Here are a couple more superb drawings done by Rowdy36 that flesh out two key aircraft of the late 1930s/early 1940s for Sieran.
First up, the Korolev RT-9 Yeger;
Delivered initially in bare metal, the RT-9 was the first Sieranian transport to be built entirely out of metal rather than the traditional composite method. The design team responsible for producing the RP-2T Massa were also behind the design of the RT-9. In fact early proposals for the airliner much more closely matched that of the Massa than its final form. The design was the result of a number of evolutions to build a modern, long range airliner capable of connecting Sieran to Europe and the Americas with minimal stops in foreign territory for fuel. The end result was a superbly streamlined airframe that later went on to influence the design of the TC-2 Chajka.
Second, we have the Litvinov PI-37 'Skopa';
Designed after experience against Japanese land and naval fighters over China, the PI-37 was a lightly built interceptor that would go on to be numerically the most important fighter in the SRAF inventory at the outbreak of war in 1942. Powered by an imported Pratt & Whitney R-1830 Twin Wasp engine and armed with two 20mm cannon in the wings with 7.62mm machine guns firing through the propeller arch, the aircraft was capable of outstanding performance when compared to its older, underpowered predecessors.
Indeed the aircraft had largely resolved the major deficiencies of its older sibling, namely lack of speed and climb rate. The PI-37s wide track undercarriage and rugged but basic construction allowed it to be built and repaired swiftly and allow it to use even the most poorly equipped airbases.
A single squadron saw service in China against the Japanese where it was found that the aircraft compared reasonably well with the Ki-43 though the Zero outmatched it in turn performance. The squadron was recalled to Sieran shortly after the Japanese attack on Anadyr and the declaration of war.