coolest video you’ll see this week.Donning all black, the tech maestro soared on what looked like a souped-up drone of his own design — dubbed the “SkySurfer” — during the brief flight over Broadway. Kowald, an engineer, called it “the world’s most powerful and solid hoverboard aircraft.” The board was put together by hand — propellers, rotors and all.“It contains about as much power as eight to 10 average houses all at the same time,” he said.Just over a month ago, Kowald, who earned a