extensive use of metal in its structure and in its outer surface.
The J 1 originated from the work of pioneering aeronautical designerHugo Junkers. The experimental aircraft never received an"A" or "E-series" monoplane designation fromIdFlieg, theArmy inspectorate of military aircraft and The Imperial German Air Service (Die Fliegertruppen des deutschen Kaiserreiches). The aircraft was known only by its Junkers factory model number of J 1 and should not be confused with the later, armoured all-metal Junkers J 4sesquiplane, accepted by the laterLuftstreitkräfte as theJunkers J.I (using a Roman numeral), from the category of armored combat aircraft established byIdFlieg.
On 12 December 1915, the aircraft made its briefmaiden flight, flown byLeutnant Theodor Mallinckrodt ofFlieger-Ersatz-Abteilung 1 (FEA 1), during which an altitude of almost 3 m (9.8 ft) was reached. Greater altitudes and performance were achieved during subsequent flights. By the end of January 1916, Junkers had been given a contract to further develop his all-metal concept and the laterJunkers J 2 single-seat fighter, which would never see front line service, followed the J 1. It is believed that the Junkers J 1 was not flown again after January 1916. In 1926, it was placed on static display at theDeutsches Museum in Munich. In December 1944, the J 1 was destroyed during anAllied bombing raid on the city.
Amongst the earlier pioneers and innovators in the field of aviation was the German engineer andaeronautical designerHugo Junkers. During his early career he had established his engineering credentials outside of the field of aviation; Junker's innovations had included the invention of a type ofcalorimeter and in the construction ofinternal combustion engines. Sometime after 1897, Junkers was first introduced to the principles and field of aviation after having received details of the concept of heavier-than-air travel fromHans Reissner, a colleague and fellow professor at theTechnische Hochschule inAachen, where Junkers held the chair of Professor of Thermodynamics.[1]
In 1907 Reissner approached Junkers, seeking his collaboration in the design and construction of an earlymonoplane aircraft; although this first effort, which flew in 1909, did not meet with much success, it was this project which has been credited with leading to Junkers pursuing a career as an aeronautical designer. Five years later Reissner, with Junkers' help, began construction of his all-metalcanard design, which he named theEnte (Duck) which first flew on 7 August 1912.[2] Junkers' firm manufactured portions of Reissner's design, including theflying surfaces andradiator. The problems encountered in constructing theEnte had led to Junkers spending considerable amounts of time working on the problems ofairframe design, including an examination of the options for the elimination of the practice ofexterior bracing of airframes. During 1910 hepatented the design for a fully cantilevered thickaerofoil tailless aircraft (now known as aflying wing) in Germany.[1]
During 1910 Junkers received a grant for the construction of awind tunnel at his research facilities in Aachen; this led to the initiation of an aerodynamic research programme that would, five years later, contribute to the design of the Junkers J 1. In 1911, Junkers resigned his professorship to dedicate his efforts to hisDessau-based engine company; he returned to Aachen upon the completion of the wind tunnel. It was not until 1915 that Junkers was able to fully devote his time to the design and manufacture of an aircraft; it was at this point that he opened a research institute, theForschungsanstalt Professor Junkers, which was assigned responsibility for the design and development of a series of fully cantilevered all-metal monoplanes.[1]
Upon the outbreak of theFirst World War in August 1914, Junkers decided to direct his efforts towards projects which would have potential military value. The majority of aircraft designers were relatively conservative and, save for some isolated examples, no advances were achieved; according to aviation historianCharles Gibbs-Smith, the pioneering work of Hugo Junkers was a notable exception. It was Junkers' efforts, along with those of collaborators such as engineersOtto Reuter, Otto Mader, head of theForschungsanstalt and Hans Steudel, director of Junkers' structural materials and testing department, that the J 1 would be produced as a private venture, in the form of what would now be termed atechnology demonstrator.[1]
Junkers and theForschungsanstalt, commenced engineering work to realize his concept for the creation of aircraft designs that would dispense withdrag-producing exterior bracing.[1] His work on Reissner'sEnte design had convinced him of the necessity to use metal as the main structural material. Althoughduralumin, which had been invented byAlfred Wilm six years earlier, was apparently the ideal metal alloy for aircraft construction it was prone to flaking and other undesirable characteristics when worked in sheet metal form. The early all-metal aircraft designs produced by Junkers used sheets of heavierelectrical steel, similar to the types of ferrous sheet metals that are typically used inlaminated-coreAC electricaltransformers.[citation needed]
On 8 June 1915, Junkers began to acquire thetooling for the J 1. According to aviation author Hugh Cowin, while it has often mis-reported as having been produced to a specification forr an aircraft intended for military service, the J 1 was instead intended to be produced purely as a research aircraft, that would lead to the production of a later line of all-metal monoplane fighter aircraft. On 12 December 1915, the J 1 made a short flight at Dessau and was then sent to the Army proving ground atDöberitz for testing, where it made the first real flight on 18 January 1916.[3]
The Junkers J 1 was an experimental mid-wing monoplane that incorporated various modern features, having acantilever wing and an entirely metal structure. Externally, the J 1 was an exceptionally clean and well-proportioned aircraft.[4] Sheet steel panels 42 cm (17 in)-wide, reinforced in load-bearing areas by additional sheets ofcorrugated steel within the comparatively-smoother outer envelope, were wrapped around the fuselage to form its external covering. This arrangement was the first use of an all-metal stressed-skin construction.[5] The rudder was of an "all-flying" design, with no fixed fin and the tail surface structure and covering also consisted of formed sheet steel, much like the wings. Theangle of incidence of the stabilizer could be adjusted on the ground.[citation needed]
The basic structure of the J 1 was built up around its centerfuselage section and the integral inboard stub wing, functioning as the aircraft'swing roots. The stub wings served as attachment points for Junkers' patented spar-less wings, which consisted of short span truss-tires sections successively layered outwards from the stub wings. Other elements fixed onto the centre section include the nose section, rear fuselage, and tail unit. Atypically for the era, the wing lacked any exterior bracing struts or wires; the only use of external bracing was for support of thehorizontal stabilisers and theundercarriage. The internal structure made use of welded strip-steel angle stock and I-beam sections in conjunction with portions of steel tubing to form its main internal structure.[5]
The innovative cantilever structure for the wings were also covered inchordwise sheet steel panels. The wing root had a depth of about 75 per cent of the height of the fuselage at the root's thickest point, and the wing had at least three aerofoil changes, along with tapering of theleading andtrailing edge angles between the wing root and the wing tip. 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 Wilm's duralumin, corrugated as first attempted with theJunkers J 3 airframe exercise of 1916–1917. The J 1 also relied on steel panels withspan-wise corrugations as a structural element hidden under the smooth outer metal covering to increase the wing's strength.[5]
The 90 kW (120 hp)Mercedes D.II six-cylinder liquid-cooledinline engine selected to power the J-1 was housed within a simple, clamshell-like horizontally splitcowling enclosing the engine'scrankcase and lower cylinder block. It featured an advanced engine radiator layout for the era, having placed the radiator in a ventral position underneath the forward fuselage; the front of the radiator housing's opening was located 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.[citation needed]
Before the Junkers J 1 could fly,IdFlieg, theInspektorat der Fliegertruppen, the aviation administration arm of the German Army, required that static load tests be performed on the J 1. This involved the usual static loading trials being carried out on the J 1's structure usingsandbags, loading and strength tests, as well as a test of the static thrust that would be obtained with the engine andpropeller combination. On 3 December 1915, these static tests were completed, followed by engine thrust tests. The Junkers factory did not yet possess a test field at Dessau, so the J 1 was transported to theFliegerersatzabteilung 1 (FEA 1) airfield in Döberitz, just west of Berlin, for its flight testing.[5]
On 12 December 1915,Leutnant Theodor Mallinckrodt of FEA 1 was assigned to taxi and briefly "hop" the J 1, which he managed to do up to almost a 3 m (9.8 ft) altitude.[5] During the course of this small flight, a gust of wind caught the starboard wing during the "hop" as the J 1 descended, resulting in the port wing tip scraping the ground and the port side of the J 1's fuselage was correspondingly bent inwards towards the rear of the wing mount. Testing was delayed while repairs were made through the holiday period at the end of 1915, after which a further round of static load tests were carried out to test the repairs.[citation needed]
On 18 January 1916, the second flight for the J 1 was carried out at Döberitz byGefreiter (Private) Paul Arnold of the FEA 1 unit. The J 1 attained an altitude of only 80 m (260 ft), following a 200 m (660 ft) take-off run, as 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 was adjusted to give level flight trim,Leutnant Mallinckrodt performed another attempt, this time reaching a maximum height of 900 m (3,000 ft) from a shorter take-off run. Handling was determined to be acceptable and the aircraft was reportedly stable during flight.[citation needed]
On 19 January, Mallinckrodt once again took the J 1 up for its only known "high performance" flight test, which consisted of a 7 km (4.3 mi) course and covered altitudes from 200–300 m (660–980 ft). During this flight, Mallinckrodt reached top speed of 170 km/h (110 mph). As a consequence of military interest in Junkers' design, the J 1 was compared to the popularRumpler C.I two-seat, armed observation biplane during flight testing. The J 1 was 30 km/h (19 mph) faster, even though the Rumpler biplane was powered by the more powerfulMercedes D.III engine. Given the lighter weight of the Rumpler's wood-and-fabric airframe, it was capable of a much greater rate of climb rate than the J 1, handicapped by its experimental steel structure.[5]
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The flight performance of the J 1 were evaluated during the test programme.[5] Information was gathered from the pilots and the ground crew that serviced it. Apparently, the welded construction of the aircraft had problems on the ground that had been encountered before. In conjunction with its sluggish performance in the air, some individuals mocked the J 1 with derogatory names, the most prominent of these being theBlechesel (Tin Donkey or Sheet Metal Donkey). Some figures, such as theDutch aviation pioneer,Anthony Fokker, praised the potential of the aircraft and the principles demonstrated, pointing to the higher speed and greater durability of prospective aircraft using such construction.[5] The handling of the J 1 was the subject of derision by Junkers' critics but the military remained supportive of refinement of the concept. By the end of January 1916, Junkers had been given a contract and theJunkers J 2 single-seat fighter followed, which would never see front line service. The J 2 bore a superficial similarity to the J 1, being more aerodynamically refined and slightly smaller, yet the two aircraft had similar structures.[5]
It is believed that the Junkers J 1 was not flown again after January 1916. The aircraft survived the First World War and was placed on static display in 1926 at theDeutsches Museum in Munich. During theSecond World War, in December 1944, the J 1 was destroyed during anAllied bombing raid on the city. A metal scale display model of the J 1 was built by a group of Junkers' factory workers following its initial flights and was exhibited at theFranklin Institute inPhiladelphia after the war; its fate is not known. During 2015, the Junkers Technology Museum in Dessau, Germany, announced that they intended to construct a full-scale replica of the pioneering J 1. To fund this, financing was sought through acrowdfunding campaign onKickstarter.[6][7]
Data from Wagner and Nowarra (1971). German Combat Planes: A Comprehensive Survey and History of the Development of German Military Aircraft from 1914 to 1945.[8]
General characteristics
Performance
