#Housewife_Note: THE ELUSIVE E-7
For many years, I was intrigued by the latest variants of the I-180, about which there was little to no information in the literature. The following text is based on a comparison of a considerable amount of archival material.
Until now, all information about the mysterious I-180 E-5 and E-7 was limited to a quote from one renowned historian:
In October, the design team at the Gorky plant completed the refinement of the I-180, the standard for serial production in 1941. This aircraft, also known as the I-180 E-5, had a more forward center of gravity, 21.8% MAC (instead of 24% on previous aircraft), due to a redesigned single-strut landing gear and slightly raked-back wing panels. The wing area increased slightly to 16.3 m2. The pilot's cockpit was enclosed by a sliding canopy, and the frontal section of the canopy included transparent armor. A number of reinforcements were added to the design: a landing light was added to the wing, and the landing gear was equipped with a 300 mm diameter wheel...
The last experimental I-180, designated E-7, was built in Moscow at Aircraft Factory No. 51 as early as 1941. This aircraft featured all the innovations of the 1941 series: a transparent sliding canopy, a single-strut retractable landing gear, a reconfigured wing... end of quote.
And now the real deal. One renowned historian didn't bother to delve into the indexing systems of three different organizations, namely, the Design Bureau of Factory No. 1, Factory No. 21, and the Design Bureau of Factory No. 51, so I'll do it for him.
OKB No. 1 had two ways of designating projects: for document flow and for internal use. For document flow, the I-180 project was coded "E," with the number designating the topic. Many are already familiar with the "internal" designation system of the early NNP: the first two digits designate the platform, and the third the modification. Thus, the I-180-1 was actually designated I-181, or E-1, the I-180-2 was I-182 or E-2, and the I-180-3 was I-183 or E-3. The codes didn't denote the serial numbers of the prototypes; they were precisely the topics, i.e., modifications. The E-4 topic was the I-184, a prototype I-180 with turbochargers. Construction of the aircraft began, but the project was canceled due to the inability to obtain turbochargers with an acceptable service life. When the I-180 entered serial production at Plant No. 21, which, as we know, had its own internal system, apparently to avoid confusion, all paperwork for Plant No. 21 was processed using their internal indexing system. Thus, the serial version of the I-180 received the code "25." As a reminder, the previous code "24" belonged to the I-16 with the M-63 engine, and the next "29" is again the I-16 M63 but with a BS machine gun.
Since the plant's documentation did not allow for any distinctions in subject matter, all I-180 variants shared the same designation. The last "25" variant built at Plant No. 21 was indeed an I-180 with a modified center section, I-185-type chassis, and drop tanks. However, this did not make it any less of a "25." Incidentally, all design drawings show it with an open cockpit. While Plant 21 was launching production, OKB No. 1 began designing three new variants of the I-180: the I-185 (with an M-90 engine), the I-186 (with an M-71 engine), and the I-187 (with an M-81 engine).
Wait a minute! If the I-183 is the E-3, and the I-184 is the E-4, then... Yes! That's right. The E-5 is the I-185, the E-6 is the I-186, and the E-7 is the I-187. As is well known, all three were built and are known to the world as the first three I-185 prototypes, and the last two even flew (incidentally, a headlight appears).
At this point, the "E" aircraft ceased to exist, because the NNP moved permanently to Plant No. 51, which had its own coding system. There, the I-185, 186, and 187 received the code "R," and two new designs, the I-185 M-82 and the standard M-71, received the codes "I" and "IM," respectively. It should be added here that the "IM" documentation first featured a canopy with bulletproof glass. Since the I-185 was planned for serial production at Plant No1, it also received the production code “62” there. Well, you get the idea...
That's the end of the story, if you read this far, well done.
P.S.
Materials used:
Correspondence on the I-180 from 1938-1940
Correspondence from Factory No. 51 from 1941
I-180 preliminary design
I-184 preliminary design
I-180 preliminary design with single-strut landing gear
I-186 preliminary design
I-187 preliminary design
Materials from OKB No. 1
Materials from OKB No. 51
P.S. 2. Understanding this topic is actually quite difficult, especially given the relocation of OKB NNP from No. 1 to No. 51. The OKB moved at a time when as many as six I-185 prototypes were in various stages of completion. The factory and design documentation is a jumbled mess, with signatures from both organizations.
Vladimir Sergeevich Ilyushin 31-03-1927 - 01-03-2010