An unmanned helicopter comprising: a propulsion system comprising: a first rotor assembly comprising a first motor coupled to a first rotor, the first rotor comprising a plurality of first fixed-pitch blades (140a, 140b); and a second rotor assembly comprising a second motor coupled to a second rotor, the second rotor comprising a plurality of second fixed-pitch blades (140c, 140d), the second rotor being coaxial to the first rotor and the first rotor assembly being stacked atop the second rotor assembly; a fuselage comprising: a power source; and a controller; and a gimbal assembly coupling the fuselage to the propulsion system, the gimbal assembly comprising: a first gimbal motor configured to control pitch of the unmanned helicopter; and a second gimbal motor being in stacked assembly with the first gimbal motor and configured to control roll of the unmanned helicopter; wherein the controller is communicably coupled to the first and second gimbal motors and is configured to provide instructions to at least one of the first or second gimbal motors in order to orient the plurality of first fixed-pitch blades and second fixed-pitch blades into a position that permits wind to rotate the first fixed-pitch blades and second fixed-pitch blades and thereby charge the power source. a propulsion system comprising: a first rotor assembly comprising a first motor coupled to a first rotor, the first rotor comprising a plurality of first fixed-pitch blades (140a, 140b); and a second rotor assembly comprising a second motor coupled to a second rotor, the second rotor comprising a plurality of second fixed-pitch blades (140c, 140d), the second rotor being coaxial to the first rotor and the first rotor assembly being stacked atop the second rotor assembly; a first rotor assembly comprising a first motor coupled to a first rotor, the first rotor comprising a plurality of first fixed-pitch blades (140a, 140b); and a second rotor assembly comprising a second motor coupled to a second rotor, the second rotor comprising a plurality of second fixed-pitch blades (140c, 140d), the second rotor being coaxial to the first rotor and the first rotor assembly being stacked atop the second rotor assembly; a fuselage comprising: a power source; and a controller; and a power source; and a controller; and a gimbal assembly coupling the fuselage to the propulsion system, the gimbal assembly comprising: a first gimbal motor configured to control pitch of the unmanned helicopter; and a second gimbal motor being in stacked assembly with the first gimbal motor and configured to control roll of the unmanned helicopter; a first gimbal motor configured to control pitch of the unmanned helicopter; and a second gimbal motor being in stacked assembly with the first gimbal motor and configured to control roll of the unmanned helicopter; wherein the controller is communicably coupled to the first and second gimbal motors and is configured to provide instructions to at least one of the first or second gimbal motors in order to orient the plurality of first fixed-pitch blades and second fixed-pitch blades into a position that permits wind to rotate the first fixed-pitch blades and second fixed-pitch blades and thereby charge the power source.