In 1928 Zaschka carried out experiments with a two-rotor helicopter at Tempelhof Airport in Berlin.
"His [Engelbert Zaschka’s] plane, the first helicopter, which ever worked so successfully in miniature, not only rises and descends verticially, but is able to remain stationary at any height. Herr Zaschka is fully aware that the perfection of his invention will be the greatest forward step in aviation since the Wright brothers made their historical hop. As he pointed out, the danger of flying would immediately be decreased by at least 80 per cent, since four fifths of the accidents in flying occur either in the takeoff or in landing. […] A motor giving thirty to forty horsepower is installed in Zaschka's present experimental machine. It is so delicately adjusted that he has been able to keep the plane at a height of several feet above the ground, with no movement either up or down."
Source: German Plane Promises New Stunts in Air, The Bee. Danville, Virginia, USA, June 25, 1927, p. 16.