A system, comprising: a vehicle; a first power source, wherein the first power source includes an internal combustion engine ; a second power source , wherein the second power source includes: a high discharge rate battery with an energy density less than or equal to 190Wh/kg; and a high energy battery with an energy density greater than or equal to 235Wh/kg; a power controller, wherein: the vehicle includes the first power source, the second power source, and the power controller and is capable of flying in a transitional mode between a hovering mode and a forward flight mode; and wherein the power controller is configured to select one or more of the first power source and the second power source to power a rotor included in the vehicle during the transitional mode; wherein the rotor included in the vehicle includes a tilt rotor and the vehicle further includes a cruise-only rotor ; and wherein the power controller is further configured to: during the forward flight mode, select the internal combustion engine to power the cruise-only rotor; and during the hovering mode and during the transitional mode, de-select the internal combustion engine so that the internal combustion engine does not power the cruise-only rotor. a vehicle; a first power source, wherein the first power source includes an internal combustion engine ; a second power source , wherein the second power source includes: a high discharge rate battery with an energy density less than or equal to 190Wh/kg; and a high energy battery with an energy density greater than or equal to 235Wh/kg; a high discharge rate battery with an energy density less than or equal to 190Wh/kg; and a high energy battery with an energy density greater than or equal to 235Wh/kg; a power controller, wherein: the vehicle includes the first power source, the second power source, and the power controller and is capable of flying in a transitional mode between a hovering mode and a forward flight mode; and wherein the power controller is configured to select one or more of the first power source and the vehicle includes the first power source, the second power source, and the power controller and is capable of flying in a transitional mode between a hovering mode and a forward flight mode; and wherein the power controller is configured to select one or more of the first power source and the second power source to power a rotor included in the vehicle during the transitional mode; wherein the rotor included in the vehicle includes a tilt rotor and the vehicle further includes a cruise-only rotor ; and wherein the power controller is further configured to: during the forward flight mode, select the internal combustion engine to power the cruise-only rotor; and during the hovering mode and during the transitional mode, de-select the internal combustion engine so that the internal combustion engine does not power the cruise-only rotor. during the forward flight mode, select the internal combustion engine to power the cruise-only rotor; and during the hovering mode and during the transitional mode, de-select the internal combustion engine so that the internal combustion engine does not power the cruise-only rotor. <EOS>