Lazarov Laz-12

 

Professor Tsvetan Lazarov was put in charge of the Department of Aircraft Engineering at the State Polytechnic in Sofia, where he kept with aircraft designs. Along with teaching and researching work, he made various designs like the Laz-9 (which we covered here ) the Laz-11 or a development of the Laz-8 with a more powerful engine, among others. 

The Laz-12 was a single-seat light-trainer aircraft designed by Prof. Lazarov together with other three of his pupils. Theoretically speaking, the Laz-12 was designed to train fighter pilots. It featured a completely retractable undercarriage, it was equipped with an RSI radio system (the same type that Soviet fighters employed) and was armed with two machine guns. The design of the Laz-12 was heavily based upon the Laz-7M and, after sending technical documentation, the construction of a prototype began in late 1952 at Plant No.14 at Lovech. 

The Laz-12 was a cantilever monoplane with a retractable landing gear and a low wing. Design was mixed: Wings were made out of wood sheathed with plywood and pasted over with nitrocellulose varnish. Tail planes were made out of wood covered with impregnated fabric. The fuselage was a truss of thin-walled steel pipes Duraluminium skin and canvas in different areas.

Although tail planes were similar to those of the Laz-7M, they had a smaller surface area. However, when tested, they had to be replaced with large-sized planes.

Flight tests were disappointing, as the aircraft didn't live up to its expectations, which forced them to make some changes like eliminating the machine guns and the radio system. This equipment removal saved the airframe 80 kg (176 lbs) at take off. In spite of these changes, performance was still far from expected, specially rate of climb and ceiling (5.500 m -18.044 ft- expected to just 3.500 m -11.482 ft- ) 

Testing was carried out with a fixed landing gear because they had to cope with a deadline and, therefore, the landing gear retraction system was not complete yet. Anyway, it's thought that even with the landing gear retracted, the Laz-12 wouldn't have achieved its expected numbers. The main reason for that failure relies on its weak engine which, with an increased wing load, it didn't yield enough power, so the test commission declared the aircraft as unpromising, further testing was cancelled and the only prototype was rellocated to Musachevo airfield, close to Sofia. Eventually both engine and avionics were removed to be used on the Laz-7M and the airframe was destroyed.

Although the Laz-12 was a failure, it took its place in the aeronautical history of Bulgaria, as many aeronautical students learned from its design.

 

Source:

 http://www.airwar.ru/enc/other/laz12.html (translated and adapted)