An unmanned aerial comprises: a motor and a propeller assembly connected to the motor comprising: a first structure fixed to the motor, having a cylindrical wall defining an inner space, with a helical slit formed through the cylindrical wall; a second structure comprising a cylinder portion, a part of which is rotatably positioned in the inner space, and at least one protruding portion protruding from the outer surface of the cylinder portion to the outside of the cylindrical wall through the helical slit; and a propeller comprising a cylindrical hub engaging with the cylinder portion of the first structure, rotating blades extending from the cylindrical hub, and at least one rib extending from the cylindrical hub toward the motor, the propeller being configured such that at least a part of the rib detachably engages with the first structure by the at least one protruding portion of the second structure.