Founded in 1895, before the dawn of flight, Junkers became a pioneer in all-metal aircraft, flying its Blechesel (sheet donkey) monoplane in late 1915. It was a spectacularly innovative design, with a semi-monocoque construction of steel ribs and stressed sheet skin. The war had made aluminium too expensive, and the manufacturing processes then available meant that the newly developed duralumin alloy couldn’t be used for sheeting. With steel as the only viable alternative, the Blechesel was overweight, giving it very poor climb performance and ponderous handling. But it was fast. With just 120hp to shift all that bulk, the clean design allowed it to reach 170km/h (106mph), considerably faster than almost all contemporary aircraft.
The lessons learned from the Blechesel bore fruit in 1919, when Junkers completed the revolutionary F.13. Even today, the machine looks startlingly modern, bearing a marked resemblance to the Piper Cherokee, launched in 1960 and still in production today. Rather than the biplane configuration chosen by most manufacturers, Junkers had produced a sleek monoplane, without external struts or wire bracing. The difficulties of using duralumin for skinning had been overcome, and the F.13 was clad in a stressed skin of the new alloy. This was corrugated to provide rigidity, a characteristic that was later widely seen in the company’s ubiquitous Ju52.
For reasons that today aren’t entirely clear, the F.13 cockpit was only partly enclosed. Although partially roofed above, the office was shielded only by a small windscreen, with a large gap above and to the sides. Had this been fully enclosed then the aircraft would undoubtedly have been faster and more economical. Passengers were more favourably treated; their cabin was fully enclosed and heated. The four seats were equipped with safety belts, themselves an innovative feature for the period.
The first flight of the prototype on 25 June 1919 showed great promise, but it also revealed some shortcomings. Before moving to full production, Junkers increased the wingspan and replaced the 127kW (170hp) Mercedes engine with a 140kW (185hp) unit from BMW.
Despite restrictions on Germany’s aircraft production in the early post-war years, the F.13 found favour with operators in many countries, including the USA, Austria and Poland. Production difficulties were eased when John Larsen Aircraft purchased a licence to build the Junkers-Larsen JL-6 in the US. Sales followed to France, Italy and Japan in 1922. The following year, the Soviet Union also bought a production licence and began building machines near Moscow.
Junkers marketed the F.13 aggressively, even setting up its own airline, Junkers Luftverkehr, in 1921 to encourage sales from German airlines. They provided finance services to spread the purchase cost. By 1924, sixteen European operators were using F.13s on regular flights.
The last commercial flight of an F.13 was in 1951, more than thirty years after its debut. In that time it served as a safe, comfortable and reliable passenger aircraft, as well as seeing service with the Red Army and even functioning as a bomber for the Republic of China.
Although no original F.13s survive today, a near-perfect replica has been built and flown by Rimowa, the luggage company whose products famously exhibit the same grooves seen on the classic little airliner.
|F-13 by numbers|
|First Flight:||15 June 1919|
|Powerplant:||1 × Mercedes D.IIIa 6-cyl.water-cooled in-line piston engine, 118 kW (158 hp)|
|Maximum Speed:||273km/h (107mph)|
|Length:||9.59m (31ft 6in)|
|Wingspan:||14.8m (48ft 7in)|
|Height:||3.5m (11ft 6in)|