Unmanned aerial vehicle having duct structure

An unmanned aerial vehicle, comprising:

• a housing comprising an upper surface, lower surface, and side surface, wherein when a height of the housing is defined to a shortest length from a portion of the upper surface to a corresponding portion of the lower surface, the height of the housing reduces from a center of the housing toward an edge of the housing, and a first slope of the upper surface from the center of the housing to the edge of the housing is smaller than a second slope of the lower surface from the center of the housing to the edge of the housing;
• a plurality of through-holes formed from the upper surface to the lower surface and symmetrically disposed when viewed from a top of the upper surface, wherein each of the through-hole comprises an inlet, throat portion, and diffuser, wherein the throat portion is adjacent to the upper surface, the inlet includes a reducing diameter from the upper surface toward the throat portion, and the diffuser includes an increasing diameter from the throat portion toward a lower portion;
• a plurality of propellers each positioned at the throat portion or at a periphery of the throat portion within one of the through-holes and configured to rotate by one of a plurality of motors;
• the plurality of motors each positioned within the diffuser within any one of the through-holes and configured to operate respectively the each of the propellers;
• and
• a control circuit positioned within the housing and configured to control the motors,
• wherein the first slope being smaller than the second slope relates to an angle β2 being larger than an angle β1,
• wherein the angle β1 being between a first imaginary line extended in a second cross-section direction from an inlet start point of a first cross-section and a second imaginary line that connects an inlet start point of a second cross-section to the inlet start point of the first cross-section, and
• wherein the angle β2 being between a third imaginary line extended in the second cross-section direction from a diffuser end position of the first cross-section and a fourth imaginary line that connects a diffuser end position of the second cross-section to the diffuser end position of the first cross-section.