Junkers Ju 252 The Junkers Ju 252 was a cargo aircraft that made its first flight in late October 1941 . The aircraft was planned as a replacement for the Junkers Ju 52 / 3m in commercial airline service , but only a small number were built as cargo aircraft for the Luftwaffe . Design and development . The original Ju 252 came about after talks between Junkers and Deutsche Lufthansa in December 1938 . Lufthansa requested a new design that would replace the Ju 52 , but offer much greater loads , seating , range and performance . Junkers responded with the EF . 77 design with a pressurized fuselage with seating for up to 35 , making it one of the larger airliners in the world at that time . It was powered by three Junkers Jumo 211 F engines , in nacelles almost identical in appearance , each complete with annular radiator and possibly as " Kraftei " unitized " power - egg " modular engine installations , to those on Jumo 211 - powered versions of the Junkers Ju 88 , replacing the BMW 132 of the Ju 52 , which dramatically improved performance . Compared to the Ju 52 , the Ju 252 was twice as heavy ( 13 , 100 kg vs . 5 , 600 ) , was over 100 km / h faster ( 440 km / h vs . 305 ) , and had dramatically improved range ( 3980 km vs . 1300 ) when fully loaded . By the time the prototype was ready to fly in October 1941 , the war was already in progress and the Luftwaffe took over development . Like earlier tail - dragger designs , the Ju 252 would normally be difficult to load when parked , owing to the sloping floor . Junkers had already pioneered - with the earlier Junkers Ju 90 ' s fifth and sixth prototype airframes during 1939 - a unique solution to this problem , the " Trapoklappe " , a hydraulically powered ventral rear loading ramp that possessed powerful enough operating mechanisms to lift the plane off its tailwheel , leveling the floor and allowing oversized cargo to be loaded directly forward into the fuselage . Even as cargo aircraft of all nations since World War II have used nosewheel landing gear undercarriage designs , the " Trapoklappe " concept of a rear loading ramp , that forms the opening rear ventral panel of the fuselage of a cargo aircraft , is a ubiquitous feature of most military airlift cargo aircraft to the present day . Although the Ju 252 was a vast improvement over the Junkers Ju 52 / 3m , the situation at that time did not permit any disruption of the existing production lines , and the Reich Air Ministry ( RLM ) was of the opinion that any replacement for the Junkers Ju 52 / 3m must make minimum demands on supplies of strategic materials and use power plants not required by combat aircraft . Junkers was then instructed to investigate the possibility of redesigning the Ju 252 in order that a considerable portion of wood could be included in its structure , simultaneously replacing the Junkers Jumo 211 F engine with the BMW Bramo 323 R engine of which surplus stocks existed . The result was the Junkers Ju 352 . Production of the Ju 252 was restricted to already completed prototypes plus those for which major assemblies had already been semi - completed , thus only fifteen transports of this type were completed before production was switched to the Junkers Ju 352 .