Zmaj Fizir FN The Zmaj Fizir FN ( Serbian Cyrillic : Змај Физир ФН ) was a plane designed crates school primary ( initial ) training of pilots in Yugoslav before World War II . It was constructed in Zmaj , a Zemun - based factory and the Rogožarski factory in Belgrade , and Albatros in Sremska Mitrovica . Design and development . The first prototype of Fizir FN ( Fizir trainer ) aircraft was designed and manufactured in Rudolf Fizir Workshop in Petrovaradin in 1929 . Rudolf Fizir ' s workshop did not have the capacity for industrial production of aircraft , their area of work was design and prototyping . Although being small , this workshop played a significant role in the development of Yugoslav aeronautics after it emerged and was used for the training of engineers who later became important and famous in our aeronautical engineering . Many successful airplane prototypes from this workshop were later produced in Yugoslav airplane factories . Fizir FN was a single - engine two - seat biplane trainer with a pair of struts on each side . The wings were rounded at the tips and the flaps were located on both the lower and upper wings . The landing gear was fixed to the hinge axis . For amortization either coil springs and rubber ( old type ) or the rings of sand ( later types ) were used . The wooden structure of the fuselage and the wings were covered with a canvas . While the aircraft was in production , it underwent several refinements , aircraft was continually being refined , so that there are several sub - types of these aircraft , depending on engines installed . Operational history . The first three aircraft was produced by the Zmaj aircraft factory for the Aero Club . Given excellent flight characteristics , the Air Force Command decided to use it to replace all training aircraft that had been in use for basic training previously . At that time , for basic training pilot schools used Ikarus SB - 1 ( Mali Brandenburg ) with a Mercedes engine 73 kW ( 100 hp ) manufactured in 1924 , so Zmaj built Hanriot H - 320 with 90 kW ( 120 hp ) Salmson engines manufactured in 1928 . In the beginning of 1931 , Zmaj produced and delivered first 20 serial Fizir FN aircraft with Walter radial engine and 10 with Mercedes 120HP inline engine . By 1939 , Zmaj produced 137 aircraft , Rogožarski fabricated 40 aircraft and in the 1940 the Sremska Mitrovica - based Albatros factory produced additional 20 aircraft of this type . Before the war , the Navy Aviation ordered four hydro Fizir FN ( Floatplane ) with float s and with a more powerful 106 kW Walter Mars engine . The production of last 10 Fizir FN aircraft started in 1943 in Zmaj for IS Croatian Air Force , but were not finished until the liberation , when they were handed over to Aeronautical Federation of Yugoslavia . During World War II , Yugoslav - manufactured aircraft were used by Italy in Albania , and by IS Croatia . Aircraft Fizir FN was reliable , easy to fly and maintain , so this plane stayed operative for many years ( almost till 1950 ) , as basic pilot training aircraft , both in military and civilian aviation , including sports flying . A copy of this plane is kept in the Museum of Yugoslav aviation at Belgrade Nikola Tesla airport .