An engineer refuels the Primoco One 100, an unmanned aerial vehicle, at Vodochody Airport near Prague, Czech Republic, May 15, 2017. The primoco UAV, Czech producer of the largest civilian unmanned aerial vehicles, set a new record with its model One 100 flying for an uninterrupted 9:01 hours at the beginning of May. Picture taken May 15, 2017. REUTERS/David W Cerny