Vertical Flight
Around 1912, the Danish aviation pioneer Jacob Christian Ellehammer became interested in vertical flight. He designed a coaxial electric rc helicopters with counter-rotating rotors that were stacked vertically. Each rotor consisted of a large aluminum ring about 20 feet (six meters) in diameter with six five-foot (1.5-meter) blades attached to the outside edge of the rotors. A cyclic pitch mechanism was used to change the pitch of the rotating blades and for control. Ellehammer made several short hops in the craft.
Two Austrians, Stephan Petroczy and Professor Theodore von Karman, built and flew a coaxial rotor gas rc helicopters during the closing years of World War I. Intended for observation, this machine included a pilot/observer position above the wooden counter-rotating rotors, inflated bags for landing gear, and a quick-opening parachute. Three 120-horsepower (89-kilowatt) rotary engines provided power. The machine achieved numerous short vertical flights restrained by cables and reached a height of more than 150 feet (46 meters).
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