A.Kay Junkers Aircraft and Engines 1913-1945 (Putnam)

Junkers J1

  The experimental J1 was the world’s first airworthy all-metal aircraft. Nicknamed ‘Blechesel’ (Tin Donkey), it was designed by Dipl.- Ing. Otto Reuter and Dr-Ing. Otto Mader in collaboration with Hugo Junkers. Earlier experiments with a French Voisin biplane had given Dr-Ing. Reiszner some initial experience, and this was increased by the construction of a canard aircraft which had its rear-mounted wings constructed from corrugated sheet iron and was based on Junkers’ early experiments. The corrugations gave the thin metal rigidity. The aircraft first flew (not altogether successfully) on 23 May 1912 and crashed in 1913.
  The construction of the J1 was extraordinarily complex for the time, and many were baffled as to why one would want to attempt to build and fly an apparently heavy iron aeroplane - and at great expense into the bargain. However, the metal used was sheet iron of only 0.1-0.2mm thick, normally used for magnetic purposes. The wing was built up of short, hollow aerofoil sections about 420mm (10.7in) wide, and each section was welded together to give a complete unit. Far from ideal, this method of construction was, however, governed by the sheet material available from Junkers’ heating and other products. Inside each section were iron ribs which gave bracing and shape to the covering, and to these was welded, with great difficulty, the thin iron covering. This covering was corrugated to give the necessary rigidity, and on top of that was welded a smooth iron skin. The assembly of the complete wing was carried out on a jig of wooden formers to ensure true alignment. Large, unbalanced ailerons were provided, and these had horns for the control cables.
  The fuselage was made by wrapping thin corrugated sheet around wooden formers and welding it, a further smooth skin being welded on top. Multiple bracing tubes connected each wing to the fuselage at three points. A tailplane of metal construction carried an unbalanced elevator, and a balanced rudder, without a fixed fin, was used. There was a fixed, braced undercarriage and a tailskid. To power the J1, a Mercedes D.II water-cooled, six-cylinder engine of 120hp was fitted. Static tests were carried out by loading test wings with sandbags to prove their soundness and strength, while bags were also hung on wooden levers attached to the wings to test the latter’s torsional strength.
  Construction of the J1 began in early September 1915 and was virtually complete by the end of November. Soon, on 12 December 1915, the J1 made its maiden flight, taking off from Doeberitz with Lt. Friedrich von Mallinkrodt (on secondment from Idflieg) at the controls. Although it was not equipped as a fighter, the aircraft was compared with fighters and demonstrated superior level speed though an inferior climb rate and turning ability owing to the extra weight conferred by the type of construction. Therefore, development pointed in the direction of reducing weight to enhance performance. One troublesome feature of the J1 was the anchoring of the wings to the fuselage, which had to occur at the pilot’s position. Despite much attention being lavished on the problem, this produced a structural weakness, which became apparent when, during a landing in January 1916, a wing cracked.
  Nevertheless, the J1 had proved that an all-metal aircraft could fly - and fly well. It was taken into the air by many excellent aviators, including Anthony Fokker, who found that its speed exceeded by 20kph (12mph) that of the fastest aircraft at that time. However, its rate of climb of about 45m/min (150ft/min) was poor, mainly because of the weight of the iron wings, caused not just by the metal itself but also by the need to make the covering strong enough to withstand the stresses imposed. The remarkable achievement of the J1 was all the more so for being carried out from start to first flight in only four months.
  After the First World War, the repaired Junkers J1 monoplane was exhibited at the Junkers Lehrschau (Junkers Educational Exhibit), Dessau, and later transferred to the Deutsches Museum in Munich where it was destroyed during the Second World War during an air raid.


Data: Span 12.95m (42ft 5in); length 8.62m (28ft 3 1/2in); height 3.5m (11ft 6in); wing area 24m2 (258 sq ft); loaded weight 1,010kg (2,227lb); max. speed 170kph (106mph); climb rate 45 m/min (150ft/min).