A helicopter comprising: a gimbal assembly; a first rotor assembly mechanically coupled to the gimbal assembly, the first rotor assembly comprising a first rotor, the first rotor comprising a plurality of first fixed-pitch blades (140a, 140b); and a second rotor assembly mechanically coupled to the gimbal assembly, the second rotor assembly comprising a second rotor, the second rotor comprising a plurality of second fixed-pitch blades (140c, 140d), the second rotor configured to be counter-rotating to the first rotor; a fuselage mechanically coupled to the gimbal assembly; a controller; wherein each of the plurality of first and second fixed-pitch blades (140a, 140b; 140c, 140d) is coupled to a hub (210a, 210b) of its respective rotor (130a, 130b) via a hinge mechanism that is fixedly coupled to a respective one of the blades and pivotably coupled to the hub and that is configured to allow each of the fixed-pitch blades (140a, 140b; 140c, 140d) to pivot from a first position to a second position, the first position being substantially parallel to the fuselage and the second position being substantially perpendicular to the fuselage; and wherein the hinge mechanism further comprises one or more protrusions, each protrusion having at least a first surface and a second surface, wherein the first surface is substantially curved and the second surface is substantially flat; and wherein each hub (210a, 210b) comprises: one or more apertures; one or more spring pistons; and a locking bar extending through the one or more apertures and biased by the one or more spring pistons to move along the first and second surfaces of the one or more protrusions when the respective blade pivots with respect to the hub, such that the locking bar either engages the first surface thereby unlocking the respective blade, or engages the second surface to lock the respective blade. a gimbal assembly; a first rotor assembly mechanically coupled to the gimbal assembly, the first rotor assembly comprising a first rotor, the first rotor comprising a plurality of first fixed-pitch blades (140a, 140b); and a second rotor assembly mechanically coupled to the gimbal assembly, the second rotor assembly comprising a second rotor, the second rotor comprising a plurality of second fixed-pitch blades (140c, 140d), the second rotor configured to be counter-rotating to the first rotor; a fuselage mechanically coupled to the gimbal assembly; a controller; wherein each of the plurality of first and second fixed-pitch blades (140a, 140b; 140c, 140d) is coupled to a hub (210a, 210b) of its respective rotor (130a, 130b) via a hinge mechanism that is fixedly coupled to a respective one of the blades and pivotably coupled to the hub and that is configured to allow each of the fixed-pitch blades (140a, 140b; 140c, 140d) to pivot from a first position to a second position, the first position being substantially parallel to the fuselage and the second position being substantially perpendicular to the fuselage; and wherein the hinge mechanism further comprises one or more protrusions, each protrusion having at least a first surface and a second surface, wherein the first surface is substantially curved and the second surface is substantially flat; and wherein each hub (210a, 210b) comprises: one or more apertures; one or more spring pistons; and a locking bar extending through the one or more apertures and biased by the one or more spring pistons to move along the first and second surfaces of the one or more protrusions when the respective blade pivots with respect to the hub, such that the locking bar either engages the first surface thereby unlocking the respective blade, or engages the second surface to lock the respective blade. one or more apertures; one or more spring pistons; and a locking bar extending through the one or more apertures and biased by the one or more spring pistons to move along the first and second surfaces of the one or more protrusions when the respective blade pivots with respect to the hub, such that the locking bar either engages the first surface thereby unlocking the respective blade, or engages the second surface to lock the respective blade.