In mid-1909, The Duks factory made their first aircraft, the Duks
airship "Jastreb." The test flights were not performed because the
factory couldn't provide the appropriate engine. The aircraft was
nevertheless shown at an aviation exhibit at the end of 1909, together
with the aircraft of famous manufacturers from Europe.
In the summer of 1910, the Duks factory made the first aircraft modeled
on the Farman HF III. It was named Duks I. It was different from the
original construction by the type and the engine power, redesigned tail
and reduced angle of the wing setting. The ENW 60HP (46kW) engine was
more powerful, but also twice the weight of the original. It turned out
that these changes didn't bring the improvement of flight performance,
and there was also a problem with the center of gravity. These flaws
were fixed during the test flights and the aircraft was delivered to its
buyer. The factory soon made another aircraft Duks II, which was
significantly lighter.
Unfortunately, the Duks biplane was not accepted as a military aircraft
by the Ministry of the Army. It was placed in the factory hangar, and it
would be delivered to the Kingdom of Serbia the following year.