The Junkers J 1, nicknamed the Blechesel, was an experimental monoplane aircraft developed by Junkers & Co.
It was the world’s first all-metal aircraft.
Manufactured early on in the First 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 both throughout its structure as had been done previously, and in its outer skins.
It originated from the work of pioneering aeronautical designer Hugo Junkers.
The experimental aircraft never received an official “A” nor an “E-series” monoplane designation from IdFlieg and the then-designated Fliegertruppe, and was officially known only 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), from the category of armoured combat aircraft established by IdFlieg, the German Army’s inspectorate of military aircraft.
The J 1 was constructed and flown only 12 years after the Wright Brothers had first flown the “Flyer I” biplane in December 1903.
On 12 December 1915, the aircraft made its brief maiden flight, flown by Leutnant Theodor Mallinckrodt of Flieger-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 later Junkers J 2 single-seat fighter, which would never see frontline service, was the follow-on to 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 the Deutsches Museum in Munich.
During December 1944, the J 1 was destroyed during an Allied strategic bombing raid on the city.
The Junkers J 1 was an experimental mid-wing monoplane that incorporated various modern features, having a cantilever wing and an entirely metal structure element.
Externally, the J 1 was an exceptionally clean and well-proportioned aircraft.
An array of 42 cm (17 in) wide sheet steel panels, reinforced in key load-bearing areas by additional sheets of corrugated 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.
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 sheet steel, much like the wings.
The angle of incidence of the stabilizer could be adjusted on the ground.
The basic structure of the J 1 was built up around its centre fuselage section and the integral inboard stub wing, functioning as the aircraft’s wing roots.
The stub wings served as attachment points for Junkers’ patented sparless 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 the horizontal stabilisers and the undercarriage.
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.
The innovative cantilever structure for the wings were also covered in chordwise 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 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 Wilm’s duralumin, corrugated as first attempted with the Junkers J 3 airframe exercise of 1916–17.
The J 1 also relied on steel panels with span-wise corrugations 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 a wider number of later-built all-metal aircraft, such as for the wings of the American Boeing B-17 Flying Fortress heavy bomber.
The 90 kW (120 hp) Mercedes D.II six-cylinder liquid-cooled inline engine selected to power the J-1 was housed within a simple, clamshell-like horizontally split cowling enclosing the engine’s crankcase 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.