The Junkers W 33 was a German 1920s single-engine low-wing monoplane transport aircraft that followed Junkers standard practice making extensive use of corrugated aluminium alloy over an aluminium alloy tube frame, that was developed from the similar but slightly smaller Junkers F 13 and evolved into the similar W 34.
Like all Junkers designs from the J 7 fighter onwards, it used a duraluminum aluminium alloy structure covered with Junkers’ characteristic corrugated dural skin.
While the Junkers W 33 was unusual when compared to the contemporary biplanes in use in the UK and the US, cantilever monoplanes were a popular design choice in continental Europe during the period, and the Junkers designs were unusual only in their extensive use of closely corrugated metal skins.
Unlike the skins on the contemporary Rohrbach Roland, those on the Junkers aircraft were not load bearing and it did not have a stressed skin structure.
The Junkers W 33 was a direct evolution of the 1919 four-seat airliner, the Junkers F 13.
The F 13 was similar to the W 33, but slightly smaller and had some detail differences.
Considerable evolution occurred in the structure of the F 13, so that later models shared more details with the W 33.
The wings had the same span as the late F 13s, though the planform differed slightly, while the length was the same as the F 13fe.
A slightly different fuselage cross section gave the W 33 a squarer cabin with a hunch-backed appearance compared to that of the F 13 and a door was provided on the port side to provide access to the freight compartment.
Early examples of the W 33 had an open cockpit much like the F 13, although it lacked the structural member that divided the pilot and co-pilot, and the corresponding and very distinctive coamings.
Some examples, such as the transatlantic machines had an early enclosed cockpit.
The 228 kW (306 hp) Junkers L5 upright inline water-cooled engine was also the same as used in the F 13fe, a more powerful engine than used in many of the F 13 variants.
The W 33 differed primarily from the W 34 in normally using an inline engine (aside from the rare dGao variant, which served as a prototype for the W 34), while the W 34 generally used various radial engines and had some minor detail improvements, such as a larger enclosed cockpit.
As was common for the time, when a wheeled undercarriage was fitted, a conventional fixed undercarriage was used with a tailwheel.
Early examples had a similar undercarriage to that used on the F 13, in which a hinged cross axle connected the two main wheels, while later examples provided an independent three-legged structure for each wheel.
The Junkers W letter may have denoted the type as a seaplane, but in practice W 33s were equipped as either landplanes or seaplanes, as needed.
As a floatplane, the W 33 was equipped with two main floats, braced to the fuselage with a forest of struts.
The prototype W 33, registered D-921, first flew as a seaplane from Leopoldshafen, on the river Elbe near Dessau on 17 June 1926.
Production began in 1927 and ran until 1934 and most of the 198 production machines were built at the Junkers works at Dessau, but a small number were assembled at Junker’s Swedish subsidiary AB Flygindustri at Limhamn near Malmö, and at Fili, near Moscow in the USSR.
Both of these plants had originally been built to avoid Allied post-war restrictions on aircraft manufacturing in Germany following World War One, that had been considerably eased by the time the W 33 was flying.
Prototype with Junkers L5 engine
Open cockpit, no windows in cargo compartment
Modified prototype with Junkers L2 engine
Enlarged cargo compartment, Junkers L5 engine
Enlarged cargo compartment, Junkers L2 engine
Like W33a with BMW Va engine
Strengthened centre wing,
Junkers L5 engine
BMW Va engine
Enlarged wing swept
Strengthened centre wing, less wing swept than d-version,