Petróczy-Kármán-Žurovec

Petróczy, Kármán and Žurovec were Hungarian and Czech[1][2] engineers who worked on helicopter development immediately before and during World War I in Budapest.

[3] In 1916, the aviator and Austro-Hungarian Army Colonel István Petróczy proposed an electrically driven rotorcraft to replace the dangerously flammable observation balloon.

His original concept was for the electric motor to be supplied by a dynamo driven by an internal combustion engine.

Dr. Theodore von Kármán was the director of the research group at Fischamend and Ensign Vilém Žurovec was an engineer there.

[3] A third design, for a small unmanned version powered by a single Gnome rotary piston engine, was constructed in 1918.

The rotors were driven from a single Austro-Daimler electric motor located centrally, beneath the observer's cockpit.

Zurovec acknowledged the support only of Petróczy, although later reports have mistakenly attributed the entire design to Kármán.

These engines were coupled together to drive a central pair of co-axial, contra-rotating two-bladed wooden propellers or rotors, of 6 m diameter, mounted above the airframe.

Landing gear again comprised rubber-fabric cushions, one large central one and three smaller ones at the end of each arm.

In this form the PKZ-2 could rise to a height of over 50 m and hover for up to half an hour, although it was unstable and remained tethered on long cables.