In the first half of the 1930s. In Yugoslavia, the development of aircraft of its own design has become more active. The activities of Yugoslav designers could be seen in 1938 at the Belgrade Aviation Exhibition. Among the other planes there was a prototype of the R-1 bomber from Zmaj.
During 1936 at the Zmaj factory, Dušan Stankov, then technical manager, and George Dukic initiated the design and construction of a reconnaissance-bomber. After tests in the wind tunnel at Warsaw and acceptance by the Yugoslavian Air Force, the project was designated Zmaj R-1 (Serbian Cyrillic: Змај Р-1). The contract for the construction of the prototype was signed in 1937. The team of designers joining Eng. Djordje Ducić and a few young engineers who worked on the design completed the prototype before the beginning of a large aerospace workers strike in April 1940, with final assembly at the military part of the airport in Zemun.
Its design was mixed - Alclad monocoque fuselage and wooden wings and tail, metal construction rudders with fabric cover. The R-1 was equipped with Hispano-Suiza 14AB engines of French production, placed in gondolas under the wing. Flaps and landing gear was hydraulically operated. The composition of the crew varied depending on the purpose of the aircraft. In the version of the bomber R-1, the crew consisted of 4 people, in the variant of the attack aircraft - 3 people. The crew of three was accommodated in separate cockpits. Aiming and firing of the armament was made from the top cockpit while the bombing were performing from the front cockpit. The plane could take on board up to 1600 kg of bombs, and one large-caliber bomb could be placed on a special device in the fuselage for attack from a dive. The attack aircraft carried a smaller bomb load, but its small arms of two 20-mm guns and two 12.7-mm machine guns were much better suited for storming enemy troops. The two Oerlikon 20 mm cannon were in the fuselage sides but this was later changed and repositioned in to the wing roots. Two more 7.9 mm machine guns were placed in the nose top and one machine gun was placed in the rear fuselage for the defense.
The first flight was on 24 April 1940, pilotted by reserve Lieutenant Đura E. Đaković, a transport pilot with Aeroput. The initial testing justified all expectations in terms of aerodynamic characteristics and performance, unfortunately on the third flight the pilot was unable to lower the landing gear and had to land with the undercarriage extended, damaging the propellers and engines. Replacement parts for the propeller and landing gear were imported from Germany and France delaying repairs considerably.
The aircraft was rebuilt so that testing could be resumed at the end of March 1941, but in early April the bombing of Zemun airport damaged the prototype Zmaj R-1 again. In late June 1941 the Germans scrapped the aircraft.
Enngines: 2 × Hispano-Suiza 14AB, 552 kW (740 hp) each
Wingspan: 14.40 m (47 ft 3 in)
Wing area: 33.80 sq.m (363.8 sq ft)
Height: 2.50 m (8 ft 2 in)
Length: 12.78 m (41 ft 11 in)
Empty weight: 2,600 kg (5,732 lb)
Gross weight: 5,094 kg (11,230 lb)
Max takeoff weight: 5,664 kg (12,487 lb)
Maximum speed: 450 km/h (280 mph; 243 kn)
Cruise speed: 320 km/h (199 mph; 173 kn)
Range: 1,000 km (621 mi; 540 nmi)
Service ceiling: 10,000 m (33,000 ft)
Rate of climb: 5.55 m/s (1,093 ft/min)
Guns: 2x 20 mm (0.787 in) Oerlikon cannon, and 4x 7.9 mm (0.311 in) machine guns
Bombload: 1,600 kg (3,500 lb) of bombs carried internally