There are three candidates for this number. As the performance diagrams from June 29, 1928, and the designation dated July 2, 1928, show, the conversion of the three-engine G 24 to a single-engine cargo aircraft was carried out under this designation. The first comparative calculations dated November 15, 1927, and envisioned a Junkers L 55 engine (575 hp).
However, the expected performance appeared too low to the JFA (Junkers Flying Club) officials. Therefore, the Junkers L 88 (850 hp) with reduction gearbox was to be used in the EF 30 project, but this engine was not even ready for testing by mid-1928.
As an alternative, the only German engine available was the BMW VIIU (650 hp), which Dipl.-Ing. Pohlmann considered somewhat underpowered for the EF 30.
Therefore, the project was also considered with foreign engines, such as the Farman 18WD (700/820 hp) and the Lorraine-Dietrich 34 (700/740 hp), as well as the Packard 2A-2500 (800 hp) for the American market. JFA was relatively late with its EF 30 project. The first single-engine G 24 had already flown at the beginning of 1928 – converted, however, not by JFA but by Luft Hansa independently at their Staaken shipyard. DLH gave the prototype, equipped with a BMW V1 engine (600 hp), the type designation F 24 and used it not as a cargo aircraft (as the EF 30 concept envisioned) but in passenger service. Gunther Ott of ADL already reported in detail on how Luft Hansa came to this independent initiative in “Luftfahrt International”, issue 1 + 2/1980. Junkers only put its single-engine prototype, based on the EF 30, into the air in February 1929. It received the
type designation W 41 and served as a test vehicle for the newly developed Junkers diesel engine FO 4 (predecessor of the Jumo 4/204).
Now to the two other “candidates” for project number 30. Wolfgang Wagner, in his book “Hugo Junkers - Pioneer of Aviation” (Volume 24 of the series “German Aviation”), initially lists EF 30 as the project designation for the Ju 52/1 m, then introduces it Then, a chapter later, it's also listed as a preliminary design for the Ju 60. An explanation for this dual designation is missing. The connection with the single-engine Junkers G 24 is not mentioned at all. Chronologically, the later Ju 60 doesn't fit the designation Ef 30 at all, while the Ju 52/1 m would certainly be within the realm of possibility.
But what about the F 24 / W 41? Two possible explanations present themselves: Either the project number 30 was initially used for the conversion to the W 41 cargo aircraft and subsequently for the larger successor model Ju 52/1 m, or Wagner simply misinterpreted the available drawings and performance diagrams of the EF 30 as a Ju 52 design, because both the F 24 and the Ju 52/1 m were initially designated as "large cargo aircraft." For the connection between the EF 30 and the Ju 60, there is only one piece of evidence: a handwritten data sheet dated July 18, 1931, which bears the inscription EF 30 in the upper right corner and on which various preliminary designs are juxtaposed—without mentioning the type number Ju 60. Otherwise, it appears in the numerous protocols and File notes documenting the development of the Ju 60 never mention an EF number.
Could it be that Dipl.-Ing. Pohlmann simply used pre-prepared JFA forms, still available from the EF 30 project planning phase, for comparing the various Ju 60 project data?
A similar case can be found in the early Ju 52 documents: A JFA form, on which the status of serial numbers 4001 to 4017 is listed under the heading “Baumuster Ju 52”, bears the inscription “K 43” in the lower left corner – the type designation for the military version of the Junkers W 34.
