Kalinin was assigned to the yard of the airline Ukrvozdukhput after the registration of the K-1 design in Kharkiv as a construction site. The yard was then renamed GROS (Graschdanskoje Opytnoje Samoleostrojenie, pilot aircraft construction for civil aviation). Shortly thereafter, it was referred to only as a "series work". Here Kalinin gathered his best employees around and planned the further development of the K-1. The planning group included I. G. Neman, S. I. Iskovich, A. J. Shcherbakov, and W. J. Krilow.
The fuselage consisted of a welded tubular steel framework and was clad with light-alloy sheet metal from Koltschug aluminum. The construction was designed as a high wing monoplane whose wings were braced to the lower part of the trunk body. The wings had an elliptical shape and were, like the tail, made of tubular steel and also covered with light metal sheets. The tail had a normal shape (tail fins strutted to the fuselage). All control surfaces were covered with fabric. The chassis was fixed and provided with a continuous axle. At the rear of the fuselage was a sprung tailspur. The pilot sat in a closed cabin.