Multi-rotor concept powers one of the most successful off the shelf Commercial drone line up in the world (DJI series).This multi rotor concept does not look potent enough; In fact it is silly and complicated. There were better concepts for vertical takeoff fighters back in 1950s, with turboprop engines. I am not sure if the same idea applies even easier now for big and small drones, as they don’t need the pilot and the required accessories:
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So the technology has been proven.