Junkers Ju 52

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 wingtips 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 Ju 52 featured an unusual corrugated duralumin metal skin, which had been pioneered by Junkers during the First World War; the corrugation served to strengthen the whole structure over a smoother approach. The fuselage was of rectangular section with a domed decking, comprising a tubular steel structure that was entirely covered by the corrugated metal skin. A port-side passenger door was placed just aft of the wings; this entrance also acted as a loading hatch for freight, the lower half functioning as a platform to ease cargo movements. The cabin had a dimensional capacity of 590 cubic feet, and was lined with numerous windows stretching forward to the pilots' cockpit. The main undercarriage was fixed and divided; some aircraft had wheel fairings, others did not. A fixed tailskid, or a later tailwheel, was used. 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 IV or Junkers liquid-cooled V-12 engine. However, the single-engined model was deemed to been 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 R-1690 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 R-1340 Wasp and 578 kW (775 hp) Bristol Pegasus VI engines.

The two wing-mounted radial engines of the Ju 52/3m had half-chord cowlings and in planform view (from above/below) appeared to be splayed outwards, being mounted at an almost perpendicular angle to the tapered wing's sweptback leading edge (in a similar fashion to the Mitsubishi G3M bomber and Short Sunderland; the angled engines on the Ju 52 were intended to make maintaining straight flight easier should an engine fail, while the others had different reasons). The three engines had either Townend ring or NACA cowlings to reduce drag from the engine cylinders, although a mixture of the two was most common (as can be seen in many of the accompanying photographs), with deeper-chord NACA cowlings on the wing engines and a narrow Townend ring on the center engine (onto which a deeper NACA cowl was more difficult to fit, due to the widening fuselage behind the engine). Production Ju 52/3m aircraft flown by Deutsche Luft Hansa before the Second World War, 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.

In a military context, the Ju 52 could carry up to 18 fully-equipped soldiers, or 12 stretchers when used as an air ambulance. Transported material was loaded and unloaded through side doors by means of a ramp. Air-dropped supplies were jettisoned through two double chutes; supply containers were dropped by parachute through the bomb-bay doors, and paratroopers jumped through the side doors. Sd.Kfz. 2 Kettenkrafträder (half-track motorcycles) and supply canisters for parachute troops were secured under the fuselage at the bomb bay exits and were dropped with four parachutes. A tow coupling was built into the tail-skid for use in towing freight gliders. The Ju 52 could tow up to two DFS 230 gliders.

Sources:
Gunston, Bill & Wood, Tony - Hitler's Luftwaffe, 1977, Salamander Books Ltd., London
Gunston, Bill - The Encyclodepia of the Worlds Combat aircraft, 1976, Chartwell Books, Inc., New York
Wikipedia: Junkers Ju 52