Unmanned aerial vehicle comprising safety guard

An unmanned aerial vehicle comprising:

• a rotor blade for providing thrust according to generation of a main stream;
• and
• a safety guard disposed to surround the rotor blade,
• wherein the safety guard comprises:
• a guide member comprising an interior surface and a an exterior surface opposite the interior surface, the interior surface disposed coaxially with and at a first distance from the rotor blade so as to have a gap between an end of the rotor blade and the interior surface, the guide member being configured to stabilize, when the rotor blade rotates, a flow field suctioned by a negative pressure, and to stably push an ejection flow when switching to a positive pressure;
• and
• a diffuser comprising an interior surface disposed coaxially with and radially spaced apart from the guide member at a second distance from the rotor blade forming a space defined by the interior surface of the diffuser and the exterior surface of the guide member, the diffuser being configured to generate a secondary flow from an exterior of the safety guard through the space toward the main stream to increase a flow rate and the first distance being different than the second distance, and the space being coplanar to the gap,
• wherein the guide member is integrally connected to the diffuser by multiple connection members which are arranged at an equal interval,
• wherein the diffuser comprises multiple concave portions and multiple convex portions that are symmetrically arranged at a bottom end, and the secondary flow is mixed toward the main stream by the multiple concave portions,
• wherein, when an inner diameter of the bottom end of the diffuser is defined as d1 and a diameter of the rotor blade is defined as d2, a ratio of d1/d2 is 60% to 70%, and
• wherein, when the diameter of the rotor blade is defined as d2 and a vertical width of the diffuser is defined as d3, a ratio of d3/d2 is 20% to 25%.