Junkers Ju 52 - Design and Development

Design and Development

The Ju 52 was similar to the company's previous Junkers W33, although larger. In 1930, Ernst Zindel and his team designed the Ju 52 at the Junkers works at Dessau. The aircraft's unusual corrugated duralumin metal skin, pioneered by Junkers during World War I, strengthened the whole structure.

The Ju 52 had a low cantilever wing, the midsection of which was built into the fuselage, forming its underside. It was formed around four pairs of circular cross section duralumin spars with a corrugated surface that provided torsional stiffening. A narrow control surface, with its outer section functioning as the aileron, and the inner section functioning as a flap, ran along the whole trailing edge of each wing panel, well separated from it. The inner flap section lowered the stalling speed and the arrangement became known as the Doppelflügel, or "double wing".

The outer sections of this operated differentially as ailerons, projecting slightly beyond the wing tips with control horns. The strutted horizontal stabilizer carried horn-balanced elevators which again projected and showed a significant gap between them and the stabilizer, which was adjustable in-flight. All stabilizer surfaces were corrugated.

The fuselage was of rectangular section with a domed decking, all covered with corrugated light alloy. There was a port side passenger door just aft of the wings, with windows stretching forward to the pilots' cabin. The main undercarriage was fixed and divided; some aircraft had wheel fairings, others not. There was a fixed tail skid, or later tail wheel. Some aircraft were fitted with floats or skis instead of the main wheels.

In its original configuration, designated the Ju 52/1m, the Ju 52 was a single-engined aircraft, powered by either a BMW or Junkers liquid-cooled engine. However, the single-engine model was underpowered, and after seven prototypes had been completed, all subsequent Ju 52s were built with three radial engines as the Ju 52/3m (drei motoren - "three engines"). Originally powered by three Pratt & Whitney Hornet radial engines, later production models mainly received 574 kW (770 hp) BMW 132 engines, a licence-built refinement of the Pratt & Whitney design. Export models were also built with 447 kW (600 hp) Pratt & Whitney Wasp R-1340 and 578 kW (775 hp) Bristol Pegasus VI engines. The two wing-mounted radial engines of the Ju 52/3m had full-chord cowlings and were noticeably toed-out, from being mounted at an almost perpendicular angle to the wing's tapered leading edge. The central engine had a half-chord cowling like a Townend ring as the fuselage behind it was increasing in diameter, though some later aircraft had deeper cowlings. Production Ju 52/3m aircraft flown by Luft Hansa before World War II, as well as Luftwaffe-flown Ju 52s flown during the war, usually used an air start system to turn over their trio of radial engines, using a common compressed air supply that also operated the main wheels' brakes.