DAR-7

Back in 1930s the chief designer of the Bulgarian State Aircraft Workshop, Herman Winter, designed various fighter aircrafts, even if Bulgaria was restricted by the Versailles treaty and was forbidden to build them.
The DAR-7, which never went beyond the prototype stage, was developed in detail and we know about its existance thanks to a folder miracolously preserved from 15th January 1931 which contained every technical data of the aircraft.
It was designed as a single-bay biplane aircraft of mixed construction. The wings were made out of wood, with the panels up to the first spars made out of birch plywood and the rest covered in linen. Wingspar of both wings were identical and were connected by streamlined racks. The tailplane was made out of metal with steel-pipes structure covered with linen.
The main fuselage structure was made out of steel pipes sheathed in the bow and above to the opening of the cabin with duraluminium tin. The rest was covered in fabric, stretched on the profiling strips and transmitting a circular cross section to the main fuselage. The cockpit was slightly armoured just at the back.
It was armed with four 7,92mm machine guns two of them placed in the nose and other two in the wings. It's not clear either if the prototype had weaponry installed and if the machine guns in the wings were installed in the upper or the lower wings.
It was powered by a radial Gnome-Rhône Jupiter engine with a maximum power of 480hp which already powered the DAR-5
The aircraft was theoretically comparable in performance to other fighters of the early 1930s like the Boeing P-12, Bristol Bulldog Mk.IIA or the Polikarpov I-5. However, it's not clear if it made any test flights and obviously, it wasn't tested in combat.

Sources:
1. http://www.airwar.ru/enc/fww1/dar7.html (translated)
2. http://bulgarianww2tanks.blogspot.com/2013/12/bulgarian-tech-tree-for-game-world-of.html